Abstract: The tolerance-cost optimization plays a central role in the design of industrial components, due to its implications in all production stages. To reduce development times and increase product quality, the systematic application of tolerance-cost optimization from the early design phases requires a deep knowledge of the tolerance effects on both product performance and production cost. However, many factors still hamper its industrial diffusion, comprising three improvement areas: data and parameters sharing, flexibility to application complexity, and integration of simulation tools. Data and parameters sharing are a key factor since directly affect the representation and information transfer of tolerances and manufacturing processes. Both tolerances-cost relations and optimization structure must be properly represented, through a knowledge modelling framework. The present paper introduces an interoperability framework for the Computer-Aided tolerance-cost optimization. Through creating instances for tolerance and manufacturing process information, the interoperability is implemented defining a systematic sequence of steps to breakdown the multi-disciplinary optimization structure. Starting from the assembly structure, with the extraction of information from the 3D models to its transfer for parametric modelling into tolerance simulation and cost estimation environments, the interoperability framework identifies input-output relations and highlights the integration provided by multi-disciplinary optimization structure. The application of the presented framework on an archetypal case study provides an analysis of the suitability of the method, highlighting the further improvements. In this way it is possible to improve the interoperability between design and simulation virtual environments, to optimize tolerances in a concurrent a multi-disciplinary manner.

Keywords: Cost estimation | Model based definition | Multi-disciplinary optimization | Tolerance design | Tolerance-cost optimization

Abstract: Preface and Acknowledgements (Editorial)

Keywords: Editorial

Abstract: Large parts produced by injection moulding are usually subjected to large deformations that may be reduced during assembly. The single parts manufacturing specification should refer to the as produced (free) state. On the other hand, the functional specification, derived from the assembly functional specification should address the “as assembled” state. Geometrical inspection, based on the functional specification requires dedicated fixtures to simulate the “as assembled” state. This contribution suggests a procedure, based on FEM simulation, to correlate the geometric specification at the “as assembled” state with the “as produced” (free) state, applied to an industrial case study. The result of the procedure are free state tolerance limits, e.g., manufacturing specification, that allows conformity of the part to the functional specification once assembled. The part may be inspected based on the manufacturing specification fixtureless during mass production. The result of the case study shows a significant reduction in position and orientation error due to the assembly process as it was expected.

Keywords: Compliant assemblies | Deformable assemblies | FEM simulation | Geometrical Product Specification | Tolerancing

Abstract: Shaft-hole pattern fits based on the Boundary Condition design criterion allows a 100% acceptability rate, but they may be not economically convenient. If the rejection rate needs to be statistically quantified and the pattern is itself the alignment feature, therefore promoted as datum feature (Intrinsic datum system), there is no trivial solution to create a tolerance stack-up: a unique assembly function cannot be determined. The focus of this contribution is “2x” patterns: different methodologies to create tolerance stack-up assessing assemblability are discussed and verified through Monte Carlo simulation. An equation to transform the variability seen from the Intrinsic datum system to the one seen from an external arbitrary reference system is given. The mutual distance between any two elements of an “nx” pattern is discussed and the implication of multiplicity and datum system is highlighted. A case, derived from an industrial case study, will be discussed by comparing the result from the simulated manual and automated assembly. A path towards “nx” patterns generalization is also presented.

Keywords: Boundary Condition | Rejection rate | Tolerance analysis | Tolerancing | Virtual condition

Abstract: Automotive market requires more and more power semiconductor modules for the realization of vehicle electrification. With respect to more conventional discrete packages, power modules have more complex manufacturing flow in which there are some process parameters that play a key role for a robust design, mechanical and hydraulic integration with the vehicle. Among these parameters, the flatness of the final product must be controlled in order to guarantee the mounting of power modules on cooling system and the proper working of thermal management. This paper would introduce the technology of liquid cooling solution for electrified vehicles’ power module, pointing out the importance of power module flatness. Then, it is proposed an experimental methodology to analyze the warpage behaviour during power at the different process steps and at the end of power module manufacturing. Measurements confirm that flatness is within admitted tolerance (200 μ m), highlighting the ceramic soldering process as the most critical for warpage modification.

Keywords: Design | Flatness | Manufacturing | Power module | Tolerances

Abstract: Variation Simulation (VS) allows early validation and certification of the assembly process before parts are built. State-of-the-art VS models of assembly systems with compliant sheet-metal parts are based on Finite Element Method (FEM) integrated with statistical approaches (i.e., Monte Carlo simulation). A critical technical barrier is the intense computational cost. This paper proposes a novel real-time physics-based VS model of assembly systems with compliant sheet-metal parts based on Reduced-Order Model (ROM). Compared to the literature on the topic, this study reports the first application of a ROM, developed for VS by using both intrusive and non-intrusive techniques. The capability of the proposed method is illustrated in a case study concerning the assembly process of the vertical stabiliser for commercial aircrafts. Results have shown that the accuracy of ROM (based on proper orthogonal decomposition) depends on the sampling strategy as well as on the number of reduced modes. Whilst a large CPU time reduction by several orders of magnitude is achievable by non-intrusive techniques (based on radial basis functions for interpolation), intrusive models provide more accurate results compared to the full-order models.

Keywords: Compliant assembly | Proper orthogonal decomposition | Radial basis functions | Real-time physics-based simulation | Reduced-Order Models | Sheet metals | Variation simulation analysis

Abstract: Snap-fit joints represent a simple, economical and straightforward way of joining two different components. The design of the snap-fit joint is usually performed evaluating peak stresses that must be tolerated by the material without incurring into failure or plastic deformations; in addition, the force needed to join and disassemble parts is estimated in relation to ergonomic issues. Finally, the retention force, that is the force required to start disjoining parts, needs to be estimated. The evaluation of peak stresses or insertion/retention/removal forces is commonly performed through finite element method, having identified the respective deformed configuration. A different approach has been here followed considering that it is not trivial to identify the most critical condition in a full joining/disjoining cycle, when complex geometries are being considered. In detail, the snap joint has been modelled as a multibody model including a flexible body, which replicates the part that undergoes major deflections during the process. The model has been validated against experimental force – time curves, recorded for an existing joint, and it has been used to optimize a parametrised snap-fit design. As a result, the joining force has been reduced up to −84%; the disassembly force has been reduced up to −86% and the retention force has been incremented up to +7%. On the whole, a numerical framework to study these joints has been established, keeping the computational time reasonably low (about 40 min for the entire insertion and removal simulation).

Keywords: Geometrical modelling | Multibody model | Plastic components design | Snap-fit joint | Tolerance analysis

Abstract: The treatment of burn scars is a much discussed and sensitive topic because an improper therapy can have a significant impact on the quality of people's lives. To accurately assess both the health of scars and the outcomes of treatment, the medical evaluation should be based on objective measurements of progression over time. To overcome the limitations of subjective assessment is to leverage, 3D scanning technologies can be used to acquire topological information about the lesions and extract a set of relevant statistical parameters describing them. Accordingly, the present work aims at addressing both efficiency and reliability of a preliminary method based on the objective investigation of the surface topography of burn scars by applying it on several patients of the Meyer Children's Hospital burns department. A commercial 3D scanner is used to acquire 3D data relative to the scars of five patients. By applying a method based on the computational analysis of scan data, a significant number of roughness-related parameters are retrieved. This information is used to create a coherent dataset that allows the severity of burn scars to be inferred objectively. The developed method facilitates the evaluation of treatment efficacy by assessing wound healing during follow-up visits.

Keywords: 3D scan | Burn scar | Surface roughness

Abstract: Aim of all designers is to optimize the product principally in term of mass. The classic manufacturing processes constraint the designer to use a limited number of parameters for obtaining the best results. New manufacturing processes like Additive Manufacturing, open the way to a new optimization strategies, one of the most important is the topology optimization. The objective function is to reduce the mass keeping other functionalities of the product intact. The starting geometry of each topology optimization can be the geometry used for the classic manufacturing method or it can be the lattice structure or a geometry with a tessellation applied by means Voronoi technique. Aim of this paper is to investigate the potential of Voronoi tessellation in the field of structural engineering. A titanium plate with Voronoi tessellation is modelled varying the number of seeds and keeping the total mass unaltered. Thanks to a finite element simulation, for each condition a modal analysis has been performed and the natural frequencies have been extracted. The paper discusses about the influence of the number of seeds to the natural frequencies of plate. This could be a new way and a starting point for topology optimization oriented to the management of natural frequency domain exploiting the Voronoi parameters.

Keywords: CAE approach | Design for additive manufacturing | Topology optimization

Abstract: PURPOSE. Digital technology has enabled improvements in the fitting accuracy of denture bases via milling techniques. The aim of this study was to evaluate the trueness and precision of digital and analog techniques for manufacturing complete dentures (CDs). MATERIALS AND METHODS. Sixty identical CDs were manufactured using different production protocols. Digital and analog technologies were compared using the reference geometric approach, and the Δ-error values of eight areas of interest (AOI) were calculated. For each AOI, a precise number of measurement points was selected according to sensitivity analyses to compare the Δ-error of trueness and precision between the original model and manufactured prosthesis. Three types of statistical analysis were performed: to calculate the intergroup cumulative difference among the three protocols, the intergroup among the AOIs, and the intragroup difference among AOIs. RESULTS. There was a statistically significant difference between the dentures made using the oversize process and injection molding process (P <.001), but no significant difference between the other two manufacturing methods (P =.1227). There was also a statistically significant difference between the dentures made using the monolithic process and the other two processes for all AOIs (P =.0061), but there was no significant difference between the other two processes (P = 1). Within each group, significant differences among the AOIs were observed. CONCLUSION. The monolithic process yielded better results, in terms of accuracy (trueness and precision), than the other groups, although all three processes led to dentures with Δ-error values well within the clinical tolerance limit.

Keywords: CAD-CAM | Complete denture | Digital denture | Digital workflow | Reference geometry measurement

Abstract: The experimental evaluation of welding-induced distortion is a topic of great interest to both the scientific and industrial communities. With the aim of addressing a specific need in an industrial context, this paper investigates the capabilities of a stereo–Digital Image Correlation (stereo–DIC) system to measure the weld-induced distortion of the front-plate of a bogie train bolster subassembly. Currently, the deviation from planarity of this surface is measured at less than five points using a CMM in the post-weld cooled state. An additional machining process is then used to bring the surface within the tolerance required to join the welded assembly to the train body through a threaded flange. The paper shows that DIC can provide accurate full-field distortion and strain maps over the entire 588 mm × 308 mm surface of the front plate. The distinct strength of DIC over the currently used inspection technique is its ability to provide highly spatially dense data that are unaffected by rigid body motion. This can be advantageous in terms of saving time in the post-weld inspection and reducing errors in the finishing process. In addition, DIC capabilities revealed important information that was not available from the CMM, such as the full-surface map of the initial deviation of the plate from its nominal geometry and its asymmetric deformation after welding. Finally, the full-field nature of the experimental data obtained allows for seamless integration with FE thermo-mechanical simulations for numerical model validation, stress calculation, and optimization of geometry and technological processes.

Keywords: digital image correlation | full-field distortion and strain map | traction frame | welding-induced distortion

Abstract: The manufacturing process may lead non-rigid parts to endure large deformations which could be reduced during assembly. The manufacturing specifications of the single parts should refer to their free state or “as manufactured” state; the functional specifications should instead address the “as assembled” state. Therefore, a functional geometrical inspection requires dedicated fixtures to bring the parts in “as assembled” state. In this paper, through a linearized model that considers fixturing and elastic spring-back, we aim to correlate the functional specification to the manufacturing specifications. The model suggests a hybrid approach called “restricted skin model” that allows to reduce the degrees of freedom considering the form error when relevant. Firstly, the framework is verified in a mono-dimensional test case. Subsequently, it is verified including FEM simulation and actual measurement for two simple assemblies. The results show that the model can correctly interpret the theoretical assembly behaviour for actual applications. The use of the “restricted skin model” approach shows a negligible difference when compared to full FEM simulation with differences of 2.1 · 10−7 mm for traslations and 6.0 · 10−3 deg for rotations. The comparison with actual measurement values showed an error of ±0.2 mm at the assembly features. Furthermore, the linearized model allows a possible real-time application during production that enables to adjust manufacturing specification limits in case of process drifting.

Keywords: Compliant assemblies | Deformable assemblies | Geometrical Product Specification | Linearized model | Restricted skin model | Skin model | Tolerancing

Abstract: PURPOSE. The aim of this study is to evaluate the accuracy of removable partial denture (RPD) frameworks produced using different digital protocols. MATERIALS AND METHODS. 80 frameworks for RPDs were produced using CAD-CAM technology and divided into four groups of twenty (n = 20): Group 1, Titanium frameworks manufactured by digital metal laser sintering (DMLS); Group 2, Co-Cr frameworks manufactured by DMLS; Group 3, Polyamide PA12 castable resin manufactured by multi-jet fusion (MJF); and Group 4, Metal (Co-Cr) casting by using lost-wax technique. After the digital acquisition, eight specific areas were selected in order to measure the Δ-error value at the intaglio surface of RPD. The minimum value required for point sampling density (0.4 mm) was derived from the sensitivity analysis. The obtained Δ-error mean value was used for comparisons: 1. between different manufacturing processes; 2. between different manufacturing techniques in the same area of interest (AOI); and 3. between different AOI of the same group. RESULTS. The Δ-error mean value of each group ranged between -0.002 (Ti) and 0.041 (Co-Cr) mm. The Pearson’s Chi-squared test revealed significant differences considering all groups paired two by two, except for group 3 and 4. The multiple comparison test documented a significant difference for each AOI among group 1, 3, and 4. The multiple comparison test showed significant differences among almost all different AOIs of each group. CONCLUSION. All Δ-mean error values of all digital protocols for manufacturing RPD frameworks optimally fit within the clinical tolerance limit of trueness and precision.

