Study On Material Removal Mechanism And Process For Micromachining Silicon Nitride Ceramic By Laser Assisted Waterjet

Laser assisted waterjet(LAWJ)micromachining technology combines the advantages of laser and waterjet technologies,such as no machining force,no pollution,negligible thermal effect and wide processing field.In order to investigate the processing performance and broaden the application of laser assisted waterjet micromachining silicon nitride ceramic,the material removal mechanism and process of laser assisted waterjet micromachining silicon nitride ceramic were studied in this thesis.The experiments were conducted to research the effects of processing parameters on grooving performance.It is revealed that the influence of material original surface topography on the-groove surface and material removal mechanism.The prediction models of groove depth and surface roughness of laser assisted waterjet micro-milling were established.The prediction model of micro size of laser assisted waterjet micro-milling silicon nitride ceramic was developed based on back-propagation artificial neural network(BP-ANN).The machining performance of silicon nitride ceramic processed by laser ablation,water assisted laser and laser assisted waterjet was compared.And the effects of processing parameters on groove width,depth,surface roughness and heat affected zone(HAZ)were discussed.It is shown that the laser assisted waterjet micromachining technology could achieve a groove with a higher aspect ratio and a lighter thermal damage than the other two processing ways.Besides,the waterjet pressure had the most significant effect on the groove width and HAZ width.The laser pulse energy had the most significant effect on the groove depth.The waterjet impact angle had the most significant effect on surface roughness.The influence of material original surface topography on groove surface formation was studied.It is indicated that the pyrolyzing zone,oxidative damage zone and softening deformation zone was figured out and the processing texture on the material original surface wouldn't improve the processed surface quality.The HAZ width on the original smooth surface was smaller than that on the original rough surface.The removal mechanism was analyzed in laser assisted waterjet micromachining silicon nitride ceramic.It can be concluded that the main material removal mechanisms of silicon nitride ceramic processed by laser assisted waterjet is the heated and softened materials and the pyrolyzed materials in the core area of laser irradiation,both removed by the waterjet.The prediction model of groove depth and surface roughness was established,and the prediction result is in good agreement with the experimental result.The effect of the interactive effect among the processing parameters on the groove depth and surface roughness was studied.It is indicated that the cross-feed has little effect on the groove depth but great effect on the surface roughness Ra.Laser pulse energy has the most significant positive effect on the groove depth.Differently,as for Ra,waterjet pressure was the most important parameter in decreasing the surface roughness.The interactions between laser pulse energy and waterjet pressure have a significant effect on the groove depth and surface roughness.It is proved that it is feasible to mill micro size and micro arrays of silicon nitride ceramic by laser assisted waterjet processing experiments.The boundary of the micro groove is straight without any edge breakage and thermal damage.The micro arrays of grooves are equally distributed and the adjacent grooves do not interfere with each other.The prediction model of micro size was established based on BP-ANN and verified by experiments.It is shown that there was a better agreement between the prediction result from the model and the experiments with an average error less than 10%.