Analysis of tool-sided surface modifications for dry deep drawing of deep drawing steel and aluminum alloys in a model process

Abstract

The concept of sustainability motivates the development of energy-saving and low-polluting production processes. A sheet metal forming process without usage of lubricants is considered as one of these green production technologies. Forming processes without the need for traditional lubricants save process steps and additional costs to remove the remaining lubrication from the workpiece after forming. In order to realize such a dry forming process and to adjust the material flow effectively, tool surfaces were modified by amorphous carbon coatings and different surface finishing processes for roughness adjustment. To verify the general feasibility of the lubricant-free metal forming process, deep drawing of rectangular cups with and without lubrication with conventional forming tools was investigated. The dry deep drawing process was modelled numerically to analyze process parameters and identify critical contact conditions. By strip drawing tests, the tribological behavior of ta-C and a-C:H coated tools with different surface treatments was investigated. The deposition process and resulting properties of a-C:H coatings were further analyzed to improve their tribological performance. The effects of the process parameters - deposition temperature and bias voltage in the deposition chamber - were investigated using the one-factor-at-a-time method. The strip drawing tests revealed a high influence of the surface roughness of coated tools on the tribological behavior. Therefore, laser based smoothing was further investigated in this study. Laser radiation at 355 nm wavelength was applied as an effective and minimum heatgenerating technique to remove the roughness asperities on ta-C coatings which are built during its growth. Finally, ta-C and a-C:H coatings were applied on tool surfaces and tested in a drawing process of strip profiles. As reference the same forming process with a conventional forming tool was carried out.