An integrated approach to the generation of assembly sequences

This paper presents a novel approach for the computerised generation of assembly sequences starting with the solid model of a product created on a PADL–2 CAD system. We have developed a methodology which permits automated extraction of pertinent geometric information from the solid model in the assembled configuration, and then an algorithmic procedure is used to generate all the geometrically feasible assembly sequences using two types of uni–dimensional matrix, which are called the contact and the translational functions. These are binary in nature, each containing six elements, and they represent the geometric relationships between a particular pair of components. All the sequences, both linear and those involving subassemblies, that satisfy the hard constraints are obtained by the interaction of the contact and translational functions in a specific manner. We have developed a representation scheme called the assembly sequence graph, which permits convenient visualisation of the large number of feasible sequences that are generated. Strategic constraints are then used to evaluate the feasible sequences, and this winnowing process is used to identify a few good sequences. These are in turn examined in detail in a quantitative manner. Using the Design for Assembly Toolkit, estimates are made of the assembly time and assembly cost of the product when each of these sequences is used, and the best sequence is the one that enables the assembly to be done at minimum cost. The procedure described in this paper will be very useful for specialists in manufacturing engineering who work in a concurrent engineering team in order to evaluate the assemblability of a design in a thorough and rapid manner.