運用低溫加工技術研究鈦合金銑削性能及刀具壽命

A Study of Cutting Performance and Cutting Tool Lifetime for Titanium Alloy Through a Technology of Low Temperature Machining

李定曄(Ding-Ya Li)

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(2014年)

https://doi.org/10.6827/NFU.2014.00068

摘要

鈦合金熱傳導係數低、彈性模數小及化學活性高等特性，在一般切削加工過程中容易致使刀刃快速升溫與磨耗，加工效率、加工精度及表面品質因而不高，是一種典型的難加工材。由國內外的研究發現，深冷加工技術已被認為可用來提高鈦合金切削效率及刀具壽命改善的有效方法。此技術亦符合現世代低能耗、清潔化及無公害的綠色製造訴求。
本研究首先應用有限元素法模擬鈦合金低溫切削切屑的成形過程。接著，運用冷風渦流管及高壓空氣進行低溫環境控制系統之建構。最後，採用兩種冷卻/潤滑條件進行實驗，其一使用低溫冷風冷卻搭配微量潤滑(MQL)，另一同樣使用低溫冷風搭配MQL並處於低溫環境控制系統內進行銑削加工。以鎢鋼端銑刀進行鈦合金之銑削實驗，利用熱影像儀和熱電偶分別監測切削區及低溫環境系統的溫度變化。再以工具顯微鏡和表面粗糙度觀測不同實驗參數組合之刀具磨耗和表面粗糙度，進行實驗數據擷取、分析與探討。結果顯示，有限元素模擬與實驗結果，其切屑皆為鋸齒狀，此可驗證有限元素法分析的正確性。在未切削時，本環境控制系統內不同空間位置溫度分佈約介於10與14℃之間，而系統內鄰近切削區的溫度約則可維持在10℃左右。然隨著銑削加工的進行，此區域環境溫度最高上升至15℃左右。有環境控制與無環境控制相比，有環境控制提供較好的冷卻效果，降低刀具自身的黏附-溶解-擴散等磨耗現象，改善BUE的生成與刀腹凹陷磨耗的發生。與乾切削相比，有環境控制的刀腹磨耗減少約82.1%~91.5%，表面粗糙度改善約23%~76.9%；切削區溫度降低約52.3%~77.8%。整體而言，運用低溫環境控制系統能有效地抑制切削區的溫升，降低切削溫度，改善銑削性能及延長刀具壽命。

關鍵字

低溫環境控制系統 ； MQL ； 刀具壽命 ； 銑削性能 ； 鈦合金

並列摘要

Titanium alloy has low thermal conductivity, small elastic modulus and high chemical activity, which may cause the cutting temperature rise rapidly around the cutting-edge and tool wear during the machining processes. Hence, machining efficiency, dimension precision and surface quality are still not so high in machining of titanium alloy which is regarded as a typical difficult-to-cut material. It is found that cryogenic cooling technique is proven as an effective way to promote the machining efficiency and tool life for titanium alloy. And this technique also comply with low energy consumption, cleaning and harmless, the main development trends in green manufacturing.

In this study, the finite element method is firstly applied to simulate the chip formation processes for titanium alloy under the low temperature machining condition. Secondly, the vortex tube is in conjunction with high compressed air to construct a low-temperature machining environment system which was mounted on a machine-tool. Finally, milling experiments were conducted under two cooling/lubrication conditions. One is combination of cold air cooling and minimum quantity lubrication and the other condition is same as the former one but the machining process is conducted within a low-temperature environment control system. Furthermore, tungsten carbide end mill and titanium alloy are used as a cutting tool and workpiece for milling experiment, respectively. A thermal imager and thermocouple system are used to detect the cutting temperature around the cutting zone and temperatures distributed in a machining environment system, respectively. Tool-microscope and surface roughness instrument are also used to measure the tool wear and surface roughness, respectively, under different combinations of the experimental parameters for titanium alloy machining. The above experimental data is sampled, analyzed and discussed thoroughly. The chip type obtained from the finite element analysis is serrated, which is consistent with the results obtained from experiment. This result can verify the correctness of the developed finite element model. Before cutting, temperature distributions within the environment control system are approximately between 10 to 14℃ for different system spatial locations, but the temperature can be kept about 10℃ around the cutting zone. However, this temperature is up to 15℃ when the milling process is proceeded. The environment control system provides a better cooling effect which may reduce the adhesion-dissolution-diffusion tool wear, improve the possible generation of BUE and crater wear on the tool flank face as compared with the machining environment without temperature control system. Furthermore, machining conducted within an environment control system, the tool wear may be reduced about 82.1%~91.5%, surface roughness may be improved about 23%~76.9%, the cutting zone temperature may be decreased about 52.3%~77.8% as compared with dry cutting situation. A conclusion can be made based on the use of a low-temperature environment control system which can effectively suppress the increase of temperature around the cutting zone and it may further lower the cutting temperature, promote the milling performance and prolong the tool life for titanium alloy machining.

並列關鍵字

Low-temperature environment control system ； MQL ； tool life ； milling performance ； titanium alloy

參考文獻

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