  Laser metal deposition (LMD) is an additive manufacturing technique, whose
performances can be influenced by several factors and parameters. Monitoring
their evolution allows for a better comprehension and control of the process,
hence enhancing the deposition quality. In particular, the deposition height is
an important variable that, if it does not match the process growth, can bring
to defects and geometrical inaccuracies in the deposited structures. The
current work presents a system based on optical triangulation for the height
monitoring, implemented on a LMD setup composed of a fiber laser, a deposition
head, and an anthropomorphic robot. Its coaxial and non-intrusive configuration
allows for flexibility in the deposition strategy and direction. A measurement
laser beam is launched through the powder nozzle and hits the melt pool. A
coaxial camera acquires the probe spot, whose position is converted to relative
height. The device has been demonstrated for monitoring the deposition of a
stainless steel cylinder. The measurements allowed to reconstruct a spatial map
of the height variation, highlighting a transient in the deposition growth
which can be explained in terms of a self-regulating mechanism for the layer
thickness.
