Selective laser melting (SLM) of AISI 316L—impact of laser power, layer thickness, and hatch spacing on roughness, density, and microhardness at constant input energy density

Abstract

In selective laser melting (SLM) the variation of process parameters significantly impacts the resulting workpiece characteristics. In this study, AISI 316L was manufactured by SLM with varying laser power, layer thickness, and hatch spacing. Contrary to most studies, the input energy density was kept constant for all variations by adjusting the scanning speed. The varied parameters were evaluated at two different input energy densities. The investigations reveal that a constant energy density with varying laser parameters results into considerable differences of the workpieces' roughness, density, and microhardness. The density and the microhardness of the manufactured components can be improved by selecting appropriate parameters of the laser power, the layer thickness, and the hatch spacing. For this reason, the input energy density alone is no indicator for the resulting workpiece characteristics, but rather the ratio of scanning speed, layer thickness, or hatch spacing to laser power. Furthermore, it was found that the microhardness of an additively manufactured material correlates with its relative density. In the parameter study presented in this paper, relative densities of the additively manufactured workpieces of up to 99.9% were achieved.

Influence of microstructural defects and the surface topography on the fatigue behavior of “additively‐subtractively” manufactured specimens made of AISI 316L

“…Due to significantly higher volume energy density E vol , L‐PBF2 results in lower porosity (−16.83 area‐%) as well as smaller average (−18.1 μm) and maximum pore sizes (−149.1 μm) compared to L‐PBF1, Table 3, Figure 6a, b. To examine the impact of laser‐based powder bed fusion process parameters on porosity and surface roughness as well as their influence on the fatigue behavior, significantly different parameter sets were used, which were determined in preliminary work [35]. Although L‐PBF1 yields high porosity, which is not representable for densities achievable with laser‐based powder bed fusion (L‐PBF), it enables an investigation of the interrelation of porosity and surface machining on the fatigue behavior.…”

“…Two sets of process parameters (L‐PBF1 and L‐PBF2) were used, which differ in scanning speed as well as laser power and hence, in E vol ( ΔE vol = 85.7 J/mm 3 ), to realize two substantially different material conditions, Table 1. These parameter sets were determined in preliminary work and ensure significant differences in porosity as well as surface roughness [35]. This enables the analysis of the interrelation between the process‐induced material condition, surface roughness and resulting fatigue behavior as well as their interaction with subtractive manufacturing process.…”

“…As additive manufacturing offers a high potential to produce safety relevant structural components, where a sound knowledge of the cyclic properties is indispensable, the presented work focuses on the fatigue behavior of specimens manufactured by laser‐based powder bed fusion. In accordance with preliminary own work, the commonly used austenitic stainless steel AISI 316L was utilized as investigated material [19–22, 26, 27, 35]. Because the “as‐built” surface of additively manufactured parts leads to a dramatic decrease of fatigue strength and additive manufacturing only offers a low level of dimensional accuracy, subtractive manufacturing of additively manufactured parts is of great interest.…”

“…In the following the expression “additively‐subtractively” represents the combination of the additive manufacturing process (L‐PBF) and a subsequent subtractive manufacturing (grinding; milling). Moreover, two sets of process parameters, which were determined in preliminary work, were utilized to realize substantially different conditions of the additively manufactured material [35]. As a reference for conventionally manufactured material, continuously cast (CC) specimens were also ground and milled.…”

Micro milling of additively manufactured AISI 316L: impact of the layerwise microstructure on the process results

“…Two parameter sets for SLM, already investigated in previous studies [16], were selected for this investigation. They significantly differ in the amount of energy supplied to a specific volume, with AM1 corresponding to the lower energy density and AM2 to the higher one.…”