  Selective Laser Melting (SLM) is an additive manufacturing technology that
builds three dimensional parts by melting layers of metal powder together with
a laser that traces out a desired geometry. SLM is popular in industry, however
the inherent melting and re-solidification of the metal during the process can,
if left uncontrolled, cause excessive residual stress, porosity, and other
defects in the final printed parts. This paper presents a control-oriented
thermal model of a multi-layer SLM process and proposes a structured model
reduction methodology with an associated reduced order model based in-layer
controller to track temperature references. Simulation studies demonstrate that
the controller is able to prevent layer-to-layer heat buildup and that good
closed-loop performance is possible using relatively low-order models.
