Study On Laser-assisted Grinding Technology Of C/C-SiC Composites

With the development of high-end equipment,various new composite materials have been applied.Since the advent of C/C-SiC composite materials,they have been applied in high-end equipment manufacturing,aerospace,military and national defense fields as thermal structure materials,friction materials and space opto-mechanical materials due to their advantages of high temperature resistance,good wear resistance,low density and good stability.The hardness,brittleness and anisotropy of C/C-SiC composites cause problems such as excessive cutting force and many surface defects during machining,making it a typical difficult-to-machine material.Therefore,this paper studied on the application of laser-assisted machining technology on C/C-SiC composites,and discussed the influence of laser energy on C/C-SiC composites,and the relationship between machining parameters and machining results in the laserassisted grinding process.On this basis,studying on the material removal mechanism and process parameter optimization.The main work of the thesis includes:(1)Influence and mechanism of laser thermal effect on C/C-SiC composites.Taking the laser power and defocusing amount as the experimental variables,let the laser follow a specific scanning path to obtain the changelet law of the thermal damage groove and thermal damage layer under different laser parameters,and discussed the mechanism of material removal due to the thermal effect of the laser,provided theoretical basis to laser-assisted grinding.(2)Experimental study on laser-assisted grinding technology.The laser-assisted grinding process experiment of C/C-SiC composites was designed,and the application of this process to machining C/C-SiC composites was studied.After Selecting the appropriate laser parameters and scanning path to process the surface of the material,carried out multiple grinding experiments.Comparing the laser-assisted grinding process experimental group with the traditional process control group,the normal grinding force decreased by up to 35.6%,and the tangential grinding force was decreased by up to 43.6%.The laser-assisted grinding process can significantly reduced the grinding force.The specific grinding energy was significantly reduced,and the machined surface quality was improved to a certain extent.(3)Study on the removal mechanism of C/C-SiC composites.A single diamond abrasive grain scratch experiment was carried out on the non-thermally damaged area and the thermally damaged area of the C/C-SiC composite material to observe the micro-morphology of the incision end of the abrasive particle,and to observe the micro-morphology and cross-sectional profile inside the scratch.The high-width ratio was used to characterize the damage degree of a single abrasive particle to the surface of the material,and to observe the scratch characteristics of the material in the thermally damaged area.The grinding removal mechanism of C/C-SiC composites in the grinding experiment was discussed by combining the results of the scratch experiment with the results of the grinding experiment.(4)Prediction and optimization of laser-assisted grinding process parameters.Due to the introduction of laser ablation in the grinding process,the effect of process parameters on the grinding force and the grinding surface roughness cannot be fitted with the functional relationship of traditional grinding.Using the excellent nonlinear fitting ability of neural network,the GABP neural network was used to predict the process parameters of laser-assisted grinding.Based on the prediction model,combined with the NSGA-II algorithm,an optimization model of laser-assisted grinding process parameters was established,and the Pareto optimal solution set of the process optimization model was generated and analyzed.