Micro-structuring and macro-structuring of deep drawing tools for dry forming condition

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Large friction forces in forming processes reduce the process limits. Generally, lubricants are therefore used to reduce friction and enlarge the process window. However, the technological advantages of lubricants are accompanied by negative economic and ecological effects. Therefore, the elimination of lubricants from deep drawing processes by means of an integrated concept of a protective coating and micro- and macro structuring of the tool is studied and analysed during this project. Within the first phase, the different technologies of the integrative approach were fundamentally analysed and the deep-drawing process with tool structuring was experimentally verified. The general feasibility was demonstrated for axially symmetric parts. In the second funding period, the process principle has been further improved. For a time efficient process design an analytical model has been developed describing the influence of input parameters on the risk of wrinkling and bottom cracks. Furthermore, a feasibility study regarding high-strength steels indicated additional advantages of a macro-structured deep drawing process over standard processes. The reduction of friction forces was pursued by investigating coating technology and micro-structuring of tools and the wear behaviour of coated and structured surfaces and the interaction with blank and tool surface were investigated. All technologies were transferred to the design of a modular tool for non axially symmetric parts. Based on these results, the third research phase has the goal to implement an industrially relevant lubricant free deep drawing process for complex parts and high strength materials. The main approach remains an integrative application of different processes in the areas of macro-structuring, coating and micro-structuring. The enhancement of the macro-structuring into three-dimensional geometries is a key factor, because it allows the direct control of the material flow in tangential and radial direction, and therefore the systematic adjustment of stresses as well as bending and unbending to specifically set part characteristics. An adjusted semi-analytical model is used for designing the macro-structures and choosing process parameters. The corresponding high requirements of the forming process regarding friction and wear of the tools will be addressed with a combined approach of coating and micro-structuring. The goal is to improve on previous results by adjusting the coating and structuring processes. Specifically, a new coating with a fluor modified ta-C layer will be implemented and the chromium bonding layer will be substituted by a nitration process. Additionally, the DLIP process will adjusted by shortening pulse times and homogenising the laser beam in order to improve the quality of the micro-structure while minimising negative effects on the substrate. All technologies will be integrated and verified using the modular deep drawing tool from the second funding phase.