移動式熱源平板加工的微應力量測與分析

Abstract

雷射是20世紀人類重大的科技發明之ㄧ，由於雷射光的擴散角極小，所以光源能聚集在極小的面積範圍，因此雷射被廣泛地應用在材料的加工。材料在加工時，由於高能量的雷射會產生熱能，使得材料會產生熱應力與熱應變，若是當熱應力超過材料本身的強度時，則會發生破壞。 本文利用非接觸式微應力量測的方法，藉由光學顯微鏡配合智慧型影像擷取與分析系統，對試片特定點進行影像分析處理，求出熱應變量反推熱應力，目的在觀察平板試片在雷射加工時的應力變化，將量測結果歸納分析以做為平板雷射熱加工參數規劃的參考。此外，為驗證本研究微應力量測結果的正確性，本研究採用有限元素軟體ANSYS，模擬動態熱源熱加工過程熱應變的變化情形。因為雷射切割是一種動態熱源負載，本研究的熱加工模擬採用ANSYS結合其參數化程式開發語言APDL，針對動態熱源負載的邊界條件進行持續與反覆地定義與更新，使模擬得以進行連續式熱源負載的平板應力分析與模擬。熱源的模式定義方面，一般將雷射熱源的分佈簡化為單點式並不符合實際熱源型式，本文為了能更貼近實際的情形，對於熱源的能量供應採用高斯函數分佈的區域熱源，同時也探討在分析過程中考慮熱焓參數對加工效果時的影響情形。 在實驗的規劃方面，本文裝置的微應力量測系統，目前可以量測到 等級的變形量，若是調高檢測倍率則可以獲得更好的解析度。觀察實驗與模擬分析的結果，在連續熱加工的材料應變量的分析與檢測的定性分析結果均呈現相同變化的趨勢。此外，本研究在分析過程中有加入熱焓與對流效應的考慮，分析結果發現有考慮熱焓與對流效應的分析例中，其應變量與殘留應力有減小的趨勢，此結果符合參考資料所提供研究數據的變化趨勢。在實驗的規劃與實作中，本實驗室(NCTU CIDM Lab.)實際組裝了非接觸式微應力量測系統，並將此量測系統架設在雷射切割機台上實際進行線上的熱應力量測，以配合理論數值分析結果的評估，藉以探討熱加工的參數有效設定值的規劃法則，用以提高雷射熱加工在平板切割等加工應用方面的效率與品質。

The research proposed a novel thermal stress analysis methodology cooperated with new designed micro thermal stress vision detection system for investigating the optimal cutting parameters on laser machining with moving heat source. In the article, we adopted the finite element analysis numerical system ANSYS as the analysis kernel. As considering for the model of the moving heat source, we proposed the application development tool (APDL) to form a iteration processes for moving boundary and moving heat source. For improving the correctness of the stress evaluation of the distribution, the non-uniform mesh generation has been designed and implemented. Thus, the simulation results of some illustrative examples have been evaluated to be a very closed quality tendency in physical phenomenon as compared with the experiment detected data in the experiment. While in the experiment process of plate cutting via laser beam, it is a challenge on the request of online detection of thermal stress and strain. In the research, a easy-install and easy-use micro stress vision detection system has also been designed and installed. The vision detection system is composed of the microscope, DVT image measurement device, special light system, and the stress calculation software program which is also developed in the current research. The vision detection system has been upgraded to be a multi object simultaneously stress monitoring system. In the article, some typical examples have been demonstrated in simulation and experiment phases for further verification. The verification data have demonstrated the advantage that proposed in the study.