不同截面電極深孔雕模放電加工渣排除效果之研究

Abstract

渣粒於雕模放電加工間隙之分部與流動是影響加工品質及速度的重要因素之一，良好的排渣方法能改善效率，加深加工深度，並且提升精度，於放電加工具極大助益。本研究針對不同寬度電極於深孔跳躍運動造成的排渣效果，得到最適的速度、跳躍高度與次數，並找出不同寬度電極跳躍排渣之特徵與關係，同時以流體力學計算、撰寫程式以模擬深孔排渣面對的問題。經由流體力學分析，過高的跳躍高度導致電極底部的壓力降低，介電液氣化，若速度過快，間隙液體來不及流入，其現象隨電極抬升而加成，直至未填滿區過大，影響排渣。經過實驗發現，於合適的速度下進行跳躍排渣可得較高的渣排除比例：速度過低將不足以帶動渣粒，過高則會造成未填滿、氣泡，當氣泡於底部佔有率超過50%時，外加協助排渣之跳躍將無法生效。其中，方形、大電極較易產生未填滿現象，窄、薄型電極則易產生間隙流速慢，渣粒滯留於底部的狀況。無論是何種電極，排渣最終須克服底部約5 mm高度之渣的帶動，而良好的混合有助於排渣。方形電極以一個大於間隙體積高度和接近加工深度1/2之雙次跳躍，排渣效果極好；針對長方形電極，雖較不容易產生氣泡，但也不易藉由渦流帶動渣粒，須以極限速度進行接近2/3加工深度之跳躍，再加上一個低於加工深度約10 mm的大跳躍進行排渣。以上兩種電極超過5次跳躍效率將遞減。薄型電極跳躍排渣具深度的限制，且跳躍次數約4到5次才可排除，以實驗搭配之線性馬達而言，深寬比超過10即無法排渣。最後，依照所得之最佳跳躍速度，發現其中之關聯性，推測薄型電極需更高的跳躍速度才可良好排渣。

The distribution and the flow of debris between gaps are important factors in die-sinking EDM. The proper debris exclusion will enhance the surface quality, machining efficiency and stability. Moreover, the machining depth could be larger. This research focused on the best debris removal capability under different electrode widths and combination of jumps. The dielectric-debris flow was simulated by the program and captured by the high speed camera. The debris can’t be driven when the jump speed is too low. When the jump speed exceeds a critical extend, there is not enough time for the dielectric to flow in, resulting the poor removal effect. As the bubbles percentage reaches 50, the additional assisted jumps are useless. The proper jump speed increases as the electrode width decreases. The well-mixed dielectric-debris fluid is good for exclusion. To attain the better efficiency and removal capability, for square electrode, the combination of the jump larger than the gap volume followed by the jump with one half of machining depth jump height is needed. As the width decreases, the jump with two-thirds of the machining depth height under maximum speed and the jump little less than the machining depth under proper speed should be used. It’s a waste of time for more jumps. For the thin-wall electrode, due to the smaller jump volume and higher proper jump speed, the quad jumps should be adopted and the removal effect is invalid while the aspect ratio exceeds ten. This paper provides an improved way to remove debris and a better understanding of debris removal facilitation mechanism.