On the dual-pulse-width laser assisted waterjet micromachining process for monocrystalline silicon carbides

A novel machining technology using a waterjet that is collaboratively assisted by two lasers of different pulse widths is proposed for hard and brittle materials, whereby a femtosecond (fs) laser is used to work with a waterjet on texturing the material surface for improved optical properties and thermodynamic behaviour, while a higher power nanosecond (ns) laser is used interactively with the fs laser to assist the waterjet in the material removal process on the textured surface, so as to increase material removal rate ( MRR ) without process induced damages to the workpiece. Using 4H-SiC wafers as the specimens, the collaborative actions of the two lasers and their effect on material removal are investigated. It is found that competitive MRR without process-induced cracks or subsurface damages to thin, hard and brittle workpieces can be achieved due to the surface textures formed by the fs laser-assisted machining phase. The effect of process parameters on the machined kerf and surface characteristics is amply discussed to reveal the material removal mechanisms. It is shown that the pulse overlap of the ns laser plays a vital role in the collaborative action of the two lasers in assisting with the waterjet material removal process, where an increase in ns laser pulse energy, pulse overlap or action time per cycle markedly increases the machining performance, while an increase in fs laser pulse energy or pulse overlap improves reduces the machined surface roughness and hance improve the machined surface quality. The increase of machining performance is attributed to the increase of the optical absorbance of the material as well as the improvement to its thermodynamic behaviour and stress response at elevated temperatures.