The need for rapid qualification and verification of low-volume production or specialised components built using AM drives the development of novel sensing and control technique for SLM processes. They need to address specific challenges, such as multi-layer deposition or complex fine features. Here, we review in-process sensing and control strategies for SLM of metal components.
Within a complex system such as SLM machine and its build chamber, various sub-systems need to be monitored: laser, beam delivery system, motion controls, powder recoating and recycling and build environment,…
Using sensing and active feedback control within each of these subsystems can compound the process repeatability and reliability. Ideally, the metal components built using SLM should be fully dense, with isotropic (or tailored) mechanical properties, tailored surface roughness and high dimension accuracy.
Many of these characteristics such as material composition, density and microstructure cannot be directly measured. But indirectly by monitoring certain characteristics of the beam-material interaction, as well as solidified regions of the deposit. For instance, literature shows that characteristics of the melt pool geometry can be used to predict deposited microstructures in Ti-6Al-4V  and Inconel 718 .
The table below  summarises the main sensing and controls currently available to monitor SLM machines.
Laser system delivery
Build chamber environment
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 Nassar, A.R., Spurgeon, T.J., Reutzel, E.W., 2014b. Intra-Layer Control via Alteration of Path Plan in Directed Energy Deposition
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