Geometric dimensioning, tolerancing and inspection

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

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

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

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

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

System engineering (SE) methods and principles are nowadays widely adopted in the product development processes, especially in the industrial sector, where saving production time and costs are primary goals. This work describes an application of a particular SE methodology, the V-model-based design, in which the system development lifecycle is divided on the basis of a graphical V-shaped scheme, called V-model. Following this approach, a new concept of charging arm for Robotic Train Inspection Monorail (TIM) of Large Hadron Collider (LHC) at CERN (Conseil Européen pour la Recherche Nucléaire) has been developed. The current charging arm version is affected by several issues and limits that have led to the necessity of a new solution. Starting from the first stages of functional requirements (FRs) definition and decomposition (left side of the “V”), a new concept has been implemented, in order to be tested for its verification and validation (right side of the “V”). As part of the principles of SE, the process has been based on virtual models of the product and on virtual simulations of its operation, rather than on the realization of time-consuming and expensive physical models and tests, even if a final physical prototype has also been built and some physical operative tests have also been carried out on it. These tests have showed that the new product appears to fulfill each one of its FRs and overcome the limits imposed by the previous version. The future commissioning and operative tests in the real operating condition and location shall definitely validate the new product.

Keywords: Additive manufacturing , Design for manufacturing , Finite element method , System engineering , V-model-based design , Virtual reality

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

Design for Sintering 2 is an EPMA Club Project aimed at improving the previously developed design procedure accounting for anisotropic dimensional changes on sintering. Goal of the project is both enlarging the reference database through the fruitful cooperation of the industrial partners and investigating in depth the mechanisms responsible for anisotropic dimensional changes. This work is focused on the second part of the project, aimed at studying the influence of compaction parameters. Axisymmetric parts characterized by different materials and geometrical parameters were produced at different green densities with different compaction strategies. Focusing the attention on the anisotropy in the compaction plane, dimensional changes were measured and evaluated, also relating them to the attainable dimensional tolerances. The influence of compaction strategy was analyzed in depth, and for the different materials and geometries the more robust process conditions for dimensional precision were highlighted.

Previous studies have systematically investigated densification in ring-shaped parts. Additionally, the effect of filling parameters on filling and green density was explored, demonstrating the strong influence of the die cavity on the origin of inhomogeneous powder distribution. A uniform density is mandatory for industrial production, so further investigation is necessary, also including the contribution of powder transfer. This work aims at investigating the effect of powder transfer on the density distribution and the geometrical precision in 2-level axi-symmetric parts. Sample geometry was compacted by varying: the filling parameters, powder transfer strategies, and compaction forces. Reference samples were produced by excluding the powder transfer step from the compaction cycle. Green and sintered density distribution were derived, highlighting the effect of filling, powder transfer, and compaction strategies.

This article introduces the Differential Entropy-based Compactness Index (DECI), a new metric for synthetically describing the spatial distribution of point clouds. DECI is founded on the differential entropy (DE) of point clouds, and if they depict a moving object distribution, the index enables real-time monitoring. Historical data analysis allows for the study of DECI trends and average values in defined intervals. Multiple practical applications are suggested, including risk assessment, congestion measurement, traffic control (including autonomous systems), infrastructure planning, crowd density, and health analysis. DECI's real-time and historical insights are valuable for decision-making and system optimization and hold potential as a feature in machine learning applications.

Keywords: 3D geometry distribution assessment , compactness index , differential entropy , point clouds , real-time , risk assessment

The analysis of motor activity has been revealed to be essential for monitoring dairy cows' behavior, with the main aim of identifying the onset of oestrus in time. Pedometers used for oestrus detection have a current average working life on the market of about 5 years. At the end of that period, devices are disposed of, posing a relevant question regarding environmental sustainability. The present work proposed a method to achieve an eco-design of pedometers compliant with the guidelines of the Green Deal. Specifically, a new thermo-plastic organic compound made of polyamide 66 reinforced with organic hemp fibers (trade name SDS Nylon) was adopted. The feasibility, benefits, and performance of this material were assessed with a major emphasis on strength, lightweight, and surface finish. The material in addition to ensuring adequate chemical and mechanical resistance is biocompatible and recyclable. It assures better animal welfare and reduces both environmental impacts and management costs for farmers. Other innovations introduced in this study consisted of the adoption of a double casing. An external case was conceived with a protective function of the measurement system and fixed to a cow's foreleg by an easy anchor system. An internal case was specifically designed to house the electronic components and to be moved from one cow to another after the pregnancy diagnosis. The solutions proposed in this research will contribute to guaranteeing pedometers a longer lifetime and better recyclability than existing commercial ones, consequently limiting the environmental load derived from their disposal.

