Method for performing a hydroforming operation

A method for performing a hydroforming operation on a hollow workpiece includes the initial step of filling the interior of the workpiece with a hydroforming fluid. The pressure exerted by the hydroforming fluid against the interior of the workpiece is below the yield strength of the workpiece so as to not change the shape of the workpiece. Then, first and second die sections of the hydroforming apparatus are closed about the workpiece. The movement of the two die sections causes some mechanical deformation of the workpiece, but the presence of the hydroforming fluid within the workpiece prevents the amount of this mechanical deformation of the hollow workpiece from being undesirably large. Thereafter, the pressure exerted by the hydroforming fluid against the interior of the workpiece is increased to above the yield strength of the workpiece. As a result, the workpiece is deformed into engagement with the first and second die sections of the hydroforming die.