工具機結構動態行為及動態切削過程之研究

An Investigation of Structure Dynamic Behavior and Dynamic Cutting Process for Machine Tools

方彥欽(Yan-Chin Fang)

指導教授 ： 林盛勇

國立虎尾科技大學/工程學院/動力機械工程研究所/碩士(2006年)

https://doi.org/10.6827/NFU.2006.00001

摘要

本文有系統將工具機相關振動問題分成三部份進行探討，那即是結構動態、配重移動衍生頭座振動及動態切削行為分析。
本研究第一部份，以五軸工具機實體為分析對象，使用SolidWorks 3D繪圖軟體建構工具機主體架構，並使用ANSYS Workbench軟體分析工具機主要元件之動態行為，如工作台、數控雙軸分度盤外架、Z軸導螺桿、滑軌、底座等元件，將3D幾何模型轉換為有限元素分析模型，進行元件模態分析並找出其各自然頻率與振動模態，以相同的方法分析整台工具機的自然頻率及所對應之模態。同時使用敲擊槌、加速度規及頻譜分析儀從事實驗以求出整台工具機的自然頻率及振動模態並與模擬結果相互比較。
第二部份使用Working Model機構運動模擬軟體，模擬有平衡配重工具機頭座做等速、等加/等減速、簡諧運動產生急停時，因配重塊慣性傳導致頭座產生彈跳情形。試著加諸彈簧及阻尼器等減振裝置連接於配重塊上，以檢視此彈跳現象之改善情形。將數值模擬結果所得之合適減振裝置參數，設計製作頭座減振裝置(避震器減振系統及質量阻尼器)，並進行銑削實驗。將CNC切削路徑規畫為坡緩及垂直步階路徑，以球形端銑刀行該路徑做鋁合金銑削加工，並以不同的進給率進行多次銑削實驗，比較兩種路徑在相鄰步階間工件角落表面振紋的產生情形，結果顯示坡緩的步階路徑，工件角落表面無任何的振紋產生，而垂直步階路徑原本角落表面漣漪般的明顯振紋，由於本改進方法的施行獲得相當大之改善。
第三部份，應用AdvantEdge有限元素切削模擬軟體，模擬工具機因機器結構動態或切削條件設定不當等因素，導致切削振動。以三種常見的動態切削形式：波紋切削(wave cutting)，切削有波紋表面的工件(wave removing)，行波紋路徑切削有波紋表面工件(wave on wave cutting)。配合不同頻率、振幅、切速、相角差及不同種類的波形動態切削形式組合，行一全程性的動態切削過程模擬探討，並觀察切削力的波動情形、塑性應變、殘留應力及完成面之品質。經由完成表面粗糙度及光滑度分析，藉以預測不同動態切削形式之切削穩定性。

關鍵字

振動模態 ； 頻譜分析 ； 平衡配重 ； 減振裝置 ； 動態切削

並列摘要

Three dynamic issues related to machine tools are investigated in this study systematically, i.e., structure dynamics, tool vibration induced from the movement of counter weight and behaviors during dynamic cutting processes.
The first part of this study is to construct a dynamic analysis model for five-axis machine tool. Solid Works 3D software is used to built the main solid structure of the machine tool components such as work table, five-axis index device, main spindle, guide way and the base of the machine tool, which are deeply related to the dynamic behavior of the five-axis machine tool. ANSYS Workbench software is then used to investigate the natural frequency and vibration modes for each component after its FEM model has been established. The dynamic response of the whole structure of the machine tool is analyzed through the assembly and simulation by Workbench. Finally, a dynamic experiment was performed in the laboratory on each important component using the measurement tools of hammer, accelerometer and spectrum analyzer to detect their natural frequencies and vibration modes.The second part of this study is to investigate the elastic jump due to the effect of the inertia of counter weight and potential energy released from the connected chain .If the machine tool head makes a suddenly stop during the constant velocity, constant acceleration/deceleration or harmonic motions. for machining of a vertical-2D plane, a flat planar simulation by using a 2D dynamic simulation software Working Model. The vibration energy absorber such as spring or damper is connected to counter weight in series trying to reduce the phenomenon of elastic jump. The design and manufacture of a vibration reduction system for machine tool head was performed based on the absorber parameters obtained from the simulation results. Milling experiments on aluminum alloy are undertaken in conjunction with various CNC cutting paths planning as vertical step or moderate step under different feed rates cutting conditions. No surface integrity changed was detected during the former cutting path. But wavy marks left on the machined surface around the corner area between subsequent steps is very obvious after milling process following the vertical step cutting and this tool vibration is significantly improved through the strategies proposed and implemented in this study.
The third part of this study is the application of AdvantEdge finite element software on the simulation of inducing vibration from the structure dynamics of machine tools and the factors due to the improper setting of cutting conditions. Three different dynamic cutting manners frequently occurred during cutting processes are introduced and analyzed in this project, i.e., wave cutting, wave removing and wave on wave cutting, and are used to approach the cutting dynamic behaviors. Apply different frequencies and amplitudes of the waves, different phase angle between successive waves and cutting velocities to simulate the whole dynamic cutting process, from the initial tool-workpiece engagement to the steady state chip formation. Fluctuation situations of the cutting force, the distributions of the residual stresses plastic strain and machined surface quality can thus be obtained. The cutting stability for various dynamic cutting manners may be predicted through the analyses of surface roughness and smoothness on the machined surface.

並列關鍵字

vibration modes ； spectrum analysis ； counter weight ； absorber ； dynamic cutting

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