Enhancing the machining performance in ns laser-waterjet hybrid micromachining of GaN by fs laser pre-texturing

Laser-waterjet hybrid machining technology shows great potential for the high-quality, efficient micromachining of semiconductor materials, but the machining of monocrystalline gallium nitride (GaN) has encountered low cutting efficiency and low quality with cracks due to its high transparency. Therefore, a novel micromachining technology is proposed in which a dry femtosecond (fs) laser is used to pre-texture the material surface for improved machinability by lasers, followed by nanosecond (ns) laser-waterjet hybrid machining on the textured surface. It is found that competitive material removal rate ( MRR ) with undetectable microcracks and subsurface damage can be achieved under selected conditions due to the surface textures formed by the fs laser. The effect of process parameters on the machined kerf and surface characteristics is amply discussed, and the optical and physical properties of the textured surface are experimentally studied to reveal the underlying mechanisms for the improvement in machining performance. It is shown that the increase of machining performance is attributed to the improved optical properties, deformability and crack resistance of the textured material at elevated temperatures. Based on the characteristics of the machining process found from the experimental work, predictive mathematical models for the major machining performance indicators are established and experimentally verified.