Geometric dimensioning, tolerancing and inspection

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.

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

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

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

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

Purpose: The aim of this in vitro study was to verify whether or not stock and computer-aided design/ computer-aided manufacturing (CAD/CAM) abutments show similar precision in the connection with the respective implants. Materials and Methods: Ten CAD/CAM titanium abutments were compared with 10 stock titanium abutments. Each abutment fit a regular-platform implant (Institute Straumann). Implants and abutments were measured independently and then connected. During the connection procedure, the torque was measured using a six-axes load cell. Then, outer geometric features of the implant-abutment connection were measured again. Finally, the assembly was sectioned to provide the analysis of inner surfaces in contact. The geometric measurements were performed using a multisensored opto-mechanical coordinate measuring machine. The following parameters were measured and compared for the CAD/CAM and stock titanium abutment groups, respectively: width of interference and interference length between the conical surfaces of the implant and abutment; and volume of material involved in the implant-abutment connection. Results: Interference width mean ± SD values of 18 ± 0.5 and 14 ± 0.5 μm were calculated for the stock and CAD/CAM titanium abutment groups, respectively. The difference was statistically significant (P = .02). Furthermore, the interference length mean ± SD values of 763 ± 10 and 816 ± 43 μm were calculated for stock and CAD/CAM titanium abutment groups, respectively. The difference was also statistically significant (P = .04). Finally, the volume of material involved in the implant-abutment connection was compared between stock and CAD/CAM titanium abutment groups; the mean ± SD values of 0.134 ± 0.014 and 0.108 ± 0.023 mm3 were significantly different (P = .009). Conclusion: Both standard and CAD/CAM abutment groups showed a three-dimensional (3D) seal activation after the screw tightening. Nevertheless, stock titanium abutments showed a significantly higher volume of material involved in the implant-abutment connection compared with that of CAD/CAM titanium abutments.

Keywords: CAD/CAM abutments , Implant-abutment connection , Stock titanium abutments

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&T (Geometric Dimensioning and Tolerancing) , Geometric inspection , GPS (Geometric Product Specification)

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

Definition of size, shape and location of defects into a mechanical component is of extreme importance in the manufacturing industry in general and particularly in high-tech applications, and in applications that can become dangerous due to the structural failure of mechanical components. In this paper, a laser-UT system has been used to define position and shape of internal defects in aluminum plates. An infrared pulsed laser is used to generate ultrasonic waves in a point of the plate and a CW laser interferometer is used as receiver to acquire the out-of plane displacements due to the ultrasonic waves in another point of the plate. The method consists of acquiring a B-Scan map on which some information on the defects in the mechanical component are visible. Storing the characteristics of the wave reflected by the defect and acquired in the B-Scan, the detection and the drawing of the defect is possible. The acquisition of the times of arrival of the waves reflected by the defect from the B-scan allows defining large parts of the shape of the defect. The times of arrival are acquired from the B-scan by analyzing the colour variations due to the wave reflected by the defect. The experiments operated from both sides of the plate allow drawing the defect in a virtual image of the plate section, from which the definition of defect shape and position can be determined.

Keywords: B-scan image analysis , Defect definition , Laser ultrasonic testing , NDE

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

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 & Inspection , Feature Recognition , Injection Moulding , Path Planning , Product Data Management , Quality Inspection , Reverse Engineering , Segmentation

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 & gas , Product manufacturing information (PMI)

In the fabrication process of aspheric glass lens and molds, shape characterization is a fundamental task to control geometrical errors. Nevertheless, the more significant geometrical functional aspect related to the optical properties is the curvature, which is rarely investigated in the manufacturing process of lenses. Algorithms for the assessment of shape and curvature errors on aspheric surface profile are presented. The method has been investigated on profiles measured before and at different steps of the membrane polishing process. The results show how surface roughness, shape, and curvature change during the polishing process as a function of the machining time.

