- 學位論文
單點鑽石車削碳化鎢之研究
The research of single point diamond turning of tungsten carbides
摘要
本研究主要是探討單晶鑽石刀具車削不同鈷含量之碳化鎢材料的加工特性，以及採用最少量潤滑 (Minimun quantity lubrication, MQL)的切削液供給方式，配合液體及氣體切削液的使用，輔助加工碳化鎢之結果。文中以刀具磨耗、表面粗糙度、表面形貌來分析碳化鎢材料之切削特性。研究結果顯示，於材料加工特性的部分，刀具磨耗會隨著材料中鈷含量及碳化鎢之燒結粒徑的增加，而有上升的趨勢。於刀具幾何形狀選擇的部分，採用負傾角20度之刀具切削碳化鎢材料相較於負傾角25度之刀具有較佳的刀具壽命及表面粗糙度。於切削液輔助加工的部分，發現以油霧方式加工碳化鎢，無法有效排除切屑，刀具會產生顯著的磨耗，這是因為切削液藉著高壓空氣進入切削區，會在刀具及工件表面形成油膜，使切屑容易黏附其上，細碎的切屑與切削液混和，在刀具與工件之間的作用類似含有強化顆粒的液體，會導致刀具大量耗損。以水溶性切削液加工碳化鎢，雖可改善切屑排除的問題，但因成分中有水存在，容易使切削刃邊(Cutting edge)產生微崩落(Micro chipping)的情況，不適用於碳化鎢的加工。以乾切削加工，可獲得較液體切削液使用下較佳之刀具壽命，但在切削刃邊會產生磨耗不均勻的輪廓，使加工表面惡化，粗糙度增加。以高壓空氣輔助加工，可促使氣體易於滲透至切削區，並具有排除切屑的效果，刀具壽命可提升約14%，表面粗糙度可降低約57%。採用低溫空氣(溫度約0°C)輔助加工碳化鎢，可以減緩材料內鈷元素的催化作用，避免鑽石石墨化的結果，獲得最佳的刀具壽命與表面粗糙度，刀具沒有產生磨耗，且加工WC-1%Co可達約2 nm Ra的工件表面粗糙度，加工WC-13%Co可達約4 nm Ra的工件表面粗糙度。
並列摘要
Ultraprecision turning of different cobalt contents tungsten carbides by different rake angle diamond tools under dry cutting and minimum quantity lubrication (MQL) with various liquid and gaseous fluids were studied. Tool wear, machined surface roughness and morphology were taken for comparison. It is found that tool wear increases with the increase of cobalt content and grain size of the tungsten carbide. Turning tool with -20°rake angle performs better than that of -25°rake angle tool. There is apparent tool wear in the application of oil mist. This is due to permeation of the cutting fluid into the cutting region aided by the compressed air. Oil films are formed on the tool and workpiece surfaces, and cause the chips to adhere on the machined surface as a result. The film in turns abrades the tool and accelerates the wear rate. The application of soluble fluid improves chip disposal, but micro-chipping of the cutting edge is observed. Comparatively, there is less tool wear under dry cutting condition than MQL with liquid fluids. However, the machined surface is deteriorated due to uneven wear of the cutting edge. With the use of pressurized air only, effect of air penetration and flushing of chips are promoted. It is noted that tool life is increased and surface roughness is decreased by 14% and 57%, respectively. Moreover, the use of cold air of about zero Celsius degree can effectively slow down the catalytic reaction due to cobalt and avoid graphitization of the diamond tool. No tool wear is detected. The surface roughness of 2 nm Ra in cutting WC-1%Co and 4 nm Ra in cutting WC-13%Co are successfully achieved.