  In laser metal deposition (LMD) the height of the deposited track can vary
within and between layers, causing significant deviations during the process
evolution. This variation has been mainly attributed to temperature
accumulation within the part due to the deposition trajectory and part
geometry. Previous works have shown that in certain conditions a
self-stabilizing process occurs, maintaining a deposit height and a constant
standoff distance between the part and the deposition nozzle. In this work, the
link between the powder catchment efficiency and the deposition height
stability is illustrated. To this purpose, an experimental system consisting of
an online measurement of the specimen weight and a coaxial optical
triangulation monitoring of the layer height was employed. Through analytical
modeling the inline height measurement and the process parameters could be used
for estimating the deposition efficiency in real-time, which was confirmed by
the direct mass measurements. The data were used for understanding how the
powder catchment efficiency varied and stabilized as the process proceeded in
different conditions. The results confirm that the track height variations are
caused mainly by powder catchment efficiency, which is governed by the melt
pool relative position with respect to the powder cone and the laser beam. For
a given set of parameters, the standoff distance can be estimated to achieve
the highest powder catchment efficiency and a regular height through the build
direction.
