CNC銑削再生式顫振預測之研究

Abstract

銑削製程因其能切削複雜的幾何形狀，以及其能達到的精度與加工效率，至今用於機械製造仍廣泛且有難以取代的特性。然而可能因為選用了不適當的加工條件，而產生了切削加工時的顫振。而其中最常見的一種為再生式顫振，再生式顫振引發會會產生破壞工件表面、減少加工精度、損害刀具與工具機壽命、降低生產效率等負面影響。由在實務上，通常會選擇較保守的加工條件，但卻降低生產效率，所以再生式顫振常常造成使用者的困擾。因此有必要建立監控的模組來改善再生式顫振。 由於再生式顫振特性為振動成長快速，因此本文從前人提出的p階代表頻率理論著手，利用線上量測切削中的訊號並進行頻域分析，觀察再生式顫振特性，改寫了p階代表頻率公式提出p階權重數值公式，再結合CUSUM方法，自動判斷合理的閥值，進而改善了其中閥值太低會造成誤判，閥值太高會延長偵測時間，且不同刀具閥值也有不同的問題。目標係達到自動判斷合理的閥值，且在顫振尚未成長完成前，提前的偵測出發生顫振以及顫振頻率，進而判斷是否為再生式顫振。若為再生式顫振，則進行即時的主軸轉速控制，達到即時抑制的效果。 本文也利用電腦程式的方式實作出監控模組，且實際進行的線上的切削與抑制，由即時量測機台振動，進行線上的頻域分析，驗證線上的顫振預測與抑制的可能性。結果表明在不同刀具直徑與銑削條件下，仍能有線上預測顫振的效果，且利用偵測到的顫振頻率計算適當的主軸轉速，在機器更改轉速動作完成後能有效的抑制顫振到穩定切削的狀態。

Because of its ability to cut complex geometric shapes, and reach good accuracy and efficiency, milling process is still widely used in mechanical manufacturing and is difficult to replace. However, the chatter vibration during cutting may be generated due to the selection of inappropriate processing conditions. The most common one is regenerative chatter, which may cause damage to the surface of the workpiece, reduce machining accuracy, damage the life of tools and machine tools, and reduce production efficiency. In practice, more conservative processing conditions are usually selected. Because of this conditions, production efficiency is reduced, and regenerative chatter often causes some troubles. Therefore, it is necessary to establish a monitoring module to improve the regenerative flutter. Since the characteristic of regenerative flutter is the rapid growth of vibration, this article starts with a p-order representative frequency theory proposed by the previous researchers. They use online measurement of the cutting signal and frequency domain analysis to observe the characteristics of regenerative flutter, and rewrite the p-order formula of representative frequency and find out a p-order weighting function. It combined with CUSUM method, which can automatically judge the reasonable threshold and improve the threshold. When the threshold is too low, it will cause misjudgment, and when it is too high, it will prolong the detection time. Different tool thresholds cause Different problems. The target system reaches a reasonable threshold for automatic judgment. Before the flutter growth is completed, the occurrence of flutter and flutter frequency is detected in advance. This system can recognize whether it is regenerative flutter. If regenerative chatter is recognized, real-time spindle speed control will start to achieve the effect of real-time suppression. This article also uses computer program to implement the monitoring module, The actual online cutting and suppression are carried out by real-time measurement of machine vibration and online frequency domain analysis to verify the possibility of online chatter prediction and suppression. The results show that under different tool diameters and milling conditions, the effect of chatter vibration can still be predicted online, and a proper spindle speed can be calculated using the chatter frequency detected by the system. This method can effectively suppress chatter vibration after the machine changes the speed and make the progress reach a stable cutting state.