Width reduction of laser microdrillings by subsequent mechanically induced plastic deformation

This work reports a novel process combination, which is capable of forming large hole matrices (100 pores/mm2) in thin stainless steel foils (10 μm<dfoil<300 μm) maintaining high processing rates and pore widths smaller than 5 μm. This technique perforates stainless steel foils with high-speed ‘on-the-fly’ laser perforation (60000 drillings/min) followed by a cold-roll forming of the laser-treated foil. The cold-roll forming leads to a pore-size reduction (in one dimension) perpendicular to the rolling direction. For the laser processing a diode-pumped, q-switched and frequency-tripled Nd:YAG laser (λ=355 nm, τ=30 ns), and a flashlamp-pumped Nd:YAG laser (λ=1064 nm, τ=57 μs) were applied. Using this process combination, minimum pore sizes of 3.5 μm have been achieved. At present, the processing efficiency of cold-rolled percussion drillings inserted with nanosecond pulse durations is lower in comparison with single-pulse ‘on-the-fly’ perforation, but in terms of quality (straight pore channel, low standard deviation of pore widths and pore widths smaller than 5 μm) well suited for various fields in filtration (e.g. particle removal) .