Study on immersion waterjet assisted laser micromachining process

The heat affected zone (HAZ), recast layer, and taper angle are the issues remained to be addressed in laser micromachining. In immersion waterjet assisted laser micromachining (IWALM) the waterjet flushes the ablated materials, plasma, and micro bubbles away from the machining area at laser pulse interval. A higher machining resolution could be obtained by reducing the laser beam through focusing system. This paper studied the mechanisms of IWALM and the effects of microbubbles explosion on the workpiece surface roughness around the entrance of machining area. With the developed experimental setup, the influences of the laser power, waterjet flow speed, and workpiece-nozzle gap were studied on the machining efficiency, taper angle, while machining microhole with diameter 0.5 mm by scanning the laser beam within waterjet diameter. In particular experimental conditions, the machining efficiency of IWALM was larger than that of laser micromachining in the air, while the workpiece thickness was smaller than 0.5 mm. Microholes with reduced HAZ and free of recast layer were fabricated by IWALM. The taper angle of the microholes processed by IWALM was 376% smaller than that by Laser micromachining in the air. Furthermore, the mechanisms of the formation of micro-pits during IWALM around the machining area were discussed, considering the explosions of micro bubbles near the workpiece surface due to the pressure difference. Experimental results indicated that a higher waterjet flow speed and smaller nozzle-workpiece gap, laser power could improve the surface quality in close to the machining area.