Structuring of forming tools for lubricant-free deep drawing

Abstract

In forming processes, lubrication is used to reduce friction and wear occurring at the contact areas of workpiece and tool, by separating these surfaces as well as transporting abrasive wear out of the sliding interface. With high interest in waste avoidance and efficient use of resources, today’s industry aims for substituting this lubrication. Thereby, deposition of surface coatings or local surface structuring offer a different way for friction reduction in forming processes. In this work, the flange area of a deep drawing tool is firstly macro-structured by milling process to decrease the contact area to the workpiece by 94%. Additionally, the pulling edge radius is coated with a hydrogen-free ta-C layer with sp3-ratio of 70%. Subsequently, the coated area is micro-structured employing Direct Laser Interference Patterning (DLIP), introducing well-defined contact areas to decrease friction and wear by locally rehybridizing the ta-C material. Also, the high-speed DLIP micro-structuring of the workpiece metal sheets is made to further reduce the contact area and lower the friction. Forming of test strips show the influence of the macro-structured flange area by reducing the friction force down to 75%. Performed tensile-bend tests on micro-structured ta-C coated cylinders could show a reduced coefficient of friction, small wear volume and resistant DLIP structures after the tribological evaluation.