Study On Process And Material Removal Mechanism For Micromachining 4H-SiC By Laser Assisted Waterjet

In order to take advantage of the theory of lase assisted waterjet(LAWJ)on machining hard and brittle materials,the process and material removal mechanism of laser-assisted waterjet micromachining for single crystal silicon carbide was studied in this thesis.The experiments were conducted to research the effect of processing parameters on the grooving geometry and the depth-width ratio as well as surface roughness.The prediction models of surface roughness and the depth-width ratio were established.And finite element simulation on the temperature field was carried out.The machining performance and the quality of single crystal silicon carbide processed by laser ablation,low pressure waterjet-assisted laser and laser-assisted waterjet was compared each other.And the effects of processing parameters on the groove depth,width,surface roughness and heat affected zone(HAZ)were discussed.It was shown that the laser-assisted waterjet micromachining technology could achieve a groove with almost non-thermal-damage on single crystal silicon carbide.Laser pulse energy was the most significant to the surface roughness of microgrooves.Machining speed was the most significant factor on the width of HAZ.Laser pulse energy,waterjet pressure,feed rate and machining times have the most significant effect on the depth of microgrooves,but feed rate and machining times have no significant effect on the width of microgrooves.And then,a microgroove was achieved with a depth-width ratio of 3:1 and its surface roughness was little.The prediction model of surface roughness and the depth-width ratio in laser assisted waterjet micromachining of single crystal silicon carbide was established as well.The accuracy of prediction model was verified by variance analysis,and it was found that the result of prediction model was consistent with the actual experimental result.A finite element simulation on temperature of laser assisted waterjet micromachining for single crystal silicon carbide was conducted using finite element software.It could be drawn that the temperature could reach to 2900K in the core machining area and the cooling effect of waterjet is obvious.The material removal mechanism of laser assisted waterjet micromachining for single crystal silicon carbide was studied.The material removal ability of waterjet increased with a proper increase in the scanning velocity of waterjet,but the increasing ratio of waterjet cause the increase of laser energy dissipation as well.The material removal mechanism of laser assisted waterjet micromachining for single crystal silicon carbide is that the single crystal silicon carbide would vaporize and pyrolysis when the temperature reached to 2900K,and that material which did not reach the decomposition temperature had a brittle-plastic transition at a high temperature and was eroded by waterjet.