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The assemblability, which is the feasibility and difficulty of assembly, will greatly affect the efficiency and quality of assembly process, so assemblability analysis plays an important role during the design stage of products. Cylindrical parts assembly is a common structure with wide applications, whose assemblability can be affected by surface deviations, especially in some precision assemblies. In this paper, a novel method is proposed for the assemblability evaluation of cylindrical parts assembly considering surface deviations. Firstly, based on the surface deviations modeling of cylindrical parts and assembly clearance calculation, the assembly posture adjustment process is defined and simulated to obtain the assemblable postures without interference between parts. Then, in the proposed six dimensional posture space, a search algorithm is established to obtain the boundary points of assemblable posture space. Afterwards, in order to represent this irregular hyperspace, the largest inscribed generalized cone of which is put forward. Finally, based on the characteristics of generalized cone, two indicators are defined to reflect the adjustable range of assembly posture, which can realize the quantitative evaluation of assemblability. The validity of the proposed method is verified by case studies of cylindrical parts assemblies with different surface deviations.

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.

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.

International audience; This paper depicts a new CAT (Computer Aided Tolerancing) system called Quick GPS (Geometrical Product Specification), for assisting the designer when specifying the functional tolerances of a single part included in a mechanism, without any required complex function analysis. The mechanism assembly is first described through positioning table formalism. In order to create datum reference frames and to respect assembly requirements, an ISO-based 3D tolerancing scheme is then proposed thanks to a set of rules based on geometric patterns and TTRS (Technologically and Topologically Related Surfaces). Since it remains impossible to determine tolerance chains automatically, the designer must impose links between the frames. The CAT system we developed here proposes ISO based tolerance specifications to help ensure compliance with the designer's intentions saving on time and eliminating errors. This paper will detail both the set of tolerancing rules and the designer's approach. The Quick GPS system has been developed in a CATIA V5 environment using CATIA VBA and CATIA CAA procedures.