Analysis of the Influence of Surface Integrity of Cemented Carbides Machined by Sinking EDM on Flexural Fatigue

Abstract Bulk forming is a manufacturing technology characterized by high tool loads. In order to reduce form deviations and increase surface qualities this manufacturing technology aims for even higher process forces, which result in larger stresses during the forming process. Consequently, the tool life of steel tools decreases drastically. A material that offers an alternative are cemented carbides due to their ability to withstand enormous compressive stresses and their resistance to wear. However, for the same reason, cemented carbides are hard to machine with conventional cutting technologies. A cost-efficient alternative is electrical discharge machining (EDM), because of its independence from mechanical material properties. Due to the brittle character of cemented carbides, one of the challenges in EDM, the reduction of the influence on the surface integrity, becomes a paramount concern. Thermal stresses caused by machining can initiate cracks that may lead to a failure of the tool after a few load cycles. The risk of crack initiation can be reduced with an appropriate machining strategy. In order to correlate the influence of surface integrity with flexural strength, load-controlled fatigue tests are conducted with two different types of cemented carbides that have each been machined with three different EDM-strategies. Along with the fatigue evaluation, the cross sections of the specimens are examined regarding their surface integrity. With these results it is possible to evaluate the impact of surface integrity of EDMed cemented carbides on the flexural fatigue.