Keywords: Accuracy | CAD-CAM | Digital framework | Metrological measurements | Removable partial denture

Abstract: The primary scope of tolerancing is to ensure functional requirements will be met by specifying geometrical tolerances. The duality principle, described within the ISO Geometrical Product Specification (GPS) standards, presents a perspective where the verification conceptually mirrors the specification. While this is a valuable model, further refinement is required to accommodate the different aims of inspection in support of the manufacturing process. This work aims to elaborate on the concept of a "geometrical verification specification" that is subordinate to the functional and/or manufacturing specifications. This verification specification may evolve as additional knowledge of the manufacturing process and inspection resources becomes available. A well-formed geometric verification specification should facilitate an appropriate inspection by any qualified operator, which in turn assures comparable measurement results across multiple instruments and facilities.

Keywords: Design for Metrology | Geometric Specififcation | ISO/TS 21619:2018

Abstract: In this paper an interactive computational methodology was developed assuming that shape and size optimization of flexible components can significantly improve energy absorption or storage ability in assembled systems with flexible components (AS-FC). A radial basis functions mesh morphing formulation in non-linear numerical finite element analysis, including contact problems and flow interaction, was adopted as optimal design method to optimize shape and size design parameters in AS-FC. Flexible components were assembled in finite element environment according to functional ISO-ASME tolerances specification; non-linear structural analysis with flow interaction analysis was performed. The results of the study showed that the proposed method allows to optimize the shape and size of the flexible components in AS-FC maximizing the system's ability to absorb or store energy. The potentiality of the method and its forecasting capability were discussed for the case study of an automotive crash shock in which the specific energy absorption was increased by over 40%. The case studied refers to a simple flexible component geometry, but the method could be extended to systems with more complex geometries.

Keywords: Crash shock absorber | ISO-ASME tolerances specification | Radial basis functions | Shape and size optimization | Specific energy absorption

Abstract: Currently, the growing need for highly customized implants has become one of the key aspects to increase the life expectancy and reduce time and costs for prolonged hospitalizations due to premature failures of implanted prostheses. According to the literature, several technological solutions are considered suitable to achieve the necessary geometrical complexity, from the conventional subtractive approaches to the more innovative additive solutions. In the case of cranial prostheses, which must guarantee a very good fitting of the region surrounding the implant in order to minimize micromotions and reduce infections, the need of a product characterized by high geometrical complexity combined with both strength and limited weight, has pushed the research towards the adoption of manufacturing processes able to improve the product’s quality but being fast and flexible enough. The attention has been thus focused in this paper on sheet metal forming processes and, namely on the Single Point Incremental Forming (SPIF) and the Superplastic Forming (SPF). In particular, the complete procedure to design and produce titanium cranial prostheses for in vivo tests is described: starting from Digital Imaging and COmmunications in Medicine (DICOM) images of the ovine animal, the design was conducted and the production process simulated to evaluate the process parameters and the production set up. The forming characteristics of the prostheses were finally evaluated in terms of thickness distributions and part’s geometry. The effectiveness of the proposed methodology has been finally assessed through the implantation of the manufactured prostheses in sheep.

Keywords: Custom prosthesis | In vivo tests | Single point incremental forming | Superplastic forming | Ti‐6Al‐4V ELI

Abstract: ASME Y14.5 and Y14.43 standards share the task to define a coherent context in which geometric tolerances may find a rational approach. Even ASME Y14.5 defines the rules, meanings, and descriptions of geometric tolerances, ASME Y14.43 applies them aiming to design and build functional gages able to check if the geometric characteristics, assigned on a drawing, have been reached in a physical component. Many of the assumptions given in the ASME Y14.5 may be understood only when the design of a functional gage is approached. The need to build such kind of device is strictly connected with the need of industry that requires best-practices able to check geometric characteristics of products in a short time. The basic elements of ASME Y14.43 are summarized in the paper and a functional gage, taken from the edition of 2011, is elaborated and discussed. The root of the American standards has been associated with the philosophical school of pragmatism in which more attention is paid to practical examples and how every theoretical conceivement must be verified by scientific experimentation.

Keywords: Functional gages | Geometric dimensioning and tolerancing | Pragmatism

Abstract: Analyzing an assembly and recognizing how the components can mate with each other in order to satisfy the functionality for which they have been designed is not a trivial task. Teaching such a problem to engineering students requires they are familiar with a set of components and how much larger or thin can be the errors intrinsically related to the technologies employed in their production. A set of steps are necessary to reasoning about the right identification of a chain of dimensions that influences a functionality. Then can be useful to have a table where collect the data, especially when the number of parts is relevant. The paper presents a new format for the table that can be used in all kinds of problems that may occur in design: analysis, analysis with constraints, and synthesis. The way how to employ such a table and the steps to solve each problem is discussed with known examples.

Keywords: Modeling | Tolerance analysis and synthesis | Tolerance stack-up

Abstract: Model-based Definition (MBD) is a known design approach that aims to an effective integration of Product Manufacturing Information (PMI) within geometrical data. By means of MBD, product requirements and specifications based on Geometric Dimensioning and Tolerancing (GD&T) can be directly associated to 3D models, improving interoperability between design and simulation virtual environments. However, especially in industrial settings, many challenges still limit MBD diffusion, such as limited knowledge and application of GD&T rules, inconsistent representation of PMI, lack of methodological and organizational approach based on PMI. As a consequence, the Dimensional Management practice based on GD&T cannot be systematically applied, and the full potential of Computer-Aided specific tools remains unexpressed. In this paper, the effective implementation of MBD for PMI during both product and process design is proved through its direct application on tolerance-cost optimization. Thanks to 3D semantic annotations, a model-based framework is suggested to validate functional requirements of a mechanical assembly and to assess production efforts, enhancing the integration between tolerance analysis and manufacturing cost tools. The interrelation of GD&T schemes enables the automated transfer of the data linked to annotations toward Computer-Aided Tolerancing (CAT) and Product Cost Management (PCM) virtual environments. Consequently, PMI guides the simulations during the multi-disciplinary optimization, proving its effectiveness in communicating engineering information and enabling the transition to digital manufacturing though MBD.

Keywords: Geometric dimensioning and tolerancing (GD&amp;T) | Model-based definition | Product manufacturing information | Tolerance-cost optimization

Abstract: Background: We compare the accuracy of new intraoral scanners (IOSs) in full-arch digital implant impressions. Methods: A master model with six scan bodies was milled in poly(methyl methacrylate), measured by using a coordinate measuring machine, and scanned 15 times with four IOSs: PrimeScan, Medit i500, Vatech EZ scan, and iTero. The software was developed to identify the position points on each scan body. The 3D position and distance analysis were performed. Results: The average and ± standard deviation of the 3D position analysis was 29 μm ± 6 μm for PrimeScan, 39 μm ± 6 μm for iTero, 48 μm ± 18 μm for Mediti500, and 118 μm ± 24 μm for Vatech EZ scan (p < 0.05). Conclusions: All IOSs are able to make a digital complete implant impression in vitro according to the average misfit value reported in literature (150 μm); however, the 3D distance analysis showed that only the Primescan and iTero presented negligible systematic error sources.

Keywords: accuracy | CAD/CAM | dental implant | digital impression | full arch | intra-oral scanner

Abstract: Qualitative and quantitative analysis of surface defects on aluminum die-cast parts is important for both quality assurance and process monitoring. In addition to the functionality and durability of the parts, the appearance of a die-cast component can be of crucial importance during the inspection of incoming goods by customers in order to ensure their functionality. Nowadays, many of the detection operations of surface defects are performed by specialized operators, but this approach is far from being sustainable for high production rates. In this context, research has focused on machine vision systems for automatic defect detection based on artificial intelligence (AI) and artificial neural networks. However, several obstacles have so far hindered a full-scale application of these intelligent systems. Images of the aluminum surface can contain a large amount of noise due to surface reflectivity and, in addition, vibrations, improper/variable ambient lighting can make automatic analysis of surface defects, which usually have an irregular shape, very difficult. This led to combining the potential of 3D scanning and measuring systems with 2D machine vision as an acquisition technology to detect surface defects. Nevertheless, the two acquisition processes present strengths and weaknesses, which mostly depend on geometrical aspects of the parts to be detected. The present paper illustrates a first attempt to combine the mentioned 2D and 3D systems into an industrial production environment. The paper presents the developed system to allow multiple acquisitions and explains how these sources of information are fed to an AI system.

Keywords: Artificial intelligence | Deep learning | High-pressure die-casting | Machine vision systems | Quality control | Surface defects analysis

Abstract: In the last years, the precision and personalized medicine is pushing the biomedical research efforts towards the direction of implant surgery requiring only 1-step approach: this goal has been achieved after the introduction of resorbable implants. The resorbable prosthetic support is indicated for temporary prosthetic applications, such as bone fractures fixation, or all those conditions usually treated with metal implants then removed with a second surgery, just after the healing of the bone defect. Biodegradable, bioactive and customizable implants for the treatment of bone fractures, both efficient in bearing the functional loads, and showing good biocompatibility and degradation properties matching the bone tissue healing, are still lacking. These premises have led to consider Magnesium (Mg) and its alloys as very promising candidates for the development of temporary, resorbable implants. However, the very high corrosion rate of Mg is the main problem, not yet solved. The material needs to be properly treated/coated, as well as manufactured, in order to design the most suitable duration of the temporary prosthesis permanence in situ. An innovative and interdisciplinary approach has been developed within the M.Era-Net ISIDE project and it is here briefly detailed with a special focus on the highlighted application fields.

Keywords: customade prostesis | Mg alloys | Reabsorbable implants

Abstract: Geometric and dimensional deviations are the main contributors on quality and cost of products. Specifically, the selection of tolerance types and the appropriate allowable range plays a central role for an effective development process. Nevertheless, the trade-off between expected performances and target costs requires skills and interaction of many areas of engineering design, especially in the early design phases. Despite many tolerance-cost optimization practices are proposed by the research community several limitations still hamper the industrial application: among them, data and parameters sharing, flexibility to application complexity, and integration of simulation tools are the main ones. Focusing on a systematic framework, an integrated modelling and simulation environment is required to take full advantage of the concurrent use of engineering software. The present paper contributes to this aim by suggesting a Computer-Aided framework that integrates Geometric Dimensioning and Tolerancing simulations and manufacturing cost estimations in a multi-disciplinary optimization environment. Advanced tools are the cornerstones of the suggested framework, enabling easy identification of the main operational steps and providing the automation of the optimization. To be validated and demonstrate the effective applicability, the framework has been applied for the tolerance-cost optimization of an archetypal case study of an automotive engine assembly. The simulation models have been integrated within the optimization, providing several configurations of tolerances from which identify the optimal one. The analysis of optimization results allows to assess the efficiency of the method, highlighting further improvements to extend its robustness, flexibility, and application range.

Keywords: Computer-Aided design | Cost estimation | Model-based definition | Multi-disciplinary optimization | Tolerance design

Abstract: Despite the large diffusion of additive manufacturing, and markedly fused filament fabrication, some quality aspects of the 3D printed parts have not been dealt with sufficiently. This applies particularly to geometric accuracy and the influence process parameters have on it. The paper describes an experiment in which 27 copies of a part were manufactured by means of a desktop fused filament fabrication device while manipulating layer thickness, printing speed, and number of contours. The effect of such process parameters on five typologies of geometric deviations and the duration of the printing process was assessed. While all the process parameters showed effects on both the printing time and some geometric deviations, the number of contours resulted as the most critical factor. The paper includes a proposal to optimize geometric accuracy and the rapidity of the process, which foresees the maximization of the number of contours, the minimization of the layer thickness, and the use of an intermediate value for printing speed.

Keywords: Coordinate measuring machine | Engineering design | Fused deposition modelling | Geometric tolerances | Process parameters | Rapid prototyping

Abstract: To compare the reference geometry approach to the best-fit (or superimposition) approach in the estimation of geometric accuracy relevant to the digital and the analog workflow to fabricate a complete denture. Starting from a model of an edentulous maxilla, the two measuring methodologies were tested to estimate the geometric accuracy of the intaglio surface of the complete dentures fabricated by CNC milling and injection molding. Eight areas of interest were defined at the intaglio surface of the denture base; a sensitivity analysis determined the minimum number of measuring points to calculate a reliable Δ ¯ error value. A repeatability analysis was performed to assess the consistency of this experimental reference geometry approach with respect to the clinic acceptable requirements. For the analog workflow, the comparison of the reference geometry results to the best-fit results showed a − 76 (post-dam) ÷ 169 µm (right flange) range of the Δ ¯ mean value for the reference geometry approach, to be compared to − 15 (left crest) ÷ 146 µm (right tuberosity) range for the best-fit approach. For the digital workflow, the same comparison showed a − 21 (left crest) ÷ 51 µm (left flange) range for the reference geometry approach, compared to a − 20 (left crest) ÷ 23 µm (left flange) for the best-fit approach. The best-fit approach results in an underestimation of mean Δ ¯ error values and their distribution over the entire prosthesis. The reference geometry approach correctly estimates error values while focusing on the identification of sources of errors in the manufacturing process.

Keywords: Accuracy | Best fit | CAD–CAM | Complete dentures | Digital manufacturing | RPS

Abstract: Aircraft seat is rated as the most unsatisfying aspect of flying; understanding the main factors impacting on passenger’s evaluations can provide a concrete opportunity for airlines to improve seat comfort and thus enhance passenger satisfaction and loyalty. Although there is a great deal of interest, the research on effective assessment strategies for subjective comfort is still underdeveloped. In this study a model-based approach for the analysis of subjective comfort data is suggested. The model adopted can be interpreted as a parametric version of the psychological process generating comfort ratings. The proposed approach is exploited through a case study concerning comfort assessment of aircraft seats designed for regional flights.

