微弧氧化製程輔助鈦金屬微銑削加工之研究

Abstract

本論文先針對微弧氧化對純鈦金屬所生成之氧化膜做參數和結合度上的探討，再針對微銑削時的毛邊、粗糙度等問題，使用了微弧氧化的製程來輔助微銑削加工鈦金屬，並比較製程前後對試片表面和切屑與刀具狀況的結果。 在兩種Duty Cycle分別為１/１０ 和 １/５的參數下，鈦金屬經過微弧氧化，氧化膜厚度都會隨著電壓作用時間(Voltage affect time)增加而增長，但製程時間(Process time)卻相差兩倍。為了抑制撓曲選擇較厚的試片，卻因薄膜生長特性必須使電壓作用時間更長，綜合以上情形所以選擇較有效率Duty Cycle為1/5的加工參數。 本實驗所使用的刀徑為0.7mm，進給為100mm/min。隨著切深增加，毛邊高度也隨著增高，且銑削溝槽兩邊的毛邊高度也因順逆銑而呈現不同的高度，順銑的毛邊相較逆銑在較小的切深即會產生，產生的高度也較高。在經過微弧氧化電壓作用時間分別為 36s、60s、90s後的薄膜厚度與切深綜合比較，可知產生毛邊當下的毛邊臨界切深(Dc)從2.8μm增加至5.8μm、8.4μm、10μm，亦即經過微弧氧化後，較大的切深才會產生毛邊。 當銑削深度較淺時，表面粗糙度高於傳統銑削理論值，這代表在這切深下，表面形成機制包括最小切屑厚度、犁切、以及彈性回復。當切深接近20μm至30μm時有最佳的表面粗糙度，之後便又逐漸變差，並與薄膜厚度沒有明顯的關係。 切屑在不同的切削深度下會導致不同的結果，代表氧化膜僅為鈦金屬表面上的物理性堆積，而沒有強力的附著於上。因此，表面氧化膜的切除相當容易，且其亦為脆性切削。

This study first discussed the parameter of the oxide film generated from MAO process, and then use the MAO process to solve the burr and surface roughness problem made by micro-milling. Then, the study compares the results of pre-processed workpiece surfaces with the processed ones. No matter the parameters of Duty Cycle is 1/10 or 1/5, both of the results show that the oxide film became thicker while the voltage affect time became longer. However, the process time of 1/10 is twice longer than that of 1/5. In addition, the study has to use thicker workpiece to avoid deflection, but it also causes film grow characteristics which will prolong the process time. Thus, this study chooses the parameter Duty Cycle 1/5 for more efficiency. This study uses the cutter with the diameter of 0.7mm and 100mm/min feed. It was found that the burr height will simultaneously increase when the cutting depth becomes deeper. Also, the different sides of the slot, causing climb or conventional milling, will give rise to different burrs heights too. Compare to the workpieces with conventional milling, the burrs heights of that with climb milling are higher and will occur in smaller cutting depth. Comparing the pre-processed workpiece with the workpieces processed by MAO with 36 s, 60 s, and 90 s voltage affect time, the study discovers that the cutting depth which leads to the formation of burrs is increased from 2.8μm to 5.8μm、8.4μm、10μm. In other words, MAO process can moderate the burr problem. When cutting depth was shallow, the measured surface roughnesses were considerably higher than the theoretical surface roughness. This indicates that the surface generation mechanism at these cutting depth will be affected by not only geometric considerations, but also the minimum chip thickness, ploughing, and elastic recovery effects. Surface roughness, which has no significant relation with the thickness of oxide film, will decrease when cutting depth approach 20μm, but begins to increase again after 20μm~30μm. Cutting under different cutting depths will result in different ways, which imply that the oxide film is only a physical accumulation on the surface of titanium. Considering that the oxide film doesn’t adhere to the metal strongly, the removal of it is easy and brittle.