Application of Tubular Hydroformed Radiator Support Assembly to GM’s New Midsize SUVs 2001-01-3089

This paper presents the product design & development efforts to apply the tubular hydroformed radiator support structure assembly to GM’s new SUVs. This represents that for the first time the space-frame type of structure assembly is used in integrated vehicle body application. The assembly is welded onto the front-end structure. By doing so, the body is greatly stiffened during the assembly process. Some benefits from this tubular design over the traditional stamped design have been realized. The product design started with all stamped radiator support assembly similar to the old design. As more and more styling, packaging, mass & structural requirements come to play, the stamped design could not satisfy all these requirements. It was found that the most efficient structure design within tight space will be using tubular structure, which can provide the largest section available by eliminating weld flanges (typically 20mm). Going through several design iterations using one-piece lower tie-bar, two brackets (one for each side) for headlamp mounting, and one-piece upper tie-bar. The final production design, which consists of six pieces of hydroformed components; all of them are welded together except the upper tie-bar, which is bolted on its extensions and can be removed for service need. The complete assembly is welded to the upper rails in the body assembly. The formability & assembly efficiency play very important roles during the product design process. As an example, only three hydroforming dies are required to make those six pieces of components. One for the U-shaped lower tie-bar, one for those two vertical pieces (cut from one hydroformed tube), & the third one is for the upper tie-bar with its two extension pieces. The upper tie-bar is hydroformed together with its extensions as one piece. Both ends of the upper tie-bar are partially smashed & completely smashed in the hydroforming process. A mechanical shear is used to trim the ends of the upper tie-bar and then it is flipped over and bolted on its two extension pieces. By doing so, the matching conjugate features from hydroforming at the joints provide improved joint stiffness. In addition, all the hole piercings are done in the hydroforming dies.

In summary, this new tubular hydroformed radiator support structure has provided us some benefits over the traditional stamped design both in product performances and manufacturing efficiency.