Keywords: Aircraft seat comfort | Laboratory experiments | Subjective data analysis | Uncertainty

Abstract: RGB-D cameras are employed in several research fields and application scenarios. Choosing the most appropriate sensor has been made more difficult by the increasing offer of available products. Due to the novelty of RGB-D technologies, there was a lack of tools to measure and compare performances of this type of sensor from a metrological perspective. The recent ISO 10360-13:2021 represents the most advanced international standard regulating metrological characterization of coordinate measuring systems. Part 13, specifically, considers 3D optical sensors. This paper applies the methodology of ISO 10360-13 for the characterization and comparison of three RGB-D cameras produced by Intel® RealSense™ (D415, D455, L515) in the close range (100–1500 mm). ISO 10360-13 procedures, which focus on metrological performances, are integrated with additional tests to evaluate systematic errors (acquisition of flat objects, 3D reconstruction of objects). The present paper proposes an off-the-shelf comparison which considers the performance of the sensors throughout their acquisition volume. Results have exposed the strengths and weaknesses of each device. The D415 device showed better reconstruction quality on tests strictly related to the short range. The L515 device performed better on systematic depth errors; finally, the D455 device achieved better results on tests related to the standard.

Keywords: Active stereo | Depth camera | Device characterization | ISO 10360-13 | LiDAR | Performance comparison | RealSense D415 | RealSense D455 | RealSense L515 | Reverse engineering

Abstract: The use of 3D digitizing tools is becoming the base for subject-specific products, such as the orthopaedic production process of orthoses and prostheses. This paper aims at comparing the metrological behaviour of low-cost devices (Kinect 1 and 2 by Microsoft, Structure Sensor by Occipital) and high-resolution active sensors (O&P Scan by Rodin4D, NextEngine Ultra HD, Konica Minolta Vivid 9i, GOM ATOS II 400 and Artec Leo) for the survey of human body parts. A calibrated flat plane and a test-field composed of eight calibrated spheres of different radii and placed at different heights were used to evaluate the standard quality parameters (flatness, probing errors in form and size and the standard deviation) for each device as recommended by the VDI/VDE 2634 guidelines. Subsequently, three different parts of a mannequin were surveyed as samples of human body parts. The results demonstrated the higher accuracy of fixed devices with respect to handheld ones, among which Artec Leo and Structure Sensor provided a satisfying level of accuracy for the orthopaedic application. Moreover, the handheld devices enabled performing a fast reconstruction of the mannequin parts in about 20 s, which is acceptable for a person that has to remain as still as possible. For this reason, the Structure Sensor was further tested with five motion approaches which identified that smooth motion provides the lowest deviation and higher reliability. The work demonstrated the appropriateness of handheld devices for the orthopaedic application requirements in terms of speed, accuracy and costs.

Keywords: 3D metrology | Biomedical applications | Human body 3D reconstruction | Low-cost 3D sensors | Probing error standard deviation | Uncertainty

Abstract: The Dimensional Management (DM) is well known as the reference methodology for the management of dimensional and geometric variations of industrial products. Over the years, it has assumed a central role, thanks to the development of a specific design approach, known as Design for Tolerancing (DFT). Based on the Geometric Dimensioning and Tolerancing (GD&T) symbolic language, DFT allows to check and verify functional and qualitative requirements from the early design phases. Although its strength and potential to improve design optimization, DFT industrial application is still limited. Consolidated design practices, complexity of tolerance specification process, lack of support from Computer-Aided tools still limit the tolerance specification to final validation of product design. The paper aims to define a tolerance specification model for systematic application of GD&T specification. The model formalizes the identification and translation of product requirements on the components geometry, through the definition of the main step of tolerance design. Based on the integration between the GD&T-based approach and parametric threedimensional CAD modelling, the model has been applied to validate the GD&T and the tolerance specification of two mechanical assemblies with common features. The methodology proves its general effectiveness to support engineers in tolerance design and selection of the most suitable GD&T schemes.

Keywords: Design for tolerancing (DFT) | Dimensional management (dm) | Geometric dimensioning and tolerancing (gd&amp;t) | Product design

Abstract: Marker-less motion capture (MOCAP) systems based on consumer technology simplify the analysis of movements in several research fields such as industry, healthcare and sports. Even if the marker-less MOCAP systems have performances with precision and accuracy lower than the marker-based MOCAP solutions, their low cost and ease of use make them the most suitable tools for full-body movements analysis. The most interesting category is relative to the use of RGB-D devices. This research work aims to compare the performances of the last two generations of Kinect devices as marker-less MOCAP systems: Microsoft Kinect v2 and Azure devices. To conduct the tests, a list of specific movements is acquired and evaluated. This work measures the improvements of the Azure in tracking human body movements. The gathered results are presented and discussed by evaluating performances and limitations of both marker-less MOCAP systems. Conclusions and future developments are shown and discussed.

Keywords: Accuracy | Kinect Azure | Kinect V2 | Marker-less MOCAP systems

Abstract: In the last years, the advent of low-cost markerless motion capture systems fostered their use in several research fields, such as healthcare and sport. Any system presents benefits and drawbacks that have to be considered to design a Mocap solution providing a proper motion acquisition for a specific context. In order to evaluate low-cost technology, this research work focuses on the evaluation of the accuracy of two categories of devices: The RGB active cameras and the RGB-D, or depth sensors devices. In particular, GoPro Hero 6 active cameras and Microsoft Kinect v2 devices have been selected as representative of the two categories. In particular, this work evaluates and compares the performances of the two systems used to track the position of human articulations. The two devices have been chosen among those available on the market after a state of the art has been completed. Before starting with the campaign of acquisition, the number of sensors and their layout have been designed to optimize the acquisition with both mark-less Mocap systems. Their comparison is based on a list of specific movements of upper and lower limbs. Each movement has been acquired simultaneously, to guarantee the same test conditions. The results have been organized, compared and discussed by evaluating performances and limitations of both solutions related to specific context of use. Conclusions highlight the best candidate technology..

Keywords: Accuracy | active cameras | GoPro | Markerless Mocap systems | Microsoft Kinect

Abstract: In injection molding production, automatic inspections are needed to control defects and evaluate the assigned functional tolerances of components and dies. With the “Smart Manufacturing” approach as a point of view, this paper resumes part of a wider research aiming the integration and the automation of a Reverse Engineering inspection process in components and die set-up. The paper compares two fitting approaches for recognition of portions of cylindrical surfaces. Therefore, they are evaluated in the respect of an automatic voxel-based feature recognition of 3D dense cloud of points for tolerance inspection of injection-molded parts. The first approach is a 2D Levenberg Marquardt algorithm coupled with a first guess evaluation made by the Kasa algebraic form. The second one is a 3D fitting based on the RANdom SAmple Consensus algorithm (RANSAC). The evaluation has been made according to the ability of the approaches of working on points associated to the voxel structure that locally divides the cloud to characterize planar and curved surfaces. After the presentation of the overall automatic recognition, the cylindrical surface algorithms are presented and compared trough test cases.

Keywords: Injection molding | RANdom SAmple Consensus algorithm | Tolerance inspection

Abstract: The optimization of the aeronautical structure manufacturing is a challenging task in the development of a new aircraft. To date, aeronautical industries are funding research about new assembly approaches based on cost reduction and increased efficiency of the assembly processes. The work here presented focused on an innovative assembly method based on the integration between statistical methods of tolerance prediction and the determinant assembly approach. The coupling tolerances between airframe components are predicted through statistical approach in order to reduce the features manufactured in assembly. This aspect contributes to a reduction of the costs due non-recurring costs. The method proposed has been tested on a dedicated case study developed in the frame of the “integrated main landing gear box” project on the CleanSky2 Research program. Tests have been conducted to check the consistency of the method and its feasibility in the industrial contexts in the case of flat-shaped component. The performed experiments confirmed the analytical study.

Keywords: Aeronautical assembly process | Determinant Assembly | Determinate Assembly | Hole to hole | Statistical distribution | Tolerance prediction

Abstract: Reverse Engineering (RE) may help tolerance inspection during production by digitalization of analyzed components and their comparison with design requirements. RE techniques are already applied for geometrical and tolerance shape control. Plastic injection molding is one of the fields where it may be applied, in particular for die set-up of multi-cavities, since no severe accuracy is required for the acquisition system. In this field, RE techniques integrated with Computer-Aided tools for tolerancing and inspection may contribute to the so-called “Smart Manufacturing”. Their integration with PLM and suppliers' incoming components may set the information necessary to evaluate each component and die. Intensive application of shape digitalization has to front several issues: accuracy of data acquisition hardware and software; automation of experimental and post-processing steps; update of industrial protocol and workers knowledge among others. Concerning post-processing automation, many advantages arise from computer vision, considering that it is based on the same concepts developed in a RE post-processing (detection, segmentation and classification). Recently, deep learning has been applied to classify point clouds, considering object and/or feature recognition. This can be made in two ways: with a 3D voxel grid, increasing regularity, before feeding data to a deep net architecture; or acting directly on point cloud. Literature data demonstrate high accuracy according to net training quality. In this paper, a preliminary study about CNN for 3D points segmentation is provided. Their characteristics have been compared to an automatic approach that has been already implemented by the authors in the past. VoxNet and PointNet architectures have been compared according to the specific task of feature recognition for tolerance inspection and some investigations on test cases are discussed to understand their performance.

Keywords: Deep learning | Injection molding | PointNet | Reverse engineering | Tolerance inspection

Abstract: In sheet metal forming, springback represents a major drawback increasing die set-up problems, especially for ultra-high strength steels. Finite Element Analysis is a well-established method to simulate the process during design, and multicriteria optimizations, for example, via surrogate models, are investigated in order to develop integrated design. Since to take into account also springback compensation die design may involve a large number of geometric variables, this paper presents a robust design formulation, based on the adoption of the shape function optimization, to describe springback in terms of weights directly associated to global shape variations of the die shape. Doing so, multicriteria optimization, which involves also die compensation, can be set up in a more intuitive approach, as requested in the preliminary steps of die design. After the introduction of the industrial problem, the mathematical formulation of the shape function optimization is presented together with its novel extension to Robust Design, which is based on the Dual Response Surface. Through a test case derived from the head part of a B-pillar, stamped from a Dual Phase sheet 1.5 mm thick, this novel extension investigates the effect of 6% variation from nominal values of initial yield stress and thickness. Results demonstrate the feasibility of the procedure, underlying that an optimal compensation may not be optimal in terms of process robustness.

Abstract: Aims: The purpose of the study was to evaluate the accuracy of a three-dimensional (3D) automated technique (computer-aided design (aCAD)) for the measurement of three canine femoral angles: anatomical lateral distal femoral angle (aLDFA), femoral neck angle (FNA) and femoral torsion angle. Methods:Twenty-eight femurs equally divided intotwo groups (normal and abnormal) were obtained from 14 dogs of different conformations (dolicomorphic and chondrodystrophicCT scans and 3D scanner acquisitions were used to create stereolithographic (STL) files, which were run in a CAD platform. Two blinded observers separately performed the measurements using the STL obtained from CT scans (CT aCAD) and 3D scanner (3D aCAD), which was considered the gold standard method. C orrelation coefficients were used to investigate the strength of the relationship between the two measurements. Results: A ccuracy of the aCAD computation was good, being always above the threshold of R 2 of greater than 80 per cent for all three angles assessed in both groups. a LDFA and FNA were the most accurate angles (accuracy >90 per cent). Conclusions: The proposed 3D aCAD protocol can be considered a reliable technique to assess femoral angle measurements in canine femur. The developed algorithm automatically calculates the femoral angles in 3D, thus considering the subjective intrinsic femur morphology. The main benefit relies on a fast user-independent computation, which avoids user-related measurement variability. The accuracy of 3D details may be helpful for patellar luxation and femoral bone deformity correction, as well as for the design of patient-specific, custom-made hip prosthesis implants.

Keywords: 3D computation | accuracy | dogs | femur

Abstract: Additive Manufacturing (AM) involves a set of production processes in which a layer-based material deposition approach to build parts is applied. These technologies are now extensively used in the industry in many cases as the main manufacturing process for making components with high shape complexity. The dimensional and geometric accuracy of the parts manufactured by means of AM are mostly determined by the specific type of additive process employed and the related process parameters. The part orientation in the build space is an important process parameter that has an influence on the stair-step effect and on the need of support structures and the subsequent post-processing refinements. In addition, the position of the part in the build volume may have an influence on the shape. These factors concur to the surface finish and to the dimensional and shape accuracy. In this paper, the flatness error on several surfaces, built on a test artefact ad hoc conceived, has been measured by means of a CMM-based setup in order to quantify the variation of the error in relation to: The orientation of the surfaces with respect to the platform, and the position of the part in the build volume of the AM machine. The test part has been produced by Direct Metal Laser Sintering (DMLS) process using the EOS Stainless Steel GP1. The test artifact has been designed with five flat surfaces at different angles with respect to the building platform. Two specimens were built in the same DMLS session with different position and alignment. The influence of the surface slope on the flatness error has been investigated. Flatness, 3D Roughness and orientation errors (parallelism, inclination, perpendicularity) have been measured and compared between both specimens.

Keywords: 3D surface roughness | Additive manufacturing | Flatness | Orientation error

Abstract: 3D reconstruction of human anatomy from cross-sectional imaging has recently gained increasing importance in several medical fields thus designating the 3D bones reconstruction accuracy, critical for the success of the whole surgical intervention. The 3D anatomic model quality depends on the quality of the reconstructed image, on the quality of the images segmentation step and on the error introduced by the iso-surface triangulation algorithm. The influence of image processing procedures and relative parametrization has been largely studied in the scientific literature; however, the analysis of the direct impact of the quality of the reconstructed medical images is still lacking. In this paper, a comparative study on the influence of both image reconstruction algorithm (standard and iterative) and applied kernel is reported. Research was performed on the 3D reconstruction of a pig tibia, by using Philips Brilliance 64 CT scanner. At the stage of scanning and at the stage of 3D reconstruction, the same procedures were followed, while only image reconstruction algorithm and kernel were changed. The influence of such selection on the accuracy of bone geometry was assessed by comparing it against the 3D model obtained with a professional 3D scanner. Results show an average error in reconstructing the geometry of around 0.1 mm with a variance of 0.08 mm. The presented study highlights new opportunities to control the deviations on the geometry accuracy of the bones structures at the stage of cross sectional imaging generation.

