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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.

The need to substantially reduce the weight of automobiles to improve performance or meet CAFE requirements has led to an increased use of lightweight materials such as aluminum. To use aluminum efficiently in auto body structures, component and joint designs and joining methods are likely to differ from those traditionally used in steel bodies. With proper design, aluminum automotive frames can efficiently meet or exceed the performance requirements for stiffness, static strength, fatigue strength and crash performance. This paper presents some joint design concepts for aluminum frames and compares the performance of joining methods such as resistance spot welding (RSW), gas metal arc (GMA) welding, weld bonding, adhesive bonding, riveting and mechanical clinching for both unibody and spaceframe construction. Recommendations for preferred joining methods are also made based on the effect of design details on joint performance and assembly.

IN WELDBONDING, a joint is produced by (a) spotwelding through an uncured adhesive bondline or (b) flowing adhesive by capillary action into the bond area after spotwelding. Weldbonding can offer higher joint strength, reduced joint weight, improved fatigue life and, in some aircraft-oriented investigations, showed reduced manufacturing costs(1,2). Although weldbonding has had repeated use in the Russian aircraft industry(3,4), it has not been widely employed in American manufacturing to date. The most intensive efforts to develop the process have resulted from contracts sponsored by the U. S. Air Force(4). The only aluminum alloys used in these investigations were the high strength aircraft alloys and the emphasis was to develop the highest strength weldbond joints with economics a secondary consideration. These studies usually included the use of special surface treatments on the aluminum, special adhesives, and carefully controlled curing conditions.