Keywords: Curvature , Glass , Grinding , Polishing , Roughness , Shape

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

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

The tolerances of welded chassis are usually defined and adjusted in very expensive trials and errors on the shop floor. Computer Aided Tolerancing (CAT) tools are capable to optimize the tolerances of given product and process. However, the optimization is limited since the manufacturing process is already mostly defined by the early choices of product design. Therefore, we propose an integrated design method that considers the assembly operations before the detail design of the chassis and the concept design of the fixture system. The method consists in four phases, namely functional analysis in the CAD environment, as-sembly sequence modelling in the CAT tool, Design Of Simulation Experiment on the stack of the tolerance ranges and finally optimization of the tolerances. A case study on a car chassis demonstrates the effectiveness of the method. The method enables to selectively assign tight tolerances only on the main contributors in the stack, while generally requiring cheaper assembly operations. Moreover, a virtual fixture system is the input for the assembly equipment design as on optimized set of specifications, thus potentially reducing the number of trials and errors on the shop floor.

Keywords: 3D tolerancing , Car chassis , Computer aided tolerancing , Design op-timization , Tolerance allocation

OBJECTIVES. The purpose of this preliminary in vitro investigation was to evaluate the accuracy of an intraoral scanner in fully edentulous arches rehabilitated with 6 implants; in this clinical condition it is particularly difficult to ensure sufficient accuracy standards. MATERIALS AND METHODS. For this study a reference metal master model was provided: it had 6 implant analogs inserted to simulate a fully rehabilitated edentulous arch with implants. A scanbody made of PEEK (Polyether Ether Ketone) was inserted in each analog and the positions of each scanbody were calibrated by means of a Coordinate Measuring Machine (CMM). The master model, fitted with the scanbodies and a silicone gingiva, was acquired with the True Definition Scanner (TDS). Several series of scans were taken, each of them consisting of 10 close acquisitions, in order to arrange the calibration of the master model and the series of scans with TDS in the same day. From the mesh of each scan, a segmentation was performed to identify known points referable to both plane and cylinder shapes of the scanbodies. This operation was automatically performed by implementing a dedicated algorithm developed in the Rhinoceros 5.0 software. RESULTS. The results herein are related to one set of 10 acquisitions of the master model. Dimensional analysis assessed the effective diameter of the scanbodies measured by TDS and was compared with the reference diameter measured using a CMM, thus obtaining the dimensional error in the body diameter of the scanbody. The values of dimensional errors varied from a minimum of 15 μm to a maximum of about 39 μm, with standard deviations of up to 9 μm. The location analysis allowed to determine the average location error of the scanbodies centers with respect to the reference positions: they were in a range from 14 to 21 μm, with standard deviations of less than 10 μm. CONCLUSIONS. Within the limitations of this in vitro study, the intraoral scanner under investigation proved to be able to scan a 6 implants full arch with a level of accuracy in line with other data reported in scientific literature, or even with smaller error rates. This level of accuracy is capable of fulfilling the accuracy requirements considered clinically acceptable.

Keywords: Full arch digital impressions , Implants , Intraoral scanner , Scanning dimension errors , Scanning position errors

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

‘Family business‘ phenomenon is considered a dominant source of growth, development, and social and economic stability within the luxury industry, representing the most widespread business model in the world. Moreover, in the current scenario, characterized by new and ever-changing dynamics of the global market, firms operating in the luxury industry need to quickly and timely anticipate competitors' next moves, monitor market tastes, adapt their products and properly communicate their positioning. For reaching this goal “family business” companies needs to improve their new product development processes by adopting innovative strategies and tools for creating an “environment for innovation” able to pursue “the right product in the right time”. In light of these considerations, the aim of this paper is to provide a methodology able to identify how and where a Collaborative Product Development/Definition and Management solution can provide company improvements.

Keywords: capability maturity model (CMM) , Collaborative product development/definition and management (CPDM) , new product development (NPD) , product lifecycle management (PLM)

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