Keywords: 3D model reconstruction | Accuracy | Computed tomography | Kernel reconstruction

Abstract: Purpose: Compare the accuracy of intraoral digital impression in full-arch implant-supported fixed dental prosthesis acquired with eight different intraoral scanner (Ios). Methods: A polymethyl methacrylate acrylic model of an edentulous mandible with six scan-abutment was used as a master model and its dimensions measured with a coordinate measuring machine. Eight different Ios were used to generate digital impression: True Definition, Trios, Cerec Omnicam, 3D progress, CS3500, CS3600, Planmeca Emelard and Dental Wings. Fifteen digital impressions were made. A software called “Scan-abut” was developed to analyse and compare the digital impression with the master model, obtaining the scanning accuracy. The three-dimensional (3D) position and distance analysis were performed. Results: Mean value of the 3D position analysis showed that the True Definition (31 μm ± 8 μm) and Trios (32 μm ± 5 μm) have the best performance of the group. The Cerec Omnicam (71 μm ± 55 μm), CS3600 (61 μm ± 14 μm) have an average performance. The CS3500 (107 μm ± 28 μm) and Planmeca Emelard (101 μm ± 38 μm) present a middle-low performance, while the 3D progress (344 μm ± 121 μm) and Dental Wings (148 μm ± 64 μm) show the low performance. The 3D distance analysis showed a good linear relationship between the errors and scan-abutment distance only with the True Definition and CS3600. Conclusions: Not all scanners are suitable for digital impression in full-arch implant-supported fixed dental prosthesis and the weight of the output files is independent from the accuracy of the Ios.

Keywords: Accuracy | Dental implant | Digital impression | Full arch | Intraoral scanner

Abstract: High-flexibility components in composite material are of great interest in many fields, from aeronautic and automotive industries to sport and design goods. Their deformation during cure process, known as spring-in and warpage, is acceptable if it is within the indicated tolerance. The research aim of the present work is to present a way to inspect a high flexible part in composite material by means of a coordinate measuring machine with a touch probe. This means to define the fixturing equipment and the measurement strategy. The developed method was applied to an L-shaped part with a very small thickness and the obtained measurements were compared with those due to a laser system. The results show a good agreement between the two measurement techniques. Moreover, the further numerical simulations validate the developed contact measurement method.

Keywords: Composite material | Coordinate measuring machine | Flexible component | Laser

Abstract: The paper deals with the problem of tolerance specification and, in particular, proposes a graph-based method and a preliminary software tool: (i) to accomplish the tolerance specification for a mechanical assembly; (ii) to verify the consistency of the specification and, (iii) to allow the tracing of relationships among parts and features of the assembly. The method adopts Minimum Reference Geometric Elements (MRGE), directed graphs (di-graphs) and a set of dedicated algorithms to tackle the problems of consistency that occur during an interactive tolerance specification activity. Finally, an application illustrates the proposed method and its actual implementation.

Keywords: Datum | GD&amp;T | graph theory | MRGE | tolerance specification

Abstract: This paper proposes a replicable methodology to enhance the accuracy of the photogrammetric reconstruction of large-scale objects based on the optimization of the procedures for Unmanned Aerial Vehicle (UAV) camera image acquisition. The relationships between the acquisition grid shapes, the acquisition grid geometric parameters (pitches, image rates, camera framing, flight heights), and the 3D photogrammetric surface reconstruction accuracy were studied. Ground Sampling Distance (GSD), the necessary number of photos to assure the desired overlapping, and the surface reconstruction accuracy were related to grid shapes, image rate, and camera framing at different flight heights. The established relationships allow to choose the best combination of grid shapes and acquisition grid geometric parameters to obtain the desired accuracy for the required GSD. This outcome was assessed by means of a case study related to the ancient arched brick Bridge of the Saracens in Adrano (Sicily, Italy). The reconstruction of the three-dimensional surfaces of this structure, obtained by the efficient Structure-From-Motion (SfM) algorithms of the commercial software Pix4Mapper, supported the study by validating it with experimental data. A comparison between the surface reconstruction with different acquisition grids at different flight heights and the measurements obtained with a 3D terrestrial laser and total station-theodolites allowed to evaluate the accuracy in terms of Euclidean distances.

Keywords: Accuracy | Acquisition grid optimization | Digital surfaces models | Ground sampling distance | Structure-from-motion algorithms

Abstract: Coordinate measuring machines (CMM's) are widely used in the field of geometrical and dimensional metrology, especially in areas dealing with quality systems and manufacturing process monitoring. Concerning PM parts, the influence of process parameters on the product characteristics can be highlighted measuring dimensions and geometrical characteristics in the green and sintered state, so that proper measurement can be used as a tool to improve production strategies. In current work, two of the extrinsic factors that can affect the measurement results in PM parts, have been investigated, namely the effect of different clamping and measurement strategies. Specific clamps have been designed aiming at ensuring the proper access to all the surfaces and the derived dimensions have been compared to those obtained as distances from the measurement plate. Different measurement strategies and data processing have been used to reconstruct features and the results have been compared also in terms of geometrical tolerances.

Abstract: In the world of powerboats competition, the high-performance sandwich-structured composites have completely replaced traditional materials. During the competition, the structure of this kind of ships is subjected to repeated impacts. It is then fundamental to understand the damage evolution in order to select the most appropriate materials and increase safety issues. The present study is aimed at analysing the behaviour of sandwich-structured composites undergoing repeated low-energy impacts. Three different materials have been analysed. Two are sandwich-structured composites used for the cockpit of offshore powerboats and differing only by the core cell thickness. The third material is composed only by the skin of the same sandwich structures, without the core. Impacts were made at three different energy levels: 15, 17.5 and 20 J. In addition to the parameters typically used for the assessment of the impact damage, a new damage assessment has been carried out by means of three-dimensional optical measurements of the imprinted volumes resulting from the impact events. This approach has allowed the definition of a correlation between the imprinted volumes and the number of impacts, until the complete perforation, for each single specimen. Finally, thanks to usual indexes and the imprinted volumes, some considerations are developed about the influence of the core cell thickness in powerboats design.

Keywords: damage accumulation | lightweight composites | offshore powerboats | optical measurements | Repeated impacts | safety design

Abstract: The use of composite structures is increasing constantly in the last years, pushed by advantages of reduced weight and high strength. Moreover, the recent scenario points out a great attention on thermoplastic matrix composites due to their intrinsic recyclability as well for their possibility to re-use and re-manufacturing. However, the adoption of these materials can be further appreciated considering the secondary material workability as far as by demonstrating the possibility to re-manufacture the thermoplastic composite. The proposed work presents an experimental analysis carried out to investigate the downstream workability of a thermoplastic composite by one of the most versatile and flexible process. Glass fiber reinforced Polyamide 6 is the investigated material and the Single Point Incremental Forming is the implemented manufacturing approach. Since the composite matrix is characterized by a glass transition temperature higher than 50 °C, an external heating source has been necessary to perform the process in “hot” conditions. The process feasibility was fully demonstrated as well as the same was optimized in order to derive proper guidelines that can drive the process designer in the method star-up.

Keywords: Downstream process | Short glass-fibers | SPIF | Thermoplastic composite

Abstract: In the present work, sheet-forming processes, i.e. super plastic forming and single-point incremental forming, have been adopted for the manufacturing of custom prostheses, instead of subtractive and additive techniques that are time- and cost-consuming for a single-piece production. Regarding concerns of the material, three different titanium alloys were used: pure titanium and two grades of the alloy Ti-6Al-4V (the standard one and the extra low interstitial one). Since no standard protocol exists to assess the mechanical performance of cranial implants, an experimental procedure has been designed and used in this work for producing polymethylmethacrylate supports, on which the cranial prostheses were firmly connected and subjected to impact puncture tests (drop tests). An experimental campaign could thus be conducted to investigate the effect on the mechanical response of (a) the titanium alloy, (b) the initial blank thickness and (c) the manufacturing process. Drop tests, carried out according to the proposed procedure, have shown no failure of the prostheses, neither in the area of the impact nor in the anchoring region and have revealed that, irrespective of the adopted manufacturing process, which does not alter the material, the amount of energy absorbed by the implants is always larger than 70%.

Keywords: Drop test | Pure titanium | SPF | SPIF | Ti-6Al-4V | Ti-6Al-4V-ELI

Abstract: Purpose: This study describes a method for measuring the accuracy of the virtual impression. Methods: In vitro measurements according to a metrological approach were based on (1) use of an opto-mechanical coordinate measuring machine to acquire 3D points from a master model, (2) the mathematical reconstruction of regular geometric features (planes, cylinders, points) from 3D points or an STL file, and (3) consistent definition and evaluation of position and distance errors describing scanning inaccuracies. Two expert and two inexpert operators each made five impressions. The 3D position error, with its relevant X, Y, and Z components, the mean 3D position error of each scanbody, and the intra-scanbody distance error were measured using the analysis of variance and the Sheffe’s test for multiple comparison. Results: Statistically significant differences in the accuracy of the impression were observed among the operators for each scanbody, despite the good reliability (Cronbach’s α = 0.897). The mean 3D position error of the digital impression was between 0.041 ± 0.023 mm and 0.082 ± 0.030 mm. Conclusions: Within the limitations of this in vitro study, which was performed using a single commercial system for preparing digital impressions and one test configuration, the data showed that the digital impressions had a level of accuracy comparable to that reported in other studies, and which was acceptable for clinical and technological applications. The distance between the individual positions (#36 to #46) of the scanbody influenced the magnitude of the error. The position error generated by the intraoral scanner was dependent on the length of the arch scanned. Operator skill and experience may influence the accuracy of the impression.

Keywords: Accuracy | CAD–CAM | Digital impression | Opto-mechanical measuring

Abstract: This paper presents a new methodology whose goals are on the one hand the formulation of a tolerance specification that is consistent with the functional, technological and control needs and, on the other, the automatic control of tolerance. The key aspect of the methodology is the digital model of the product, referred to as GMT (Geometric Model of Tolerancing), which gives a complete, consistent and efficient description of its geometrical and dimensional properties with the aim of being able to specify, simulate, manufacture and inspect them. By means a real test case, the potentialities of a first implementation of the proposed methodology are critically discussed.

Keywords: CAT (Computer-Aided Tolerancing) | GD&amp;T (Geometric Dimensioning and Tolerancing) | Geometric inspection | GPS (Geometric Product Specification)

Abstract: A new method for secondary features segmentation, performed in highdensity acquired geometric models, is proposed. Four types of secondary features are considered: fillets, rounds, grooves and sharp edges. The method is based on an algorithm that analyzes the principal curvatures. The nodes, potentially attributable to a fillet of given geometry, are those with a certain value for maximum principal curvature. Since the deterministic application of this simple wor king principle shows several problems due to the uncertainties in the curvature estimation, a fuzzy approach is proposed. In order to segment the nodes of a tessellated model that pertain to the same secondary features, proper membership functions are evaluated as function of some parameters, which affect the quality of the curvature estimation. A region growing algorithm connects the nodes pertaining to the same secondary feature. The method is applied and verified for some test cases.

Keywords: Computational geometry | Features extractions | Fuzzy logic | Mechanical engineering computing | Region growing algorithm

Abstract: Underwater manipulation is an essential operation for performing a diverse range of applications in the submerged environment that, in spite of the hostile and unstructured environment, it requires high precision and reliability of the robotic arm. The paper presents the evaluation and characterization of the kinematic performances of an underwater robotic arm mounted on a light work class ROV. The arm analyzed in the study is a re-engineered version of a commercial hydraulic manipulator whose geometry and end-effector have been modified. Moreover, the arm has been equipped with a set of encoders in order to provide the positioning feedback. The test conducted in laboratory focused on the measurement of accuracy and repeatability in order to evaluate the limits of the arm architecture. This work has been carried out in the context of the CoMAS (In situ conservation planning of Underwater Archaeological Artifacts - http://www.comasproject.eu) project in which the possibility to develop a ROV able to perform maintenance operations in underwater archeological sites has been investigated.

Keywords: accuracy | forward kinematics | repeatability | robotic arm | underwater manipulator

Abstract: This work presents Reverse Engineering and Computer Aided technologies to improve the inspection of injection moulded electro-mechanical parts. Through a strong integration and automation of these methods, tolerance analysis, acquisition tool-path optimization and data management are performed. The core of the procedure concerns the automation of the data measure originally developed through voxel-based segmentation. This paper discusses the overall framework and its integration made according to Smart Manufacturing requirements. The experimental set-up, now in operative conditions at ABB SACE, is composed of a laser scanner installed on a CMM machine able to measure components with lengths in the range of 5÷250 mm, (b) a tool path optimization procedure and (c) a data management both developed as CAD-based applications.

Keywords: Computer Aided Tolerancing &amp; Inspection | Feature Recognition | Injection Moulding | Path Planning | Product Data Management | Quality Inspection | Reverse Engineering | Segmentation

Abstract: PMI annotations are widely used to support the Model Based Design within modern companies. In particular, the introduction of digital annotations marks the transition from the 2D drawings to the 3D representation in many manufacturing and design companies. However, today the implementation of the PMI technology presents some limits, such as the lack of functions to generate structure templates to be applied to similar CAD models. The proposed approach aims to overcome the limits of traditional tools which are not able to add a PMI annotation’s structure from one model to another one. The paper describes a method to reuse digital PMI annotations in a new model during the design phase, where the annotations are inherited from similar CAD documents. The proposed approach is based on two levels of geometric analysis: the searching of similar template models from an XML database, and the identification of the related geometric entities, which are used as associated objects for the definition of 3D annotations. The test case is focused on the automatic generation of PMI annotations for exhaust duct items used in oil & gas applications. The proposed tool has been developed within a software program called Duct Designer, which is used for the CAD automation of duct items. Particularly, the test case enhances the retrieval and reuse of sizing schemes from previous 3D models in order to obtain an automatic rebuilding of the geometric annotations.

