Dry deep drawing of a rectangular cup assisted by volatile media injected from laser-drilled microholes

Abstract

Technical, economic and legal requirements lead to increasing demands on lubricants in sheet metal forming. Moreover, the effects of lubricant application on the environment become more and more relevant. The long-term goal in sheet metal forming is to reduce the amount of lubricant used in order to conduct sheet metal processing without lubricants in future. Based on the efforts of dry forming, a new procedure for the lubrication of deep drawing processes with volatile media as lubricant substitution is being developed at the University of Stuttgart. This method enables the insertion of an intermediate medium under high pressure through laser-drilled microholes into the tribological system without subsequent, cost-intensive cleaning processes as the volatile media evaporate without residue when the pressure is reduced to ambient pressure. During the first and second funding period of this research project, a general applicability of volatile media as lubricant substitutes was demonstrated by means of strip drawing experiments and a simple academic test component of an Ushaped profile. For this purpose, several problems in the area of fluid supply to the tool were solved. In this report, new findings from investigations of the pressure state of volatile media in the tool contact zone, depending on number, nozzle type and arrangement of laser-drilled microholes, are presented. In addition, results of the optimized laser drilling process are included. These investigations serve as a base for the new, more realistic implementation of the new approach of dry forming in a deep drawing tool. The design of this tool for the deep drawing of a rectangular cup is presented here in detail. Initial investigations of the deep drawing process have also shown that volatile lubricants can be used to realize a significantly enlarged process window compared to conventional lubricants. This promising result shows the wide range of applications for the new tribological system in deep drawing processes.