Additive Manufacturing Processes by Sanjay Kumar

Author:Sanjay Kumar
Language: eng
Format: epub
ISBN: 9783030450892
Publisher: Springer International Publishing

Fig. 6.6Minimizing shadowing effect in off-axial powder deposition: (a) inclined laser beam and inclined off-axial nozzle, (b) inclined beam and perpendicular nozzle, (c) perpendicular beam and inclined nozzle

If the powders, instead of getting just heated, get melted then the creation of melt pool on the substrate will no longer be required as a means to melt powders and the problem associated with creating and controlling the melt pool will be over. There are the following reasons why powders are not melted: (a) powders are not small enough; powders used in this process are from the size of about 20 micron and above, these powders are not small enough to be melted in such small laser-powder interaction time. If these powders could be of sub-micron size, they can melt but using sub-micron or nano-sized powder is not possible as these cannot be fluidized (Geldart 1973) and accelerated using carrier gas. During acceleration, they agglomerate and no longer remain an isolated small powder small enough to be melted. If powders are very small, they will vaporise and can form plasma which will attenuate laser beam. If powders are not very small, then they will partially vaporise which will give rise to recoil pressure on the powder and which will change the direction of the flow of the powder (Sergachev et al. 2020). Which powder is small and which one is very small depends upon experimental conditions. (b) Laser energy is not sufficient – focal length of laser beam is small which does not let the powder to have sufficient interaction with the beam to gain sufficient laser energy for melting; this can be overcome by increasing the focal length as well as increasing the laser power. Increasing the focal length to a big length, though possible by optics, will bring an additional problem to have a big focussed powder stream matching that big length. Increasing the laser power may vaporise the substrate in the course of melting the powder unless the laser is diverted by additional optics. Thus, the problem can be overcome and liquid drops (by melting powders) will fall on the substrate, which on being continued will give rise to a 3D structure. But, overcoming this problem will bring a question mark on an effort for overcoming this problem; the aim of the process is not to facilitate complete melting on the way but the opposite – to prevent even an isolated case of powder melting on the way; besides there are more economic and energy-efficient ways to create liquid drops than using expensive powders and laser.

Download

Copyright Disclaimer:
This site does not store any files on its server. We only index and link to content provided by other sites. Please contact the content providers to delete copyright contents if any and email us, we'll remove relevant links or contents immediately.