Variation propagation modeling of multistage machining processes enables variation reduction by making an accurate prediction on the quality of a part. Part quality prediction through variation ...propagation models, such as stream of variation and Jacobian-Torsor models, often focus on a 3-2-1 fixture layout and do not consider form errors. This paper derives a mathematical model based on dual quaternion for part quality prediction given parts with form errors and fixtures with
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-2-1 (
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>3) layout. The method uses techniques of Skin Model Shapes and dual quaternions for a virtual assembling of a part on a fixture, as well as conducting machining and measurement. To validate the method, a part with form errors produced in a two-stationed machining process with a 12-2-1 fixture layout was considered. The prediction made following the proposed method was within 0.4% of the prediction made using a CAD/CAM simulation when form errors were not considered. These results validate the method when form errors are neglected and partially validated when considered.
Metal additive manufacturing (AM) has become a predominant process for manufacturing complex metal parts. However, research on controlling the geometric tolerances of the metal AM printed parts and ...assemblies is scarce. This paper presents a methodology to conduct a geometric tolerance and manufacturing assemblability study of the parts manufactured by metal AM. An assembly benchmark test artifact (ABTA) is designed to include mating features with given assembly conditions based on geometric tolerancing quantifiers. For virtual analysis, prediction phase ABTA samples are generated by using systematic and random field theory deviations. The prediction phase deviations are then calibrated using deviations from a numerical simulation based on thermo-mechanical finite element model of the part. These samples or ‘skin model shapes’ are subjected to geometric tolerance and assemblability study. For experimental validation of the method, geometric tolerance quantification and actual assembly was conducted on laser powder bed fusion (LPBF) fabricated parts. The comparative analysis of the experimental and virtual results validates the new methodology and its ability to provide reliable information regarding assemblability, size dimensions and geometric tolerances. The method can be extended to any AM process for performing a virtual tolerance and manufacturing assemblability study.
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•Benchmark designed with mating components to conduct experimental geometric tolerance and manufacturing assemblability study.•A hybrid approach presented for geometric tolerance estimation of the benchmark using random field theory and thermo-mechanical simulations.•The method is used to extract standardized geometric dimensioning and tolerancing (GD&T) quantifiers.•The method is validated with experimental GD&T characteristics and manufacturing assemblability.
Variability is unavoidable in the realization of products. While design must specify ideal geometry, it shall also describe limits of variability (tolerances) that must be met in order to maintain ...proper product function. Although tolerancing is a mature field, new manufacturing processes and design methodologies are creating new avenues of research, and modelling standards must also evolve to support these processes. In addition, the study of uncertainty has produced widely-accepted methods of quantifying variability, and modern tolerancing tools should support these methods. The challenges introduced by new processes and design methodologies continue to make tolerancing research a fertile and productive area.
Mesh models have been widely employed in current CAD/CAM systems, where the workpiece is considered as made up of a number of features limited by natural boundaries. The natural boundaries among ...features are in most cases edges where an abrupt change of point differential geometry properties occurs. However, such features and underlying surface portions could also be connected smoothly without an abrupt change at the natural boundaries. In the context of ISO GPS (Geometrical Product Specifications and Verification) Standards, partitioning is a fundamental operation that decomposes a mechanical part into independent surface portions for a functional specification purpose. In this paper, an enhanced mesh partitioning method is proposed to enable a feature-based decomposition considering kinematic invariance classes. The proposed two-step method includes an initial partitioning based on sharp edge detection and an enhanced partitioning process based on non-sharp edge rectification. The partitioning criteria rely on two surface descriptors derived from shapes’ principal curvatures: Curvedness and Shape Index. To refine the boundary points on non-sharp edges, conformal geometry is exploited during the enhanced partitioning process by mapping the 3D surface onto a 2D unit disk. Connecting regions without abrupt changes at their natural boundaries are well partitioned after the boundary rectification process. A statistical evaluation process is used to address invariance class identification for each partitioned surface portion on the part. Experiments and results on different mesh models are presented to demonstrate the effectiveness of invariance class partitioning for ISO GPS.
