工具機等切削力控制與刀具磨耗關係之探討

Abstract

在電子技術日趨成熟的發展下，加工過程中的即時監控可行性增加，切削監控最常見的方式是以切削力做為加工狀態參考，本研究應用等切削力控制系統，提升加工效率。文獻當中對於等切削力控制系統，多集中於討論控制器演算方法的設計，也預期此方法能夠對刀具壽命有正向影響，然而較少針對刀具磨耗影響的探討。本研究討論銑削加工中，設計等切削力控制系統，利用掃頻系統識別方法，建立系統動態特性與設計等切削力控制器，並討論等切削力控制技術對刀具磨耗的影響。 本研究提出以掃頻訊號輸入，進行系統鑑別取得系統動態方程式，由主軸電流負載取代傳統動力計量測切削力，透過控制理論，設計等切削力PI控制器，並利用根軌極法找出系統穩定控制參數範圍。實驗結果在變動切削條件與刀具磨耗情況下，主軸電流負載可以於1秒內到達設定參考值，並穩定控制。此方法大量減少系統識別流程，並能夠快速設計控制器，對於機台老化等因素，需要重新了解系統動態時，有顯著的幫助。 比較等切削力控制下與無控制切削加工，觀察磨耗量測結果發現，兩者在加工時間與刀具磨耗關係中，沒有差異，與過去文獻不同，在刀具受力穩定下，等切削力控制無減緩刀具磨耗的效果。觀察控制器輸出訊號發現，隨著刀具磨耗增加，不同的參考電流附載值，有明顯訊號特徵，可做為刀具磨耗量的判斷依據。

The ACC (adaptive control system with constraint) system is developed with cutting dynamics model and the cutting tool wear is investigated under the ACC system. A process of building ACC systems is present in this work including modeling the dynamics of cutting process and design of PI controller. It has been proposed that the measurement of cutting force by using dynamometer can be replaced by the spindle current of the machine tool. Therefore, dynamics models which relate the feedrate and spindle current are modeled by system identification method with swept sine input signal during cutting processes. With the model, the PI controller is designed for the ACC system. The experiment of control performance is compared with simulation results. On the other hand, to investigate effects on tool wear with the ACC system, tool wear is measured at predefined intervals. It turns out that the performance of the adaptive controller is good fits with simulation and stable under the cutting condition. However, with the ACC system, there is no significant effect on reducing the tool wear, and setpoints of reference spindle current in ACC system is important parameters for tool life.