静電誘導給電法を用いた微細放電加エの加工安定性の向上

摘要

This paper describes the machining characteristics of the electrostatic induction feeding method. With the conventional relaxation pulse generator normally used in micro electrical discharge machining, since the gap voltage begins rising after the end of the previous discharge, it is difficult to keep the minimum necessary discharge interval between pulse discharges to recover the dielectric breakdown strength of the gap. Thus, localized discharge and abnormal arc easily occur, resulting in machining instability. Moreover, since discharge even occurs before the capacitor is fully charged due to the long time constant of the RC circuit, it is difficult to obtain uniform discharge energy per pulse. In contrast, with the electrostatic induction feeding method, since only a single discharge occurs for each cycle of the periodic pulse voltage, the discharge gap can be cooled regularly during the discharge interval, resulting in stable machining. Therefore, machining characteristics of the electrostatic induction feeding method were investigated using the machining system newly developed for micro-hole drilling. Machining results show that the machining speed of this pulse generator is higher than that of the relaxation pulse generator in micro-hole drilling, especially when rotation speed of the tool electrode is low.%1．緒　　　言微細加工の手段として放電加工は最も有力な加工法の一つである1）．微細放電加工においては一般に，容易に短いパルス幅の放電電流が得られるため，図1（a）に示すRC放電回路が用いられている．しかしRC放電回路では，放電終了直後からコンデンサの充電が始まり，極間電圧が上昇し始めるため，必要最小限の休止時間が確保されていない．従って，前の放電によって生じたプラズマが消沈する前に放電が生じてしまうことがあるため，放電頻度を高くしようとすると放電集中や異常放電が生じ易くなる．そのため，加工面への熱的ダメージが生じ易く，また加工速度が低下する．