本論文主旨在探討脈衝式含釹鐿鋁石榴石晶體(Nd:YAG)雷射，對不鏽鋼材質(SS304L)銲接時，其雷射能量吸收機制，並以吸收率描述此焊接過程之能量吸收行為。利用實驗量測得焊點剖面形狀參數，如銲池寬、銲池深、銲池斷面積及銲池體積大小，與有限元素法(FEM)模擬所得結果，以進行銲接過程中此吸收率值之估算。模擬過程中採用高斯(Gusaaian)分佈描述雷射光束切面之能量密度分佈情形。為驗證此經由單脈衝實驗估算結果值之精確性，乃將此估算出之雷射脈波吸收率，代入有限元素模型中。模擬多重雷射脈波之焊接情形，並將模擬結果與實驗結果進行比對以確定其精確性。吸收率之估算結果顯示，吸收率與雷射輸出之脈衝能量成反比，結果亦顯示由銲池斷面積或銲池體積比對可得較穩定吸收率值。此外，再利用有限元素法之熱彈塑模式模擬此脈衝雷射焊接焊接之固化過程，顯示銲池於固過程中，因相變化造成之收縮現象，導致熔池固化後極複雜之殘留應力分佈。此殘留應力分佈將造成雷射焊接域之收縮變形，此銲後變形特徵是造成精密銲接，如光電元件成品良率之關鍵因素。

The energy absorbing behavior of stainless steel 304L during the pulsed Nd:YAG laser welding is investigated in this thesis. The equivalent absorptivity is estimated from the comparison of measured and finite element method (FEM) results simulated melting pool shape parameters, e.g. pool width, pool depth, cross-section area and total volume of the pool. To simulate the actual pulsed laser beam, the energy density of heating source is performed as a Guassian distribution in the transection of a circular laser beam. For evaluating the feasibility and the accuracy of the estimated equivalent absorptivity, the multi-pulsed Nd:YAG laser welding is simulated by using the estimated absorptivities. A good agreement between this simulated and measured melting pool shapes are found in the multi-pulsed laser welding. The equivalent absorptivity can be interpolated from different parameters of the molten pool. However, absorptivity curve fitted from the cross-section area and total volume of the melting pool provide a more stable value. Results also indicate that the absorptivity and the pulse energy are in inverse proportion. The thermal-elastic-plastic FEM model is employed to simulate the fusion and solidification process of the pulsed laser welding. A complicate residual stress distribution introduced from the shrinkage in the solidification process is also calculated and presented. The distribution of post-weld-deformation near the melting pool has also been studied in this thesis. This post-weld-deformation may be a key factor in high precision laser welding, e.g. laser packaging for the optoelectronic components. The absorptivity estimated in this thesis may be helpful to simulate the laser welding process accurately.

Acknowledgements
Contents
List of Figures
List of Tables
Abstract
Nomenclature
Chapter 1 Introduction
1.1. Background and motivation
1.2. Literature review
1.2.1. Temperature profile for laser welding
1.2.2. Absorptivity
1.2.3. Residual stresses
1.3. Organization of the thesis
Chapter 2 Numerical methods for Nd:YAG laser welding
2.1. Introduction
2.2. Description of the problem
2.2.1. Absorbed mechanism of laser welding
2.2.2. Characteristics of laser power distribution
2.2.3. Numerical model details
2.2.4. Assumptions in the FEM model
2.3. Associated theories
2.3.1. Equations of mechanics
2.3.2. Equations of heat transfer
2.3.3. The analysis model of coupling
Chapter 3 Experimental and numerical results
3.1. Experimental equipments
3.1.1. Laser source
3.1.2. Workstation for laser welding
3.1.3. The power meter and detector
3.2. Environments and laser parameters
3.3. The estimating equivalent absorptivity for a stainless steel
3.3.1. Definition of the absorptivity
3.3.2. Estimation of equivalent absorptivities
3.3.3. Solidification of the molten pool
3.3.4. Multi-pulsed Nd:YAG laser welding
3.3.5. The effect of gold plating on the equivalent absorptivity of 304L stainless steel
Chapter 4 Conclusions
Appendix A
Appendix B
Appendix C
References
Vita

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