CIRPP Modeling of Products at the Assembly Level

The main function of assembly is to combine components into subassemblies and assemblies thus forming a finished product with certain characteristics. In that way, each component keeps its geometric characteristics, i.e. the characteristics of its quality (quality of treated surface, tolerances of shapes and position, etc.), which allows proper functioning of the product.

A product designer determines its hierarchical structure, number of components and their appearance, selection of materials, selection of the processing technology and assembly method, tolerances and quality of final treatment. Assembly is, therefore, basically defined during the stage of simultaneous design of products and processes.

CAD/CAPP/CAM integration aims at improving processes of product and technology design thus considerably reducing the production price, i.e. at providing conditions for easier and more economical technology of processing and assembly. As the assembly costs represent a significant part (25–65%) of the production price, Design for Assembly (DFA), together with the Computer Aided Assembly Process Planning (CAAPP) closes the interaction in the processes referring to the design of products, processing technologies and assembly.

With respect to modeling in the component domain, the problem becomes considerably complex in investigations of approaches and ways of modeling the assembly structure, i.e. the executive bodies of functions and processes.

Assembly primitives are defined while modeling for assembly and they are represented by relations between functional and effective surfaces defined at the component level, respecting the hierarchical structuring of products.

The analysis of forming primitives of assembly starts from the function of the mentioned assembly. On the basis of functional requirements, it is necessary to recognize the function holders, i.e. the executive bodies for the level at which a primitive is defined, and then the skeletons of the subassembly and assembly are formed.

The definition of the assembly structure is based on the principles of Design for Assembly as the main strategy of simultaneous design. The goal of this strategy is to produce easier and cheaper products, so that, according to some authors, DFA is considered to be the key to successful design in the competitive environment.