STUDY ON HIGHER REMOVAL RATE OF CEMENTED CARBIDE BY EDM

研究发现，当硬质合金在空气中高温加热时，碳化钨WC在620℃左右可以分解成钨和碳。一般来说，电火花加工(EDM)的可加工性是由热性能决定的，而不是由材料的机械性能决定的。如果基于WC分解的电火花加工硬质合金，就有可能在620℃的较低温度下加工硬质合金。在本研究中，为建立具有较高材料去除效率的电火花加工，进行了各种实验，得到了以下结果：(1)解释了硬质合金在水中电火花加工的分解过程。碳化钨在有氧的情况下可以分解成钨和碳。由于电火花加工将使用去离子水作为介质液体，因此去离子水中存在溶解氧(DO)和电解产生的氧。结果表明：(1)X射线衍射图上只检测到钨的存在。(2)碳化钨中分离出的碳与去离子水中的氧反应生成二氧化碳气体。由此发现，在去离子水中电火花加工硬质合金时，碳化钨碳化钨可分解为钨和碳。(2)DO浓度对材料去除速率的影响一般可溶于水中的最大氧量为20 mg/L。在去离子水中进行电火花加工时，溶解氧过饱和。在DO浓度较高的去离子水中，材料的去除效率比DO较低的去离子水高出30%左右。

It was found that when a cemented carbide is heated at elevated temperature in the air, a tungsten carbide WC can be decomposed into tungsten and carbon at about 620 ℃. Generally, the machinability with electrical discharge machining (EDM) is governed by thermal than by mechanical material properties. If a cemented carbide can be machined by EDM based on the decomposition of WC, it is possible to machine a cemented carbide at a lower temperature of 620 ℃. In this study, the various experiments were conducted to establish the EDM with higher material removal rate, and the following results are obtained.(1) Explanation of decomposed process for cemented carbides machined by EDM in waterA tungsten carbide can be decomposed into tungsten and carbon under the existence of oxygen. As the EDM will be done using deionized water as a dielectric liquid, the dissolved oxygen (DO) and oxygen generated electrolytically exist in the deionized water. The following results are obtained.(1) Only a tungsten W was detected in the debris through the X-ray diffraction pattern.(2) Carbon separated from WC reacts with oxygen in the deionized water to form carbon dioxide gas.From above results, it was found that when cemented carbides were machined by EDM in the deionized water, tungsten carbide WC could be decomposed into tungsten and carbon.(2) The influence of DO concentration on the material removal rateIn general the maximum amounts of oxygen which can be dissolved in the water is 20 mg/l. The EDM was done in the deionized water where the dissolved oxygen is supersaturated. In the case of the deionized water with higher concentrated DO, the material removal rate is about 30 % higher than that of the deionized water with lower concentrated DO.