Effect of plasma confinement on laser shock microforming of thin metal sheets

Laser shock forming is conceived as a non-thermal laser forming method of thin metal sheets using the shock wave induced by laser irradiation to modify the target curvature. The plastic deformation induced by the shock wave and the direct plasma pressure applied on the material generate a residual stress distribution in the material finally leading to its bending. Using water as a confinement medium for the plasma the pressure can be increased around 10 times and the final deformation has a dramatic increase. The effect can be made clearly apparent in thin specimens (up to 1 mm). In the present study thin (100 μm) stainless steel (AISI 316) strips (1 mm long and 300 μm wide) in single and double pinned configurations have been investigated. A Nd:YAG Laser (1064 nm) with 10 ns of pulse length (FWHM) and an energy of 21 mJ per pulse is focused in the strip (spot diameter of the spot = 500 μm). Experimental and numerical studies of the influence of plasma confinement in the process and number of applied pulses are presented. The study shows that the final bending of the specimens can be controlled on a relative wide range by a stable quasi-proportional relation to the number of applied pulses and, what is considered as of major importance, that plasma confinement increases the generated pressure and thus the bending in the target. Laser shock microforming in confined configuration is considered as a technique allowing the successful processing of components in a medium range of miniaturization.