Keywords: Digital annotations | Model-based definition (MBD) | Oil &amp; gas | Product manufacturing information (PMI)

Abstract: Titanium and its alloys are widely used in cranioplasty because they are biocompatible with excellent mechanical properties and favor the osseointegration with the bone. However, when Titanium alloys have to be worked several problems occurred from a manufacturing point of view: the standard procedure for obtaining Titanium prostheses is represented by the machining processes, which result time and cost consuming. The aim of this research consist to introduce alternative flexible sheet forming processes, i.e. Super Plastic Forming (SPF) and Single Point Incremental Forming (SPIF), for the manufacturing of patient-oriented titanium prostheses. The research activities have already highlighted the potentiality of the investigated forming processes that can be alternatively used taking into account both the damage morphology and the need of urgency operation. In the present work, the way of manufacturing the Ti prostheses by SPF and SPIF is described. A comparative analysis has been performed, thus highlighting the peculiarities of the investigated processes and the prostheses feasibility.

Keywords: Single Point Incremental Forming | Super Plastic Forming | Titanium alloy

Abstract: During manufacturing, porcelain whiteware changes its shape due to the sintering process. For this reason, leader companies in the field of ceramics apply strict controls on final products in order to reach high quality standards. Typically, three quality parameters are considered: drop of the bottom, bending of the rim and roundness. To date, the assessment of such parameters is still based on visual inspections and manual measurements. In the present paper, authors propose a new quality assessment procedure based on reverse engineering (RE), able to measure the most relevant quality parameters in an effective, reliable and repeatable way.

Keywords: 3D model | 3D reconstruction | 3D scanning | measurement | porcelain | porcelain tableware | quality control | quality parameters | reverse engineering | whiteware

Abstract: In this paper, the problem of the evaluation of the uncertainties that originate in the complex design process of a new system is analyzed, paying particular attention to multibody mechanical systems. To this end, the Wiener-Shannon's axioms are extended to non-probabilistic events and a theory of information for non-repetitive events is used as a measure of the reliability of data. The selection of the solutions consistent with the values of the design constraints is performed by analyzing the complexity of the relation matrix and using the idea of information in the metric space. Comparing the alternatives in terms of the amount of entropy resulting from the various distribution, this method is capable of finding the optimal solution that can be obtained with the available resources. In the paper, the algorithmic steps of the proposed method are discussed and an illustrative numerical example is provided.

Keywords: Complexity | Design | Fair division | Multibody systems | Non-probabilistic entropy | Uncertainty

Abstract: Modern engineering systems are getting complex and integrate multi-physical objects. The Model-Based System Engineering (MBSE) seems to be the best way to manage complex system design and the Systems Modeling Language (SysML) may be considered one of the computer languages to perform the designing of a complex system. MBSE also seems to be a valid solution to integrate tolerance specification into design process. In particular, in the present work SysML is used to create a set of libraries containing simple and complex volumes, primary datum and tolerance zones, according to ASME Y14.5M and ISO 1101 standards. The generation of these libraries is based on the Technologically and Topologically Related Surfaces (TTRS) model and uses the set of thirteen positioning constraints able to represent every condition between assembly features. The paper summarizes the characteristics of the created SysML objects, able to represent Datum, Datum Reference Frame (DRF) and tolerance zones. In particular, the Datum included in ASME Y14.5-M are modelled. Then, all the tolerance zones included in both standards are modelled. Finally, a three-step procedure is summarized to preliminary illustrate the way of use the developed set of SysML objects.

Keywords: Assembly tolerance specification | Model-based Systems Engineering | SysML | TTRS model

Abstract: This paper introduces the novel concept of fixture capability measure to determine fixture layout for the best assembly process yield by optimizing position of locators and reference clamps to compensate stochastic product variations and part deformation. This allows reducing the risk of product failures caused by product and process variation. The method is based on three main steps: (i) physics-based modelling of parts and fixtures, (ii) stochastic polynomial chaos expansion to calculate fixture capability, and (iii) fixture capability optimisation using surrogate modelling. The methodology is demonstrated and validated using the results of an aerospace wing sub-assembly joined by riveting technique.

Keywords: Fixture Capability | Fixture Layout Optimisation | Polynomial Chaos | Surrogate Model

Abstract: One of the most important parameters to be controlled during the production of textile yarns obtained by mixing pre-colored fibers, is the color correspondence between the manufactured yarn and a given reference, usually provided by a designer or a customer. Obtaining yarns from raw pre-colored fibers is a complex manufacturing process entailing a number of steps such as laboratory sampling, color recipe corrections, blowing, carding and spinning. Carding process is the one devoted to transform a “fuzzy mass” of tufted fibers into a regular mass of untwisted fibers, named “tow”. During this process, unfortunately, the correspondence between the color of the tow and the target one cannot be assured, thus leading to yarns whose color differs from the one used for reference. To solve this issue, the main aim of this work is to provide a system able to perform a spectral camera-based real-time measurement of a carded tow, to assess its color correspondence with a reference carded fabric and, at the same time, to monitor the overall quality of the tow during the carding process. Tested against a number of differently colored carded fabrics, the proposed system proved its effectiveness in reliably assessing color correspondence in real-time.

Keywords: Carding process | Color assessment | Spectral camera sensor | Spectrophotometry

Abstract: Reverse Engineering (RE), also known as "CAD reconstruction", aims at the reconstruction of 3D geometric models of objects/mechanical parts, starting from 3D measured data (points/mesh). In recent years, considerable developments in RE were achieved thanks to both academic and industrial research (e.g. RE software packages). The aim of this work is to provide an overview of state of the art techniques and approaches presented in recent years (considering at the same time tools and methods provided by commercial CAD software and RE systems). In particular, this article focuses on the "constrained fitting" approach, which considers geometrical constraints between the generated surfaces, improving the reconstruction result. On the basis of the overview, possible theoretical principles are drafted with the aim of suggest new strategies to make the CAD reconstruction process more effective in order to obtain more ready/usable CAD models. Finally, a new RE framework is briefly outlined: the proposed approach hypothesizes a tool built within the environment of an existing CAD system and considers the fitting of a custom-built archetypal model, defined with all the a-priori known dimensions and constraints, to the scanned data.

Abstract: This paper presents the advancements of an automatic segmentation procedure based on the concept of Hierarchical Space Partitioning. It is aimed at tolerance inspection of electromechanical parts produced by injection moulding and acquired by laser scanning. After a general overview of the procedure, its application for recognising cylindrical surfaces is presented and discussed through a specific industrial test case.

Keywords: Computer aided tolerancing &amp; inspection | Hierarchical space partitioning | Injection moulding | Reverse engineering

Abstract: In this paper we analyze the capabilities of a routine, based on Fuzzy logic, for elaborating a data set coming from a CMM (Coordinate Measuring Machine). We will show how to obtain, during holes measuring, the best measure, so that the approximation error is minimized. Moreover the CMM on-board software can elaborate these data and select the mathematical representation of the stored data, by identifying quotes, measures, axes, diameters, tolerances and so on. Information on measured parts is usually elaborated by an algorithm based on the least square squared error method, in order to evaluate the good shape of the hole; our purpose is to propose a new kind of approach, based on the Inferential Fuzzy system method, both to reduce the number of measured points, and to obtain the same accuracy. Our approach enables to measure the holes with a number of points lower than those usually needed for the CMM software. Thus time spent for obtaining a good measure is significantly reduced.

Keywords: Accuracy | Coordinate Measuring Machine | Fuzzy inference | Holes measurement | Precision

Abstract: The present work collects some results of the three-years Research Program "BioForming", funded by the Italian Ministry of Education (MIUR) and aimed to investigate the possibility of using flexible sheet forming processes, i.e. Super Plastic Forming (SPF) and Single Point Incremental Forming (SPIF), for the manufacturing of patient-oriented titanium prostheses. The prosthetic implants used as case studies were from the skull; in particular, two different Ti alloys and geometries were considered: one to be produced in Ti-Gr23 by SPF and one to be produced in Ti-Gr2 by SPIF. Numerical simulations implementing material behaviours evaluated by characterization tests were conducted in order to design both the manufacturing processes. Subsequently, experimental tests were carried out implementing numerical results in terms of: (i) gas pressure profile able to determine a constant (and optimal) strain rate during the SPF process; (ii) tool path able to avoid rupture during the SPIF process. Post forming characteristics of the prostheses in terms of thickness distributions were measured and compared to data from simulations for validation purposes. A good correlation between numerical and experimental thickness distributions has been obtained; in addition, the possibility of successfully adopting both the SPF and the SPIF processes for the manufacturing of prostheses has been demonstrated.

Abstract: Cranioplasty is a surgery in which a prosthesis must be anchored on skull bone to repair a defect. One of the most used materials is the titanium. However, titanium prostheses could be made using the incremental sheet forming (ISF). Since titanium and bone are characterized by different Young modules, a detailed design of anchoring system is required to avoid cranial rupture. Aim of this study was to present a design procedure in order to identify the optimal anchoring system in case of craniofacial prostheses made with ISF. In detail, an optimization process and a predictive model for bone stress were used, choosing the numerical outputs of different FEM analyses as input data. The results indicate that our predictive and optimization models are accurate and, so, that this procedure could be very helpful for the prosthesis design, as demonstrated by the application of the procedure to a real case study.

Keywords: Anchoring system | Design procedure | Incremental sheet forming | Titanium prosthesis

Abstract: Melt rheology in injection molded metastable supercooled liquid metal of Zr44-Ti11-Cu10-Ni10-Be25 alloy may induce selective crystallizations. High mobility Be, Cu and Ni atoms have been observed to differently crystallize in bulk metal glassy supercooled liquids. Here, we analyze the result of morphological microscopic observation conduct on Bulk Metallic Glass (BMG) with composition of a commercial liquid metal alloy (LM001B). The injection molded plate has been supplied by “Liquid Metals Technologies Inc, Ca USA” and manufactured using an Engel injection molding machine operating at 1050-1100°C; the observed sample then has been cut by water jet. FEI Scios Dual-Beam has carried out the microscopic observation. Particularly, through a cross section, we observe the presence of crystalline phases on the short-range order. We investigate the presence of short-range order clusters, their distribution and the effect that they could cause on the alloys’ behaviors and properties.

Keywords: Bulk glass metals | Chemorheological model | Cold crystallization | Rheology | Segregation

Abstract: Remote Laser Welding (RLW) is a joining technique more recent than the most known and widely adopted (mainly in the automotive field) resistance spot welding technique (RSW). While RLW offers much more benefits than RSW (higherprocess speed, less number of operating robots, decreased factory floor footprint, reduced overall process costs), it also adds issues related to process planning and quality control of welded joints. The European Commission, under the ICT-Factories of the Future programme of FP7, funded a project, starting from January 2012 and just ended on June 2015, titled &quot;RLW Navigator - Remote Laser Welding System Navigator for Eco Resilient Automotive Factories&quot; which aims at developing an innovative Process Navigator for planning, integrating, testing and validating applications on the use of RLW in the automotive assembly addressing today&#39;s critical needs for frequently changing operating conditions and product-mix provisions. The project results are a set of toolboxes able to offer very useful tools to plan and control the RLW joining process. The key word that mainly describes the provided ICT-based solutions is Optimisation: from the optimisation of the working cell, by analysing several layout configurations, to the optimisation of robot path and weld sequencing for assigned product and process constraints; from the fixture optimisation (involving the best clamp configuration) starting from real/non-ideal shape parts, to the optimisation of process laser parameters to guarantee higher welded join quality. The applicability of these software tools goes beyond the automotive field and this makes the provided solutions much more interesting for the industry.

Abstract: One of most demanding tasks in the manufacturing field is controlling the variability of parts as it may affect strongly the deliverability of key characteristics defined at the final (product) assembly level. Current CAT systems offer a good solution to the tolerance analysis/synthesis task, but to handle flexible objects with shape errors more effort is needed to include methods able to capture the elastic behaviour of parts that adds more variability on the final assembly. Usually, sheet metal assemblies require dedicated fixtures and clamps layout to control the gap between parts in the specific location where a join must be placed. Due to the variability of parts the position of clamps can also be varied. The paper describes a FEM-based method able take into account part flexibility and shape error to parametrically analyse sheet metal assemblies by acting on some key parameters to look for the optimal clamp layout that guarantee the gap between parts to be under control after joining parts together. This method offers, with respect to commercial solutions, the ability to model fixtures, clamps and different joint types with no matter on the node positions of the mesh. Locations of such elements are based on the shape functions defined at element (shell) mesh level and modelled as local constraints. So the user can generate a mesh without a previous knowledge of the exact positions of clamps, for example. This allows to conduit a parametric analysis without remeshing the surfaces and with no need to physically model the clamps. An aeronautic case study is described with a four-part assembly riveted on a quite complex fixture by using several clamps.

Keywords: Clamp layout optimisation | Compliant assemblies | Free shape variability | Sheet metal parts | Shell.

Abstract: The production of prostheses is still not completely optimized, especially for those districts where both functional and aesthetic requirements have to be combined with the urgency of intervention. The prostheses manufactured by machining using CAD/CAM techniques represent the conventional way to obtain a "custom-made" part. However, the above-mentioned solutions are penalized by the too long manufacturing time. This limit can be overcome by using an innovative metal-forming process, i.e. the Incremental Sheet Forming (ISF), which also allows to obtain complex patient-specific geometries even if characterized by a lower precision compared to the conventional process. In this paper, alternative approaches to manufacture a skull prosthesis (i.e. conventional milling and ISF) are compared from technological and economical points of view.

