Supporting Welding Methods for Future Light Weight Steel Car Body Structures 2002-01-2091

In the continuous struggle to improve car body properties, and at the same time reduce the weight of the structure, new materials and body concepts are being evaluated. In competition with more self-evident lightweight materials such as aluminium and plastic composites, new and different grades of high-strength steels with various surface coatings are being introduced. From experience it is known that to be able to weld and join these steel grades under high-volume conditions, it is necessary to perform comprehensive testing to establish those assembly parameters which give a superior and reliable weld quality.

To meet the demands of cost-effective low volume production, we can notice a tendency to move away from traditional uni-body concepts and into the direction of space-frame structures. These can preferably be manufactured out of high-strength steels by using production methods like roll-forming, hydro-forming and hot-forming. The challenge arise when these components shall be assembled to form a rigid body structure, as this type of car body architecture favours single-sided joining methods, about which there is still a limited knowledge and experience in modern body shops.

This paper will focus on the gas metal arc welding process as a suitable tool to assemble light weight steel car body structures. It will describe basic weld tests performed on relevant material grades and combinations with different surface coatings, but will also address the problems that occur at complex three-dimensional welding. For that reason advanced assembly fixtures, as well as hydro-forming tools for the manufacture of parts simulating a generic structural node, have been developed at the Volvo Cars Joining Centre. Results from these welding trials, and from static and fatigue testing of such nodes, will be thoroughly described.

At the end follows a discussion on other suitable single-sided welding methods such as laser welding and brazing techniques, and recommendations and guidelines are given about which method to choose in regard to desired product properties and production requirements.