臺灣博碩士論文加值系統

隨著科技的進步及成熟，積層製造的應用也越來越廣，其中以材料為金屬的選擇性雷射熔融更是具有相當大的潛力，無論是航太業的高精密度或是生醫產業的客製化等特色皆具備此能力，另外，在許多傳統產業無法加工的材料與產品都得已實現。但也因為金屬粉末材料加工的限制性導致:製造成本高、製程時間長、參數控制嚴苛等原因而無法普及，其中以參數控制需耗費龐大資源於每種材料；故希望透過本研究縮短其參數最佳化過程，並透過吸收率的分析來觀察其粉末與製程參數之間的關係，使得參數最佳化過程所耗費資源減少。
本研究開發金屬粉末隨機落球模型，建立其邊界條件結合堆積判定後，利用Matlab演算可獲得各種類型或幾何的金屬粉末堆積模型，並透過切層演算獲得金屬粉末層，並且將金屬粉末資訊透過Macros程式編寫匯入光學軟體Zemax，透過Zemax之光線追蹤分析其金屬粉末於高能量之平行雷射光束下的吸收率。除此之外，也將選擇性雷射熔融之振鏡掃描系統建立於Zemax之吸收率分析，考慮振鏡掃描系統之桶型畸變與枕型畸變所產生之光點誤差及掃描入射角的不同之吸收率分析，並且比較未使用振鏡掃描系統。比較結果後，其在振鏡系統之吸收率影響可以忽略不計。其吸收率分析了不同光束半徑、不同粉末材料、不同粉末粒徑與分布對吸收率之影響並且分析其粉末總體吸收率，將吸收率以微觀角度分為散射吸收與直接吸收，並且定義其最佳的切層厚度以供實驗作為基準，從模擬結果發現，其切層厚度建議於粉末之中心粒徑附近為主。為了驗證此模擬模型，於SLM機台中製作四種不同切層厚度的正方體塊材，由實驗結果發現，使用其模擬模型之建議的切層厚度，具有較佳的尺寸、表面粗糙度與緻密度。

With the mature advancement of science and technology, application of the additive manufacturing is more and more widely. Among them, the metal material in selective laser melting (SLM) has a great potential in the future. Because of high cost for manufacturing, long production cycle and strict parameters in controlling etc, these reasons cause the SLM not to be universal. So, this thesis studis on the optimized process on metal powders by absorptivity and scattering effect.
By the raining model, any size distribution and the type of material for the deposition of metal powders can be simulated. The information of metal powders is imported into Zemax by program coding of Macro and analyzing of the absorptivity of metal powders under high-energy laser beam. Also, galvanometric scanning system in SLS was simulated in Zemax to analyze absorptivity of energy from the metal powders. The results between using galvanometric scanning system of SLM and without using the one of SLM are compared each other. It is found that the effect of galvanometric scanning system to the absorptivity of metal powders can be neglected. In order to analyze the effect of laser spot size, powder particle size distributions, powder material on the absorptivity of powder bed, and the non-sequential ray tracing simulations were implemented in Zemax. It is found that in the case of powder particles size with Gaussian distribution, the suggested powder layer thickness is around the value of the mean size of powder particles. In order to verify this simulation model, the parts with different layer thickness were manufactured by SLM machine. In experiments, it is found that by using the suggested powder layer thicnkess from simulation, the quality of final parts in terms of packing density and surface rougness is better than the other values of powder layer thickness.

Abstract I
中文摘要 III
致謝 V
Table of Contents VI
List of Tables IX
List of Figures XI
Chapter 1 Introduction 1
1.1 Preface 1
1.2 Research Motivation and Purposes 3
1.3 Thesis Overview 6
Chapter 2 Research Methods and Processes 7
2.1 Simulation for Deposition of Metal Powder Layer 7
2.1.1 Type of Deposition of Metal Powder Layer 7
2.1.2 Basic Introduction for Deposition of Metal Powder Layer 9
2.1.3 Theory of Deposition of Metal Powder Layer 11
2.2 Optics in Metal Powder 20
2.2.1 Absorptivity 20
2.2.2 Complex refractive index 21
2.3 Non-sequential ray tracing and absorptivity analysis 22
2.3.1 Non-sequential ray tracing 22
2.3.2 Absorptivity analysis 24
Chapter 3 Analysis Setup for Absorptivity of Metal Powder 28
3.1 Validation on Absorptivity Model 28
3.2 Analysis of absorptivity of metal powders in SLM system 33
3.2.1 Improvement on absorptivity model 33
3.2.2 Simulation Method 34
3.3 Spot analysis and Simulation Results 37
Chapter 4 Optimization Process Parameters by Absorptivity Analysis 42
4.1 Optimization in Process Parameters 42
4.2 Simulation Model and Results 43
4.2.1 Simulation Method 43
4.2.2 Simulation Results for Layer Thickness Optimization 44
4.2.3 Simulation Results in Different materials 47
4.2.4 Simulation Results in Different spot sizes 49
4.3 Simulation Results in Different Powder Sizes 53
Chapter 5 Experiments for Optimization in Process Parameters 56
5.1 Parameters in different 3D machine. 56
5.1.1 Process Parameter in Optimization in SLM system 57
5.2 Experimental Setup for Selective Laser Melting 58
5.2.1 Selective Laser Melting 58
5.2.2 Preprocess in SLM 60
5.3 Experimental Results for different layer thickness 62
5.3.1 Results for Surface roughness 62
5.3.2 Results for Microstructure and Density 63
Chapter 6 Conclusions and Future Work 66
6.1 The parameters for different powder distribution, marterial and spot size 66
6.2 Future Work 70
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