Abstract: This study presents a genetic algorithm-based methodology for reconstructing the nominal profile of airfoils belonging to the NACA four- and five-digit series. By minimizing the geometric deviations between measured point clouds and parametrically generated airfoil profiles, the algorithm identifies the best-fitting nominal geometry. The approach was implemented using Rhino 8, Grasshopper, and the Galapagos plugin, and validated through extensive testing on 3D-printed samples. Across 200 test runs, the algorithm consistently identified the correct nominal geometry, demonstrating robustness despite inherent stochastic variability and computational challenges. The average number of iterations needed to converge was found to be 953 across all cases. This methodology offers a valuable tool for reverse engineering and metrological applications, providing a parametric and efficient alternative to traditional free-form surface reconstruction.

Keywords: Airfoil Design | Airfoil inspection | Genetic Algorithm | Reverse Engineering

Abstract: Additive Manufacturing (AM) is no longer limited to prototyping, as it is gaining an increasingly large market share. With this expansion, there is a growing demand for the development of standardized rules to establish product specifications and verification procedures. AM offers unique opportunities in free-form shape design and multi-material processing, in contrast to traditional manufacturing processes and communication methods. Because of AM’s unique features, existing standards struggle to describe its product specifications. New regulations are therefore under development This paper reviews the state of the art in Additive Manufacturing (AM) product specification. This research examines the most up-to-date literature and standards published by the ISO, and ASME committees. A research gap has been identified in the accurate determination of design intent, which is crucial for defining product specifications. “Profile tolerance” is recognized as the most versatile specification for free-form geometries; however, new tools can be developed to control lattice structures. Additionally, the authors identified a significant gap in the assessment of dimensional and geometrical deviations in AM processes, as these are often estimated using geometrical benchmarks designed for subtractive technologies. Finally, verification remains one of the most critical aspects of AM products. Computed Tomography (CT) currently represents the only viable approach for measuring inaccessible features; however, standardized reconstruction methods are still lacking, as is a specification method tailored specifically for this measurement technique.

Keywords: Additive Manufacturing | DfAM | Dimensional and Geometrical Specification | Product Specification

Abstract: This work presents a computational framework for tolerance chain analysis based on multivariate statistical modelling accommodating both prescribed moments and correlations. The proposed method generates multivariate datasets matching either measured or proposed component characteristics, enabling realistic statistical virtual assembly. By using a transformed multi-variate Normal distribution, it is possible to represent the mean, variance, skewness, kurtosis, and covariance structure of the real parts\' geometric variability. This allows tolerance propagation analysis that reflects actual manufacturing variability. Applications include predictive assembly simulations, functional tolerance optimization, and data-driven design verification in industrial contexts.

Keywords: Design optimization | Tolerance Stack-Up with covariance | Tolerancing

Abstract: The phase-down of high global warming potential (GWP) refrigerants motivates low-charge flooded evaporators, for which enhanced external pool boiling on tube surfaces is essential. Pool boiling of the low-GWP azeotropic blend R515B is investigated on a smooth copper tube and on three integrally finned copper tubes (16 mm OD) with fixed fin pitch (≈0.81mm) and fin heights of 0.09, 0.14, and 0.25 mm, corresponding to height-to-pitch ratios (h/p) of 0.11, 0.16, and 0.31, at saturation temperatures of 10–40 °C over a wide heat-flux range. Relative to the smooth surface, the integrally finned tubes deliver a substantial enhancement and show higher heat transfer coefficients at higher saturation temperatures. For all h/p values, the heat transfer coefficient (HTC) increases quasi-linearly with heat flux up to a distinct transition, after which the growth rate of heat transfer coefficient with heat flux decreases. The transition heat flux varies systematically with h/p and saturation pressure, revealing a trade-off whereby larger h/p improves pre-transition performance but promotes earlier transition. High-speed visualization links the transition to bubble growth beyond the inter-groove spacing and coalescence across adjacent grooves, which reduces independent nucleation sites and limits liquid replenishment. Based on this mechanism, a dimensionless criterion is formulated to combine geometric confinement and capillary effects with heat-flux-driven vapor generation, suggesting a path to generalize the transition condition across geometries through h/p (and related spacing scales).

