The dimensional quality of sheet metal assembly with welding-induced internal stress

Abstract

The present paper is the first to propose a minimum stress criterion for the minimum dimensional variation during sheet metal assembly. The weld sequence affects the dimensional variation owing to the welding process. A case study illustrates the minimum stress criterion on dimensional variation. This paper proposes a generic design criterion for sheet metal products and processes that would produce minimal stress-induced dimensional variation for spot-welded sheet metal assemblies. The process design proposes a minimum strees build-up by using the ‘sheet metal ironing welding technique’ in the weld sequencing design. The product design proposes a minimum stress build-up design criterion to manage the accumulation of stress. The proposed product and process design methods enable automotive body design engineers to create a quality product with minimum dimensional variation caused by the manufacturing stress within the body-in-white structure. Moreover, this facilitates the industry's objective of building a high quality automotive body with minimum stress. This is an important factor in contributing to the superior quality of the body panel fits. It also helps to reduce the quality-related warranty costs. This paper primarily focuses on the development of a joint design guideline by exploring the relationship between the dimensional variation and the stress build-up. First, the automotive assembly process design will be introduced. A simple analysis of a one-dimensional assembly is produced. A three-dimensional structural analysis of a box assembly is investigated for the effect of stress build-up within a structure on the dimensional instability or variation. Then a three-dimensional finite element analysis of an assembly with weld sequencing of two imaginary parts is produced. An experimental industrial trial has confirmed the validity of the simulation methodology. Then a welding sequence design guideline is produced based on the previous simulation result, followed by a joint design guideline to help improve the design of dimensionally robust design.