Keywords: Anchoring system design | Prostheses modelling | Skull manufacturing

Abstract: Purpose: The study aims to evaluate three-dimensionally (3D) the accuracy of implant impressions using a new resin splinting material, "Smart Dentin Replacement" (SDR). Materials and Methods: A titanium model of an edentulous mandible with six implant analogues was used as a master model and its dimensions measured with a coordinate measuring machine. Before the total 60 impressions were taken (open tray, screw-retained abutments, vinyl polysiloxane), they were divided in four groups: A (test): copings pick-up splinted with dental floss and fotopolymerizing SDR; B (test): see A, additionally sectioned and splinted again with SDR; C (control): copings pick-up splinted with dental floss and autopolymerizing Duralay® (Reliance Dental Mfg. Co., Alsip, IL, USA) acrylic resin; and D (control): see C, additionally sectioned and splinted again with Duralay. The impressions were measured directly with an optomechanical coordinate measuring machine and analyzed with a computer-aided design (CAD) geometric modeling software. The Wilcoxon matched-pair signed-rank test was used to compare groups. Results: While there was no difference (p=430) between the mean 3D deviations of the test groups A (17.5μm) and B (17.4μm), they both showed statistically significant differences (p<.003) compared with both control groups (C 25.0μm, D 19.1μm). Conclusions: Conventional impression techniques for edentulous jaws with multiple implants are highly accurate using the new fotopolymerizing splinting material SDR. Sectioning and rejoining of the SDR splinting had no impact on the impression accuracy.

Keywords: Accuracy | Edentulous jaw | Implant impression technique | Impression copings | Passive fit | Splinting material

Abstract: In the aerospace sector, tolerance allocation and inspection of many components must provide not only for ease of manufacturing and cost reduction but also for reliability and safety requirements. Computer Aided Tolerancing and Inspection (CAT&I) methods based on Reverse Engineering techniques may enhance production quality assessment with significant reduction of the time-to-market. This paper presents an original reverse engineering methodology that is being developed to achieve the complete automation of the inspection process starting from the design requirements (dimensional and geometrical tolerances) as they generally appear in the component's official drawings. After a brief presentation of the proposed methodology and its possible implementation oriented to non-planar surface recognition, an aeronautical component made by beta-forging of Ti6Al4V Titanium Alloy powders is presented as test case. The discussion of the procedure allows to point out its benefits in terms of (a) more efficient management of the inspection process and data consolidation; (b) more thorough comprehension of the real component; and (c) a better understanding of possible feedbacks to be applied in design or manufacturing. Finally some remarks about the limits of the proposed methodology are shown and possible enhancements, that have been already planned to be applied, will be described. © 2014 IEEE.

Keywords: beta-forging | Computer Aided Tolerancing and Inspection | Reverse Engineering | Segmentation | Ti6Al4V Titanium Alloy powders

Abstract: ABSTRACT: This paper presents a point cloud segmentation based on a spatial multiresolution discretisation that is derived from hierarchical space partitioning. Through part type recognition it aims to simplify Computer Aided Tolerance Inspection of electromechanical components avoiding cloud-CAD model registration. A voxel structure subdivides the point cloud. Then, through a suitable surface partitioning, it is linked to component volumes by means of the morphological components of the binary image that is derived from voxel attributes (‘true state’ if points are included in a specific cluster or ‘false state’ if they are not). The proposed approach is then applied on a din-rail clip of a breaker, made by injection moulding. This case study points out the suitability of the approach on box-shaped components or with normal protrusions, and its limits concerning the assumptions of the implementation.

Keywords: computer aided tolerance inspection | reverse engineering | segmentation

Abstract: The increasing integration between electronics and mechanical engineering brings to the industrial market very hi-tech sensors, often non-linear, capable of more than a single input and single output. A problem more and more relevant for sensors like these is calibration. Classic linear calibration procedures, when applied to this extremely engineered sensors, lead to poor accuracy and are generally not satisfactory. The case study is the calibration of a bi laser based position sensor, in particular a positive sensitive detector, that is an optical position transducer based on series of photodiodes commonly used as multidimensional sensor. To perform the calibration a micrometric positioning table was used to test the whole photodiode active area in both directions. The sensor studied showed a very linear behaviour in the central region of the working range, and a limited nonlinearity closer to the range limits and was to be used to verify robot movement capabilities; to reduce uncertainty associated with nonlinearities, a set of nonstandard, non-linear, calibrations were performed, pointing out residual values in order to compare different algorithms. In a previous work, authors have already tested a linear model against an algorithm based on radial basis functions (RBF) and Nelder-Mead simplex method. Object of this paper is the definition of a procedure based on RBF and genetic algorithms for multi-dimensional interpolation of data cloud and a comparison between this updated procedure results and the ones of the previous studied algorithms. The reference model for calibration was a black box with two inputs, X and Y position of the laser spot, and two outputs, voltages Vx and Vy, while the calibration procedure was split in two separate layers, one for each output depending on both inputs. Given N data points in a M-dimensional environment and N values that represent the non linearity residual, purpose of the algorithm is to approximate a data cloud with a real function, that is represented as a sum of a polynomial (linear) part and I. radial basis functions, each associated with a different center (node) and weighted by an appropriate coefficient, that the procedure also allow to assess. When no starting guess for nodes are given in input, nodes coordinates are the output of a non-linear optimizer based on a genetic algorithm, whose goal is to locally minimize the objective function. The algorithm stops itself whenever it reaches a certain tolerance level, a user specified number of nodes or when the previous iteration has a better value of the objective function. This study has been performed for various RBF classes, and shows an increased accuracy, thus a better metrological behaviour, with respect to the standard linear (planar) calibration model traditionally used.

Keywords: Calibration | Genetic algorithm | Multi input | Radial basis function | Uncertainty

Abstract: In the last few years the need for methodologies capable of performing an automated geometric inspection has increased. These methodologies often use 3D high-resolution optical digitisers to acquire points from the surface of the object to be inspected. It is expected that, in the near future, geometric inspection will be requiring more and more the use of these instruments. At present geometric inspection is not profiting from all the opportunities attainable by 3D high-resolution optical scanners or from the numerous tools which can be used for processing the point cloud acquired from the inspected product. For some years now, these authors have been working on a new methodology for automatic tolerance inspection working from a 3D model acquired by optical digitisers. In this paper all the information recognisable in a scanned object is organised into a new data structure, called Recognised Geometric Model (RGM). The final aim is to define a representation of the inspected object for the automatic evaluation of the non-idealities pertaining to the form, orientation and location of the non-ideal features of the acquired object. The key concept of the proposed approach is the capability to recognise some intrinsic nominal properties of the acquired model. These properties are assumed as references to evaluate the non-idealities of the inspected object. With this approach the references of geometric inspection are searched for in the inspected object independently of a tolerance specification and of the availability of a 3D nominal representation. The high-level geometric information within RGM depends on the rules used for its identification. The capability to recognise specific categories of nominal references offers the possibility of introducing new tolerances to be specified. The proposed approach has been implemented in original software by means of which a specific test case has been analysed. © 2012 Springer-Verlag France.

Keywords: Automated inspection | ISO tolerancing | Three-dimensional metrology

Abstract: The present paper proposes a novel general approach to automatically calculate the variational parameters for planar or cylindrical features for a given set of tolerance specifications, according to ANSI or ISO Standards. Variational parameters correspond to those directions along/around which variation, in terms of small translation and rotation, may propagate for a given feature with tolerance specifications. A graph representation of these tolerance specifications is adopted and it is used along with screw theory and Davies's laws to automatically calculate the variational parameters, and then the net variational space of each toleranced feature, by capturing nominal geometries directly from a CAD environment (SolidWorks). From screw theory, twist matrices, able to capture the motion properties of any kinematic joint in mechanical assemblies, are here adopted at part level and collected for every feature-to-datum relationship. Davies's laws are then recalled to put those matrices together to calculate the variational parameters. In this way, both single-datum and multi-datum tolerance specifications can be handled. The proposed approach for the automatic calculation of variational parameters could be successfully implemented in a more general expert system for designing mechanical assemblies where an added-value interaction could allow user to detect relationships between geometric features. In this way, the leading of activities aimed to tolerance analysis could be accomplished both during the preliminary design stages and throughout the manufacturing and reviewing sessions. © 2012 Springer-Verlag France.

Keywords: CAD automation | Graph representation | Mechanical networks | Screw theory | Tolerance analysis | Variational parameters

Abstract: In the variational modeling of assemblies it is important to define the location of a part both in absolute terms and with respect to the position/orientation of other assembled parts. The present paper proposes a programming optimization approach to solve this problem. The algorithm, by using the heuristic Nelder-Mead technique - combined with a penalty function - simulates and solves sequential assembly strategies to find the optimal geometric configuration of a rigid part with variational features satisfying all the assembly constraints in the given sequence. The algorithm best aligns mating features avoiding, at the same time, feature-to-feature interferences, and automatically calculating the amount of movement the part being assembled must obey to satisfy assembly constraints, at that state of the assembly process. Thus, different assembly sequences can be simulated also including variational features. © 2013 The Authors.

Keywords: Assembly simulation | Constrained optimization | Rigid assemblies | Sequential constraint solver | Tolerance analysis

Abstract: In this paper a procedure based on a statistical approach to manufacturing for the analysis of tolerance chains is reported. In particular, the proposed approach can be summarised into two main steps. First, each single technological operation (for example, the drilling of a hole) is simulated by extracting, from a statistical distribution typical of the machine tool, the parameters characteristic of the manufacturing procedure. Then, a simulation is performed, to verify if the real features of the part can simultaneously fit the virtual gage. This method of acceptance/rejection of a part is according to the ISO/ASME standards and is representative of the real functional requirements of the part. © (2013) Trans Tech Publications, Switzerland.

Keywords: Manufacturing | Statistical | Tolerancing

Abstract: In mechanical design, geometrical specifications and dimensional tolerances are commonly used to avoid final product malfunction and to allow for assembly integration. Geometric specification usage, in particular, has many manufacturing and durability implications, the feasibility of their measurement and verification, however, is often neglected and the influence of measurement uncertainty in their evaluation underestimated. Often geometrical specifications are defined without considering measurement uncertainties, or measurability at all: it is not uncommon to find approved specifications prescribing unverifiable geometry, or dimension tolerances that exceed state-of-art measurements. This article explores the case study of orthogonality between a circular hole and the plane on which it is drilled, evaluated using a Coordinate Measuring Machine. Such specification is defined, according to ISO 14253, as the angle between the plane normal and cylinder axis. Uncertainty of points coordinates obtained can, however small, play a key role in the final evaluation of orthogonality: if the specified tolerance is thigh enough it is also possible to have misalignment uncertainty higher than the tolerance itself. The authors propose the results of a mathematical and numerical model, meant to help the designer to define specification to assess the relationship between cylinder-plane misalignment measurability, CMM uncertainty and features dimensions. © 2013 EDP Sciences.

Keywords: Geometric specification | Measurability | Orthogonality | Tolerances verification | Uncertainty

Abstract: The increasing integration between electronics and mechanical engineering brings to the industrial market very hi-tech sensors, often non-linear, capable of more than a single input and single output. A problem more and more relevant for sensors like these is calibration. Classic linear calibration procedures, when applied to this extremely engineered sensors, lead to poor accuracy and are generally not satisfactory. The case study is the calibration of a bi-dimensional laser based position sensor, in particular a positive sensitive detector, that is an optical position transducer based on series of photodiodes commonly used as multidimensional sensor. To perform the calibration a micrometric positioning table was used to test the whole photodiode active area in both directions. The sensor studied showed a very linear behaviour in the central region of the working range, and a limited nonlinearity closer to the range limits and was to be used to verify robot movement capabilities; to reduce uncertainty associated with nonlinearities, a set of nonstandard, non-linear, calibrations were performed, pointing out residual values in order to compare different algorithms. In a previous work, authors have already tested a linear model against an algorithm based on radial basis functions (RBF) and Nelder-Mead simplex method. Object of this paper is the definition of a procedure based on RBF and genetic algorithms for multi-dimensional interpolation of data cloud and a comparison between this updated procedure results and the ones of the previous studied algorithms. The reference model for calibration was a black box with two inputs, X and Y position of the laser spot, and two outputs, voltages Vx and Vy, while the calibration procedure was split in two separate layers, one for each output depending on both inputs. Given N data points in a M-dimensional environment and N values that represent the non linearity residual, purpose of the algorithm is to approximate a data cloud with a real function, that is represented as a sum of a polynomial (linear) part and L radial basis functions, each associated with a different center (node) and weighted by an appropriate coefficient, that the procedure also allow to assess. When no starting guess for nodes are given in input. nodes coordinates are the output of a non-linear optimizer based on a genetic algorithm, whose goal is to locally minimize the objective function. The algorithm stops itself whenever it reaches a certain tolerance level, a user- specified number of nodes or when the previous iteration has a better value of the objective function. This study has been performed for various RBF classes, and shows an increased accuracy, thus a better metrological behaviour, with respect to the standard linear (planar) calibration model traditionally used.

Keywords: Calibration | Genetic algorithm | Multi input | Radial basis function | Uncertainty

Abstract: In order to avoid final product malfunction and to allow for assembly integration, geometric specifications and dimensional tolerances are commonly used in mechanical design. However the feasibility of geometric specification measurement and verification is often neglected and the influence of measurement uncertainty in geometric tolerances evaluation underestimated. The authors propose updated results of a mathematical and numerical model, based on Monte Carlo simulations, developed in order to define a measurability threshold of geometric tolerances in relation to measurement uncertainty and geometric parameters, such as feature dimensions, meant to help the designer to define measurable geometric specifications. Starting from EN ISO 14253-2:2011 and EN ISO 14253- 3:2011 standards, a perpendicularity tolerance between a cylindrical feature and a planar one has been simulated. A mathematical model has been defined for each feature, in order to assess both misalignment and its uncertainty when starting from the estimate of geometric entities obtained from point coordinates measured by a Coordinate Measurement Machine (CMM). Monte Carlo Analysis of these simulation underlined how geometric parameters, such as dimensions of the features involved, can act as magnifiers for measurement uncertainty when verifying a geometric specification: there could be cases where this magnification effect could lead to non-measurability of misalignment and non-verifiability of the geometrical specification requested.

