Fixture optimization for sheet panel assembly considering welding gun variations

Sheet panel assembly in automotive body manufacturing typically involves fixturing (including locating and clamping), joining (especially welding), and unclamping. Research has shown that the choices of fixturing schemes are important and that fixture optimization can generally improve the assembly dimensional quality with reduced assembly distortions. However, these research studies generally modelled weld guns as constant disturbances (such as deterministic forces) without considering the weld gun variations to avoid the complexity of Monte Carlo simulations. In the current paper, a fixture optimization model is formulated to minimize the assembly dimensional variations under welding gun variations. It is shown that, by using the proposed weld gun variations model, an assembly variation simulation can be converted to a deterministic assembly model, eliminating the need for Monte Carlo simulation. The efficiency improvement makes it feasible for a full scale optimization solution for optimal fixture locations with welding variations. The current paper further introduces the fixture-element models for continuous variable optimization in finite-element analysis, an enabler for fixture optimization. Numerical examples are shown to demonstrate the proposed methods.