超音波及雷射輔助切削技術應用於氧化鋯銑削之研究

Application of Ultrasonic and Laser Assisted Machining Techniques for Zirconia Milling

張世安(Shih-An Jhang)

指導教授 ： 林盛勇

國立虎尾科技大學/工程學院/機械與電腦輔助工程系碩士班/碩士(2015年)

https://doi.org/10.6827/NFU.2015.00154

摘要

近年來，氧化鋯等難切削硬脆材在生醫、精密儀器、航太等產業之應用日趨廣泛，尤其在生物醫學方面的運用特別活躍。隨著需求量不斷增加，對於氧化鋯各種加工品質的要求也日益嚴苛。目前從事氧化鋯加工的業者大多以雕銑、精磨或拋光等方式為之，加工製程較為繁雜且成本也較高，所以尋求縮短製程及有效節省成本等方面的突破，為當前加工技術之重要課題。氧化鋯具有高脆性、高強度、高硬度、低延展性及低導熱性等性質導致切削性差，在加工過程中刀具易產生快速磨損，加工表面易產生裂紋及破裂等缺陷。因此，改善氧化鋯切削性能、加工效率及刀具壽命的提升為長期以來相關業者最關心的課題。
本文建構一整合雷射與超音波混合式輔助切削系統，加以設計、製作、架設與測試，應用於氧化鋯硬脆材之銑削加工。使用田口法直交表將三因子（進給速率、徑向切深、主軸轉速）三水準進行製程參數組合規劃，選用碳化鎢彩鑽鍍層刀具及極細微粒碳化鎢矽鈦鍍層刀具，針對氧化鋯進行側銑加工實驗。以加工完成面之表面粗糙度為目標函數，同時受制於切削力的拘束條件，運用田口法因子反應表及簡易因子反應曲線數值模擬分析，依序執行各類銑削實驗，以加速較佳製程參數之求取。所執行的銑削實驗計有無輔助、超音波單項輔助、雷射單項輔助、超音波及雷射雙重輔助等。每類實驗所得之結果運用上述因子反應表及反應曲線數值分析，逐步進行三因子水準的替換，每類實驗留下各因子表現較佳的兩水準，而表現最差的水準替換成因子反應曲線所計算的推薦值，做為下一類輔助銑削實驗的水準，以此類推循序漸進，以加速各因子較佳水準的搜尋。於實驗過程中使用動力計監測銑削力的變化，以工具顯微鏡觀測加工完成面形貌及刀具磨耗，並以表面粗度儀進行表面粗糙度量測。上述兩搜尋法所求得之較佳製程參數透過銑削實驗加以驗證。除此之外，本文同時探討超音波及雷射預熱輔助切削結合製程參數各別及綜合表現之效應。結果顯示，田口法因子反應與因子反應曲線數值分析所得之較佳製程參數，經實驗驗證發現兩者皆可得到近乎相同的較佳表面粗糙度與表面形貌，但後者可得到較高的加工效率。於相同製程參數下，雷射預熱輔助相較於無輔助減少切削力約30~40%。當較大徑向切深時，超音波輔助系統較無法完全發揮其輔助作用的改善功能，但依上述較佳製程參數的逐步調整，於最終的混合式輔助切削系統實驗下，明顯改善了切削紋路與表面粗糙度。在雷射預熱與超音波雙重輔助下，切削性能的綜合表現皆優於無輔助及單項輔助，本文驗證了混合式輔助切削系統的優異性。

關鍵字

氧化鋯 ； 超音波輔助 ； 雷射輔助 ； 切削性能 ； 田口法

並列摘要

Hardened and brittle material such as zirconia has gradually become the important materials for biomedical, precision instruments and aerospace technology industry applications in recent years. In which biomedical application is particularly active. As its demand is increased constantly, various requests on machining qualities of zirconia are also more stringent. At present, the main machining ways on zirconia are almost with engraving milling, grinding lapping or polishing and these machining processes are too complicated and too much wasted. Therefore, seeking a breakthrough for shortening the process and saving the cost effectively is an important issue for the machining workers. Because zirconia have the properties of high strength, high hardness, large brittleness, less malleability, low thermal conductivity and hence low machinability, it causes the cutting-tool wear quickly during the machining process. Also, the crack and damage, and edge-indentation are easily generated on the machined surface and outer edge, respectively. Therefore, enhancements of cutting performance and processing efficiency, and promotion of cutting-tool life for zirconia machining are the most concerned issues in industry for a long time.
In this study, an integration of ultrasonically and laser assisted machining system is constructed for zirconia brittle material milling. This hybrid system is thus designed and fabricated, and mounted on a machine-tool system for working test. Three levels of three factors such as feed rate, radial depth of cut and spindle speed were selected in this study and orthogonal array of Taguchi method was applied for process parameter planning. General and extra-fine particle tungsten carbide cutting tools with diamond and TiSi coating, respectively, were used in the side-milling experiments of zirconia workpiece. The machined surface roughness and cutting force are used as objective function and subjecting constraint, respectively. The execution of different assisted machining types of milling experiments on zirconia were performed in series and Taguchi factor response and a numerical analysis on the simple response curves are applied together for accelerating the better process parameter determination. Various assisted machining types such as without assistance, ultrasonically assisted, laser-assisted and an integration of ultrasonically and laser-assisted milling were conducted sequentially in this study. Each experimental result obtained from the above assisted machining type is individually dealt with by factor response and numerical analysis of response curve at the same time, and the levels of each factor are alternatively switched to other values gradually. Two better levels of each factor are preserved preparing for the next assisted milling experiment while the worse level of the factor is replaced by the better one which is recommended by the numerical analysis of response curve. Follows up this rule of factor level substitution repeatedly in each type of assisted machining experiment, the better process parameters are determined accordingly. Dynamometer is used to monitor the variation of cutting force. Tool wear, edge-indentation, chip morphology and surface morphology of the zirconia will be measured by tool-microscope off-line. Surface roughness measurement through a non-contact optical instrument is also performed. The high spindle speed cutting experiment for zirconia will be undertaken to validate the two sets of better process parameter combination resulting from factor response and numerical analysis of response curve, respectively. The effects of each process parameter and their combinations on cutting performance and productivity of zirconia machining are also investigated in this hybrid assisted machining system of ultrasonic vibration and laser spot preheating. The results show that two better process parameters combinations both from Taguchi factor response and numerical analysis of response curve can obtain nearly the same preferred surface roughness and surface morphology, but the process parameter of the latter method exhibits a higher processing efficiency. Under the same process parameter combination, laser-assisted machining the cutting force may be reduced about 30 to 40% as compared with that without laser spot preheating assistance. The ultrasonically assisted machining system may not bring into full play on cutting performance improvement when a larger radial cutting depth is encountered. But a significant improvement on machined surface left mark and surface roughness is emerged from the hybrid assisted machining system of ultrasonic vibration and laser spot preheating under the cutting conditions obtained by a successive adjustment of the better process parameter determination just mentioned above. The overall cutting performance in the hybrid assisted machining system is better than those without assistance or with single assisted machining system only. Hence, this study verified the superiority of a hybrid system of the ultrasonically and later assisted machining on zirconia milling.

並列關鍵字

zirconia ； ultrasonically assisted ； laser-assisted ； cutting performance ； Taguchi method

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