WEB Laser powder bed fusion (L-PBF) of pure Cu by application of a green laser sourceThursday (24.09.2020) 10:40 - 10:55 S: Structural Materials 1 Part of:
Additive manufacturing of pure copper via laser powder-bed fusion (L-PBF) represents a special challenge due to its physical and thermal properties as the complete and defect-free melting of powder is associated with considerable difficulties: (i) the laser-beam reflection is very high (approximately 98%) for wave lengths of about 1060 nm (red), as it is commonly used for the L-PBF process, and (ii) the high thermal conductivity of Cu. A large beam reflection results in a low process efficiency, since the major amount of the laser power is reflected and not available for powder melting. The high thermal conductivity causes a rapid loss of the spot energy required for heating and melting of the surrounding material. Therefore, L-PBF of Cu is associated with the risk of unstable process conditions with inadequate local energy supply, preventing the manufacturing of dense and defect-free components. One solution is the application of a green laser source as the degree of absorption increases with the use of a laser with a smaller wavelength as 1030 nm. Accordingly, a green laser with wavelength of 532 nm has a degree of absorption of approximately 45%. The L-PBF machine which was used in this work is equipped with both, a red and green laser and therefore optimized for additive manufacturing of Cu and Cu alloys.
In this study, custom-made copper powders with a purity of 99.99% of Cu are generated by gas-atomization where metal droplets are solidified and cooled down by rapid cooling. These powders are used for L-PBF and the functional and mechanical properties as well as the density and the microstructure are correlated with the building parameters. As a result, the parameter-microstructure-property relationship will be deduced in order to quantify the melting behavior. A comparison with samples produced with a red laser source complements the fundamental investigations on L-PBF of pure Cu with a green laser source.