Tube Hydroforming Process Development with the Aid of Computer Simulation

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. To obtain an optimized cross section of the tube for the hydroforming, a die pre-forming operation is developed. The pre-forming is also an opportunity to avoid pinching during the hydroforming die close. With optimized cross sections of the pre-formed tube, a minimum amount of material needs to be redistributed around the circumference as the tube expands to fill the die cavity during the hydroforming. In the hydroforming operation, process variables such as internal pressure, tube end feeding and tool geometry were optimized with the simulation to improve the forming safety margin of the process.