多晶鑽石之線切割放電加工特性研究

Abstract

多晶鑽石(Polycrystalline diamond，簡稱PCD)為近年來工業界廣泛使用之材料，其優點除了擁有近似單晶鑽石之優良機械性質外，還能配合目的被加工為所需之形狀。多晶鑽石最常被用於切削加工，而其中一項最新應用是使用於晶圓拋光墊(pad)之鑽石修整器(diamond conditioner)，其為使用放電加工方式將多晶鑽石切割出如金字塔形狀之陣列，稱為ADD TM(Advanced Diamond Disk)。但PCD 因其高硬度及高耐磨性，不適於使用傳統加工，因此本研究使用不受加工材料硬度及韌性等限制之線切割放電加工方式對多晶鑽石進行切割。 由於多晶鑽石為一多種材料之複合體，其材料性質與一般金屬材料不同，因此本研究分別就三大部分進行實驗與觀察，藉以了解多晶鑽石進行線切割放電加工之特性，以作為日後加工之參考，研究結果發現：(一)改變各個參數對其進行線切割放電加工，可發現PCD 與一般金屬之加工趨勢相近，但放電加工效率較低，其適用之參數範圍也較窄。加工後PCD 上表面之缺陷會因on time 增加而增加，因加工液流量加大及多晶鑽石朝下擺放而減少，此外PCD 放電過後也會導致PCD 和WC 間的間隙加大。(二)使用鉬線極與鎢線極對多晶鑽石進行加，其速度因線極導電度不佳與殘留之潤滑劑而較低，加工後之PCD 表面狀況也不佳。(三)元素六(Element Six)公司新發展出一種多晶鑽，擁有小晶粒好放電加工但卻耐磨之特性，其放電參數對加工效率之趨勢，大致與一般多晶鑽石相同，且加工後之PCD上表面品質相當好，PCD 與WC 間之間隙也較小。

PCD (polycrystalline diamond) is an intergrown mass of randomly orientated diamond particles in a metal matrix. PCD is usually used as cutting tool due to its extremely high hardness and abrasion resistance. One of its new applications is the diamond conditioner for polishing pad in CMP process. The PCD array of pyramid shapes called ADD TM by traditional machining processes is not an easy task due to its extremely high hardness and abrasion resistance. EDM process is considered one of the potential candidates to machine PCD because of the conductive element of Cobalt (Co) contained in PCD. In this paper, wire EDM process is chosen and its machining characteristics are discussed. The material properties of PCD are different from the general metallic materials owing to its multi-materials compound. In order to understand the machining characteristics of PCD by wire-EDM three parts of experiment are conducted. (1) By changing the parameters during the wire-EDM process, the tendency of machining efficiency in cutting PCD is found to be similar to that of cutting general metallic materials. But its value is lower and the suitable parameters are fewer. The defects on the upper surface of PCD increase under a larger ignition on time condition, and decrease with PCD side placing downward and under a higher water flow rate condition. In addition, after the wire-EDM process, the gap between PCD and WC becomes noticeable. (2) Using Molybdenum (Mo) wire and Tungsten (W) wire as the electrodes of wire-EDM to cut PCD, the efficiency is low because of the inferior electric conductivity and the inherent lubricant on the electrodes. The quality on the upper surface of PCD is poor after wire-EDM machining. (3) Using brass wire as the electrode, cutting a new kind of PCD which not only has a good EDM ability but also a good abrasion resistance developed by Element Six with wire-EDM process is studied. The tendency of machining efficiency approximates to that of cutting other kinds of PCD. But the quality on its upper surface is satisfactorily good and the gap between PCD and WC is also smaller.