Precision Truing Of Arc-shaped Diamond Grinding Wheel And Grinding Of Aspheric Optics

Hard brittle materials such as optical glass and silicon carbide have been widely used as aspheric lens and other optical devices due to their high hardness,good chemical stability and low thermal expansion coefficient.Advanced optical systems have brought forward higher requirements for aspheric processing of hard brittle materials.Especially,high form accuracy and high surface quality are required.The arc-shaped diamond grinding wheel is often used in aspheric grinding.The arc profile accuracy of which directly affects the accuracy of aspheric grinding.Therefore,precision truing of the arc-shaped diamond wheel is very important for precision aspheric grinding.In this paper,a new truing method with high efficiency and accuracy and error compensation method for the arc-shaped diamond wheel was proposed.And the precision grinding of ellipsoidal surface of BK7 optical glass was realized by using grinding error compensation method and CeO2 slurry assisted grinding method.Firstly,a helical interpolation precision truing method was proposed for the resin bonded arc-shaped diamond grinding wheel.The geometric relationship model between the diamond wheel and truing wheel was established.The precision truing of the diamond wheel with arbitrary arc radius could be achieved by changing dressing parameters.The tool setting error of z axis and y axis,and the measurement error of the truing wheel radius in truing process were analyzed.The mathematical prediction models of truing errors were established.Based on the prediction models,an error compensation scheme of the helical interpolation truing method was proposed.The error values could be calculated by fitting the wheel profile error curve after truing.Then,these three kinds of errors would be compensated one by one.The profile error(peak-valley value)of wheel arc profile after truing with error compensation could be reduced to 5?m from 19 ?m,and it was well distributed.Meanwhile,dressing of the diamond wheel was also achieved by this truing method.After aspheric grinding by the well-trued diamond grinding wheel,form error(PV)of the fused silica in YZ section was reduced to 5 ?m from 15?m.The form accuracy of aspheric surface increased 66%by precision truing of diamond grinding wheelAccording to the characteristics of the grinding method used in this paper,the grinding error sources of ellipsoid BK7 glass were analyzed in YZ and XY projection planes respectively.It was found that the main errors in XY section affecting the grinding accuracy were the measurement error of the diamond wheel radius and the wear error of wheel radius.The mathematical prediction model of the measurement error of the diamond wheel radius was established and verified.And the relationship between the wear of the diamond wheel radius and the accumulated grinding depth was obtained through grinding experiments.Based on these error analysis,a grinding error compensation scheme was proposed to compensate the above two errors one by one.The form error(PV)of glass in XY section was reduced to 2?m from 4 ?m.So the rinding accuracy was effectively improved.In order to improve the surface quality of the aspheric surface after precision grinding,a CeO2 slurry assisted grinding method was presented in this paper.The effects of particle size and mass fraction of CeO2 on grinding force,surface quality and wheel wear were studied by grinding experiments of BK7 glass.The experimental results show that the CeO2 slurry assisted grinding method could effectively reduce the surface roughness and crack damage.Better surface quality could be obtained by this method.At the same time,the CeO2 slurry could reduce the wear of the diamond grinding wheel.The roughness of the ellipsoidal BK7 glass after grinding assisted with the CeO2 slurry could reach 10 nm.