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Over the past several decades, significant gains in automobile fuel efficiency have been achieved through down-sizing, aerodynamic design and drive train improvements. As performance limits are approached in these areas, aluminum is being used to further reduce body weight by up to 40% compared to steel. In anticipation of the continued demand for more fuel efficient automobiles, aluminum sheet component unibody and extrusion and cast component space frame designs have been studied to address joining and structural performance. Joint geometries unique to specific body designs clearly illustrate the need for close linkage of the design and assembly functions. Joining and assembly methods that provide static and dynamic structural integrity, 15 to 20 year durability and that can be integrated into robust manufacturing systems are key to aluminum usage for auto body structure.

This paper describes work conducted to understand the process mechanisms which cause electrode deterioration and inconsistent weld quality when welding aluminum auto body sheet. Surface objectives were found to be different at the outer and inner surfaces of the sheet. Various surface treatments were investigated and compared to arrive at an optimum treatment. Best overall results were obtained with a conversion coated inner surface and an arc-cleaned outer surface applied immediately before welding. Results were verified with an extended life test which produced more than 7,000 welds without a dud.