應用考慮刀具磨耗之學習控制技術於銑削加工

Application of learning control on milling process considering tool wear

陳翰霖(Han-Lin Chen)

指導教授 ： 李貫銘

國立臺灣大學/工學院/機械工程學研究所/碩士(2021年)

https://doi.org/10.6342/NTU202103816

摘要

銑削加工於製造業中廣泛應用，傳統上通常會避免嚴苛的加工條件，固定主軸轉速與進給率等切削條件進行加工，以避免不可預期的損壞，雖確保了穩定性，卻也因為使用了較為保守的參數，使得加工效率保有提升空間，隨著工具機技術發展日趨成熟，對於提升加工效率的需求迫在眉睫。藉由適應性控制即時調整進給率的變化維持等負載，可以有效提高加工效率，但是由於硬體設備溝通速度的限制，導致進給率劇烈變化，使工件表面品質下降。
文獻中提到學習控制根據以往加工所蒐集的加工數據，事先規劃加工參數，提高加工效率，參數均為加工前設定，故沒有硬體限制。由於文獻中對於刀具磨耗較少討論，因此，本研究擬將學習控制加入回饋控制，於加工中適時調整進給率，以進給率作為刀具磨耗監控指標。本研究透過等進給實驗建立主軸電流、進給率與刀具磨耗之關係，並以刀具強度為參考，設定參考電流，以多次實驗平均設定初始進給率，使起始電流即為參考電流。再者，以刀具磨耗設定判斷加工結束與換刀之進給率下限。最後，分析不同磨耗下進給率與主軸電流之間的關係，建立進給率調整依據，以達到在加工中以主軸電流為參考訊號適時調整進給率，將主軸電流維持於參考值。
實驗結果顯示，本研究所設定的控制參數，除了主軸電流可以維持於參考值附近以外，於進給率到達下限時，刀具磨耗也可以維持於實驗設定範圍內，防止刀具過度磨耗。於槽、端銑混合加工中，本研究設計槽、端銑之間的進給率互相轉換之函數，利用該函數以及先前建立之學習控制參數，亦能利用進給率作為刀具磨耗監測指標，並且透過調整進給率將主軸電流維持於參考電流附近。再者，相較於等進給率加工，材料移除率、刀具壽命與表面粗糙度均有較優異的表現。

關鍵字

學習控制 ； 回饋控制 ； 主軸電流 ； 刀具磨耗 ； 表面粗糙度

並列摘要

Milling Process is a machining method which is widely used in metal cutting. Traditionally, cutting parameters such as spindle speed and feed rate are fixed to avoid unpredictable situation. Although stability is ensured, the processing parameter is relatively conservative. With the development of metal manufacturing, the demand for improving efficiency is urgent.
Through adaptive control to adjust the feed rate to maintain constant load in processing, it can effectively improve the milling efficiency. However, due to the limitation of the communication speed of the hardware, the feed rate changes drastically, leaving tool marks on the surface of the workpiece. It’s mentioned in the literature that learning control can improve the processing efficiency through the analysis of the data collected in the past and set parameters in advance. It is expected to get rid of the limitation of hardware communication speed because the parameters set beforehand. In addition, there is less discussion about tool wear due to the study of learning control.
This research proposed a method that combine feedback control with learning control. The learning control parameter contains initial feed rate. Initial feed rate is established by several times of iteration. The purpose of initial feed rate is to sustain spindle current near the reference value, and the reference value is set by tool strength. But tool wear is not considered in learning control. So, the feed back control is introduced. The feed back control is used to adjust feed rate in order to keep the spindle current near the reference value. The parameters contain feed rate lower limit and feed rate adjustment method. Feed rate lower limit is set to prevent severe tool wear. The method of feed rate adjustment is set to adjust feed rate via the relationship between current and feed rate. The results show that the spindle current can be maintained near the reference current during the process. And the tool wear can be maintained within a certain range when the feed rate reaches the lower limit. Surface roughness can also be maintained within a certain range. In the two-dimensional milling, the function of the feed rate conversion between the slot and the end milling is designed, using this function and the parameters established previously can achieve the purpose of using feed rate as tool wear monitoring and maintaining the spindle current near the reference value. Compared with constant feed rate milling, material removal rate, tool life and surface roughness have better performance.

並列關鍵字

Learning control ； Feedback control ； spindle current ； tool wear ； surface roughness

參考文獻

[1] Li, H. Z., H. Zeng, and X. Q. Chen. "An experimental study of tool wear and cutting force variation in the end milling of Inconel 718 with coated carbide inserts." Journal of Materials Processing Technology 180.1-3 (2006): 296-304.

[2] Elbestawi, M. A., T. A. Papazafiriou, and R. X. Du. "In-process monitoring of tool wear in milling using cutting force signature." International Journal of Machine Tools and Manufacture 31.1 (1991): 55-73.

[3] Ulsoy, A. Galip, Yoram Koren, and Fred Rasmussen. "Principal developments in the adaptive control of machine tools." Journal of Dynamic Systems, Measurement and Control 105.2 (1983): 107-112.

[4] Yang, Min-Yang, and Taik-Min Lee. "Hybrid adaptive control based on the characteristics of CNC end milling." International Journal of Machine Tools and Manufacture 42.4 (2002): 489-499.

[5] Y.Altintas. " Prediction of Cutting Forces and Tool breakage in milling from feed drive current measurements."Journal of Engineering for Industry. ASME(1992):386-392