立式加工中心機結構特性與銑削穩定性之探討

Structure Characteristics and Milling Stability Analysis for a Vertical Machine-Tool

陳柏翰(Bo-han Chen)

指導教授 ： 林盛勇

國立虎尾科技大學/工程學院/機械與電腦輔助工程系碩士班/碩士(2013年)

摘要

隨著3C產業的蓬勃發展及其產品需求量的持續暢旺，相關零組件的加工製造勢必講求快又有效率，且甚多元件製程又回到使用工作母機做切削加工，使得工具機的需求量呈現躍進式的成長。高速、高剛性、高精度及高穩定性乃工具機性能的關鍵性指標。若能掌握機台結構本身的剛性與動態特性，將有助於結構設計製造上的補強及避免結構共振與顫振的發生。而切削穩定性資料庫的建構，可供加工業者作為製程參數的選用依據，將有助於工具機容量(capacity)的發揮及生產速率的提升並有效地增進其附加價值。因此，發展工具機結構特性與切削穩定資料庫之建構，以預測合適的製程參數組合，讓使用者在穩定切削條件下進行加工，乃為工具機業者當前努力的方向與課題。
本研究主要以實務性的做法來探討立式加工中心機結構特性與銑削穩定性。首先，將加工中心機進行數值與實驗模態分析，探討加工中心機結構的自然頻率、阻尼比與模態振型。透過實驗模態分析求得五大部件及整機系統的結構特性，並用來修正數值模擬分析模型，使數值分析模型等效於實際結構，作為後續結構改善設計之依據。接著，執行刀具-主軸動剛性實驗，藉以求取此子系統的動態剛性與對應頻率，匯入切削穩定性預測軟體CutPro，建立起由刀具構型、工件材料與切削條件等製程參數組合所對應之銑削穩定性耳垂圖，據以探討銑削過程的動態行為。從穩定性耳垂圖判別穩定/不穩定邊界各區塊座落點的銑削參數，透過銑削實驗的方式，從實驗中擷取動態銑削力、刀具振動頻譜及工件完成面等銑削性能參數，完成以多面向切削性能參數交叉判辨顫振之有無，以驗證分析軟體預測之結果。本實驗模態分析結果顯示，在主軸迴轉頻率範圍內共計有八個模態容易引發結構共振頻率，加工條件規劃時必須避免使用這些激振頻率的對應轉速。銑削穩定性分析方面，切削力、振動頻譜及工件完成面所呈現的結果型態有助於判斷顫振的有無，以交叉判認的方式予以克服，成功地建立起切削顫振的判認準則。有效的預測加工機銑削的特性，可供加工業者作為製成參數的選用，並有效地提升銑削加工之效率。

關鍵字

模態參數 ； 頻率響應函數 ； 再生式顫振 ； 穩定性耳垂

並列摘要

Following the rapid growth of 3C industry and its continuous prosperity of products demanding quantities, the processing demands of related components must be particularly on high-speed and efficiency, furthermore, the multi-elements process is returned to employ the machine tool for cutting processing, thus, the demanding quantities of machine tool show a leapfrog growth. The key indexes of machine tools’ functions are high speed, high stiffness and high stability. If the stiffness and the dynamic characteristic of the machine tools’ structural body can be controlled, it will be helpful to reinforce the structural design manufacturing and to avoid the occurrence of structural resonance and vibration. The construction of database of cutting stability may provide the processors the preference basis of process parameters, and it will be helpful to develop the capacity of the machine tools, the promotion of the production rate and increasing the additional values efficiently. Thus, to develop the structural characteristics of machine tools, to construct the database of cutting stability, to predict the suitable combinations of process parameters and to allow users proceed the process under the stable cutting conditions are current topics and striving direction of machine tool manufacturers.
The study mainly discusses the structural characteristics of upright processing Vertical center Machine and the stability of cutting in a practical manner. First of all, proceeding the numerical and the experimental model analysis of the processing center machine, discussing the natural structure frequencies of the processing center machine, damping ratios and vibration models. Through the experimental model analysis, obtains five major components and structural characteristics of the whole machine system and correct the numerical simulation analysis model to be equivalent to the actual structure, and takes it as basis for the following design modification of the structure. Then, proceeding the stiffness experiment of cutting tool-drive shaft to obtain the dynamic stiffness and the corresponding frequency of this subsystem, implementing the cutting stability prediction software CutPro, setting up the corresponding milling stability lobe diagram of which compose by process parameters of cutting tool types, workpiece materials and cutting conditions. These will be employed as basis to discuss the dynamic behavior of milling process. According to the stability earlobe chart, determining the milling parameters locate within the stable/unstable boundaries and through the the method of milling experiment, and getting milling parameters of dynamic milling forces, vibration frequency spectrum and Workpiece surface finish of the cutting tools, finishing the cross-determination of the existence of vibration by multi-phase cutting function parameters and verifying the prediction results of software analysis. The result of the model analysis reveals that there are 8 models in the range of axis rotation frequency are induced the structural resonance frequency easily, it must be avoided to use the speed of these vibration exciting frequencies when planning the processing conditions. For the milling stability analysis, the result of cutting force, vibration resonance frequency spectrum and Workpiece surface finis are helpful to determine the existence of vibration, it can be overcome by cross-determination and set up the determination standard of cutting vibration successfully. Efficient prediction of characteristics of milling machine tool can provide the processors the preference basis of process parameters and upgrade the efficiency of milling process effectively.

並列關鍵字

modal parameter ； frequency response function ； regenerative chatter ； stability lobe diagram

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