Keywords: Enhanced tubes | Heat transfer coefficient | Low-GWP refrigerant | Pool boiling

Abstract: Geometrical Product Specification (GPS) plays a critical role in ensuring functional compliance, manufacturability, and verifiability across the product development lifecycle. Recent research has highlighted the evolutionary nature of specifications: from functional (FunSpec) to manufacturing (ManSpec), verification (VeriSpec), and contractual (ConSpec) documents; yet the allocation of clear responsibilities among stakeholders remains underdeveloped. This paper proposes the integration of the RACI (Responsible, Accountable, Consulted, Informed) matrix into the ISO GPS workflow as a structured means to clarify roles, responsibilities, and communication pathways across design, manufacturing, and quality assurance domains, therefore building upon the responsibility principle presented in ISO 8015. Starting from the specification document types presented in ISO/TS 21619 and the interaction between these document types, this study introduces a RACI-supported framework that maps stakeholder involvement to each stage of specification evolution. A possible implementation example demonstrates how the method enhances transparency, prevents overlaps or gaps in responsibilities, and supports compliance with industrial standards such as ISO 9001. The results suggest that embedding RACI within GPS workflows strengthens interdisciplinary collaboration, reduces ambiguity, and lays the foundation for responsibility-aware product specification management.

Keywords: Geometric Specifications Management | Geometrical Product Specifications | ISO GPS | RACI matrix

Abstract: Digital workflows have revolutionized dentistry, especially when it comes to fabrication of complete dentures through Computer-Aided Design and Computer-Aided Manufacturing (CAD-CAM) procedures. Digital articulators manage to simulate mandibular movements and are emerging as alternatives to mechanical articulators like the Gerber semi-adjustable model. Despite being a promising tool, digital articulators require refinement in order to grant consistent functionality and effective occlusal balance. The aim of this research is to present a semi-automated MATLAB tool designed to compare trajectories from different articulator types—digital versus analog—used in dental practice. Validation of the MATLAB tool compared to existing data demonstrates its reliability and effectiveness. Sensitivity analyses assess the tool's robustness under various settings. Results suggest optimal input parameters and settings ensuring precision. Future developments may include integrating anatomically-based reference systems and advanced metrics for rotational analysis of condylar path elements (CPEs), thereby enhancing digital dentistry potentialities. Ultimately, the semi-automated MATLAB tool represents a significant step towards improving dental occlusal analysis, bridging the gap between analog and digital methodologies and enabling comparison among these tools.

Keywords: Complete dentures | Dental articulators | Intermaxillary record | Kinematic comparison | Pathway reconstruction

Abstract: Additive manufacturing components are prone to defects, including warping and cracking, which can significantly impact their mechanical performance. Determining deformations in lattice structures remains challenging. This paper presents a methodological framework for computing deformation matrices in additively manufactured lattice samples using 3D scanning. The sample’s geometry is acquired through 3D scanning, registered to a reference model, and vertices are determined and used for computing deformation metrics, including volumetric scaling factors, isovolumetric scaling, and angular deformations. A sensitivity analysis comparing four association criteria demonstrates the reliability of the Gaussian Best Fit Plane External. Assessing deformation in lattice structures can be useful for optimizing printing parameters and compensating for process-induced deformations.

Keywords: 3D scanners | Additive Manufacturing | Deformations | Lattice Structures

Abstract: This paper focuses on the applicability of various new product development (NPD) models to small and medium-sized enterprises (SMEs) and the challenges they face, including limited resources, informal innovation systems, and difficulty obtaining external feedback. Traditional NPD models offer structure but may be too rigid for SMEs, while Agile methodologies provide flexibility but can be challenging to implement outside the software industry. Hybrid models, blending traditional and Agile approaches, offer a good compromise. Through comparative analysis, the study evaluates the strengths and weaknesses of different NPD models in the SME context. By utilizing modern technologies like additive manufacturing and artificial intelligence, the NPD process can be accelerated, aligning with Agile principles to provide faster feedback and enhance overall efficiency. In conclusion, SMEs are encouraged to consider hybrid solutions to innovate and compete effectively.

