Development and Evaluation of Tool Sided Surface Modifications for Dry Deep Drawing of Steel and Aluminum Alloys

Abstract

Avoiding negative effects of conventional lubrication in forming operations stimulates research on lubricant free forming processes. Increased friction and wear due to direct contact between tool and workpiece surface lead to insufficient forming results in dry forming operations. Dry deep drawing of rectangular cups with conventional tools reveals cracks and wrinkles. This necessitates the development of tool sided surface modifications which face the challenges of lubricant free forming. As former results of tribological investigations have shown, adhesion is the dominant friction and wear mechanism. Therefore, diamond-like carbon coatings are applied to decrease adhesion. The mechanical properties of a-C:H:W- and ta-C-coatings are systematically analyzed to reduce friction and wear. Additionally, micro features are generated by laser texturing of a-C:H:W coatings to control material flow by locally adapted frictional conditions. The effects of different feature edge geometries and the feature orientation are investigated in ring-on-disc tribometer tests. Depending on the deposition parameters some a-C:H:W coating variants show reduction of adhesion for DC04. However, in contact with aluminum alloys no improve of tribological conditions could be achieved. ta-C coatings affect the reduction of friction and wear in contact with DC04 and aluminum and show high potential for application in dry forming processes. Depending on adhesion affinity of the workpiece material, micro features can increase friction by adjusting their edge geometry, orientation and area coverage. The tribological behavior of selected surface modifications is finally analyzed in the strip drawing test. The obtained results gain basic knowledge for development of surface modifications towards realization of lubricant free deep drawing by a tailored tool concept.