等負載銑削加工之主軸負載參考值設定流程

Abstract

傳統的工具機加工方法中，通常採固定進給率進行加工，而為了避免損害刀具或機台，通常會設定較保守的加工條件，因此加工效率仍然有改善的空間，而適應性控制器透過即時調控進給率來達成穩定主軸負載，並適時地提高進給率，能夠提升加工效率。 雖然目前已有許多適應性切削的研究，但在建立系統的動態特性時，通常只基於單一軸向的直線路徑。本研究嘗試於雙軸向的直線路徑與弧形路徑進行系統鑑別實驗，以取得不同軸向的系統動態特性。並且透過實驗探討弧線路徑以及直角轉彎適應性切削的可行性。 本研究中亦提出一套設定主軸負載參考值的流程，配合進給率下限的設定，不但能夠使保持工件表面粗糙度小於設定值，同時還可以透過進給率控制訊號變化估算更換刀具的時機。實驗結果表示，當可接受之工件表面粗糙度為1.3µm，適應性切削之加工效率較固定進給率切削高出65%，且當可接受之工件表面粗糙度越大，適應性切削於加工效率上之優勢將更為明顯。

Constant feed force milling is considered as high performance machining in the literatures. However, it is difficult to implement this technology in the industry because there is not any method to set proper parameters in this control system. In this study, an adaptive control system with constraint (ACC) is first developed based on cutting dynamics. The cutting dynamics is obtained by system identification under various tool paths, including straight path in x-direction, straight path in y- direction and curve path. Result shows that cutting dynamics obtained under different path are almost the same, which makes developing the controller of the cutting system easy. Also force signal is replaced by spindle current signal because it is easier to collect spindle current signal in machine tools. Impact of tool wear on the control system is investigated with experiments. It is found that the ACC system can remain stable even if the open-loop gain remains below a certain value even if tool wears. A procedure to determine tool life is proposed in this work based on establishing the reference of the spindle current signal and the corresponded lower limit of the feedrate. It turns out that with this procedure, surface roughness, an index of tool life, can be kept under a predetermined level.