Systematic approach to process parameter optimization for laser powder bed fusion of low-alloy steel based on melting modes

Abstract

In the metal additive manufacturing (AM) process of laser powder bed fusion (LPBF), there are a limited number of materials suitable for producing parts with high density and desired mechanical properties. To establish novel materials, it is essential to determine optimized process parameters in order to overcome process-related challenges and mitigate defects such as lack of fusion, keyholing, and balling. Scaling laws based on thermophysical properties and process parameters can be used to transfer knowledge from other materials or LPBF systems. In this work, a scaling law is used to adjust process parameters for single-track experiments over a wide range, which are laser power PL (100–1000 W), scan speed vs (300–2500 mm/s), and laser spot size ds (0.08–0.25 mm). Compared to existing studies, the parameter range is thus extended towards large laser spot sizes and high laser powers. The scaling law used is based on the calculation of the normalized enthalpy $$\frac{\Delta H}{{h}_{s}}$$ Δ H h s . The ratio of the deposited energy density $$\Delta$$ Δ H and the melting enthalpy hs correlates with the dimensions of the melt pool. According to the aspect ratio $${\delta }_{\mathrm{c}}$$ δ c of the melt pool of each single track, the respective melting mode—conduction, transition, and keyhole mode—was identified. The process parameters of the single tracks in transition mode were used to optimize the density of the LPBF specimens with varying hatch distance hd (0.06–0.12 mm), resulting in specimens with a relative density of > 99.8%. The proposed methodology can accelerate the process parameter finding for new alloys and avoid process-related defects. Graphical Abstract

Mechanical Properties of Ti Grade 2 Manufactured Using Laser Beam Powder Bed Fusion (PBF-LB) with Checkerboard Laser Scanning and In Situ Oxygen Strengthening

“…Major players in the metal AM industry, such as EOS GmbH, GE, Nikon/SLM Solutions, Aconity GmbH, IAMG and Renishaw, are offering parameter sets for fabricating parts from commonly used metal materials (such as Ti grade 1-5, Co-Cr/Co-Cr-Mo, AlSi10Mg, various steels, nickel alloys, and copper alloys) with densities close to the theoretical values. While these parameter sets benefit beginners in the AM industry, they often require modifications for different part shapes, sizes, and support structures to meet end-user surface quality and mechanical strength requirements [7][8][9]. Additionally, the parameters provided by manufacturers typically need adjustments when switching to a new powder supplier or to powder with a slight difference in purity or particle size.…”