Analysis of discharge-dependent surface integrity of cemented carbide forming dies machined by sinking EDM and its influence on the tribological characteristics and the resulting fatigue behavior

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Cemented carbides have a growing potential as a tool material in metal forming because of their great resistance to wear and high compressive strength. They are characterized by an increased hardness compared to steels and simultaneously increased bending strength compared to ceramics. The flexural strength in this context is an essential material parameter for tool design, as bending stresses are often critical failure reasons. The further spread of hard metals as a tool material for active elements in metal forming are however conflicted by high material- and particularly high processing costs. Due to its independence from mechanical material properties, Electrical Discharge Machining (EDM) is a key technology for the machining of cemented carbide forming dies. However, machined carbide tools often show a toughness that remains below expectations. One reason for this is the lack of process knowledge to adapt the tool surfaces specifically to the requirement profile. On the other hand, the results presented in the state of the art and the previous work show that the final component strength can be specifically and significantly increased through adequate process design within the entire process chain. The objective of the project involves the scientific and structured analysis of the influence of discharge-dependent surface integrity of EDM (Sinking EDM) on the resulting tribological and mechanical behaviour of components made from cemented carbide materials.In the previous research phase, several issues were raised and should be answered over the course of this subsequent research period. A full factorial experimental design should be used to create a model that can physically explain the dependence of surface integrity from the process energy. The general applicability of the model should be verified on a second machine tool. The description model of the tribological material behaviour has shown non-linearities that need to be investigated during additional experiments. Another effect that has not yet been scientifically described, is the geometrical shape deviation occurring upon machining of cemented carbide. Information on the cause of this effect should be gathered by varying the electrode material and the machining parameters. In order to show the applicability of EDM for the machining of cemented carbides, several subsequent treatment steps should be examined. These findings should be used to design and manufacture multiple cold forming dies from cemented carbide, which are going to be tested under realistic conditions. Finally a model should be created from all the findings made in both research periods. This should be used to derive recommendations for users, machine tool and material manufacturers.