SIMPLIFICATION IN POLISHING METAL MOLD OF CEMENTED CARBIDE MACHINED BY EDM USING OXIDATION

近年来，硬质合金由于其优异的耐磨性和耐热性，在各种模具中得到了广泛的应用。然而，在金属模具制造过程中，硬质合金的电火花加工会产生热影响区（HAZ），其中存在许多裂纹和微孔。在目前的情况下，热影响区是通过抛光去除的，而抛光依赖于手工抛光。然而，这种工艺延长了加工时间，增加了金属模具的生产成本。因此，提出了一种用氧化法代替机械去除法的表面改性新方法。所提出的方法使用硬质合金表面的高温氧化，软化具有许多孔隙的层，以便可以通过钢丝刷轻松地去除它们。结果表明：(1)电火花加工硬质合金产生的热影响区可以通过氧化处理完全去除。氧化表面由钴氧化物和钨氧化物组成。(2)除去氧化物后剩余的晶体结构转变为碳化钨（WC）的六方晶格，结构稳定。因此，表面改性方法有望极大地促进金属模具制造过程中的抛光。

Recently, the use of cemented carbides has become widespread for various kinds of meal molds because of their superior wear and heat resistance. However, the heat-affected zones (HAZ), in which ihere are many cracks and microcraters, are generated by electrical discharge machining (EDM) of cemented carbides during the metal mold manufacturing process.Under the present situation, HAZ are removed by polishing, which is dependent on hand finishing. However, this process extends the machining time and increases the cost of production of metal molds.Therefore, a surface modification method using oxidation is proposed as a new surface modification method instead of the mechanical removal one. The proposed method uses a high-temperature oxidation of the surface of cemented carbides, softening the layrs with many pores so that they can be easily removed by rubbing with a wire brush.The following results were obtained :(1) The heat-affected zones generated by EDM of cemented carbides could be completely removed by this oxidizing treatment. The oxidzed surface is comprised of cobalt and tungsten oxides.(2) The crystal structures remaining after oxide removal are transformed into the hexagonal lattice of tungsten carbide, WC,in a stable structure. Consequently, the surface modification method is expected to greatly facilitate polishing during the metal mold manufacturing process.