Fig. 6 Hatch distance
Focal Distance
Optimal convergence of the maximal laser intensity and the localized spatial concentration of the powder beam is referred to as the focal distance. Xiong Y. et al. looked at how the working distance and relative location of the laser beam’s focal plane affected microstructure and characteristics. With varying working distances, microstructures with and without alternating sublayers can be created. When the Co binder in the top portion of a previous deposition layer is remelted, large WC particles may develop for the microstructure with alternating sub-layers produced across a longer working distance. Particle coarsening was insignificant for the homogeneous microstructure that was deposited across a shorter working distance. Working distance has no discernible impact on density. But using a shorter working distance produces more consistent microstructure and hardness values, which is crucial for using cermets .
The process parameters discussed above are machine parameters. Non-machine parameters, powder morphology and powder purity are also affect the properties of the parts that are being produced.
Conclusion
Higher laser power used to acquire dense structures by avoiding porous region. However, it my result small grain size which lower hardness and other mechanical properties. Furthermore, increasing laser power affect surface roughness of printed parts.
In LENS scanning speed is one of the decisive parameter. As scan speed getting lower, laser beam exposed to the material for long period of time, then it creates heat affected zone. In the other hand, if the scan speed is too fast metal will not properly melt.
Reducing powder feed rate results porous zone since enough powder not fill space between two parallel lines. On the other hand, a higher powder feed rate lead to damage the integrity of build layer that result part non-uniformity.
Unidirectional deposition pattern deposited overhand has uneven surface and create voids on end side of the path. In contrast, surface of overhang through the round trip deposition path is flat and symmetric.
To get homogeneous microstructure shorter focal distance is preferable. But, working distance has no such impact on density.
Hatch distance and layer thickness are parameters responsible for porosity if too large and creates built layer inconsistence if the two are too small independently.