近年來3D列印技術興起，在3D列印的領域中，選擇性雷射燒熔(Selective laser melting, SLM)因為材料為金屬且成品的機械強度優於鑄造品，可達到鍛造品的水平，被視為最具發展潛力的技術。本研究使用工業上常用的AA6061鋁合金材料作為實驗及模擬對象，以單層列印試件為基礎，隨後藉由商業軟體FLOW-3D計算孔隙率模組，該模組能計算三維空間下建立的隨機粉床的體積比，藉由此粉床模型，得出孔隙率，令粉床層的假設更為合理。由於鋁合金在列印過程容易產生裂痕，而此方向的研究工作，仍然未見報導，此鋁合金在國際3D列印界有極大的產業需求。在本研究中，利用LS-DYNA的Johnson-Cook model對應變、應力進行分析。利用微拉伸實驗所得的應力應變和破壞應變，結合MATLAB軟體中的實數編碼遺傳演算法(Real-Coded Genetic Algorithm)模組得出J-C模組的參數，再藉由此J-C模組找出發生裂痕的加工參數和延伸行為。從實驗結果得知，雷射間距對於裂紋發生的影響相比雷射功率和掃描速率較小，但仍然會對表面粗糙度造成影響，雷射能量密度越大，也就是雷射間距越小時，表面粗糙度越好。透過模擬及實驗的對比，可以得知J-C模組能夠很好得預測裂紋的發生，且能模擬出裂紋會垂直雷射掃描方向延伸的行為，再透過溫度場的模擬結果推測垂直延伸的原因。透過固定雷射功率改變掃描速率與固定掃描速率改變雷射功率的分析，能夠發現能量密度增加時，但裂紋發生機率會變高。由於表面粗糙度和裂紋都會影響成品的機械強度，因此在最佳化參數的選擇上，選擇較高的雷射能量密度，但不發生裂紋的加工參數。

This research aims to analyze the appearances of the selective laser melting (SLM) printing results. To explore the physic phenomena of the metal powder being heated through laser, a SLM theory model was built through a commercial numerical simulation software LS-DYNA. The three-dimensional theory model established some physical mechanisms such as equivalent powder bed, laser heat source, Johnson-Cook model, and phase change etc.
AA6061, a commonly used material in industry, but cracks appear in process of SLM. AA6061 was used in simulations of this research for conducting SLM to analyze the interactions between hatch distance, laser power and scanning speed. In addition, we also analyze thermal stress and fracture strain. Through the experiments, it is found that thermal stress increases when melting AA6061 start solidifying. Thermal stress plays an important role in cracks of the sample. By means of Johnson-Cook model, one can analyze fracture strain. The effects of various laser processing parameters to prevent cracking were discussed. To validate the accuracy and reliability of the theory model, compare the computation results with the experiment results. Computation results is consistence with the experiment results. It assures the reliability of the theory model. Through computation results and experimental results, we found that the cracks would occur as Laser energy density (LED) increase. We also found that surface roughness would be improved when LED increase. Consequently, we should select higher LED to get well surface roughness but could not exceed the LED which cracks appear.

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