刀具材質對工具機切削穩定性之影響

Effect of Tool Material on the Machining Stability of a Milling Machine

銑削加工過程中刀具產生顫振將嚴重影響工件表面精度，並危及刀具與工具機的壽命。為了避免顫振的發生，通常會選擇較為保守之加工條件，但卻降低生產效率。如何在生產效率及減少顫振發生間取得平衡，則需建立一套避免顫振的加工準則。在加工實務上，刀具切削性能表現，除了受刀具對工件材質之切削力學行為所影響以外，取決於工具機主軸刀具對切削負荷之動態響應。因此，欲發揮CNC 機台主軸刀具切削性能，必須充分瞭解主軸刀具之動態特性以及其切削穩定性範圍，藉此才可以依據最終切削範圍需求，選用適當主軸刀具系統，以獲得最佳切削加工品質與價值。本研究旨在探討刀具材質對主軸刀具系統動態特性與切削穩定性之影響。研究中，分別使用碳化鎢以及高速鋼兩種不同材質刀具，組裝在主軸刀柄筒夾上進行振動實驗，取得刀具端之頻率響應函數，再導入刀具與工件材質之切削負荷係數，預測該刀具之全方位切削穩定性範圍，藉以評估該刀具之切削穩定性。研究結果顯示，碳化鎢銑刀與高速鋼銑刀分別表現出不同切削穩定性範圍，其軸向臨界切深亦隨進給方向之變化而改變，顯示不同材質刀具確實會對機台切削穩定性有明顯之影響。另外，主軸在Z 軸向移動時亦會改變機台切削穩定性範圍，此種改變亦受刀具材質所影響，其變化程度有顯著差異。應用本研究發展全方位切削穩定性分析法則，將可建立主軸刀具系統在規劃加工行程內之最佳穩定切削深度，提供選用切削條件之決策依據。

Chatter vibration induced by self-excitation during the chip generationprocess may produce poor surface quality and cause damage to the cuter andmachine tool. To avoid the occurrence of chattering, machining operation was performed under poor conditions with more conservative considerationin tooling selection, but the productivity and efficiency of material removalcould be reduced. It is therefore important to establish the machiningcriteria for achieving optimum material removal rates with the highestmachining stability. On the other hand, according to the machining mechanic,chattering is eventually caused by the dynamic interaction betweenthe spindle tool system coupled with machine frame structure and the cuttingprocess. Besides, the machining behavior can be characterized in terms ofthe stability lobes diagram. Therefore the prediction of machining stabilityis not only of great importance for the design of a machine tool towardhigh-precision and high-speed machining, but also can provide informationfor selecting adequate cutting conditions to achieve stable machining withoutchattering.This study was aimed to present the criteria for the evaluation of themachining stabilities of a milling machine tool. For this purpose, we firstconducted the vibration tests on the spindle tool to assess the tool tip frequencyresponse functions along the principal modal axis. And then, basedon the orientation dependent stability analysis model proposed in this study,we evaluated the variation of the dynamic characteristics of the spindle tooland the corresponding machining stabilities at a specific feeding direction.Following the stability analysis model, the limited axial cutting depths forstable machining within the whole interested feeding directions were obtained.Current results demonstrate that the stability boundaries and limitedaxial cutting depth of a specific cutter were affected to vary with thechanging of the feeding direction and the feeding height of spindle head. Itwas also noticed that the tool material affect the dynamic characteristics andmachining stability of the spindle tooling system. It is believed thatrealizations on the variations of the machining stabilities of a spindle toolingsystem within the entirety of feeding directions can provide a valuablereference for the selection of machining conditions in tool path planning.