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The manufacturing process of a cross member rail begins with a thin walled tube and comprises forming operations of tube bending, pre-forming and final hydroforming. Computer simulation has been used to optimize each forming operation to reduce tool cost and lead-time by providing virtual tryout before hard tool construction begins. This paper summaries the process development with the aid of computer simulation of hydroforming of a cross member rail. Tube bending process has been modeled as rotary draw bending with 3-ball mandrel. The mandrel size is critical to control thinning and buckling at the outside and inside of the bend, respectively. After bending, the circumference of the tube at the bend area is reduced by about 6%. This bend circumference reduction has to be considered during the product design stage, especially for the bend where end feeding can hardly be reached in the hydroforming.

The manufacturing process for a frame rail consists of tube bending, pre-expansion, pre-forming and finalhydroforming a thin walled tube. Process variables such as internal pressure, end feeding and tool geometry were optimized with simulation to improve the forming safety margin of the process. The shape of cross-sections at critical locations along the tube was predicted for each forming operation. Simulation predicted the high forming pressure would severely limit material movement around the circumference when in sliding contact with die walls. A pre-expansion operation reduced sliding contact and enhanced the effect of tube end feeding. The tube was pre-formed to generate an optimum shape for final hydroforming.Simulation predicted the least thinning and most uniform strain distribution resulted if the tube had the proper “folded” shape when loaded into the finalhydroforming die.