本研究使用離散元素法(Discrete Element Method, DEM)模擬在選擇性雷射燒結或雷射熔融過程中粉末床的溫度分佈，發展考慮相變化的顆粒體熱傳理論與隨溫度變化的熱物理性質，建立相關的基準測試，並探討顆粒粒徑與雷射掃描路徑對粉末床溫度分佈的影響，研究結果顯示，在雷射掃描期間，顆粒床溫度的上升主要來自於雷射掃描的能量，而非來自傳熱機制。在製程參數與雷射掃描路徑相同條件下，表層平均溫度隨掃描時間呈線性增加，而且粒徑越小則溫度越高，溫度分佈較為均勻。在製程參數與雷射掃描時間相同情況下，短路徑掃描溫度略高於長路徑掃描溫度，而且短路徑掃描造成較集中的高溫區域，而長路徑掃描造成溫度比較廣泛的分佈範圍。此外，在雷射初始掃描過程中，顆粒床的溫度尚未達到材料熔點溫度時，考慮熱物理性質(熱傳導係數、密度與比熱)隨溫度變化的效應，對於顆粒床溫度預測有其影響性，但顆粒床的溫度超過材料熔點溫度時，由於相變化主控顆粒床的溫度，因此較無影響性。;The purpose of this study is to investigate the temperature distribution of powder beds during selective laser sintering or melting by using Discrete Element Method (DEM). The model of heat transfer for granular assemble was developed that consider phase change and temperature-dependent thermal physical properties of the materials. The benchmark tests were established to verify the proposed model of heat transfer. The effects of particle size and scanning pattern on the temperature distributions in the powder bed were explored. Numerical results show that during the laser scanning process, the rise of temperature in the powder beds is mainly caused by laser energy input, not by the heat transfer mechanism. Based on the same processing parameters, such as laser power, scanning speed, spot size, hatch space and scanning pattern, the average temperature in the surface of the powder bed increases linearly with the scanning time, and the powder beds with smaller particles exhibit higher temperature as well as more uniform temperature distribution. The temperature for the short track is slightly higher than that for the long track. The short track results in a more concentrated high-temperature area, while the long track results in a wider temperature distribution. Moreover, at the initial scanning stage of the laser heating (within the melting point of the materials), considering the temperature-dependent thermal physical properties is required in calculating the temperature field. However, beyond the melting point of the material, the temperature-dependent thermal physical properties takes a little effect, because the phase change dominates the rise of the temperature.
