Hot Draw Mechanical Preforming of an Automotive Door Inner Panel

A novel sheet metal forming technology based on aspects of both warm forming and superplastic forming has recently been developed. The new forming process, referred to as hot draw mechanical preforming (HDMP), uses two sequential steps to form a panel within a single tool at elevated temperature. In the first step, the cushion system acts on a binder and upper die to draw the blank over a punch which serves to draw in metal from the perimeter of the blank. In the second step gas pressure is applied to finish the panel details. This two step process of drawing in metal followed by gas forming can result in a significant expansion of the forming envelope for conventional AA5xxx series aluminum sheet alloys commonly used within the automotive industry. Similar to SPF, the HDMP process is performed within a single forming press equipped with heated platens and using gas pressure to shape the component during elevated temperature forming. However, the HDMP process utilizes a blankholder to control the flow of material into the forming cavity during the drawing stage and therefore requires the addition of an integrated cushion system in the bed of the press. HDMP dies are of interest in automotive applications because they maintain the low-investment attributes of SPF tooling while also significantly reducing the forming time as compared to conventional SPF. This work details the CAE based design of an HDMP die to form a one-piece aluminum door inner that can not be formed with conventionally forming processes. Critical aspects addressed in the development of the die include manufacturing targets, part design for manufacturing, and die design for operation at elevated temperature.