Keywords: Agile | Hybrid Models | New Product Development Process (NPD) | SCRUM | Small and Medium-sized Enterprises (SMEs) | Traditional NPD

Abstract: This study aims to define the assembly shift for “nx” fit patterns, considering scrap and the influence of increasing elements. The methodology includes rejection rate estimation via Monte Carlo simulation, gap distribution estimation, and assembly shift computation based on gap distribution. It also proposes a design methodology for dimensioning tolerances to meet assembly shift requirements. Results show narrower assembly shift distributions with more pattern elements, revealing an exponential relationship.

Keywords: Assembly shift | Boundary Condition | clearance fit | Rejection Rate | Tolerance Analysis | Virtual Condition

Abstract: When pattern of fits are not designed following the boundary condition design criterion, the rejection rate due to failure in assemblability need to be considered. Since in a pattern of fits it is not possible to define an assembly equation it is not trivial to create a tolerance stack-up. The paper proposes a strategy to achieve a generalized rejection rate computation for nx patterns based on an interpolation model derived from Monte Carlo simulations. The rejection rate as function of the number of element in the pattern is simulated for different size and location tolerances. An exponential convergent function is fitted to the data and a generalize regression model is used to estimate the function parameters. Validation of the proposed methodology is provided.

Keywords: Boundary Condition | Rejection Rate | Tolerance Analysis | Tolerancing | Virtual Condition

Abstract: This paper presents a novel metrological approach for the functional geometric characterization of lifting airfoils, utilizing an Iterative Closest Point (ICP) algorithm to assess deviations in camber, thickness, and form. Traditional geometric specification methods, such as line profile tolerances, often fail to capture the full impact of geometric deviations on airfoil performance. In response, the proposed methodology addresses this limitation by linking airfoil geometry more closely to functional requirements. The new methodology was validated using synthetic datasets and real-world data, demonstrating robustness in the absence of noise and highlighting areas for improvement in noise handling. The findings suggest that the ICP-based method is a valuable tool for airfoil manufacturing, enhancing conformity checks against design specifications.

Keywords: Airfoil Metrology | Form Error Analysis | Geometric characterization | Iterative Closest Point | Quality Control in Aerospace Design | Tolerance Verification

Abstract: PURPOSE. This study aims to compare the occlusal trueness and precision of teeth manufactured using two modern digital milling processes. MATERIALS AND METHODS. A total of 38 complete dentures (CDs) were fabricated and analyzed. CDs in Group 1 (monolithic) (n = 19) were produced using a monolithic bicolor resin disk, whereas in Group 2 (oversize) (n = 19) were fabricated using the oversize process, which involves two separate resin disks of different colors. Two investigation methods were developed to evaluate trueness and precision: cusp area analysis and cusp vertex analysis. The study included three levels of analysis: a comparison of the two measurement methods, an evaluation of the monolithic versus oversize processes, and an assessment of under-and overcontouring inaccuracies. RESULTS. Statistical analysis using the Welch two-sample t-test, the non-parametric Wilcoxon signed-rank test, and the modified signed-likelihood ratio test (SLRT) revealed a statistically significant difference (P < 2.2 × 10-16) between the two measurement methods (vertex vs. area) for both the monolithic and oversize groups, with the vertex method demonstrating greater accuracy.The analysis of over-and undercontouring inaccuracies revealed that 55% of the surface for the monolithic process exhibited overcontouring, compared to 99% for the oversize process, indicating a strong tendency toward surface roughness in the latter. CONCLUSION. The monolithic milling method exhibited significantly superior accuracy compared to the oversize process (P < 05). Additionally, the Reference Point System (RPS) metrological method proved more reliable thanthe best-fit method for comparing complex structures, offering more accurate estimates of both trueness and precision. © 2025 The Korean Academy of Prosthodontics This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (https://creativecommons.org/licenses/by-nc/4.

