Optimization of Process and Tool Development for Hydroformed Frame Rail Using FEM Simulation

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.