CNC工具機主軸熱變形補償

Abstract

隨著科技的進步，使用者對於工具機的精度、準確度以及加工應用的能力，要求愈來愈高也愈來愈精細。而熱誤差在工具機的精度影響中，佔了很大的比例，其中又以主軸熱變形最受到關注。產生主軸熱變形的因素有很多，例如因主軸旋轉與主軸軸向移動所產生的軸承磨擦生熱，主軸馬達電力驅動所產生的電熱能與主軸冷卻等因素。 一般克服主軸熱變形的方式分為主動與被動：主動的方式則是透過在設計機台時，藉由有限元素的輔助軟體分析機器的熱源分佈，再針對熱源影響較大的部分進行補強；或者針對熱源、氣流的產生及流向進行考慮，進而使用低熱傳導係數的材料進行機器的設計與組裝。例如使用大理石取代傳統的鑄件以及陶瓷軸承取代鋼珠軸承..等。被動的方式則是利用數學模型預測主軸熱變形對軸向位移的影響，進而進行補償使主軸熱變形對機台的影響降至最低。在成本的考量下，主動的抑制熱誤差花費較高，處理時效上也較長。被動的抑制熱誤差則花費低，且開發時程較短。主動抑制比較可以有效的解決熱誤差的根本源頭。被動抑制則是在熱誤差產生後，再利用補償軟體進行軸向的控制，使熱誤差造成的軸向偏移降至最低。這兩種方法，皆有不少的文獻資料進行討論。 在時程、成本與不變更機械結構設計的考量下，本論文在利用線性回歸分析的數學基礎上，建立主軸熱變形的泛用補償模型來預測主軸熱變形，並進行即時的補償。且在多變動的主軸轉速下進行實機驗證，最終可以將主軸在Z方向及X方向的熱變形維持於20μm內。

With advance in technology, the precision and accuracy of machine tools and manufacturing processing have improved significantly, meeting the requirement of modern applications. The thermal distortion error still affects the accuracy of machine tools, accounting for a large proportion of dimension error. There are many reasons for the spindle thermal distortion error such as friction heat of spindle rotation and spindle axis moving at bearing, spindle motor electrical driving, spindle cooling strategies, etc. Methods to overcome the spindle thermal distortion can be divided into active and passive approaches: Active approach is meant by effort spent on minimizing thermal distortion at the design stage of machine, assisted by the finite element analysis software, simulating the heat distribution of the machine, reducing the effect of heat source on machine. With consideration of reducing the effect of heat generation, heat convection and heat conduction in mind, materials of low thermal conductivity, conductivity should be used . Previous studies have, proposed to replace the traditional grey iron casting with marble, ceramic ball bearing with steel ball bearings and etc. Passive approach is by means of using mathematic model to predict the influence of the spindle thermal deformation error for the axial distortion. Then compensates it to decrease the error. If cost is under consideration, active approach takes more money and developing time than passive approach. Active approach depress the influence of heat source. On the contrary, the passive one is to compensate the error which is generated by the heat. Both of them is discussed by many theses and references. In this thesis, with considering developing time, cost and without making changes in mechanical design of the machine, a general mathematic model of spindle thermal deformation is constructed to predict the error and compensates in real time, Check the result on the machine with variation spindle speeds and under to control the heat deformation of Z and X direction in 20 μm.