工具機系統特性與銑削動態之研究

An Investigation on Characteristics of Machine-Tool System and Milling Dynamic

宋孟儒(Meng-Ru Song)

指導教授 ： 林盛勇

國立虎尾科技大學/工程學院/創意工程與精密科技研究所/碩士(2010年)

摘要

摘 要
振動易造成結構的共振或疲勞從而破壞結構，因此瞭解結構本身的動態特性，將可避免共振的發生以及不必要的損失。經由一系列的實驗，可對結構系統的振動特性及結構動態特性設計提供依據。
本文針對CNC工具機銑床結構，進行整機模態測試、結構動剛性實驗及銑削穩定性實驗，藉此探究結構動態之特性。首先從事整機模態測試，求得結構各階模態參數即自然頻率、模態振型及阻尼。將所得資料匯入實驗模態分析軟體(ME’scope)，檢視各階模態所對應的實際振型。接著在動剛性實驗方面，改變頭座高度分別對主軸與刀把給予各軸向激振力，檢視所對應軸向動剛性之變化。最後規劃不同銑削參數(切削速度、進給率、軸向切深)搭配順銑及逆銑方式，檢測其切削力、主軸振動以及工件表面紋路，分析與探討不同銑削參數的組合對切削穩定性的影響。
模態實驗結果顯示，Mode 1至Mode 3其模態振型影響結構之部件為頭座與立柱。而Mode 4及Mode 5所對應的模態振型，主要變形部件為工作台與鞍座，這兩個模態的彎曲變形將造成接合面可能的分離。動剛性實驗結果顯示，當頭座Z軸高度從-100mm降至-300mm時，X軸向結構動剛性從217 N/μm變化至106 N/μm，對切削穩定性將有所影響。銑削實驗結果顯示，當切削速度143.3 m/min、進給率400 mm/min及切削深度0.5 mm時，加工表面出現顫紋，與穩定切削之情況比對研判該銑削條件組合已發生切削顫振。以上這些結果可作為日後銑削加工參數規劃之參考。

關鍵字：模態測試、動剛性、切削穩定性、頻譜分析

關鍵字

模態測試 ； 動剛性 ； 切削穩定性 ； 頻譜分析

並列摘要

Abstract

The vibration easily deduce the structure resonance or fatigue and as a result of structure damage. Therefore, the dynamic characteristics of the structure itself should be studied and able to avoid the occurrence of resonance and unnecessary loss dissipation. Through a series of experiments that can provide a basis of vibration and dynamic characteristics and as a reference for a structure system design.
This study aims to investigate the dynamic characteristics for a CNC milling machine tool by conducting the modal testing, dynamic stiffness, and cutting stability experiments. First, the machine modal testing is proceeded to obtain the structure modal parameters, which include the natural frequency, mode shape, and damping. These data are then collected and input into the analysis software (ME'scope) and each mode shape corresponding to each different mode is obtained from the modal testing. On the structure dynamic stiffness aspect, three mutual perpendicular forces are individually applied on the spindle and the tool holder when the headstock is set at different specific height locations. And the continuously change of the axial dynamic stiffness in each corresponding axis can then be inspected. Finally, different milling parameters (cutting speed, feed rate, axial depth of cut) with up-milling and down-milling manners are combined together to investigate the variations of cutting force, spindle vibration, workpiece surface roughness, and the analysis of cutting stability.
Modal testing results show that the mode shapes corresponding to Mode 1 to Mode 3 mainly related to the deformation in headstock and column structure components of the machine tool. While the main deformation parts corresponding to mode shapes of Mode 4 and Mode 5 are work-table and saddle and these two modes exhibit bending deformation behavior will possibly making the joint interface to separation. The results from dynamic stiffness experiment show that when the headstock moved along Z-axis from -100 mm height location down to -300 mm, the dynamic stiffness of the structure in X-axis component may be changed from 217 N/μm to 106 N/μm, which will have some impact on milling stability. The results from the milling experiment show that vibration marks left on the machining surface obviously under the conditions of cutting speed 143.3 m/min, feed rate 400 mm/ min and axial depth of cut 0.5 mm during up-milling, and this phenomenon is judged as the chatter occurrence when comparing with those cases of stable milling operation. These results can be utilized as a reference for milling parameter planning in industry.

Keywords: modal testing, dynamic stiffness, cutting stability, spectrum analysis

並列關鍵字

modal testing ； dynamic stiffness ； cutting stability ； spectrum analysis

參考文獻

參考文獻

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