Spatter reduction in nanosecond fiber laser drilling by means of an innovative nozzle

Pulsed wave fibre lasers are becoming a popular industrial tool in microprocessing due to their many positive features, such as high beam quality, high reliability and high productivity, which are fundamental to machining small, precise features of industrial applications. However, the lasers' use in the machining of ultraprecise features, such as small holes, is hindered by the fact that commercial pulsed wave fibre lasers commonly operate with pulse durations in the nanosecond regime. Such long pulse durations mean that the material is thermally removed, which results in the production of a melted layer and thermal damage in the bulk material. Consequently, the typical thermal defects of the melting regime, such as spattering of recast material around the hole, taper, heat-affected zone and poor hole circularity, are found in materials machined with these lasers. This paper proposes a design for an innovative nozzle that combines the high productivity of nanosecond fibre lasers with an improvement in the quality of the machined holes by reducing the spatter production in titanium laser percussion drilling. The innovative nozzle is based on the suction effect created by the Venturi principle that prevents the deposition of melted and vaporised material on the workpiece surface. The influence of the nozzle configuration and shielding gas on hole quality is investigated after the laser percussion drilling of 0.5-mm-thick titanium sheets, in which the process conditions that allow maximum productivity are used. The innovative nozzle produces a remarkable decrease in spatter on the entrance hole surface without affecting the other quality features, such as hole diameter, circularity and taper, while preserving the high productivity obtainable with a standard nozzle.