Powder recycling is accepted as a key commercial advantage in Selective Laser Melting technology. Yet, surprisingly, little to no information is publicly available on this topic. So what’s the catch?
In Electron-beams systems, the back-scatter of electrons at the layer surface produces local electrical charge build-up and electrostatic ejection of particles from the powder bed: ’smoking’.
A few months ago, we were wondering about process control in powder bed fusion of reactive powders. What are the impacts of particles’ surface contamination on the fabrication of metal components? And what are the best ways to minimise it during the complete manufacturing cycle?
Then, very few studies were trying to assess the impact of powder particles surface chemistry on the process (powder spreading, melt wettability, pores formation, etc…) and on the final product characteristics (relative density, etc).
As more data get publicly available, we can present the results of a detailed investigation aiming to 1) understand the effects of powder surface chemistry, 2) minimise particles surface contamination on the finished products and 3) improve SLM process control.
Process control in powder bed fusion of reactive metal powders: oxides, hydroxides, hydrated oxides and water films
The limited understanding of the complex relationships between alloy composition, temperature, relative humidity, oxide coverage, and the effects of these parameters on processing and powder flow motivates a key question: how much variation can be expected during powder bed fusion. In other words, how are additively manufactured parts and their properties affected at the current level of atmosphere control during storage and machining of powders?
Effect of particles size distribution and packing density on the formation of balling defects during SLM of In718
Balling is a defect that can occur when the molten pool created during selective laser melting (SLM=L-PBF) becomes discontinuous and breaks into separated islands. In this post, we report and discuss how the powder particle arrangement impact the bead geometry and formation of balling defects during SLM.
During powder bed fusion processes, the laser power intensity decreases as the beam penetrates through the powder bed. The depth at which the absorbed intensity decreases to 1/e (~37%) of the initial absorbed intensity  is defined as the Optical Penetration Depth (OPD. Estimating the correct powder absorption and OPD values is critical to model powder bed fusion processes and predict the properties of the finished components.
Powder production routes, actual AM process and recycling methods all influence particles characteristics. In powder bed fusion, these properties affect the homogeneity and density of the powder layers spread across the build platform and, in turn, the process repeatability and the parts quality. Quantifying a combination of factors defining a ‘good’, process-able powder is still required for AM. Yet little has been studied to link traditional powder measurements to its flowability and to its AM process-specific spreading abilities. In this post, let’s discuss suitable parameters and values to qualify flowability of metal powders for selective laser melting (SLM).
Aluminium alloys are notoriously difficult materials to cast or weld. Their naturally high reactivity with the environment favours oxidation and moisture pick up that promotes pores formation during solidification. Among other mechanisms, gas porosity need to be addressed. In casting, this can be done by adjusting the cooling rate . In welding, it can be done by scanning the surface . This post addresses a few ways to decrease hydrogen porosity formed during Selective Laser Melting.