Investigation On Mechanism Analysis For Underwater Laser Hole-trepanning In SiC Ceramic Sheets

Silicon carbide(SiC)ceramics,as non-oxide structural ceramics,have been widely used in aerospace,chemical,electronic and other industrial fields because of their excellent hardness,chemical stability,corrosion resistance and heat resistance.However,due to the inherent hard and brittle characteristics of SiC ceramics,the traditional mechanical drilling method is time-consuming and laborious,so it is difficult to meet the processing of microholes.Compared with the traditional mechanical drilling method,laser drilling method is an effective ceramic drilling method.However,there are some defects in laser drilling,such as large taper,recasting layer thickness,poor roundness and microcracks,which affect the quality of the processing hole.In this paper,SiC ceramics were cut by pulsed laser in water,and the quality and morphology of microholes were improved by underwater laser drilling.Firstly,the characteristics of laser beam,the physical process of laser drilling and the mechanism of underwater laser drilling are introduced,and the principle of underwater pulsed laser drilling is described in detail.The construction of underwater femtosecond / millisecond pulse laser hole cutting experimental platform is briefly introduced,and the experimental equipment and measuring equipment as well as the processing methods of materials in the whole experimental process are introduced.Through the simplification and assumption of the two-dimensional model,the finite element model of two-dimensional millisecond pulsed laser ring cutting and drilling is established.The change of the entrance and exit diameter of the hole under different repetition frequency is simulated and analyzed,and the simulation results are compared with the experimental results,which provides a basis for the follow-up underwater pulsed laser cutting experiment.Then,the SiC ceramics were immersed in water to carry out the experimental study of millisecond pulse laser ring cutting and drilling,and the effects of water and different process parameters on the morphology and quality of micropores were studied.The results show that the aqueous medium improves the orifice morphology,increases the outlet diameter of the hole,reduces the taper of the hole,increases the amount of material removed by laser,reduces the redeposition materials and attachments on the inner wall of the hole,and reduces the microcracks on the inner wall of the hole.Inhibit the oxidation of the hole wall.Finally,the SiC ceramic was immersed in water and the experimental study of femtosecond pulse laser cutting hole layer by layer was carried out.By changing the repetition rate of laser pulse,the effects of water medium and laser pulse repetition frequency on the quality and characteristics of laser drilling were studied.The results show that after using water medium,the outlet diameter of the hole is increased,the taper of the hole is reduced,and the amount of material removed by laser is increased.The redeposited material residues near and around the hole entrance are significantly reduced,which reduces the roughness of the hole wall and restrains the oxidation of the hole wall.The recasting layer and cracks of the hole wall are reduced.Water inhibits the formation,duration and upward diffusion of laser-induced plasma,especially underwater plasma.It effectively reduces the energy loss caused by plasma,makes more laser energy ablation the bottom of the material,and enhances the laser removal of the material.