Laser beam micro-machining under water immersion

Abstract

Underwater laser beam machining is considered as one of the alternative approaches to minimize the undesired impacts of dry laser beam machining (LBM) such as coarse machining kerf, high re-deposition of melt debris, and thermal damages. The underwater laser beam machining is equally suited for the fabrication of micro-features like 3D cavities, micro-holes, and micro-channels. In most of the literature studies, the water in dynamic mode (flowing with certain flow rate) is generally used to reduce the melt re-deposition and to improve the machining kerf and surface roughness. This study presents the use of water in static mode (still water with zero flow rate) rather dynamic mode, for the fabrication of micro-channels in nickel-based superalloy (Inconel 718). Instead of reducing the melt re-deposition, static water allowed to deposit more debris within the machining zone. This re-deposition is used to participate in micro-channel formation. After every initial passing scan, the re-deposited melt debris are piled up at the middle region of main channel that disturbs the beam focus at middle region. Due to focus disturbance, the piled up debris gets removed by partial melting of the central region and base metal remains unaffected due to partial heating. The main channel finally divided into two sub-channels. Geometrical characteristics (width, depth, and taper angle) were considered as the process responses in order to study the effects of laser power, pulse repetition rate, and laser scan speed. The results revealed that among other parameters, laser scan speed mainly influenced the geometrical characteristics of micro-channels.