Control of Porosity in Parts Produced by a Direct Laser Melting Process

Abstract

Recent advances in direct laser melting (DLM) have demonstrated its great potential for manufacturing three-dimensional porous metal parts. Various combinations of powder layering and processing parameters can be set to adjust the porous properties of the final parts. This study presents the effects of powder morphologies and process parameters on porosity formation during DLM. Four types of Fe-powders composed of spherical or non-spherical particles with different sizes were experimentally investigated. Furthermore, the laser processing parameters, such as laser energy density, laser focus, and line spacing, which have a significant effect on the results, were characterized. In the case of a mixed powder composed of spherical and non-spherical powders, the packing density decreases as the non-spherical powder size increases. The porosity of the laser-melted layer increases with the degree of size misfit between the non-spherical and spherical powders. Decreased laser absorption and enlargement of the powder-depleted zone as a result of decreased packing density increases the porosity during DLM. The overall results show that the porosity of DLM parts could be actively controlled by adjusting the process parameters and powder morphologies.

The Influence of Particle Shape, Powder Flowability, and Powder Layer Density on Part Density in Laser Powder Bed Fusion

“…Irrinki et al [14] investigated the processability of three WA powders and one GA 17-4-PH stainless steel powder and found that the GA powder generally yielded parts with less porosity, but were able to process the WA powder into parts with comparable densities and mechanical properties at sufficiently high energy densities. Jeon et al [15] processed four Fe-powders, of which three were mixtures of spherical and non-spherical powders. They found an increase in the part porosity of blended powders for increasing size misfit between the spherical and non-spherical powders.…”

Analysis of Melt-Pool Behaviors during Selective Laser Melting of AISI 304 Stainless-Steel Composites

“…Because the gas atoms are released from the lattice in the heat-affected zone, yielding a longer liquid lifetime in samples with a high weight percentage of reinforcement, e.g., 7 wt%, may result in the formation of a higher amount of gas. It is reported that this phenomenon may cause the formation of porosity in SLM-produced parts [35]. This was explored by multi-line formation tests shown in Figure 7, where the presence of cracks is evident in the reinforced sample with 7 wt% Al 2 O 3 -ZrO 2 , seen in Figure 7f.…”

Evaluation of Ti–Mn Alloys for Additive Manufacturing Using High-Throughput Experimental Assays and Gaussian Process Regression

“…It often incorporates computer-controlled lasers as power sources and produces near-net shapes with sufficiently accurate dimensions as the final product [ 55 ] to eliminate the need for rough machining, making it popular in industry [ 52 , 53 , 56 , 57 ]. Due to characteristics such as its great reliability [ 53 , 54 , 58 ] and the low porosity [ 59 , 60 , 61 ] of the final products, LENS is widely employed in the customization and repair of intricate mechanical parts, including turbine blades [ 54 , 62 , 63 , 64 , 65 , 66 ]. The ability to control, independently, the powder flow from separate powder feeders in LENS allows for creating chemical gradients in the AM components [ 67 , 68 , 69 , 70 , 71 , 72 ].…”