Fig.5 Powder flow rate vs porosity
In
LENS, powder feed rate is crucial as well. If the feed rate is reduced,
there could not be enough powder to fill the space between two parallel
lines, leading to porous zones. On the other hand, a thicker layer
produced by a high feed rate may damage the integrity of the following
build layers or result in part non-uniformities. The height of the
deposited bead is mostly influenced by the powder flow rate. This is due
to the fact that more material is capable of entering the melt pool and
forming beads. The width of the bead can also be influenced by the
powder flow rate, but this often only happens when the extra bead width
is fused to the rest of the deposited material and not the substrate
itself. It can be seen in Fig. 4 that for a constant laser power of
250W, lowering the powder flow rate results in a 0.8% decrease in
sample porosity .