摘要
本文主要以有限元素法模擬雷射成形製程，研究將分成兩個部份，第一部份探討由於不均勻的熱應力產生之穩態變形，另一部份研究急速不均勻的熱應力所產生暫態振動現象，並進一步提出減振控制方法。
研究中使用CO2雷射，考慮高斯分佈能量形式之固定熱源，加熱於不鏽鋼試件上，使試件產生振動並彎曲變形。在有限元素之穩態變形分析部分，採用三維元素來模擬熱塑變形過程，分析過程將採熱機耦合分析（Coupled thermal-mechanical analysis），進行溫度、變形與殘留應力之分析，並討論由於塑性變形產生的熱量對於變形量的影響；而在暫態振動部分，將使用熱機非耦合分析（Uncoupled thermal-mechanical analysis），將分析過程分為熱傳模式與力學模式兩種，考慮材料的慣性及彈塑性行為，研究由於急速不均勻熱應力所引發之振動行為，並提出一簡單之減振方式。此外將進一步討論不同的加工參數對於穩態變形及暫態振動的影響，並規劃一系列實驗來與分析結果作比較，以驗證有限元素模擬的可行性。
結果顯示，數值模擬與實驗結果相當接近，在穩態變形部分，雷射成型製程之熱機耦合效應並不明顯，但對局部之應力應變還是有影響，而試件成形角度隨著功率增加、板件厚度減少、光徑的減少、加熱時間增長而增加。在暫態振部分，板件頻率會因熱應力影響而較低頻，板件反彈振幅受下降深度影響，下降深度越大，反彈振幅越大。而板件下降深度隨板件厚度減少、功率及光徑增加、加熱時間增長而變大。此外，本文利用控制多發雷射擊發間隔時間，成功的達成減振效果，且確認對於多發雷射擊發試件振動之行為為非線性振動問題。

Abstract

The object of this thesis is to analyze the laser forming processing for a thin metal plate with the finite element method. The thesis was divided into two parts: one is the thermal deformation problem of the thin plates induced by thermal stress and the other is the vibration problem induced by thermal stress with a superposition method to reduce it.

CO2 laser was used as a pulse energy source to heat the metal plates. The laser beam was focused on 304 stainless steel plates as a point heat source. In the analysis of the thermal deformation of the thin plates, the plate deformation was simulated numerically and verified experimentally. The non-linear finite element method software, ABAQUS, was used to simulate the deformation problem of the coupled thermal-mechanical system in three dimensions. The time-dependent temperatures, stresses, strains and bending angles during the forming process were calculated. The process parameters affecting the bending angles were also investigated.

In the analysis of the vibration problem induced by thermal stress, the plate vibration was simulated and measured. The non-linear finite element method solved by ABAQUS, was used to simulate the thermo-mechanical problem in three dimensions. The time-dependent temperatures, and displacement during the process were calculated. The process parameters affecting the displacement were also investigated.

There is a good agreement between the numerical simulation and the experimental observations in both studies of the plate deformation and vibration. A superposition method with multiple laser pulses was provided to reduce the plate vibration and it was verified with numerical and experimental approaches.

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