Research on the influence of SLM process parameters on surface forming quality
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摘要:
较差的表面成形质量是选区激光熔化技术(selective laser melting, SLM) 在应用与推广中亟待解决的问题，凹凸不平的成形表面给SLM制备零件的力学性能和耐腐蚀能力带来了诸多不利影响. 文中通过SLM制备了包含向上、向下表面的45°倾斜试样以及包含垂直表面的90°垂直试样，以此3种不同典型建造角度的成形表面作为研究对象，对比研究了不同建造角度之下的表面成形特征，并分析讨论其成因，认为45°倾斜试样的上表面主要呈现为阶梯与轻微颗粒粘附特征，颗粒的严重粘附与团聚现象出现在下表面，90°垂直表面的成形质量则主要受到粘附颗粒的影响；结合表面三维形貌观察与非接触式表面粗糙度测量，对比探究了激光功率和扫描速度两种主要工艺参数对表面成形质量的影响规律. 最终，在各自的工艺参数窗口下，分别得到了4.0 μm、21.6 μm和7.8 μm的最光滑表面，优化的参数组合使得表面粗糙度水平实现了44%、47%和56%的降低效果. 此外，还从激光热输入、粉末颗粒与熔池热过程等角度分析了3种不同建造角度的目标表面上不同表面特征在变化的工艺参数下的转变规律，解释了工艺参数的影响规律并提出有助于获得更优表面成形质量的参数组合策略.
Abstract:The inferior surface forming quality is a pressing issue that needs to be addressed for the application and promotion of SLM technology. The uneven forming surface has adverse effects on the mechanical performance and corrosion resistance of parts fabricated by SLM. Samples with a 45° inclination containing both up-facing surface and down-facing surface, as well as 90° vertical samples with vertical surfaces were fabricated by SLM. Taking these typical surfaces with 3 different construction angles as the research object, the surface formation characteristics under different construction angles were studied and compared, then the causes of these characteristics were analyzed and discussed. The SEM images showed that the up-facing surface of the 45° inclined sample mainly exhibited characteristics of stairs and slight particles adhesion, while severe particles adhesion and aggregation phenomena occured on the down-facing surface. The formation quality of the 90° vertical surface was primarily affected by the particles adhesion. Combining observation of the three-dimensional surface topography with non-contact surface roughness measurement and comparison, the influence of 2 main process parameters, laser power and scanning speed, on the surface formation quality was explored. Ultimately, under their respective process parameter windows, the smoothest surfaces of 4.0 μm, 21.6 μm, and 7.8 μm were achieved, and the optimized parameter combinations resulted in a reduction in surface roughness of 44%, 47%, and 56%, respectively. Additionally, the transformation patterns of different surface characteristics on the target surfaces of the 3 different construction angles under varying process parameters were analyzed from perspectives such as laser energy input, powder particles, and molten pool thermal processes. This helped to explain the influence of process parameters and propose strategies for parameter combinations leading to better surface formation quality.
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图 3 样件设计示意图
Figure 3. Schematic of specimens design. (a) 45° inclined specimens；(b) 90° vertical specimens
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图 7 不同建造角度下的表面形貌
Figure 7. Surface morphologies of different building angles. (a) 45° up-facing surface；(b) 45° down-facing surface；(c) 90°vertical surface
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图 8 不同参数组合下45°倾斜试样上表面的表面粗糙度水平
Figure 8. Surface roughness of 45° up-facing surface with different parameters combination
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图 9 不同参数组合下45°倾斜试样上表面的三维轮廓
Figure 9. 3D profile of 45° up-facing surface with different parameters combination
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图 10 不同参数组合下45°倾斜试样下表面的表面粗糙度水平
Figure 10. Surface roughness of 45° down-facing surface with different parameters combination
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图 11 不同参数组合下45°倾斜试样下表面的三维轮廓
Figure 11. 3D profile of 45° down-facing surface with different parameters combination
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图 12 不同参数组合下90°垂直表面的表面粗糙度水平
Figure 12. Surface roughness of 90° vertical surface with different parameters combination
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图 13 不同激光功率下90°垂直表面的三维轮廓
Figure 13. 3D profile of 90° vertical surface surface with different parameters combination
表 1 IN738LC粉末的名义化学成分(质量分数，%)
Table 1 The nominal composition of IN738LC powder
含量范围 Ni Cr Co Mo W Ta Al Ti Nb C B Zr 最小值 余量 15.7 8.0 1.5 2.4 1.5 3.2 3.2 0.6 0.09 0.07 0.02 最大值 余量 16.3 9.0 2.0 2.8 2.0 3.7 3.7 1.1 0.13 0.01 0.08 
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表 2 SLM工艺参数
Table 2 SLM process parameters
适用区域 建造角度
θ/ (o)激光功率
P/W扫描速度
v/ (mm·s−1)扫描间距
H /μm表皮 45°向上表面 60，90，120 300,400,500 50 90°垂直表面 — — — 45°向下表面 60，80，100 800， 1000 ，1200 50 轮廓 45°向上表面 150 300 — 90°垂直表面 100，140，180 500，700，900 — 45°向下表面 50 1600 —
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