Numerical Simulation of Melt Hydrodynamics in Laser Micro Processing of Metals

Abstract

Laser material processing at micro-meter domain can be used for a plethora of applications such as micro drilling, micro welding, micro cutting, micro-texturing as well as micro polishing. In laser micro-cutting, welding and drilling, a high power laser (Intensity ~1010 W/m2) is used to melt and vaporize the material to produce high penetration welds, kerf cuts, and high aspect ratio micro holes. Whereas, in the case of laser texturing, conduction mode welding and polishing, the laser power density is sufficiently low to allow only melting of the material. With the irradiance of high-intensity laser, generation of highly dynamic melt pool occurs due to the presence of vaporization induced recoil pressure, Young Laplace surface tension force, and thermo-capillary shear stress. The melt pool convection results in geometrical defects such as recast layer, porosity, spatter formation, humping, protuberances and melt ripples. These defects pose a severe challenge towards industry utilization of laser micro processing, where precision and repeatability is of utmost importance. Therefore, a competent numerical model considering three co-existing phases (solid-liquid-gas) is developed to predict defects and characterize different regimes through insights on micro-scale melt hydrodynamics. This paper gives an overview of characteristic melt pool hydrodynamics and associated defects in laser micro-processing operations. The developed model has been validated using experiments obtained with 1.07 μm SPI fiber laser.