Keywords: Accuracy | Complete denture | Computer aided manufacturing | Metrology | Milling machine

Abstract: This work introduces the concept of variable-dependent admissible limits for tolerance stack-up analysis, where limits adapt based on geometrical and non-geometrical variables. Unlike traditional methods that assume fixed limits, the proposed approach integrates these dependencies into both variational and Monte Carlo analyses, enabling broader tolerances while maintaining functionality. A case study from the automotive sector demonstrates the methodology's effectiveness.

Keywords: Non-geometrical stack-up | Product development | Tolerancing

Abstract: In product design and development, achieving the desired performance requires meeting specific product requirements within defined boundaries. These requirements are encapsulated in the Product Definition Dataset, which consists of two key models: the Nominal Model and the Specification Model. The Nominal Model outlines the product's properties, features, and relationships, while the Specification Model defines the targets, boundary conditions, requirements, allowable variation, and interrelationships essential for meeting these targets. This study focuses on the relationships between variable quantities and the limits set by geometrical product specifications. Currently, the limits defined within geometric specifications are considered static, excluding maximum and minimum material conditions. This implies that each variable is treated independently, meaning the actual state of one variable does not influence the functional limits of others. However, in actual parts and assemblies, variable quantities do affect each other, as they are not independent. In this paper, we explore the link between specifications and the variables they define through a case study, with the aim of fulfilling product requirements more effectively. By establishing these connections, it becomes possible to produce functional parts with greater allowable variation and reduced costs, while ensuring that specifications are grounded in actual performance requirements and physics. This approach aims to enhance the flexibility of product manufacturing and streamline the process of meeting both functional and cost-related objectives.

Keywords: Design Optimization | Functional Specification | Geometric Specification | Tolerance Optimization | Variable Correlation

Abstract: Purpose: To compare condylar path elements (CPEs) in edentulous patients using fully adjustable (FA) and semiadjustable (MS) digital articulators. Materials and Methods: A total of 10 patients with at least one edentulous arch were included. Arch relation records were digitally set in the articulators using two approaches: The MS group employed standard mean occlusal parameter values, while the FA group used individual values obtained using a digital arch motion-tracking device. Differences in CPEs, represented as Δ-values, were statistically analyzed using nonparametric Wilcoxon signed-rank test and post-hoc Tukey test. These analyses evaluated overall differences between FA and MS articulators, identified the regions with the greatest Δ-errors, and determined the percentage of movement required for statistical significance. Results: CPEs differed significantly between MS and FA articulators. Significant variations were observed in individual CPEs (P < .001), with motion percentage significantly influencing Δ-values (P < .001). Notably, within the first 20% of CPE MS pathways, significant differences were found within the initial 2 mm of movement, a critical range for prosthetic rehabilitation. Conclusions: This study highlights statistically significant differences in CPEs between MS and FA digital articulators, particularly within the initial 2 mm of movement. These findings underscore the importance of precise CPE replication for occlusal design of complete dentures.

Keywords: Aged | Dental Arch | Dental Articulators | Female | Humans | Jaw Relation Record | Jaw, Edentulous | Male | Mandibular Condyle | Middle Aged | Mouth, Edentulous | Movement

Abstract: This study introduces a numerical methodology for computing the statistical assembly shift in patterns of fits, addressing scenarios with variable numbers of elements and scrap caused by assembly failure. Using Monte Carlo simulations, the methodology estimates rejection rates, determines gap distributions, and calculates assembly shifts while considering both intrinsic and external datum systems. The findings indicate that adding more elements to a pattern reduces assembly shifts exponentially, presenting a design opportunity to control alignment and optimize component performance. A case study involving engine block and cylinder head alignment demonstrates the methodology’s applicability to real-world mechanical design. Three approaches for tolerance stack-up are evaluated: the standard Root Sum Square (RSS) method, where assembly shift is treated as a worst-case scenario; a proposed RSS method that models the assembly shift as a Gaussian distribution with a standard deviation derived from Monte Carlo simulations; and the Monte Carlo approach, which considers the full shape of the assembly shift distribution. By comparing these approaches, the study underscores the effectiveness of the proposed methodology in capturing the statistical behavior of assembly shifts. This work contributes a robust tool for tolerance analysis, advancing the precision and accuracy of pattern fit modeling and assembly shift evaluation in mechanical design.

