Influence of forming directions on surface quality of 316L stainless steel produced by selective laser melting additive manufacturing

Abstract

Different forming directions have significant impact on surface quality in additive manufacturing. This study is aimed at exploring how different forming directions influence surface quality in additive manufacturing. First, experiments were designed to prepare 316L stainless steel by selective laser melting additives manufacturing in different forming directions. Besides, the surfaces of samples manufactured by additives manufacturing in different forming directions were tested using a 3D surface profiler and a scanning electron microscope. In this way, their 3D profile maps, surface roughness values, and scanning electron microscopy images were obtained. Furthermore, the surface quality was characterized by four parameters, the maximum height-S z , the maximum valley depth-S v , the standard deviation of height-S q , and the arithmetic average height-S a . The following results were obtained: (1) Different forming directions correspond to close upper surface roughness S a values, the minimum and maximum values of S a being 7.16 um and 8.20 um, respectively. S a is the smallest among the four parameters (S z , S v , S q , and S a ), shows good stability and statistical significance. (2) In the same forming direction, the upper surface roughness values follow S z >S v >S q >S a ,S z is the largest, exceeding 800 um, average value S a is the smallest reaching 7.36 um. The values of S q , S z , and S v vary when the forming direction changes; specifically, all of them increase when the forming direction changes from a vertical direction to planar and lateral directions in turn. (3) In different forming directions, the values of S z , S v , S q , and S a vary on different surfaces (XOY, YOZ, and XOZ surfaces), but their variations are basically similar. Meanwhile, the S z , S v , S q , and S a values of the free surfaces are at least 10 times greater than those of the printed surface. (4) In the selective laser melting additive manufacturing process, it is necessary to reasonably select a forming direction for parts with different dimensional parameters on each side. High-quality workpiece can be obtained with a reasonable forming direction. The proposed method serves as references for the selection of forming direction of selective laser melting additive manufacturing and provides a new method to improve the surface quality of parts by additive manufacturing.