Research On The Crack Trajectory Control Method Of The Al₂O₃ Ceramics Materials Crack Growth Inducted By Microwave

As one of the most widely used advanced ceramic materials,Al₂O₃ ceramics have played an indispensable role in the national defense,aerospace,machinery,microelectronics engineering.However,due to its high brittleness and hardness,cutting Al₂O₃ ceramics with high efficiency and quality has always been an intractable problem.The hot cracking cutting method with laser as the heat source has been widely employed in cutting hard,brittle glass,and some other materials.In recent years,the hot cracking method with microwave as the heat source has been proposed to break through the limitation that laser hot cracking cannot cut non-transparent materials.Whereas,the crack trajectory of hot crack cutting exists the phenomena of deviation.The research on crack trajectory control is the only way for the development of microwave hot crack method.In this paper,the physical process of microwave thermal crack cutting was analyzed theoretically and the heat source equation of microwave heating was established at the same time.On this basis,the finite element simulation model of microwave heating ceramics and thermal stress driven crack growth process were established by ABAQUS software.The reliability of the model was verified by experiments correspondingly.The influence of key parameters of graphite coating and pre-crack parameters on hot cutting of Al2O3 ceramics by surface heat source was studied.The effects of the thickness and width of the graphite coating on the processing ability of hot crack cutting and the crack trajectory deviation were summarized by conducting process tests and observing the machining results under an over depth microscope.The control mechanism of the graphite width on the crack trajectory was also explained by simulating the temperature field and stress field exactly.The effects of prefabricated cracks with different widths on the initial crack migration were also investigated by means of ultrafine wire saw and ultraviolet laser correspondingly.The ability to control crack migration by two sides heat source,surface prefabrication path and local cooling was also investigated.By simulating the distribution of stress field and the process of crack propagation,the reasons for the control of crack migration by the double-sided heat source method and the surface prefabrication path method were explained.The superior processing ability of the double-sided heat source method was also verified by the experiments of thick ceramic slice cutting and multi-layer ceramic slice cutting in the meantime.A local jet cooling device was innovatively set up to perform the hot crack cutting experiments by cooling method.The crack trajectory control effects of the aforementioned three methods were evaluated by measuring the trajectory offset and surface roughness,etc.Finally,the curve track of microwave cracking method was also carried out,which indicated that the curves of crack extension process in three crack deviation phenomena,in turn affecting the quality of processing.From the simulation results of the mechanism of the interpretation of these phenomena by the finite element method,corresponding the technological experiments of microwave power,heat source movement speed,and width of graphite coating for trajectory deviation curve are also further studied.