Study On The Surface Processing Technology Of Thin And Thin Walled SiC_f/SiC Composite Materials

SiC fiber-reinforced SiC ceramic matrix composites(SiCf/SiC composites)have many advantages,such as high hardness,high temperature resistance,good chemical stability,radiation resistance,small thermal neutron absorption cross section,etc.,and have broad application prospects in aerospace field.In the energy field,because of its economy,safety,high accident fault tolerance features such as widely followed,but SiCf/SiC composite materials,high hardness and brittleness,anisotropy,within a large number of blowhole defects,easy to produce in the process of machining burr,a variety of machining defects such as broken fiber fracture,matrix,at the same time it has large length,small diameter,wall thickness,in the process of machining hard to positioning,clamping,and prone to fracture phenomenon,tremor,therefore a second time processing difficulties seriously restrict the development of SiCf/SiC composites.In this paper,the external surface processing technology of SiCf/SiC composite thin-walled pipe fittings is studied,and the clamping method and processing technology of the workpiece are explored,as well as the removal mechanism,machining defects,surface roughness and tool wear law of the workpiece.The specific research contents are as follows:(1)According to the structural characteristics of thin and thin wall SiCf/SiC composite pipe fitting,the method of locating the inner hole at both ends was proposed,and one end was clamped and one end was floated axially to support it.Two kinds of diamond cutting tools are compared through experiments.The processing technology of high speed point grinding is put forward and the experimental platform is built.(2)Explore the mechanism of action of abrasive particles on fiber bundles in different directions,to explore the removal mechanism of materials,and to observe and analyze the machining damage and defects of materials,including pipe fitting fracture,crushing,burr,fiber brittle fracture,etc.;(3)Explore the influences of spindle speed,grinding depth,tool feed speed and abrasive diameter on the surface micro morphology and roughness value,and obtain the best range of process parameters.It is concluded that the abrasive wear is the main form of tool wear.Based on the experiment of tool wear,the law of tool wear and grinding distance is obtained,and it is found that the electroplated diamond grinding head with a particle size of 80 is most suitable for the grinding of the material,and the strategies to reduce the influence of tool wear on the workpiece diameter,reduce the number of tool changes and improve the machining efficiency are put forward.The processing of 300 mm long workpieces obtained good processing results...