Formation of SS316L Single Tracks in Micro Selective Laser Melting: Surface, Geometry, and Defects

Zhiheng Hu,Jun Wei,Balasubramanian Nagarajan,Rui Huang,Wei Zhai,Xu Song

doi:10.1155/2019/9451406

Abstract

To fabricate complex parts with a fine resolution and smooth finish, micro selective laser melting (SLM) has been developed recently by combining three attributes: small laser beam spot, fine powder size, and thin layer thickness. This paper studies the effect of the micro-SLM process parameters on the single track formation of 316L stainless steel. The surface morphology, geometrical features, and defects have been analyzed in detail. The results highlight that laser power and scanning velocity have a significant effect on the formation of single tracks. The single tracks fabricated through micro-SLM with varying process parameters are classified into four types: no melting, discontinuous, continuous but unstable, and continuous tracks. Besides, the top surface of the tracks is observed with “double-crest” morphology, due to the high recoil pressure gradient generated by the extremely fine spot size. In addition, molten pool geometry (width, depth, and height) has been characterized to study the mode of the molten pool in micro-SLM. Finally, the occurrence of two typical defects within the tracks, keyhole pore and cavity at the edges, has been studied.

Highlights

Additive manufacturing (AM) processes manufacture the three-dimensional (3D) parts layer by layer according to a digital model and have a significant development in the past two decades [1]
All the abovementioned research studies highlight that the process parameters including laser power, scanning velocity, and layer thickness have a significant effect on the formability, geometry, surface topography, and defects of the single tracks in Selective laser melting (SLM)
To the best of our knowledge, there are hardly any research works on the process behavior and the underlying mechanisms during micro-SLM. erefore, this paper is focused on the influences of the process parameters on the surface, geometry, and defects of the single tracks fabricated by micro-SLM. 316L stainless steel (SS316L) has been chosen as the material for the study. e underlying process mechanisms in the formation of single tracks during microSLM have been proposed

Summary

Introduction

Additive manufacturing (AM) processes manufacture the three-dimensional (3D) parts layer by layer according to a digital model and have a significant development in the past two decades [1]. SLM systems use the laser beam size of tens to hundreds of microns [5, 6], powder size of 20–50 μm, and the layer thickness ranging between 20 μm and 100 μm Since these parameters significantly influence the part resolution, SLM has limitations towards microfabrication. Yadroitsev et al [8] fabricated 316L stainless steel single track samples and studied the relationship between the process parameters and the geometry using the ANOVA method. All the abovementioned research studies highlight that the process parameters including laser power, scanning velocity, and layer thickness have a significant effect on the formability, geometry, surface topography, and defects of the single tracks in SLM. Erefore, this paper is focused on the influences of the process parameters on the surface, geometry, and defects of the single tracks fabricated by micro-SLM. To the best of our knowledge, there are hardly any research works on the process behavior and the underlying mechanisms during micro-SLM. erefore, this paper is focused on the influences of the process parameters on the surface, geometry, and defects of the single tracks fabricated by micro-SLM. 316L stainless steel (SS316L) has been chosen as the material for the study. e underlying process mechanisms in the formation of single tracks during microSLM have been proposed

Experimental Details

Results and Discussion

Conclusion