單點鑽石超精密車削碳化鎢之研究

A Study of Single Point Diamond Turning of Tungsten Carbide

廖怜怡 ； 廖運炫

《機械工業雜誌》 414期 (2017/09) Pp. 57-64

摘要

本研究主要是探討兩種單晶鑽石刀具超精密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，來輔助加工碳化鎢。研究結果顯示，於刀具幾何形狀的選擇，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，導致刀具大量耗損。以水溶性切削液加工碳化鎢，則因成分中有水存在，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%。採用約0°C的低溫空氣輔助加工碳化鎢，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及WC-13%Co可達約2 nm R_a及4 nm R_a的工件表面粗糙度。

關鍵字

單點鑽石車削 ； 碳化鎢 ； 刀具磨耗 ； 表面粗糙度

並列摘要

Machining characteristics of single point diamond turning (SPDT) for different cobalt contents tungsten carbide with various rake angle tools are discussed. Conditions under dry cutting, minimum quantity lubrication (MQL) with various cutting fluids, and compressed air were studied. Wear and morphology of the cutting tool and roughness of the machined surface were taken into consideration for performance assessment. Experimental result shows that turning tool with -20° rake angle performs better than that of -25° rake angle tool. Apparent tool wear is observed in the application of oil mist due to permeation of the mineral oil into cutting region with the aid of compressed air. Therefore, an oil film is formed on the surface of tool and workpiece which causes the chips to adhere to the machined surface. These chips in turn abrade the tool and lead to severe tool wear. MQL with water miscible emulsion improves chip disposal, but micro-chipping of the cutting edge takes places. Comparatively, there is less tool wear under dry cutting condition than MQL. Nonetheless, the machined surface is deteriorated due to uneven wear of the cutting edge. Application of the pressurized air without any cutting liquid promotes air penetration and chip flushing. Compared with condition under dry cutting, for turning WC-1%Co the tool life is increased and surface roughness is decreased by 14% and 57% respectively. The use of the compressed air of about zero degrees Celsius is then proposed. It is verified that there is rarely any wear since graphitization of the diamond tool which is catalyzed by cobalt in tungsten carbide can be effectively retarded. Mirror surfaces with surface roughness in Ra of 2 nm for cutting WC-1%Co and 4 nm for cutting WC-13%Co are successfully achieved.

並列關鍵字

Single Point Diamond Turning ； Tungsten Carbide ； Tool Wear ； Surface Roughness