Assembly Synthesis for Stiffness, Dimensional Adjustability and Manufacturability

A method that identifies the optimal components set, joint designs and corresponding subassembly partitioning for a Body-In-White (BIW) made of the aluminium space frame (ASF) is presented where the structural stiffness, dimensional integrity and components manufacturing / assembly cost are considered as the objectives. The optimization problem is posed as a simultaneous determination of the location and types of joints in a structure selected from the predefined joint library combined with the size optimization for the cross sections of the joined structural frames. The join library is a look-up table containing following three components: 1) the geometry of the feasible joints at each potential joint location, 2) the cross sectional designs of the joined frames and 3) the structural characteristics as the equivalent torsional spring models. Structural stiffness of the entire structure is evaluated by finite element analyses of a beam-spring BIW model constructed based on the joints and joined frames. The dimensional integrity of the assembly is calculated by evaluating how easily the adjustment of the critical dimensions in the structure can be achieved during the assembly process. Finally, manufacturing cost and assembly costs are estimated by considering the manufacturing and assembly procedures based on the geometries of the components and joints. The optimization problem is solved by multi-objective evolutionary algorithms using a graph-based crossover operator. The BIW of a middle size passenger car is decomposed as the case study where the representative optimal designs are selected from the resulting Pareto front and trade-offs among stiffness, dimensional integrity and manufacturing/assembly cost are discussed.