選擇性雷射熔融之掃描軌跡對工件變形研究

Abstract

本論文以粉床式積層製造平台為基礎，透過一般往復式掃描策略與三種不同狀態的2-zone掃描策略(分別為不鋪粉、鋪粉、與鋪粉但改變二次軌跡功率)進行單層熔融，多層熔融與傾斜塊製作實驗。目的為探討不同掃描策略對工件彎曲變形的影響。為了找出成型狀況較好的參數，本論文固定雷射功率為74 W，首先從可穩定成型的單線速度參數作單層熔融實驗，進一步找出表面形貌與平整度較好的線間重疊率參數後，分別以各策略之最佳重疊率參數作多層熔融實驗，製作一定高度的方形立體塊並探討其高度與內部形貌。最後透過不同角度的傾斜塊製作實驗，以不同掃描策略對各角度的翹曲變化趨勢與斜邊形貌作探討，找出不同掃描策略對工件變形的影響。 根據上述實驗結果，一般的往復式掃描策略的工件內部緻密度較差，但在製作工件時擁有良好的精度，在懸空程度較大的角度參數下工件的彎曲變形程度較小。而2-zone掃描策略的工件內部緻密度較好，但補粉之後其平均層厚增加量過大而無法完成傾斜塊實驗，而沒有鋪粉的策略在各角度的變形量上皆大於往復式掃描策略，並在懸空程度較大的角度參數下產生翹曲角大幅度變形的狀態。

In this thesis, a selective laser melting (SLM) system based on a powder bed fusion platform with an expended laser beam is constructed. The effect of parts deformation by Raster Scan Strategy and 3 kinds of 2-zone Scan strategy (non-refill, refill and refill with different power of 2nd scan track) are investigated. First, multi-track structures were formed by 74W CW-laser and optimized scan speed. In each of the Scan Strategy, different track-overlapping rate were studied, and the best parameters of each strategy is adopted to fabricate multi-layer structures. In multi-layer experiment, morphology of the cross-section and the height of the parts were investigate. Finally, the over-hanging parts is fabricated by different angle of the overhanging surface. According to the experiments result, Raster Scan Strategy is bad for the parts density but its build accuracy is quite good. In 2-zone strategy, refill strategy can’t build over-hanging parts as the thickness of each layer is much more than the design value, and the non-fill strategy has more dense part compare to the Raster Scan Strategy. We found that 45̊ of the parts has serious warp on the top of the overhanging surface.