Variation simulation of sheet metal assemblies for geometrical quality : parameter modeling and analysis

Doctoral thesis, 2005

The automotive industry deals with an increased demand for virtual verification of the geometrical quality of the product. The aim is to reduce the need for adjusting the assembly process to deliver a product with high quality. In addition, it is expected that a virtual development process reveals and solves potential quality problems at an early stage. To manage this, geometry related production problems must be solved during the design stages by developing robust concepts. One of the biggest challenges for sheet metal assembly is the geometrical variation introduced during the joining process. During joining the parts are subjected to forces and geometrical variation that will cause assembly to deviate from nominal geometry. The assembly variation will influence the fulfillment of functional, assembly and aesthetical requirements. Reliable virtual verification enables new design and process solutions that are rejected today due to uncertainty of the fulfillment of geometrical requirements. A reliable virtually verified component also minimizes the risk of failure with outsourced body assembling. This research project focuses on variation simulation of sheet metal assemblies for geometrical quality. The objective is to understand how sheet metal assemblies can be designed and evaluated for robustness. The approach is to identify, model and verify parameters that influence assembly geometry and variation. Variation simulation models have been used and developed to analyze the influence of the welding process and part and process variation on assembly geometry. The models have been verified against production inspection data. The main contributions of the research lie in: • the knowledge of parameters that influence the geometry of sheet metal assemblies and understanding design limitations that impact the parameters, • the knowledge of how parameters can be modeled and understanding what modeling aspects need to be considered for a high level of accuracy of the simulation results, • the knowledge of how sheet metal assemblies can be designed for robustness. The main conclusion is that variation simulation of sheet metal assembly is a complex task that requires access to inspection data and the involvement of many modeling aspects in order to achieve a high level of accuracy of the simulation result. The focus in early design stages should therefore be to analyze the robustness of the concepts rather than numerical verification of the geometrical requirements.