Keywords: Assembly shift | Boundary condition | Clearance fits | Monte carlo simulation | Rejection rate estimation | Tolerance analysis | Transition fits

Abstract: Virtual assembly has become a popular trend in recent years and is used for various purposes, including selective assembly and adaptive tooling. Monte Carlo approaches based on Finite Element Method (FEM) simulations are commonly used for production applications. However, during the design phase, when testing different configurations and design options, a variational method is more suitable. This paper aims to test different implementations of the Method of System Moments applied to the second-order tolerance analysis method when actual distributions, which are non-centered and non-normal, are used as input for the simulation. The study reveals that the simulation results can significantly vary depending on the simulation settings in some cases. As a result, a series of best practices are highlighted to improve the accuracy and reliability of the simulation outcomes.

Keywords: Assembly simulation | Computer-aided tolerancing | Tolerance stack-up | Virtual assembly

Abstract: In tolerancing activities focusing on the allocation of geometrical tolerances, many critical issues originate from the non-optimal assignment of responsibilities among the organization units involved. This paper aims to depict relations between different tolerancing activities and relevant specifications, assigning them to the proper actor and, therefore, expanding the ISO 8015:2011 “responsibility principle”. A classification among tolerancing activities, specifications, and media is proposed; a horizontal hierarchical framework among functional, manufacturing, and verification specifications and a vertical hierarchical framework along the supply chain are discussed. Examples of both hierarchical structures are presented.

Keywords: functional specification | functional tolerancing | geometrical product specification | ISO/TS 21619:2018 | manufacturing specification | manufacturing tolerancing | tolerance specification | verification specification | verification tolerancing

Abstract: This paper presents a possible functional geometric specification for a lifting airfoil including the definition of functional tolerance limits (tolerance synthesis) and an associated inspection procedure. The proposed specification scheme is derived from the analogy between the mating of the airfoil with a fluid field and the consolidated example of the mating of a prismatic element in its site. The airfoil thickness is defined as a non-constant size with non-constant tolerances and the airfoil shape is prescribed with a non-constant profile of a line tolerance applied to the median airfoil line. The tolerance synthesis is based on XFLR5 software and Computational Fluid Dynamics (CFD) simulations. The inspection procedure uses the data acquired with a laser probe elaborated in Geomagic Wrap, GOM inspect and MATLAB. The overall process has been applied to a case study allowing to define limits and proposing a set of possible improvements regarding, particularly, the geometric specification of the leading and trailing edges of the airfoil.

Keywords: Airfoil | Geometric Inspection | Geometric Specification | Tolerance Synthesis

Abstract: This paper proposes a tool to analyze the diffusion and knowledge of the ISO GPS language in both industry and academia. A survey has been designed based on the maturity model concept to achieve this goal. Six Key Performance Indicators (KPI) arguments have been defined: general concept, datum systems, geometric tolerances, dimensional tolerances, modifiers and indications, and tolerance stack-up. Per each of these, three assessments are proposed, and a rating is given based both on self-assessment and unbiased check questions. The result is a survey that takes between 10 to 15 min to be filled out. The assessment is based on both knowledge and usage. The defined survey, through testing, proved to be a simple and usable tool to test the actual diffusion and knowledge of the ISO GPS language thanks to its shortness and the different levels of analysis it allows.

