超精密鑽石車削鐵系金屬之研究

現今對於精密零件的需求不斷的增加，其中用於生產精密元件之超精密車削加工技術在近年更是有突破性的發展與應用。超精密車削技術中刀具的選擇與使用，以鑽石刀具最具發展潛力應用性亦最廣，鑽石有優良的機械、化學性質，使之與超精密加工技術相互搭配有著加乘的效果，然而鑽石刀具卻無法直接對最常使用的含鐵系金屬之材料進行加工，強烈的化學性磨耗會使鑽石刀具的壽命急劇縮短。本研究主要是探討以人工單晶鑽石配合超精密車床加工NAK80模具鋼等含鐵系元素之金屬之加工特性，並分析不同的切削環境對於鑽石刀具磨耗的影響，最後提出合適的改善方法，在保持一定的工件表面品質下，降低刀具磨耗的發生，提升刀具壽命。由實驗結果發現，切削溫度、刀具接觸時間及刀具工件間的積屑黏屑問題，是鑽石刀具加工NAK80時影響刀具壽命、工件品質的主要因子。對於改善刀具磨耗的策略包含選擇改變切削液與其添加劑及改變切削溫度，切削液的選擇以太古油水溶液搭配氮化硼粉末添加劑有最佳的磨耗改善效果，與乾切削相比，其刀腹磨耗進步幅度可達40%，而工件表面粗糙度也有70%以上的改善，透過薄膜層狀的氮化硼粉末於切削區域刀具與工件間產生物理性隔絕，可減少石墨化催化反應的發生，使刀具磨耗速率降低；降低切削溫度則可趨緩鑽石石墨化的反應速率，然直接降溫常會造成工件收縮而產生加工不完全之問題，研究中以預冷方式在液態二氧化碳冷卻加工下，鑽石刀具磨耗與工件表面粗糙度與乾切削時相較則各有近80%與60%的減少幅度，同時可克服低溫加工的形變問題；最後比較切削液的改變、低溫環境中加工與混合式改善方法對鑽石刀具磨耗的影響，歸納出以液態二氧化碳降低加工區域之溫度為最有效之抗磨耗輔助手段。

關鍵字

超精密加工；單點鑽石車削；鐵系金屬；刀具磨耗

並列摘要

The demand of precision products has increased recently, and there is breakthrough in the development of ultra-precision turning technology for producing precision components. Diamond tool has been widely used in ultra-precision turning because of its excellent mechanical and chemical properties. However, we can’t cut ferrous metals or any material that contained ferrous metal by using the diamond tool directly, since the graphitization leads by combination of ferric and carbon in diamond causes the tool serious chemical wear. The main purpose of this research was to study the machining characteristics of ultra-precision turning NAK80 steel by using single crystal diamond tool, and analyze the tool wear in different machining environment. In the end, we presented several methods to suppress the tool wear cause by graphitization. According to the result, cutting temperature, contact time and chip built up on tool edge or workpiece are the most important factor to effect tool life. By using sulfated castor oil solution with BN powder, tool life as well as surface roughness would be improved. Compared with dry cutting, it was noted that tool wear was decreased by 40%, and roughness was decreased by 70%. It was believed that BN powder can serve as a physical barrier, preventing the catalytic reaction between carbon and Ferric. On the other hand, after pre-cooling to prevent incomplete cutting from direct cooling, there was 80% reduction in tool wear and over 60% improvement in surface roughness by using liquid CO2 as coolant in turning, causing by slowing down the reaction rate of graphitization. Finally, the effect of combining cryogenic method with adjusted cutting fluid or other assisted method in turning ferrous metals has been discussed. In summary, the most effective way to improve the tool wear is cryogenic turning with liquid CO2.

並列關鍵字

ultra-precision machining ； single point diamond turning ； ferrous meta ； tool wear

參考文獻

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超精密鑽石車削鐵系金屬之研究

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