The rise of artificial intelligence techniques provides new opportunities in the robust design and tolerancing fields. These technological growths require adapting new practices. In this paper, a new ...tolerance allocation approach based on supervised machine learning (decision tree) and Monte Carlo simulation is proposed. The most important branch of the decision tree which is generated based on the results of the Monte Carlo simulation, is analysed and the best tolerances to be allocated are defined in terms of quality/cost trade-off. The effectiveness of the proposed approach is demonstrated and discussed through a non-linear problem: a Jansen linkage study.
The tolerancing process impacts the product quality, the production cost and scrap rate. Tight tolerances allow to assure product performance; loose tolerances to reduce production cost. The ...tolerance allocation of a complex system is performed under uncertainty. In fact, the accuracy of the behaviour simulation of the system significantly affects the tolerance analysis result, and thus the tolerance allocation result. Therefore, a method is proposed to perform tolerance allocation based on the Dempster Shafer theory, Monte-Carlo simulation and genetic algorithm. The application of the proposed framework is demonstrated through a complex case study.
The use of lattice structures produced using additive manufacturing (AM) is of great interest to the aerospace and medical industries because of their potential for strength/weight optimization. ...However, their use is often limited due to challenges in qualification. Recent standards proposed for the definition and verification of lattice structures created using AM attempt to address these gaps. In this work, a lattice component is designed using a repeated unit cell and theoretical supplemental surfaces (TSS), brought forth in ASME Y14.46, are used to define the bounding geometry of the component. Two planes and a sphere are used to define a datum hierarchy that will be used to qualify the component. A measurand is defined by a spherical TSS and is later used to evaluate the quality of datum registration. The component is produced using a laser powder bed fusion process and then measured using focus variation microscopy, X-Ray computed tomography, and a coordinate measuring machine (CMM). The three data sources are then registered using a refined sampling registration based on the CMM points. The effect of CMM data acquisition strategy on the quality of the registration is then examined. Results show that CMM planning based on optical measurements of the component, as opposed to the designed geometry, show significant improvement in the quality of registration. This work highlights the importance of sampling location in tactile measurements of components produced using additive manufacturing and recommends that definition of inspection locations/methods be integrated into the design cycle of AM parts.
Traditionally, the geometric quality of assembled products has been evaluated by deviation from nominal values. However, the increased use mixed materials in especially automotive industry, in ...combination with an increased use of non-rigid simulation, open up for other evaluation criteria to complement the traditionally used deviation. The stiffness of a part or subassembly will, in combination with its deviation from nominal, give rise to different amounts of energy needed to join it to other parts. In this paper, the energy needed for joining is suggested as an evaluation criterion, complementary to geometric deviation, to judge the severity of the deviation.
Geometric deviations are inevitably observable on manufactured workpieces and have huge influences on the quality and function of mechanical products. Therefore, many activities in geometric ...variations management have to be performed to ensure the product function despite the presence of these deviations. Dimensional and Geometrical Product Specification and Verification (GPS) are standards for the description of workpieces. Their lately revision grounds on GeoSpelling, which is a univocal language for geometric product specification and verification and aims at providing a common understanding of geometric specifications in design, manufacturing, and inspection. The Skin Model concept is a basic concept within GeoSpelling and is an abstract model of the physical interface between a workpiece and its environment. In contrast to this understanding, established models for computer-aided modelling and engineering simulations make severe assumptions about the workpiece surface. Therefore, this paper deals with operationalizing the Skin Model concept in discrete geometry for the use in geometric variations management. For this purpose, Skin Model Shapes, which are particular Skin Model representatives from a simulation perspective, are generated. In this regard, a Skin Model Shape is a specific outcome of the conceptual Skin Model and comprises deviations from manufacturing and assembly. The process for generating Skin Model Shapes is split into a prediction and an observation stage with respect to the available information and knowledge about expected geometric deviations. Moreover, applications for these Skin Model Shapes in the context of mechanical engineering are given.
•We explain the core concept and fundamentals of Skin Model Shapes.•Skin Model Shapes are Skin Model representatives from a simulation perspective.•Approaches for the Skin Model Shape generation in discrete geometry are highlighted.•Overview over applications for Skin Model Shapes in mechanical engineering is given.
The geometric freedom associated with additive manufacturing (AM) processes create new challenges in defining, communicating, and assessing the dimensional and geometric accuracy of parts. Starting ...from a review of the ASME-GD&T and ISO-GPS current practices, a new approach is proposed in this paper. The new approach combines current tolerancing practices with an enriched voxel-based volumetric representation scheme to overcome the limitations of standard methods. Moreover, the new approach enables a linkage between product design optimization and product verification with respect to the AM process chain. A case study is considered to demonstrate the concept.
Additive manufacturing (AM) became an advanced research topic due to its ability to manufacture complex shapes. But the ability to achieve predictable and repeatable shapes is critical. Therefore, to ...optimize the design of an additive manufactured product, tolerancing is a key issue. This paper focuses on geometrical quality assessment of an AM product. It includes a process oriented geometrical model to predict the surface roughness and dimensional deviations, and a geometrical simulation tool to assess the impacts of these deviations on the geometrical behaviour of the joint. An application of the approach is illustrated through a case study.
•A method is proposed for tolerance analysis of gear trains.•Shaft misalignment, center distance errors and backlash are estimated from part tolerances.•Tolerance stackups are calculated by solving ...equivalent force analysis problems.•Results are shown for compound gear trains with spur and helical gears.
Assembly-level geometric errors such as backlash, center distance errors and shaft misalignments may adversely affect the operation of a gear train. The tolerance analysis method proposed in the paper estimates these errors from tolerance specifications on gears and mounting parts (shafts, bearings, housings). The problem is solved by analogy with an equivalent problem of force analysis: on a properly defined structure, external forces correspond to the assembly-level error, and calculated internal forces and support reactions provide the sensitivities of part tolerances on the total error. Previously developed for generic assemblies, the approach proves especially simple for gear systems compared to existing methods of tolerance analysis, as it relies upon structural analysis procedures that are customary in mechanical design. The method based on static analogy includes a two-level classification of geometric errors, which helps overcome the complexity of tolerance analysis problems for gearings. Two examples of gear trains of different types and configurations are presented to demonstrate the calculation procedure and verify its correctness by comparison with geometric considerations.
Tolerance analysis aims to evaluate the functional requirement of mechanical assemblies in the design stage. As one of the typical tolerance analysis methods, the polytope model has shown great ...potential in Computer-Aided Tolerancing (CAT) field based on a series of constraints. However, existing research outcomes on this topic rarely consider form defects and the combined effects of form defects and surface deformations. This limitation may cause inaccuracy of tolerance analysis results. Hence, this paper integrates form defects and surface deformations in polytope-based tolerance analysis. Specifically, form defects are considered based on the concept of Skin Model Shapes and surface deformations are calculated based on a Conjugate Gradient-Fast Fourier Transform (CG-FFT) method. Then, the modeling method of the new polytope model is elaborated based on surface types and different types of constraints. Moreover, a case study is conducted to explain the procedure of polytope-based tolerance analysis. Through operations of the polytopes, tolerance analysis results are obtained, and the comparison with conventional polytope analysis results shows the considerable effects of form defects and surface deformations. It is expected that the proposed method can have a more realistic and accurate analysis result because of its consideration of real surface contact status.
PDF
