Novel Extrusion Punch Design for Improved Lubrication and Punch Ejection

The extreme surface expansion and pressures observed during the backward extrusion process can have adverse effects on the surface of the workpiece and the life of the punches used in the process. After the forming process is complete, the ejection of the punch can further damage the part surface and reduce tool life because the pressures on the land of the punch remain quite high. The research presented in this investigation aims to reduce or eliminate the galling and surface damage for the backward extrusion process by creating a new class of punch which can create the opportunity for lubrication transport to the area underneath the punch and lessen the damaging conditions during punch ejection. The proposed tooling divides the traditional punch into two pieces, a hollow punch body and an insert with micro channels for lubrication transport. The tooling was developed and used in a series of tests to determine the benefits of the new punch. Preliminary data shows that the extrusion loads for proposed punch are similar to the conventional punch, but the surface finish is significantly enhanced using the modified punch design and the galling is minimized. Furthermore, there is a marked reduction in the ejection load required to remove the punch from the part after forming.