Keywords: Geometric Specification | ISO GPS | Maturity Model | Survey

Abstract: This paper proposes a methodology to compare the trajectories from different articulators - both physical and digital - during lateral and protusive movements. In the case of digital articulators, the articulated models are digitally moved and exported in position; in the case of mechanical articulators, the models are locked into position and 3D scanned. The digital models in position, both digital and scanned, are aligned to a common reference system and a maxilla-based reference system is tracked. The trajectories are defined as interpolating splines through the maxilla-based reference system origins. A Gerber mechanical articulator and an “Artex CR adjustable” virtual articulator were compared. The repeatability of the mechanical trajectory is found to be less than 184 microns. The resting position of the two articulators is found significantly different meaning that a bias is introduced by the operator in the analogic protocol. The trajectories have significantly different shapes as expected coming from two different articulator models. The proposed methodology proved to be a valid means to compare different articulators.

Keywords: 3D Scanners | Articulators | Complete Dentures | Trajectory Reconstruction

Abstract: Multi-material additive manufacturing enables the opportunity to combine multiple materials within the same part, allowing for an expanded range of properties that can gradually change inside the design space. This category of materials is commonly referred to as functionally graded materials (FGMs). However, FGMs currently face several limitations and challenges in terms of design and manufacturing, such as compatibility, distribution design, and prediction of mechanical properties. Furthermore, when dealing with parts possessing complex micro/meso-structures, finite element simulation often becomes a costly and time-consuming process. Among various additive manufacturing technologies, fused filament fabrication allows the combination of multiple thermoplastic materials within the same nozzle during the deposition process, thereby creating FGMs. This process, known as coextrusion, enables the gradual deposition of materials adjacent to each other while changing their fractions. Moreover, the deposition direction shapes the distribution of materials within each deposited layer, influencing the material structure and the resulting mechanical properties. A recent study proposes a preliminary model describing the deposition mechanism, which has been confirmed by experimental tests. This model delineates the section of the material deposited based on the tool path and process parameters, such as layer thickness and hatching space. To expand upon these findings, this paper applies a homogenization approach based on finite element analysis to the deposition model. This approach enables the description of material mechanical properties based on the material fractions, tool path, and other process parameters. Additionally, this study presents a methodology to tailor the mechanical properties according to the printed part’s orientation around the print bed.

Keywords: FFF | FGM | Functionally graded materials | Fused Filament Fabrication | Homogenization | Multi-material coextrusion | Representative Volume Element | RVE

Abstract: This paper presents the dynamic evolution of definitions and information related to ISO-conforming geometrical tolerancing (i.e., ISO GPS) and corresponding documents. It aims to elucidate the relationships between different specification types while analyzing the incremental information introduced at each stage. Special attention was devoted to the responsibilities associated with each added piece of information. Furthermore, inter- and intra-company communications of geometric specifications are differentiated. The presented study is based on the specification types introduced by ISO/TS 21619:2019: functional, manufacturing, verification, and contractual, each communicating specific, but obviously interrelated information. This highlights the evolving nature of information in technical product documentation. However, the hierarchy and interconnectivity of the specification types are still open tasks for standardization, research and practice. This study present the evolution and integration of geometric specifications within product development; therefore establishing a foundation for future research in geometric specification management.

Keywords: Geometric Specifications Management | Geometrical Product Specifications | ISO GPS

Abstract: This research consists in a detailed analysis of the ISO Geometrical Product Specifications (GPS) system's knowledge and usage in Italy. Data was collected by means of a questionnaire, from a wide range of industrial sectors and academic institutions. The dataset encompasses 143 responses, forming the basis for an in-depth examination of ISO GPS system implementation in Italy. This analysis involves three levels of comparison: (1) an examination of knowledge level and typical usage between Beginners and Experienced individuals, (2) an investigation into ISO GPS adoption patterns in Industry and Academia, with and without specific ISO GPS training, and (3) an exploration of differences among professionals who are responsible for conveying geometric specifications and those in charge of interpreting and applying them. The findings reveal significant insights into ISO GPS implementation in both academic and industrial domains. They highlight the need for the improvement of ISO GPS education offer and the development of more effective utilization practices, with potential implications for future ISO GPS standards development strategies.

