- 學位論文
薄型電極尺寸及界面活性劑對跳躍排渣影響之研究
Study of Electrode Size and Surfactant Effects on Thin-wall Electrode Jump Debris Removal in EDM
摘要
在雕模放電加工中，渣粒與氣泡的分布與流動是具有相當影響力的因素之一，良好的排渣策略可以改善材料移除率、加工深度、工件的表面粗糙度與精度等，以及提升操作的安全性，對放電加工有很大的助益。而薄板電極在加工中會有渣粒難以排除的情形，本研究將探討採用線性馬達進行薄型電極跳躍排渣時適合的參數，討論不同薄型電極之尺寸對於跳躍運動中流體的影響，並試驗加入界面活性劑後對整體排渣效果是否有所改善。本文首先以流體力學的觀念計算不同尺寸電極所會造成的差異，得到電極寬度越大越容易發生填不滿的現象，不利於渣粒排除。接著實際以線性馬達模擬電極的跳動，發現不同階段中產生的氣泡機制不同，一開始產生的氣泡是因為壓力變化造成；後段產生的大面積氣泡則是因為填不滿效應發生，另外速度越快、高度越高氣泡越容易產生，所占面積也越大。放速渣粒進行實驗後發現較小的電極最適合的跳躍高度為60 mm；較大電極適合的跳躍高度為80 mm、速度400 mm/s，這個參數下會產生些許氣泡，而這些小氣泡上升的過程會帶動渣粒運動幫助混和，但排渣比例仍然只有30%左右。接著加入不同種類的界面活性劑，比較其差異，發現HLB值為1.8的SPAN#85對所有尺寸的電極排渣皆有改善，而最適合的濃度因電極尺寸不同而有所變化。最後改變模擬排渣的初始條件，在底部增加氣泡以模擬真實加工情況，發現加入SPAN#85後可以增加43%的排渣比例，推測在實際加工時加入界面活性劑能夠有效幫助薄型電極的深孔跳躍排渣。
並列摘要
The distribution and the flow of debris between gaps are important factors for die-sinking EDM. The proper debris exclusion will enhance the surface quality, machining efficiency and stability. Moreover, the machining depth could be larger. However, difficulty in excluding debris occurs when using thin-wall electrode. This research will focus on finding proper parameters for electrode jump debris removal with linear motor. Discussing the size effect of thin-wall electrode, and observing the influence of adding surfactant in the dielectric. This research starts from calculation, and finds that wider electrode size leads to harder debris removal. Then simulating the jumping motion of electrodes with linear motor, discovering that there are different mechanisms of bubble generation in the gap, one is caused by pressure differences, another is because that the fluid can’t filled the cavity the electrode make while lifting. Also higher and faster the electrodes jump, the easier the bubbles generate. The proper jumping height for less wide electrode is 60 mm. But for wider electrode, proper parameters are 80 mm for height and 400 mm/s for speed, in this condition, small bubbles appear at the bottom of gap, helping the mixture of debris. But the remove ratio is still about 30%. After that, addition of different kinds and concentration of surfactant is conducted. It reveals that SPAN#85, with HLB value of 1.8, benefit the debris exclusion of all size of electrodes. Finally adding bubble from the bottom of the gap, finding that with SPAN#85 surfactant, the remove ratio will rise by 43%.