CC BY
0The 30th International Conference on Advanced Laser Technologies
ALT'23
LM-P-3
Instabilities and ablation under laser melting of powder layers
Yu. Chivel
Additive Technologies Lab ,220019 Minsk,Belarus Merphotonics,42100 Saint Etienne,France
email address: yuri-chivel@mail.ru
The ejected liquid droplets, spatter, can be seen during the selective laser melting process in many cases. This is not considered as a deviation from the technological regime and it is perceived as inevitable. But it is not so. Particulate emissions lead to defects in the layers, the outer surface geometry violations and may even cause damage of the power optics because the particles have velocities of several meters per second. At keyhole regime [1] (q>= 3MW / cm2) , under intense evaporation, the main cause of spatter is vapor recoil pressure [1]. But as experiments show, particle emissions are also observed in the absence of evaporation [2,3] in conduction regime . In addition some instabilities of the melting process also lead to defects and catastrophic decline in the accuracy and quality of products.
Process of melting of the thick metal powder layers in the absence of an evaporation was investigated under temperature control. Ejection of dispersed particles from the overheated melt has been observed and investigated. Also ejection of very fine green powder particles can be observed [3,4] due to gas heating in the porous structure before melting . Mechanisms of the melt penetration into loose powder bed have been determined. Instability of the contact surface between the melt and powder revealed by in experiment has been studied and is defined as the Rayleigh - Taylor instability [5] of the boundary between the powder layer and the melt layer.
Numerical simulation of the Rayleigh - Taylor instability suggest that instability develops starting from small scale passing to the large-scale structure.
0.05 0.10
0.15 0.20
0,3 mm b
0.25
t,s
Fig. 1 (a) Image of the melting process when scanning with droplet release . Powder CoCr . P= 80W ,. Scan speed - 100 mm/s. (b) - The development of Rayleigh Taylor instability for 0,3 mm mode, viscosity of powder - 0.5 Pa s.
References.
1.Ly, A.M. Rubenchik, S.A. Khairallah, G. Guss, M.J. Matthews, Scientific Reports 7(1),4085 (2017)
2.Chivel Yu., Petrushina M., Smurov I., Appl. Surf. Sci. , 254, 820 (2007) 3 .Chivel Yu. , Physics Procedia , 41, 897 (2013)
4.Gusarov A. ,Smurov I. ,Proceedings SMT - 26; Lyon, 51(2012).
5.Chandracekhar S., Hydrodynamic and Hydromagnetic Stability, Oxford Press( 1961) p.505.
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