Selective laser sintering (melting) of stainless and tool steel powders: Experiments and modelling

Abstract

When a laser beam scans once across the surface of a metallic powder bed, the resulting track may be continuous with a crescent or an elliptic cross-section, irregularly broken, balled or only partially melted. This paper reports what laser powers and scan speeds lead to what types of track, for a CO2 laser beam focused to 0.55 mm and 1.1 mm diameters, scanning over beds made from M2 and H13 tool steel and 314S-HC stainless steel powders. Beds have been made with particle size ranges from 300 μm to 150 μm, from 150 μm to 75 μm, from 75 μm to 38 μm, and less than 38 μm. Measurements are also reported of bed physical properties that are used in a finite element model to predict melt pool dimensions and temperatures. Boundaries between regions of different track formation are explained in terms of melt surface temperature gradients, melt pool length-diameter ratio instabilities, and transitions from partial to complete melting. Implications for building metal parts in powder beds without supports are considered. The modelling is briefly extended to multi-track and multi-layer processing, to conclude that bonding by remelting between layers, while still maintaining control of the melt flow, places severe constraints on the maximum allowable layer thickness.

Additively Manufactured Inconel 718 : Microstructures and Mechanical Properties

“…The purpose at that early phase was mainly to understanding the SLM process [120][121][122], and with the development of SLM process the focuses and aims gradually shift to exploring the possibilities of manufacturing high-value added components. The most commonly reported SLM iron-base alloys include 316L stainless steel [123][124][125][126][127][128].…”

A review on measurement science needs for real-time control of additive manufacturing metal powder bed fusion processes

“…Soylemez et al, mentioned that while melt-pool cross-sectional area is a key descriptor, melt-pool length was known to affect deposited bead shape, so they proposed using length-to-depth ratio (L/d) as a descriptor in their process mapping efforts [141]. Childs et al, also mentioned that L/d ratio determined the boundary between continuous and balled tracks when scanning on powder beds without a solid substrate [142].…”

“…One interesting approach by Birnbaum et al, used a finite element model to look at transient changes to melt-pool geometry given a step change in laser power with the specified intent to apply in thermal imaging feedback control [17]. [142], [145] * Used as a general term assuming higher conductivity in proximity to previously solidified regions, the build plate, or build up of solidified layers ** Measurement of the fused or solidified material mass or size may be used as an indicator of melt-pool size.…”

Investigation into Effects of Scanning Speed on in Vitro Biocompatibility of Selective Laser Melted 316L Stainless Steel Parts

“…With an increased demand for fast and less expensive product development, rapidly manufacturing parts from metal powders without moulds becomes more and more desirable [1,2]. Additive manufacturing (AM) has received great attention over the past decade [3], [4], [5].AM by selective laser melting (SLM) is an advanced manufacturing process which uses lasers to melt metal powders one layer at a time to produce components from 3D CAD models, as shown in Fig.…”