This work investigates the transport phenomena and the mechanisms of droplet formation during a laser-based, thin film micro-machining process. The surface of the target material is altered through laser-induced material flow in the molten phase induced by a tightly-focused laser energy flux. Experimental and numerical investigations of the laser-induced fluid flow and topography variations are carried out for a better understanding of the physical phenomena involved in the processes.
As with many machining techniques, debris is often generated during the laser machining process. Experimental parametric studies are carried out to correlate the laser parameters with the topography and droplet formations. It is found that a narrow range of operation parameters and target conditions exist for ‘clean’ structures to be fabricated.
The stop action photography technique is employed to capture the surface topography variation and the melting development with a nanosecond time resolution and a micrometer spatial resolution. Numerical simulations of the laser-induced surface deformation are also performed to obtain the transient field variables and to track the deforming surface. The comparison between the numerical and experimental work shows that, within the energy intensity range investigated in this work, the surface deformation is attributed to the surface-tension-driven-flow, and the recoil pressure effect plays an insignificant role in surface topography variation. Instability of the fluid flow in the laser-induced molten pool is shown to be a possible cause of debris formation.