  Powder Bed Fusion (PBF) is a type of Additive Manufacturing (AM) technology
that builds parts in a layer-by-layer fashion out of a bed of metal powder via
the selective melting action of a laser or electron beam heat source. The
technology has become widespread, however the demand is growing for closed loop
process monitoring and control in PBF systems to replace the open loop
architectures that exist today. Controls-based models have potential to satisfy
this demand by utilizing computationally tractable, simplified models while
also decreasing the error associated with these models. This paper introduces a
controls theoretic analysis of the PBF process, demonstrating models of PBF
that are asymptotically stable, stabilizable, and detectable. We show that
linear models of PBF are structurally controllable and structurally observable,
provided that any portion of the build is exposed to the energy source and
measurement, we provide conditions for which time-invariant PBF models are
classically controllable/observable, and we demonstrate energy requirements for
performing state estimation and control for time-invariant systems. This paper
therefore presents the foundation for an effective means of realizing closed
loop PBF quality control.