•A two-step enhanced partitioning process for ISO GPS is developed.•The interpretation of the feature principle in a systematic and algorithmic way is presented.•A robust evaluation of existing discrete curvature estimation methods is described•Two surface descriptors, Curvedness and Shape Index are adopted for partitioning.•Conformal geometry is used to solve the partitioning problem in a lower dimension
Selective laser melting (SLM) is a promising metal additive manufacturing technology, which holds widespread applications in numerous fields. Unfortunately, it is arduous to predict the real geometry ...of SLM part, which impedes its further development, while the morphology of melt pool, influenced and determined by process parameters, poses a crucial influence on the overall part geometry. Nonetheless, the association between process parameters and melt pool morphology is still unclear. Hence, it is indispensable to explore relevant solution to address this issue. For this purpose, this paper proposes a new model to directly establish the mathematical relationship between process parameters and melt pool structure for SLM process. In this model, the status of melt pool is first qualitatively analyzed via the defined synthetic process index, and three types of melting states are differentiated including low melting, intermediate melting, and high melting, which could cover different melt pool modes. Then, the computational model involving more physical mechanisms integrating mass conversion, heat exchange, and temperature field is constructed. Melt pool critical geometries including the height, width, depth, and length could be computed through the model. In order to validate the correctness of the proposed model, published experimental observations and existing models are compared. Calculation results from the proposed model show high consistency with the experimental samples and better accuracy than existing empirical models. Its applicability in melt pool classification and prediction is also verified, laying foundation for geometric simulation of SLM object which is successively shaped melt-pool by melt-pool.
The management of geometrical variations throughout the product life cycle strongly relies on the gathering, processing, sharing and dissemination of tolerancing information and knowledge. While ...today, this is performed with many manual interventions, new means for automatic information processing are required in future geometrical variations management to make full use of new digitalization paradigms, such as industry 4.0 and digital twins. To achieve this, the paper proposes the term tolerancing informatics and investigates new concepts and means for automatic information processing, novel information sharing workflows as well as the integration of tools for next generation geometrical variations management. In this regard, the main aim of the paper is to structure existing tolerancing informatics workflows as well as to derive future research potentials and challenges in this domain. The novelty of the paper can be found in providing a comprehensive overview of tolerancing informatics as an important enabler for future geometrical variations management.
In the current era of increased customization, changing manufacturing systems and business globalization, effective use of product design information and knowledge generated from the product model ...can facilitate the decision-making of an assembly sequence by providing feasible product relationships and a viable semantic foundation. To enrich such semantics, a geometry-enhanced ontology modelling and reasoning framework is proposed in this paper to explicitly express relevant concepts for assembly sequence planning (ASP). A rule-based reasoning mechanism based on Ontology Web Language Description Logics (OWL-DL) and Semantic Web Rule Language (SWRL) is also suggested to clarify implicit relations by incorporating reasoning units (RUs) to process complex geometric information. This framework is then validated with a complex case study related to assembly sequence planning.
Position and orientation deviations (PODs), being affected by surface deviations, occur after parts are assembled, which directly affects the performance of mechanical products. Moreover, mechanical ...parts are generally assembled with multiple constraint planes, and the generated PODs are influenced by the type of positioning. Therefore, the PODs of multiple planes should be computed in the design stage according to the predicted surface deviations, to control the product performance. However, even though the POD computation of multiple planes has been researched, the effects of surface deviations and multiple types of positioning cannot be considered simultaneously. To address this problem, this study proposes a point-by-point-contact-based approach. The six-point positioning principle is employed to determine the possible number of contact points on each mating plane. The surface deviations are modeled from the perspective of manufacturing errors. Furthermore, the contact points on each mating plane are determined successively using both the strategies of progressively approaching position and of the orientation and recursion of contact points. As a result, the PODs are acquired. The feasibility and usefulness of the proposed approach are verified through a case study. Herein, effects of surface deviations and multiple types of positioning on PODs are unified as contact point variations. Consequently, this approach is expected to assist with accurately controlling the POD influence on the performance of mechanical products in the design stage.
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