Static and oscillation superimposed ring compression tests with structured and coated tools for Sheet-Bulk Metal Forming

Abstract

Forming tools with tailored surfaces or functional surface modifications offer great potential for the adaption and optimization of forming processes. However, the interaction of the resulting tribological conditions with additional process oscillations and lubricants has not yet been sufficiently investigated. In the field of sheet-bulk metal forming the superimposition of oscillations is a new, highly promising approach for optimizing the forming of metallic materials. The aim of this study is therefore to investigate the forming behavior of metallic materials with an oscillation superimposition in combination with structured tool surfaces. In order to examine to what extend the friction factor and the forming force can be influenced by structured surfaces and PVD-coatings ring compression tests were conducted to re-create the real process conditions. The experiments were carried out statically and with an oscillation superimposition in the main force flow of the machine under lubrication and dry conditions. Occurring interactions between surface applications, lubrication and oscillation superimposition are identified and analyzed within the context of this work. Thereby, three different deterministic surface structures of the ring compression tools were considered. A radial and tangential arrangement of a wave-like structure as well as an isotropic honeycomb structure were applied on the forming tools by means of micromilling. For a lubricated and vibration superimposed process, especially the isotropic honeycomb structure caused a significant decrease in friction. This was attributed to the formation of lubrication pockets. Despite the reduced friction, in some cases no reduction of the forming force occurred by using an oscillation superimposed forming process. This behavior was attributed to damping effects caused by the lubricating pockets.