Keywords: Geometric Specifications Management | Geometrical Product Specifications | ISO GPS | Training

Abstract: One commonly overlooked design rule advises against relying on bolts to ensure alignment between parts. Bolted connections often require a significant nominal size difference between screws and holes to avoid interference during assembly. Using the boundary condition design criterion, it is possible to define dimensional and location tolerances for this purpose, but it typically results in clearance being expected, thus accurate alignment cannot be assured. Despite this, many industrial practices still utilize bolted connections (or more broadly, shaft-hole connections) to align different parts. While automated assembly lines might resolve alignment issues through robotic arms, such designs lack robustness, especially when viewed from a design-for-maintenance perspective. During service or maintenance, correctly reassembling bolted parts can become a challenging task. This paper aims to address these issues by applying tolerance stack-up analysis to various possible geometric specifications. The study will explore the impact of a dedicated alignment feature and analyze the influence of material conditions on the geometric specification quantifying rejection rates. To accomplish this, a straightforward assembly involving two parts bolted together will be examined. The study will assess the effects of different specifications, encompassing both functional specification (representing assembly conditions) and non-functional specification (based on fiducial features).

Keywords: Bolted connections | Design methodology | Geometric Specification | technologies | tools

Abstract: In this paper, a possible application of the DfA (Design for Assembly) principles to deformable parts is proposed. The efficiency of an assembly is expressed with the DfA index, which is influenced by the number of parts compared to the “minimum number of parts” and the assembly time. Deformable parts, if unsupported, can exhibit deformations outside functional limits; however, when assembled, they often need to behave like rigid parts. To achieve the necessary rigidity, a large number of constraints are added. Having a high number of anchor points between a part and the rest of the assembly induces a high assembly time and therefore a low DfA index. This paper aims to provide a methodological framework for designers to define optimal anchor point locations to achieve the desired rigidity with the minimum number of anchor points possible, thereby minimizing assembly time and maximizing the DfA Index. The procedure is based on modal analysis. Subsequent anchor points are added until the predefined rigidity measure, as the natural frequency, is reached. The procedure is validated through a simple case study and then applied to two cases derived from actual industrial applications. It is also shown how the procedure allows for an actual reduction of anchor points.

Keywords: Constraints optimization | Deformable parts | Design for assembly | DfA | Mechanical interface design | Modal analysis | Product architecture

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: 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: Material extrusion additive manufacturing enables us to combine more materials in the same nozzle during the deposition process. This technology, called material coextrusion, generates an expanded range of material properties, which can gradually change in the design domain, ensuring blending or higher bonding/interlocking among the different materials. To exploit the opportunities offered by these technologies, it is necessary to know the behavior of the combined materials according to the materials fractions. In this work, two compatible pairs of materials, namely Polylactic Acid (PLA)-Thermoplastic Polyurethane (TPU) and Acrylonitrile Styrene Acrylate (ASA)-TPU, were investigated by changing the material fractions in the coextrusion process. An original model describing the distribution of the materials is proposed. Based on this, the mechanical properties were investigated by analytical and numerical approaches. The analytical model was developed on the simplified assumption that the coextruded materials are a set of rods, whereas the more realistic numerical model is based on homogenization theory, adopting the finite element analysis of a representative volume element. To verify the deposition model, a specific experimental test was developed, and the modeled material deposition was superimposed and qualitatively compared with the actual microscope images regarding the different deposition directions and material fractions. The analytical and numerical models show similar trends, and it can be assumed that the finite element model has a more realistic behavior due to the higher accuracy of the model description. The elastic moduli obtained by the models was verified in experimental tensile tests. The tensile tests show Young’s moduli of 3425 MPa for PLA, 1812 MPa for ASA, and 162 MPa for TPU. At the intermediate material fraction, the Young’s modulus shows an almost linear trend between PLA and TPU and between ASA and TPU. The ultimate tensile strength values are 63.9 MPa for PLA, 35.7 MPa for ASA, and 63.5 MPa for TPU, whereas at the intermediate material fraction, they assume lower values. In this initial work, the results show a good agreement between models and experiments, providing useful tools for designers and contributing to a new branch in additive manufacturing research.

Keywords: additive manufacturing | coextrusion | fused deposition modeling | material extrusion | material modeling

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: 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: 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