Keywords: Dimensional parameters | Geometric tolerances | Measurability threshold | Measurement uncertainty

Abstract: In a previous paper (Di Angelo, L., Di Stefano, P. and Morabito, A., 2011. Automatic evaluation of form errors in high-density acquired surfaces. International Journal of Production Research, 49 (7), 2061-2082) we proposed an original methodology for the automation of the geometric inspection, starting from an acquired high-density surface. That approach performed a recognition process on the acquired data aiming at the identification of some intrinsic nominal references. An intrinsic nominal reference was detected when a geometric property was recognised to be common to a set of adjacent points in the 3D data set representing the acquired object. The recognition of these properties was carried out based on some rules. Starting from these concepts, a new specification language was defined, which is based on recognisable geometric entities. This paper expands the category of intrinsic nominal references to include new mutual intrinsic orientation, location and dimensional properties pertaining to 3D features. This approach involves the automatic construction of a geometric reference model for a scanned workpiece, called recognised geometric model (RGM). The domain of the representable entities within the RGM strictly depends on the rules used for the recognition of the intrinsic properties. In particular, this paper focuses on the rules for the recognition of the orientation and location properties between non-ideal features. When using the RGM, tolerances are specified according to the set of available and recognisable intrinsic nominal references. Based on the geometric product specification, the RGM data structure can be queried to capture some quantitative information concerning special intrinsic geometric parameters and/or non-idealities. © 2012 Copyright Taylor and Francis Group, LLC.

Keywords: automated inspection | ISO tolerancing | shape recognition | three dimensional metrology | triangular meshes

Abstract: This article proposes a mathematical approach for the definition of a multiple input calibration diagram, based on a two step sequence, iteratively defining a set of radial basis functions and fitting its parameter to experimental data. Different radial basis functions have been evaluated and compared, focusing on Gaussian and multi-quadratic elements. The case studied used to test this method is the calibration of a bi-dimensional laser based position sensor believe that the method could be generalized and applicable to all transducers presenting multiple outputs, multiple inputs and localized non-linearities.

Keywords: Calibration | Multi input | Radial basis function | Uncertainty

Abstract: In the functional design process of a mechanical component, the tolerance allocation stage is of primary importance to make the component itself responding to the functional requirements and to cost constraints. Present state-of-the-art approach to tolerance allocation is based on the use of Statistical Tolerance Analysis (STA) software packages which, by means of Monte Carlo simulation, allow forecasting the result of a set of user-selected geometrical and dimensional tolerances. In order to completely automate and optimize this process, this work presents a methodology to allow an automatic tolerance allocation, capable to minimize the manufacturing cost of a single part or assembly. The proposed approach is based on the Monte Carlo method to compute the statistical distribution of the critical to quality characteristics and uses an optimization technique based on Genetic Algorithms. The resulting procedure has been integrated in an off-the-shelf variation analysis software: eM-TolMate (by Siemens AG). Both the description of the optimization algorithm and some practical applications are presented in order to demonstrate the effectiveness of the proposed methodology. © 2012 Asian Network for Scientific Information.

Keywords: Functional design | Genetic algorithms | Monte carlo method | Tolerance allocation

Abstract: In this paper the authors present an original methodology aiming at the automation of the geometric inspection, starting from a high-density acquired surface. The concept of intrinsic nominal reference is herein introduced in order to evaluate geometric errors. Starting from these concepts, a new specification language, which is based on recognisable geometric entities, is defined. This work also proposes some surface differential properties, such as the intrinsic nominal references, from which new categories of form errors can be introduced. Well-defined rules are then necessary for the unambiguous identification of these intrinsic nominal references. These rules are an integral part of the tolerance specification. This new approach requires that a recognition process be performed on the acquired model so as to automatically identify the already-mentioned intrinsic nominal references. The assessable errors refer to recognisable geometric entities and their evaluation leaves the nominal reference specification aside since they can be intrinsically associated with a recognised geometric shape. Tolerance specification is defined based on the error categories which can be automatically evaluated and which are an integral part of the specification language. © 2011 Taylor & Francis.

Keywords: automated inspection | form error evaluation | GPS tolerancing

Abstract: Variation analysis of assemblies is a strategic task in many industrial applications. Parts manufactured through plastic deformation processes exhibit appreciable shape deviations from the nominal geometry due mainly to spring-back phenomena. When these parts are assembled, initial shape deviations at part level highly influence the final assembly shape. This work focuses on the modeling and simulation of shape errors in order to perform variation analysis of compliant assemblies. The aim is to simulate variational shape of parts according to a small number of control points chosen on the part geometry through a morphing mesh procedure. These points are typically related to measurement or inspection points of manufactured parts. From the mesh model of parts, mesh nodes are moved by applying the morphing procedure. In particular, in order to assure control points belong to the "perturbed" shape, a linear-constrained approach is adopted. The so-morphed parts are used to accomplish the variational assembly analysis following the classical place, clamp, fasten, and release cycle. In order to achieve statistical results, Monte Carlo simulation is performed: a set of control points driving the perturbed parts is generated at each iteration; these parts are then assembled and results are stored. Numerical results are compared with ones coming from commercial software that uses a linear approach based on the sensitivity matrix.

Keywords: Geometric covariance | Monte Carlo FEA | Morphing mesh | Shape errors | Variational assemblies

Abstract: The core of the paper is focused on the experimental characterization of four different 3D laser scanners based on Time of Flight principle, through the extraction of resolution, accuracy and uncertainty parameters from specifically designed 3D test objects. The testing process leads to four results: z-uncertainty, xy-resolution z-resolution and z-accuracy. The first is obtained by the evaluation of random residuals from the 3D capture of a planar target, the second from the scanner response to an abrupt z-jump, and the last two from direct evaluation of the image extracted by different geometric features progressively closer each other. The aim of this research is to suggest a low cost characterization process, mainly based on calibrated test object easy to duplicate, that allow an objective and reliable comparison between 3D TOF scanner performances. © 2011 SPIE-IS&T.

Keywords: Accuracy | Characterization | Precision | Range sensor | Resolution | Standardization | TOF laser scanner

Abstract: In this paper, a general methodology to do tolerance analysis of rigid assemblies is proposed. Firstly, tolerance specification sets, according to GD&T or ISO specifications, are translated into variational features by using 4∈×∈4 homogenous transformation matrices. In particular, planar and cylindrical features are considered. Then, once all variational features are modeled, assembly constraints among parts are introduced. To solve assembly constraints, an assembly transformation matrix is evaluated. By using point, line, and plane entities and their combinations, kinematic joints are modeled. A numerical procedure is proposed to solve fully and over-constrained assemblies. The best-fit alignment among variational mating features is performed by using optimization algorithms. The proposed method for tolerance analysis of rigid part assemblies allows to simulate different assembly sequences. Finally, in order to show the effectiveness of the proposed methodology, three case studies are described and analyzed. © 2009 Springer-Verlag London Limited.

Keywords: Assembly constraints | Assembly simulation | Feature modeling | GD&amp;T/ISO specifications | Tolerance analysis | Variational features

Abstract: The need for a designer to have a tool able to do motion and constraint analysis, to check for the under-constrained and/or over-constrained status of an assembly, is strategic in a design contest where several changes are made during the design process by using CAD. Traditional kinematic tools provide little information on over-constraints at 3D level. Screw theory has been already used in mechanical assemblies, in a top-down design, to do motion and constraint analysis. This theory is here used to analyze mechanical assemblies in the contest of a feature-based CAD system. The structure of the CAD assembly is captured and described as assembly graph, similar to Datum Flow Chain, through which the motion or constraint status of any part (in terms of twist and wrench matrices), can be obtained. The underlying algorithm is based on the Kirchoffs rules successfully applied by Davies to mechanisms. How to automatically create the assembly graph, detect the useful loops and then write the loop kinematic equations is described. Three case studies are presented related to CAD assemblies of mechanisms built up in SolidWorks® CAD system by Dassault Systèmes from which assembly constraints have been acquired. Copyright © 2010 by ASME.

Abstract: Often a designer has the problem to apply a suitable system of geometrical and dimensional tolerances to an assembly. The right solution is not unique, in fact it depends on the chosen parameters. If the tolerances have to be optimized, some important parameters have to be taken into account, e.g. the efficiency of each prescription, or if this last is reachable, or it can be verified and how much the realization costs. The authors opinion is that a statistical approach based on the Monte Carlo Method is very useful when the tolerances chains are complex. This paper shows an application of this method in order to verify the functional alignment between two assemblies and a critical analysis of the uncertainty in phase both of the component design and test. This study has been developed thanks to the strict requirements imposed by ESA (European Space Agency) on the components that Thales Alenia Space has to realize within the LISA Pathfinder experiment. The very critical aspect of this work is to reciprocally align two cylindrical elements of two different assemblies. The specifications require 100 μm as maximum linear displacement and 300 μrad as maximum angular displacement. Moreover this prescriptions have to be verified also when the two elements are independently moving. To be able to reach such strict accuracy level the components have been assembled in an ISO 100 class cleanroom and the work space was a 3D Coordinate-Measuring Machine (CMM). The cylindrical elements have a 10 mm diameter, so the value of the measurement uncertainty associated with the alignment check is fundamental. Starting from the different uncertainty sources, the measurability and verifiability of the alignment have been considered and evaluated. The overall uncertainty has been assessed by numerical simulations which have taken into account the dimensional, geometrical and form tolerances as well as the instrumental uncertainty of the 3D CMM. This estimation has been positively validated by a session of repeated measurements. Numerical simulations have also allowed performing a sensitivity analysis, in order to give information about which sources more contribute to the overall uncertainty. Copyright © 2010 by ASME.

Abstract: The performance of 2D digital imaging systems depends on several factors related with both optical and electronic processing. These concepts have originated standards, which have been conceived for photographic equipment and bi-dimensional scanning systems, and which have been aimed at estimating different parameters such as resolution, noise or dynamic range. Conversely, no standard test protocols currently exist for evaluating the corresponding performances of 3D imaging systems such as laser scanners or pattern projection range cameras. This paper is focused on investigating experimental processes for evaluating some critical parameters of 3D equipment, by extending the concepts defined by the ISO standards to the 3D domain. The experimental part of this work concerns the characterization of different range sensors through the extraction of their resolution, accuracy and uncertainty from sets of 3D data acquisitions of specifically designed test objects whose geometrical characteristics are known in advance. The major objective of this contribution is to suggest an easy characterization process for generating a reliable comparison between the performances of different range sensors and to check if a specific piece of equipment is compliant with the expected characteristics. © 2010 by the authors.

Keywords: 3D measurement | Accuracy | Laser scanner | Metrological characterization | Pattern projection | Resolution | Uncertainty

Abstract: The effect of the sintering temperature on the dimensional and geometrical precision of a 3%Cr-0.5%Mo- 0.5%C ring-shaped part produced in an industrial plant was studied. The part was compacted to 6.8 g/cm3 green density and sinter-hardened at 1120°C, 1250°C, 1300°C and 1350°C. Despite the large shrinkages (up to 1.24% at the highest temperature), dimensional and geometrical characteristics do not worsen noticeably on sintering, except for the dimensional tolerances on the diameter, which anyway keep a good precision level, from IT3 to IT4-IT5 (internal diameter) and from IT5 to IT6-IT7 (external diameter). According to the results, sintering at high temperature up to 1350°C does not seem to impair the most important characteristic of sintered parts, i.e. the precision. © 2010 Metal Powder Industries Federation.

Abstract: The dimensional and geometrical characteristics of Charpy bars produced with two different steels were investigated to evaluate the effect of increasing the sintering temperature from 1120 °C (conventional sintering temperature) up to 1350 °C. The problem was approached from the Geometric Dimensioning and Tolerancing (GD&T) point of view, referring to the standard ASME Y14.5 (2009). The dimensional and geometrical characteristics were evaluated using a Coordinate Measuring Machine (CMM), measuring the surfaces by scanning mode. The work highlights that the increase in the sintering temperature, aimed at improving the mechanical properties, does not prevent the main benefit of this technology, i.e., the possibility of producing parts with good dimensional and geometrical precision. Moreover, a methodology establishing the measurement procedures and data processing, to be used in future work for the characterisation of more complex shapes, was defined. © 2010 Elsevier B.V.

Keywords: Geometric dimensioning and tolerancing | Powder metallurgy | Shrinkage

Abstract: Purpose - The purpose of this paper is to investigate a method for comparing the scanning and reproducing accuracy of highly shaped objects like plaster casts used in dentistry. Design/methodology/approach - Theoretical considerations on errors introduced by the scanning systems and subsequent point clouds data elaboration have led to a method to estimate the accuracy of the whole process. Suitable indices have been chosen and computed at each stage. As a final result, the overall chain, scanning and reproducing systems can be assessed. In order to validate the proposed method casts have been scanned by means of commercial systems and then reproduced by using different rapid prototyping technologies, materials and parameters. Error indices have been computed and reported. Findings - Since it is not possible to define reliable and meaningful reference models for non-standard shapes, an absolute accuracy value for the scanning process cannot be stated. Anyway the proposed method, thanks to relative performance indices, allows the comparison of different acquisition systems and the evaluation of the most performing manufacturing chain. Practical implications - The study provides a method to assess the relative performance between commercial systems both in scanning and reproducing stage. Originality/value - In literature, some studies on the accuracy of scanning devices have been found but they are based on standard geometrical features. In this paper, the problem of complex shapes in absence of reference model is addressed instead. Copyright © Emerald Group Publishing Limited [ISSN 1355-2546].

Keywords: Accuracy | Dentistry | Rapid prototypes | Structural analysis

Abstract: While parallel kinematics micropositioners offer high repeatability in positioning with respect to their own reference frame, the accuracy of absolute positioning with respect to a second, fixed, reference frame largely depends on the knowledge of the relative position between the two. Here will be presented a method for a rapid estimation of these relative positions based on subsequent movements of a positioner under a CMM and evaluation of position uncertainty.

