| Glass-ceramic,as an optical hard and brittle material,has higher hardness and strength than ordinary glass due to its unique atomic structure.In addition,it has lower thermal conductivity and coefficient of thermal expansion,good optical properties,and wide application value in fields such as imaging,electronics,aerospace,and chemistry.At present,the commonly used machining techniques for glass-ceramic include grinding,polishing,grinding wheel grinding,turning,etc.However,conventional mechanical machining requires high costs,long machining cycles,single machining shapes,and poor material removal effects,which seriously limit the expansion and application of glass-ceramic.Therefore,it is urgent to develop a reliable,efficient,and low-cost glass-ceramic machining technology.Laser-assisted machining(LAM)is the most widely used thermal assisted machining technology for hard and brittle materials.Compared with other assisted machining technologies,LAM has advantages such as low cost,high efficiency,and good surface finish.LAM has conducted scientific experiments and academic research on materials such as monocrystalline silicon,hardened glass,engineering ceramics,and carbides,while LAM work on glass-ceramic urgently needs to be developed and validated.This dissertation is the first to conduct research on laser-assisted fast tool servo(LAFTS)and in-situ laser-assisted machining(In-situ LAM)for glass-ceramic,exploring the cutting mechanism of glass-ceramic LAM.The aim is to achieve efficient,reliable,and high-quality laser-assisted machining of glass-ceramic material.The specific work of this dissertation is as follows:(1)Numerical simulation of temperature field in laser-assisted machining of glassceramic is carried out.Based on the interaction mechanism between laser and glass-ceramic,the thermal physical parameters of glass-ceramic are obtained through experimental measurements.A three-dimensional transient heat transfer model of glass-ceramic is established using COMSOL Multiphysics numerical simulation,revealing the temperature field distribution law of glass-ceramic under static and dynamic rotation.The thermal stress and deformation generated by laser irradiation on glass-ceramic demonstrate that laser action can promote the brittle plastic transition of glass-ceramic.Based on the numerical simulation of the temperature field of the actual workpiece model,the prediction and optimization of the laser focusing diameter in actual machining have been achieved.(2)Research on the performance of LAFTS device for glass-ceramic is carried out.A LAFTS device is designed and developed for cutting optical free-form surfaces of glassceramic.The stiffness and amplification ratio of the flexible hinge mechanism in the device are calculated and analyzed using the flexibility matrix and elastic beam method.The displacement output characteristics of the flexible hinge mechanism and the overall device are verified using finite element numerical simulation and displacement measurement experiments,respectively.The device serves as a carrier to conduct static and dynamic temperature measurement experiments on laser-assisted diamond cutting of glass-ceramic in situ,providing reference for the parameter selection of actual laser-assisted machining experiments.Finally,laser-assisted fasst tool servo machining experiments are conducted using the device to verify its feasibility for laser-assisted fast tool servo machining of optical free-form surfaces.(3)A study on surface roughness and tool wear in glass-ceramic LAFTS is carried out.Based on the Taguchi method(TM),orthogonal experiments are conducted on glass-ceramic LAFTS,and the results shows that LAFTS can significantly improve the surface machining quality compared to pure FTS cutting.Based on response surface methodology(RSM),response surface experiments for glass-ceramic LAFTS are designed,a quadratic regression model for surface roughness prediction is established,and the optimal combination of machining parameters that minimize surface roughness on a global scale is obtained.TM is used to conduct orthogonal experiments on LAFTS tool wear,the optimal combination of machining parameters based on TM to minimize tool wear is obtained.At the same time,artificial neural network(ANN)is used to train the machining parameters and experimental results in the orthogonal experiments,and the training results are input into genetic algorithm(GA)to calculate and predict the optimal combination of machining parameters based on ANN to minimize tool wear.Finally,multiple sets of LAFTS experiments are conducted to compare the advantages of TM and ANN in predicting and optimizing the optimal cutting conditions for tool wear.(4)Experimental study of in-situ LAM of glass-ceramic is carried out.Based on the insitu LAM device developed by the research group,orthogonal experiments are conducted on the in-situ LAM of glass-ceramic.By measuring the cutting force and sub surface morphology of the workpiece after machining,it was proved that in-situ LAM can significantly reduce cutting force compared to conventional cutting,effectively reduce material sub surface damage,and improve surface integrity.Based on RSM response surface experiments and ANN training fitting,the optimal combination of machining parameters for minimizing cutting force on a global scale is obtained.The reliability of RSM and ANN in predicting and optimizing the optimal cutting conditions for cutting force is verified through multiple sets of in-situ LAM experiments.On the basis of orthogonal experiments,the surface roughness of the workpiece and the microstructure of the chips are observed,further verifying that in-situ LAM can effectively promote the brittle plastic transition of glass-ceramic materials compared to conventional cutting,and improve the surface machining quality.Pareto genetic algorithm is used for multi-objective optimization analysis of cutting force and surface roughness,obtaining the optimal machining parameters that minimize both cutting force and surface roughness,and verifying the ideal effect of multi-objective optimization through practical experiments.LAM experiments are conducted at different laser heating positions and different tool rake angles,and the results shows that in-situ LAM is more suitable for high-precision and high-quality cutting of glass-ceramic end face,and high negative rake angle tools are more conducive to improving the machinability and cutting quality of glass-ceramic.This dissertation is the first to conduct research on LAFTS and in-situ LAM for glassceramic.LAM can effectively promote the brittle to plastic transition of glass-ceramic material and improve the cutting performance of glass-ceramic.The research content of this dissertation provides a certain research foundation for the cutting mechanism and parameter optimization of LAFTS and in-situ LAM of optical hard and brittle materials. |
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