Research On Cutting Method Of Thermal Cracking Ceramics With Low Microwave Absorptivity And Silicon Wafer Using Surface Heat Source

For its excellent mechanical,thermal,electrical and optical properties,ceramics play an irreplaceable role in high-tech industry and advanced manufacturing field.However,due to the material property of high hardness,high melting point and brittleness,it tends to result in the mechanical damage in surface and sub-surface of the workpiece material or the thermal damage in the cutting kerf.With the characteristics of no material removal,good section quality and small damage,thermal-cracking cutting method is gradually applied to cutting hard and brittle materials such as glass and ceramics.However,there are still some problems such as insufficient processing capacity,indeterminacy of crack propagation mechanism and lack research of trajectory control when using surface heat source to cut ceramic materials.Therefore,in this paper,we use microwave surface heat source to cut ceramic materials with low absorptivity for microwave and laser surface heat source to cut silicon wafer materials to do some theoretical and experimental research on crack propagation mechanism,crack trajectory revising and controlling,processing capacity and section quality in surface heat source cutting ceramic materials.In this paper,the surface heat source models for cutting silicon wafers and ceramics with low absorption for microwave were established respectively.The finite element models of surface heat source heating ceramic materials were established,and the accuracy of the finite element models were verified by heating ceramics experiments.The distribution characteristics of temperature field and stress field of the two materials under the action of surface heat source were simulated and analyzed.Based on the simulation results of temperature field and the analysis of its distribution characteristics,it is found that the depth of the highest temperature region has an important influence on the temperature gradient along the surface and the depth direction of material.Based on the simulation results of the stress field and the analysis of its distribution characteristics,it is found that the depth of the maximum compressive stress zone has an important influence on the gradient and depth of the tensile stress zone before and after the surface heat source.A thermal-cracking model of cutting ceramics was established based on the finite element model of heating ceramic material with single surface heat source.The simulation and experimental research on the thermal-cracking of ceramics with low absorption for microwave by using microwave surface heat source were carried out.It is found that the crack-propagation paths on the upper and lower surfaces of the workpiece is inconsistent under the action of single surface heat source.Combined with fracture mechanics theory,the deviation mechanism of crack propagation under single surface heat source was analyzed,and a microwave limited absorption method was proposed to revise the offset of crack-propagation path.The effectiveness of this method was verified by simulation and experimental research.The mechanism of microwave limited absorption method revising the offset of crack-propagation path is revealed.The influence of microwave limited absorption method on section quality was discussed.This research showed that the unstable propagation mode tends to appear in thermal-cracking of ceramics with single surface heat source.In order to solve the problems on crack propagation in single surface heat source cutting method,thermal-cracking method with dual surface heat source in microwave cutting ceramic material was proposed.Through the simulation of the temperature field of heating the ceramics by dual surface heat source,it is found that more than 90% of the scanning section forms a heating type similar to the volume heat source.Then,based on the stress field and crack propagation simulation,the crack initiation mechanism and propagation mode were explored.The stress distribution characteristics of crack front edge were analyzed,and the reason for high crack-propagation quality under the dual surface heat source was revealed.Through the cutting experiment,the advantages of dual surface heat source over single surface heat source were analyzed,and the influence of microwave power and cutting speed on the deviation propagation of cracks and the crosssection quality under the action of dual surface heat source were studied.The experimental results showed that microwave cutting of 8 mm thick alumina ceramics with high-quality can be achieved by dual surface heat source.The processing capacity of the surface heat source is greatly improved by using dual surface heat source.The research on controlling the crack-propagation path and the optimization for the quality of cross section in cutting silicon wafer with laser surface heat source are carried out.It is found that the crack-propagation tends to deviate from the ideal path in asymmetric cutting mode when the pre-crack is on the end of workpiece.Based on the cutting simulation,the deviation mechanism for crack-propagation under the condition of asymmetric cutting was revealed.The simulation and experimental research on thermalcracking method with pre-crack on the surface of workpiece were carried out to solve the problem of trajectory deviation in the method of pre-crack on the end of workpiece.The method of surface heat source is on the reverse side of surface pre-crack was proposed.It is found that the method can change the crack propagation mode under the conventional method and obtain the effect of non-offset propagation.The mechanism of non-offset crack propagation was revealed.The experiment research on asymmetric cutting silicon wafer based on the method of heating the reverse side of surface pre-crack were carried out.The effect of laser power,depth and width of the pre-crack groove,and laser scanning speed on the kerf quality of silicon wafer were studied.The technological strategy to obtain high quality of cutting kerf was put forward.