Keywords: Accuracy measurement | Hexapod | Positioning | Uncertainty

Abstract: Resolution analysis represents a 2D imaging topic for the use of particular targets for equipment characterization. These concepts can be extended in 3D imaging through the use of specific tridimensional target object. The core of this paper is focused on experimental characterization of seven different 3D laser scanner through the extraction of resolution, accuracy and uncertainly parameters from 3D target object. The process of every single range map defined by the same resolution leads to different results as z-resolution, optical resolution, linear and angular accuracy. The aim of this research is to suggest a characterization process mainly based on resolution and accuracy parameters that allow a reliable comparison between 3D scanner performances. © 2009 SPIE-IS&T.

Keywords: 3D Scanner | Accuracy | Characterization | Resolution | SFR | Target Object

Abstract: Incremental Forming is a flexible and innovative sheet metal forming process able to form complex shapes without the need of any expensive die. In this way, expensive fixtures are avoided obtaining a cheaper production, more advantageous for small production batches. Anyway, more than the process slowness, the geometrical accuracy represents the most important drawback today. In particular, two kinds of geometrical errors can be observed on a sheet component incrementally formed: the presence of elastic springback that modifies the imposed final depth, that "moves away" from the designed one, and the undesired bending effect of the sheet, which undergoes to the punch action. Several studies which tend to optimise the equipment and/or the tool path, in order to reduce the profile diverting, were executed. In this paper, an experimental investigation was carried out in order to test and introduce a new approach able to solve the above problem. More in detail, the test were executed applying an additional backdrawing phase, after the conventional negative deformation. Different testing conditions were evaluated during the experimental campaign and critically compared in the analysis. © Springer/ESAFORM 2009.

Keywords: Accuracy | Incremental sheet forming | Sheet metal forming

Abstract: Geometrical tolerances control of mechanical components requires methods and tools in order to improve the efficiency of process in terms of time. Dedicated software systems in order to plan and simulate the control and hardware tools in order to rapidly acquire the needed 3D information can support the process improvement. In this context it is important to use the 3D CAD (Computer Aided Design) model, as base to plan and pilot the whole process. The aim of present work is to describe an automatic geometrical tolerances measurement system usable during the design stage. It is based on three main tools: a CAD-based modular software tool, in order to plan, simulate, and pilot the whole verification process, a 3D optical digitizer, as shape acquisition system, and a multi-axis Degree of Freedom (DoF) robot arm in order to move the digitizer. This paper is focused on the developed algorithms to optimize the 3D views acquisition planning. Surface Normal Method and Visibility Map concepts have been reworked for range scanner positions determination and the optimal path is computed by a graph of alignable simulated scans. Experimental test cases are reported in order to show the system performance. ©2009 IEEE.

Abstract: This work describes an automated artificial vision inspection (AVI) system for real-time detection and classification of defects on textile raw fabrics. The tool (software + hardware) is directly attached to an appositely developed appraisal equipment machine (weave room monitoring system) and the inspection is performed online. The developed tool performs (1) the image acquisition of the raw fabric, (2) the extraction of some critical parameters from the acquired images, (3) an artificial neural network (ANN)-based approach able to detect and classify the most frequently occurring types of defects occurring on the raw fabric and (4) a standard image processing algorithm that allows the measurement of the geometric properties of the detected defects. The reliability of the tool is about 90% (defect detected vs. effectively existing defects), that is, similar to the performance obtained by human experts. Once detected the defects are correctly classified in 88% of cases and their geometrical properties are measured with a sub-pixel precision.

Keywords: Artificial neural network | Image processing | Raw fabrics | Real time

Abstract: It is well known that the geometrical accuracy is a very relevant problem in Incremental Forming operations, since the material is not well sustained and, then, the elastic springback plays a significant role during the process. A number of researches are involved in the study of geometrical precision after the forming stage but considering the sheet clamped to the equipment. However, it is well known that material coupling is carried out after trimming, when it could change its shape after the new equilibrium. In the paper here addressed the above concept is kept in touch and a wide experimental campaign has been set-up in order to acquire experimental information on the effect of unclamping and trimming after incremental forming processes. The obtained results are able to suggest to the process designer some best practices which are accurately discussed in the paper.

Keywords: Incremental forming | Precision | Sheet metal forming

Abstract: In this paper a statistical method for tolerances analysis and cost evaluation is presented. Statistical tolerances analysis is performed by assuming the Chase and Greenwood mean shift model, providing an original systematic approach to evaluate the mean shift factor. The proposed approach allows for the analysis of manufacturing costs for different confidence levels of the variables to be optimised. The interaction between customer requirements, design parameters and process variables, are taken into account by incorporating the process planning models and conceptual and embodiment design solutions. The cost analysis is performed by selecting the most appropriate driver for each component of the cost due tolerances. Cost driver parameters are evaluated over product life cycle, in different design domains (customer, design and process) and also include the customer satisfaction (quality loss).

Keywords: Cost analysis | Mean shift model | Tolerance analysis

Abstract: The present work presents the devising of a new highly automated artificial vision inspection (AVI) tool for real-time defect detection and classification on circular knitting machines. The tool is based on the combination of statistical analysis, Image Processing and an artificial neural network (ANN) approach. The tool (software + hardware) is directly attached to a circular knitting machine and the inspection is performed on-line during other common operations like laser cutting and ironing. The automatic inspection allows the real-time detection and classification of the most frequently occurring types of defects on knitted fabrics, which are significant for purposes of quality control and fabric grading. The reliability of the detection tool, i.e. the ratio between defect detected and effective defects is about 93%. The AVI system has been developed by the Department of Mechanical Engineering, University of Florence (Italy), and the textile research centre Tecnotessile s.r.l. of Prato (Italy).

Keywords: Image processing | Knitting machines | Neural network | Radon transform | Real time | Skewness

Abstract: This work provides an automatic and non-intrusive tool to objectively monitoring the raising process by measuring the height and the density of the fibres emerging from a raised cloth (pile). These parameters are assessed by a numerical procedure, which elaborates the images provided by an appositely developed machine-vision system. The proposed approach allows the investigation and the control of the raising process and has been validated by experimental measurements performed on a set of specimens (cloths) with several raising degrees. The comparison between the results obtained by the proposed procedure and the ones coming from a widely accepted textile-measuring device (fabric assurance by simple testing, FAST) is also provided. © 2005 Elsevier B.V. All rights reserved.

Keywords: Cloth raising | Image processing | Machine-vision design | Pile density | Pile height

Abstract: Incremental forming applications are currently increasing in industry, especially for the production of small batches or single components. In fact, sufficient know-how is now available for the manufacture of simple products. However, further efforts are required to reduce the drawbacks of typical incremental forming processes, which compromise important advantages in terms of costs and flexibility. First of all the duration of the process, usually a few minutes, influences this kind of process, even if the operations are carried out on high-speed digitally controlled units. A tendency to produce inaccurate parts can reduce industrial interest with respect to incremental forming. Different approaches could be proposed to reduce this drawback, and a feasible and easily implemented strategy is the design of modified trajectories able to take into account both springback effects and stiffness reduction owing to specific clamping equipment. In this paper, such a strategy is pursued by integrating an on-line measuring system, composed of a digital inspector and a computer numerically controlled (CNC) open program. The geometry obtained is sampled in particular steps and an appropriate routine modifies the coordinates of the future punch path. This procedure of automatic control has been developed using an effective finite element (FE) code. An experimental design illustrates the potential use of the suggested methodology. © IMechE 2005.

Keywords: Incremental forming | Net shape | Sheet metal forming

Abstract: Incremental Forming processes have been introduced in the recent past as an alternative to the money consuming stamping technology, when small batches have to be manufactured. Anyway, they introduce some advantages in terms of flexibility and material formability but, also, some problems such as the dimensional accuracy decreasing. In this paper, a particular application is carried out taking into account the development of an innovative technique to produce a customised ankle support. In this way Incremental Forming process has been selected for the sheet profiling, exalting the role that this technology may play when single complex product has to be manufactured. The producing procedure finishes with a measure of the dimensional accuracy that shown a good result for the desired application. © 2005 Elsevier B.V. All rights reserved.

Keywords: Ankle support | Incremental Forming | Reverse engineering

Abstract: Experimental, analytical and numerical methods of measuring the surface density of the pile of napped fabrics are presented. Surface density of pile is defined as the ratio between the weight of the pile extending above the fabric and the area of the sample to which it belongs. Samples were weighed, shaved and reweighed and the area of the sample was calculated from the number of pixels on a high-resolution image. The density of the fibre removed was estimated as the difference in density of the sample before and after shaving. A non-intrusive analytical method based on the height, diameter and number of pile fibres and a numerical method are described. Calculations based on pure wool and wool blend are presented and compared with the results obtained using the experimental method.

Abstract: As known, incremental forming is a flexible and innovative sheet metal forming process which allows complex shape shells forming without the need for any die. For these reasons, incremental forming is nowadays suggested for rapid prototyping and customised products. The present paper is focused on material formability in incremental forming and, in particular, on the evaluation and compensation of elastic springback. The latter significantly modifies the imposed shape. For this purpose, a deeper assessment of the process was developed following three different approaches. First of all, a wide experimental investigation on the influence of some relevant process parameters was developed. At the same time, an explicit FEM analysis of incremental forming process was carried out in order to verify its effectiveness and, as a consequence, its ability to be used as a design tool. Furthermore, the obtained parts were analysed by a reverse engineering technique and the measured geometry was numerically compared with the desired one, with the aim to quantify the geometrical discrepancies. In this way, an integrated numerical/experimental procedure is proposed in order to limit the shape defects between the obtained geometry and the desired one. © 2004 Elsevier B.V. All rights reserved.

Keywords: FEM | Geometrical accuracy | Incremental forming

Abstract: Incremental forming is nowadays increasing its presence in industry as a new but interesting process, especially for production of small batches or unique components. Anyway, relevant efforts have to be spent in order to reduce the typical incremental forming processes drawbacks that risk to belittle the high advantages in terms of costs and simplicity. In fact, the process duration, usually equal to several minutes even if the operations are carried out on high speed numerical controlled units, and a certain tendency to produce no precise parts, can reduce industrial interest about incremental forming. A possible strategy to reduce the latter item is the design of modified trajectories able to take into account both the springback effects and the stiffness reduction due to the particular clamping equipment. In this paper the above introduced strategy is pursued integrating an on-line measuring system, based on a digital inspector, and a CNC open program. The actual geometry is acquired in some remarkable points and a compensation routine modifies the coordinates of the future punch path. The modification policy has been developed by using an effective FE code. An experimental verification shows the good potentiality of the suggested methodology.

Abstract: Tolerance design plays an important role in the modern design process by introducing quality improvements and limiting manufacturing costs. In this paper a method for statistical tolerance analysis and synthesis is presented. This method is implemented using the mean shift model of Chase and Greenwood, providing a systematic approach to evaluate the mean shift model method considers all the principal factors that affect the statistical sum of a certain number of assembly dimensions. In particular, the considered factors include the mean shift ratio, the confidence level, the number of dimension of the assembly and the tolerance assortment between the component dimensions. An implementation of the mean shift model for tolerance synthesis is described. The tolerances synthesis is performed in an unusual way, taking into account in the optimization process the typical parameters that affect the product variability. For this purpose the method uses four types of condition for the dimensional tolerances: fixed tolerance value, fixed mean shift ratio, fixed mean shift and fixed natural variability. Furthermore, in the optimization process, the service variability is considered under two conditions: fixed and valuable service variability. A case study is presented and the results of some simulations are discussed.

Keywords: Mean shift model | Tolerance analysis and synthesis

Abstract: This article presents a review of a commercial computer-aided tolerance analysis tool, eM-TolMate, which is embedded in four major CAD systems (Catia [1], UG [2], Pro/E [3], SDRC [4]). eM-TolMate combines the Monte Carlo statistical simulation techniques with an internal tolerance management system and identifies the key characteristics (i.e. dimensions/clearances of interest) of nominal component models that are critical to proper assembly. Features and tolerances are directly created in CAD models and both single component or multi component analyses are available. For assemblies, eM-TolMate offers the capability to apply user-defined assembling rules or to automatically detect mating conditions. Actual features are varied within the specified tolerance range, and standard or user-defined statistical distributions are used in simulation runs to determine variations of key characteristics. It also offers the capability to rank tolerances based on contribution to the variation, so the user can identify where tolerances need to be tightened or can be loosened. eM-TolMate [5] represents a useful tool in tolerance analysis of mechanical assemblies.

Abstract: In this paper is analysed the problem, using soft models, of soft dependence of parameters in design systems. A new form of computing, called Soft Computing, is recently used in many emerging disciplines because it is tolerant to imprecision, uncertainty and partial truth. The Soft Computing uses many disciplines as Bayesian inference and maximum entropy method. The logic relationship that ties the different elements can be defined more easily using the axioms of soft design emanating from MinEnt principle. The fundamental axiom of design is: valid design has minimum values of information and depends on a finite and limited number of independent, or soft dependent, parameters. © 2002 Published by Elsevier Science B.V.

Keywords: Axiomatic design | Entropy | MaxEnt | Soft Computing | Soft design | Uncertainty

Abstract: Screw Theory is well known to do kinematic computations. Recently it has been used to create kinematic models of assembly features so allowing to do assembly analysis. Motion Limit Analysis uses the mathematics of screw theory to model the ability of mechanical assembly features to allow or constrain rigid body motions in six degrees of freedom. A user of this theory is able to determine the directions and quantitative amounts of possible finite rigid body motions of a part that is being added to an assembly via calculation applied to a defined set of assembly features. The ability to calculate rigid body motions of a part is important for enabling in-process adjustment during assembly to precisely establish key assembly dimensions. MLA software is a part of a suite of software programs used to do assembly analysis.