Study On Surface Quality Of Ultrasonic Vibration Grinding Of SiC Ceramics

The reflectors made of SiC ceramics are used in various optical systems.However,there are some problems in the process of grinding silicon carbide ceramics,such as large grinding force,high surface roughness,difficult to improve grinding efficiency and surface quality.In particular,when using small diameter grinding silicon carbide optical surface and inner hole,the quality problem of the material surface is more serious.Ultrasonic vibration grinding(UVG)combines conventional grinding(CG)with ultrasonic processing,which is a composite grinding technology suitable for hard and brittle material processing.It can effectively reduce the grinding force,improve the material removal rate,reduce the surface roughness,and improve the quality of the grinding surface.In view of the existing problems in the grinding of SiC ceramics,the surface quality in UVG of SiC ceramics was studied in this paper.The main work contents and conclusions are as follows:(1)Based on the analysis of the grinding process of the small-diameter grinding wheel,it was found that when the linear velocity of the small-diameter grinding wheel and the contact length between the abrasive particles and the workpiece was smaller,the maximum grinding thickness of a single abrasive particle would be larger;when the number of effective abrasive particles was smaller,the overlapping degree of abrasive scratches would be reduced and the volume of residual materials would be larger;when the extension rod of the grinding wheel was longer,the rigidity of the system would be poor and the grinding process would be larger.It was proposed that the above phenomenon will make it difficult to improve the grinding efficiency and quality.The kinematic analysis of ultrasonic vibration grinding was carried out,and the surface creation mechanism of ultrasonic vibration grinding was studied.It was found that ultrasonic vibration grinding is very suitable for the grinding of small diameter grinding wheel.(2)A comparative test of UVG and CG of SiC with small diameter grinding wheels was carried out.The effect of the main process parameters on the quality of the ground surface was analyzed.The results showed that compared with CG,the trajectories of the abrasive grains in UVG overlapped with each other,the surface morphology of the workpiece was more uniform,and the surface quality was higher;and UVG reduced the grinding force and suppressed the low frequency vibration of the system,improved the rigidity of the system,made the grinding process more stable,and improved the surface quality.The grinding force of UVG decreased with the increase of grinding wheel linear speed and ultrasonic amplitude,and decreased with the feed speed and grinding depth of the workpiece.The variation of surface roughness with grinding parameters and ultrasonic amplitude was the same as that of grinding force.In the range of grinding wheel linear velocity v_s=1.88~15.07m/s,workpiece feed velocity v_w=375~3000mm/min,grinding depth a_p=0.005~0.035mm,ultrasonic amplitude A=0.5~4.6?m,ultrasonic vibration grinding can reduce surface roughness perpendicular to the grinding direction by 2.0%~33.8%,normal grinding force by 1.9%~30.8%,and tangent grinding force by 1.6%~22.1%.When the grinding wheel linear speed v_s=15.07m/s,the workpiece feed speed v_w=1000mm/min,the grinding depth a_p=0.01mm,and the ultrasonic amplitude A=4.6?m,the lowest surface roughness R_a=0.25?m can be obtained by UVG.The variation of surface roughness with grinding parameters and ultrasonic amplitude was the same as the grinding force.The effect of UVG was more obvious when the grinding wheel linear speed and workpiece feeding speed were lower.(3)UVG of SiC ceramics can achieve lower grinding force and surface roughness and higher surface quality without improving the linear speed of the grinding wheel;under the same grinding force and surface roughness,UVG can select higher workpiece feed speed and grinding depth,so as to improve grinding efficiency.Therefore,UVG can effectively solve the problems existing in grinding of SiC ceramics with small diameter grinding wheel.