Macro and Micro Structuring of Deep Drawing's Tools for Lubricant Free Forming

Abstract

In today's industry waste avoidance and efficient use of resources is becoming more significant due to economic and environmental requirements. Decreasing usage of lubricants in forming processes such as deep drawing offers a high potential regarding these efforts. A radical approach, which leads to the highest savings, is the realization of a complete lubricant free deep drawing process – the lubricant free forming. The approach in this paper is to find out a method for eliminating the lubrication in deep drawing process, by means of macro structured tool, in order to control of the friction forces and the material flow and also coating them with an adapted coating film. This paper presents an overview of the basic process principles and first analytical and experimental results. Based on initial FE simulations, a macro structured tool for deep drawing is simulated to be compared with conventional tools. The required punching force, change in sheet thickness during the process and also shear stress on the flange are compared in these simulations. Because the draw edge radius is the most critical part of deep drawing regarding the frictional force, draw bend test is used to enable the analysis of this area. Hence a cylindrical specimen, which is already coated with tetrahedral amorphous carbon (ta-C), is used. Through Direct Laser Interface Pattering, it is possible to change the surface properties of the ta-C films selectively by local graphitization, delamination or by removal. The paper presents results of experimental and numerical investigations with the special tool set carried out with blanks made of steel DC04. The results will be discussed regarding the process limits and the potential for future applications.