Keywords: biocompatible materials for FDM , custom design , digital product optimization , stand-alone smart device , tolerances assignment

This article reports the analysis and preliminary design of a passive, wearable, upper limb exoskeleton to support workers in industrial environments in a vast range of repetitive tasks, offering an effective strategy to reduce the risk of injuries in production lines. The system primary purpose is to compensate for gravity loads acting on the human upper limb. The proposed exoskeleton is based on 6 Degrees-of-Freedom (DoFs) kinematics with 5-DoFs for the shoulder joint (two displacements plus three rotations) and 1-DoF for the elbow. Gravity compensation is implemented with passive elastic elements to minimize weight and reduce cost. A detailed analytical tool is developed to support the designer in the preliminary design stage, investigating the exoskeleton kinetic-static behaviour and deriving optimal design parameters for the springs over the human arm workspace. By defining specific functional requirements (i.e., the user&#x2019;s features and simulated movements), computationally efficient optimization studies may be carried out to determine the optimal coefficients and positions of the springs, thus, maximizing the accuracy of the gravity balancing. Two different solutions for the arrangement of the elastic elements are investigated, and obtained results are validated with a commercial multi-body tool for some relevant movements of the user&#x2019;s arm.

Keywords: design optimization , gravity balancing , Upper limb exoskeleton , virtual prototyping , wearable devices

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

The Panel method is an approach for the estimation of the lift of 3D models which is faster than CFD. This can be useful especially in the conceptual design stage where several configurations should be evaluated in a reduced time with a limited computational cost. However, the meshing of the 3D body surface with rectangular panels can be a time-consuming activity because the designer should define from scratch a cloud of points that matches the external surfaces of the tested object to obtain consistent panelling. Therefore, a voxelization-based methodology has been developed to obtain the panels' position, speeding up and automating the model preparation process. The obtained discretization has been integrated into a panel method available in the literature. Four case studies, of increasing complexity, have been analyzed to investigate the capability of the innovative voxel-based panel methodology. A parametric study has been carried out to study the effect of the voxel grid dimension on the accuracy of the results. Benchmarking values of lift coefficient obtained from literature or xFoil software have been used to evaluate the precision that can be achieved with this approach. The results show a good agreement between the voxel-based panel method and the literature when the overall pressure distributions and aerodynamic coefficient values are considered. Higher errors are noticed with drag.

Keywords: Fluid dynamics , Panel method , Potential flow , Voxelization

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

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

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

Close-range photogrammetry (C-RP) is a widespread and efficient technology to obtain digital models of physical objects. Typical limitations as sharped geometry, shiny surface finishing and light conditions can be overcome by using high-end equipment, which results in increased costs and requires specific skills in human operators. This paper aims to investigate whether a low-cost and simplified approach to C-RP makes it suitable for the 3D acquisition of bodywork components and similar free-form artefacts, as an affordable alternative to 3D scanning in fields where a lower value of accuracy is required. Hence, two commercial C-RP software were used to 3D capture handcrafted car body panels and compare the C-RP models using a 3D scan as a reference within an inspection software. Two case studies are considered: a 1:5 scale model of the front bonnet of a Ferrari 250 Testa Rossa from 1958 and a head lamp housing of a Ferrari 275 GTB from 1962. Considering the complexity of double curvature surfaces and the reflection due to material and surface treatment, both these artefacts require some pre-processing operations and an adequate set-up to perform image acquisition. These case studies represent a relevant application for the field of classic vehicle restoration, where C-RP could be a promising technique to support panel beaters and craftsmen during rebuilt operations of masks and bodywork spare parts of high-end historic cars.

Keywords: 3D capturing , 3D digital model , car body panel , Classic vehicle restoration , Close-range photogrammetry , Geometric inspection

This paper presents a systematic approach to model and simulate the influence that the variation of process parameters has on the final quality of an injection moulded component. In the first phase, we define a multi-steps procedure to develop a reliable digital model of the injection moulding process by the fine-tuning of the part cavity and the mould elements (e.g. detail simplification, discretization and mesh density, elements modelling, etc.) using real data as validation. In the second phase, we investigate the correlation between selected process parameters and the final tolerances of the moulded component, based on a Design of Experiments. As a case study, we selected the body of a mass airflow sensor for an automotive high performance engines, made of polybutylene terephthalate reinforced with glass-fibre, which presents roundness issues on functional features. The effects of the injection velocity and packing pressure on the deformation of the component are investigated, identifying the best combination of their values that leads to compliance with the roundness tolerances on its functional features. The injection moulding Computer Aided Engineering (CAE) software Moldex3D (CoreTech) is used to run the simulations, and the results are finally validated by comparing the experimental data obtained from the injection moulding machine that produces the component.

Keywords: Design of Experiments , Injection moulding , Simulation-based design approach , Tolerances , Warpage

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&T) , Model-based definition , Product manufacturing information , Tolerance-cost optimization