Preform design in hydroforming by the three-dimensional backward tracing scheme of the FEM

Many hydroforming operations require a pre-formed tube in order to fit the tube into the hydroforming die cavity and reach the desired shape at the end of the process. Hence it is crucial how to produce a suitable preform shape for the successful hydroforming starting from a round-like tube. In this study, a novel FEM program for design of preform in a hydroforming, which is based on a rigid–plastic approach and the backward tracing scheme, has been constructed with careful treatment of die–workpiece interface. The backward tracing technique is introduced to predict an appropriate pre-formed configuration and determine the initial tube dimensions from the desired final shape. The developed program is applied to a hydroforming process of a box expansion in order to get the uniform wall thickness after hydroforming, and the conceptual application has been proved to be successful on its effectiveness and feasibility.