- 學位論文
高深寬比雕模放電加工渣排除效果之研究
Study of debris exclusion effect in a high aspect ratio cavity fabricated by die-sinking EDM
摘要
雕模放電加工(EDM)中加工渣粒在間隙中的分佈與流動是影響加工速度與加工精度的重要因素，因此排渣模式的建立對於加工的穩定性以及效率的提升有很大的助益。本研究針對電極排渣跳躍運動的模式作探討，企圖找到電極跳躍高度以及運動速度對間隙中渣粒和加工油流體流動的影響，進而推論出利於深孔加工進行的電極跳躍模式。本研究先建立流體力學模型分析方型電極在抬升時，運動速度對渣流體流動的影響。實驗上使用線性馬達平台讓電極作高速跳躍運動，搭配架設高速攝影機之觀測系統，觀察渣粒流體在間隙中流動的狀況。經由分析發現，電極運動速度太大時，會讓底部區的流體壓力低於其蒸氣壓，液體開始變成氣體，使得流體內有氣泡產生。透過觀測系統觀察知道方型電極於深寬比為10的深孔加工，當電極跳躍高度為20mm，運動速度為200mm/s時開始明顯有氣泡產生，相對地深寬比為2.5的淺加工並無觀察到此種現象發生。此外，電極跳躍高度大於加工深度的1/4時，可以觀察到渣粒排除的效果產生。因此在進行方型深孔加工時，使用大的跳躍高度搭配接近氣泡產生的臨界運動速度，可以得到較好的渣排除效果，若是想要減少非加工的時間，可以將電極下壓時的速度增加，減少電極跳躍的時間，但同時仍能保持渣排除的效果。在薄型電極深孔加工的狀況下，電極以高速抬起時並未見到有氣泡的產生，且加工孔狹窄，排渣不易，需要搭配大於1/2加工深度的跳躍高度及300mm/s的運動速度，才能達到排除渣粒的效果。
並列摘要
Debris distribution and dielectric fluid flow within the machining gap in electrical discharge machining (EDM) are important factors related to stable and precision machining. Hence understanding of the debris removal process is essential in improving EDM process. In this research, electrode jump motion with different jump heights and speeds was investigated to comprehend its effect on the fluid flow and debris-fluid interaction. A simplified fluid dynamics model characterizing the motion of the square shape electrode was established to study theoretically the effect of electrode jump speed on the debris-fluid flow. A setup to realize the electrode motion was designed. The Z-axis equipped with a linear motor was used to provide high speed jump function. The flow images were recorded by a high-speed camera, and the flow of the debris inside the hole was captured for analysis. Analytical results show that the fluid pressure at the bottom region of the electrode would reduce with the increase of electrode jump speed. Bubbles are generated once this pressure falls below the vapor pressure of the fluid. For the square shape electrode, it is found from the experiment that bubbles are prone to occur when the machining depth is increased. The result also shows that debris can be excluded easier when the electrode jump height is larger than 1/4 machining depth. Furthermore, using a large jump height incorporated with an electrode jump speed near the critical speed of bubble generation results in the most effective debris removal. On the other hand, the flow field of a high aspect ratio thin and flat electrode is different from that of the square electrode. There is no bubble generated during high-speed jump motion. The findings of this paper can be taken as the basis for choosing appropriate parameters of electrode jump motion in EDM deep-hole drilling.