A comparison between micro milling pure copper and tungsten reinforced copper for electrodes in EDM applications

Abstract In today's continuously growing demand for components with increasingly smaller dimensions and features, micro milling is gaining more significance. However, for the mass production of components with micro features, injection molding is still customary in order to keep target costs. Due to high requirements regarding lifetime and resistance to wear, the molds are made of hardened steel. The shaping of those molds involves electrical discharge machining (EDM), because the process is independent of the material hardness. As a work tool for EDM, electrodes made of pure copper (Cu) and tungsten reinforced copper (WCu) are commonly used. The quality and reliability of the eroded shapes are determined to a high extent by the quality of the electrode deployed. For this reason, micro milling is a crucial factor in the process chain and its impacts have to be evaluated. This paper explores the key factors which have to be considered in micro milling pure copper and tungsten reinforced copper for micro features of electrodes. Due to scaling effects, micro milling differs strongly from macro milling. For mastering this process, a new approach to identify cutting edge geometry and the influence of the common milling parameters and material properties is required. Two flute micro milling tools with diameters as low as 200 μm and a cutting edge as low as 3 μm are applied for examination. To generate suitable cutting conditions with such small tools, extremely high rotational speeds of the spindle are required. Here it is chosen to be 200.000 rpm. The size of the minimum uncut chip thickness for both materials is discussed. Optimal process parameters and conditions for micro machining both materials are derived concerning process forces as well as burr and wear formation.