Automatic Assembly Sequence Planning for Axisymmetric Products

Abstract

Introduction: In industrial manufacturing the production of mechanical assemblies is demanding in all its stages. Due to the increasing complexity of products, design, management, and end of life phases are becoming very onerous and time consuming tasks [8]. As a consequence, in the last decades, technologies have been studied to facilitate production and automate di erent manufacturing operations to reduce time and costs of production, avoid human errors and increase product quality as well as industrial collaboration. In this regard, Assembly Sequence Planning (ASP) is considered one of most challenging topic in the industrial manufacturing eld, and still deserves to be explored and further developed. ASP aims at algorithmically identifying the order in which components have to be assembled to obtain the nal product. It starts from a CAD assembly model and, by analyzing and extracting part geometric features and relations, returns admissible sequences. Multiple solutions can exist on how mounting components with each other, but the selection of one sequence rather than another has great e ect on assembly feasibility, complexity, and accuracy. Moreover, ASP is known to be a very hard combinatory problem while the assembly parts numbers become important [13]. To reduce the complexity, Subassembly Identi cation (SI) often precedes the sequence planning, in order to apply sequence generation approaches to each subassembly reducing the amount of parts to consider at the same time. However the main weakness observed is that all the data extracted basically relay on geometric information, while the engineering meanings of the assembly/subassembly and its components are not considered. For example, knowing if all the parts are arranged in a speci c manner, e.g along a common axis or connected by screws with a precise orientation, would be bene cial in the selection of the assembly direction. Or else, the awareness of deformable components (e.g. circlips, O-ring, etc.) or fasteners allows to make conclusions on their assembly order even when the geometric analysis of precedences is ambiguous. The work here presented is placed in this context and, speci cally, it deals with axisymmetric clusters, i.e. connected groups of parts symmetrical to an axis, all aggregated along the same direction. These groups of parts deserve to be singularly analyzed because they are elements occurring frequently in mechanics, that most of the time can be treated independently of the larger assembly containing them (e.g. crankshafts, pulleys and rollers). Distinctive features of axisymmetric subassemblies are the mounting techniques (i.e. threading by sliding or tting hollow parts into the axis), the fasteners included (i.e.