Subsurface Damage Mechanism In Ultrasonic Vibration Assisted Grinding Of K9 Optical Glass

Optical glass is widely used in aerospace,microelectronics and other fields because of its good optical properties,but its brittle and rigid material characteristics make it easy to form surface and subsurface defects in the process of precision grinding of optical glass elements.It affects the machining quality and efficiency,and the subsurface damage also has a significant impact on the follow-up polishing workload.Ultrasonic vibration assisted grinding is a rapidly developing composite machining technology.Compared with conventional grinding,it has some technical advantages in surface roughness,subsurface damage and removal rate of brittle-hard materials.However,the mechanism of ultrasonic vibration assisted grinding of optical glass has not been fully grasped.In order to further understand the mechanism of ultrasonic vibration assisted grinding of optical glass,especially the subsurface damage of the subsequent polishing process,the subsurface damage mechanism in ultrasonic vibration assisted grinding of K9 optical glass was studied in this paper.The main elements include:Firstly,based on the indentation deformation region,the equivalent characteristic radius calculation methods are proposed to evaluate the equivalent fracture toughness.The prediction model of subsurface damage depth in ultrasonic vibration assisted grinding of optical glass and the depth model of Vickers indentation crack in ultrasonic vibration are derived,which provide theoretical guidance for further experimental research.Secondly,the ultrasonic vibration indentation experiment by using single random-shape diamond grits of K9 optical glass was carried out,and a new variable equivalent mean contact pressure was proposed.The equivalent feature radius was used to calculate the equivalent mean contact pressure of the indentation deformation region under ultrasonic vibration and non-ultrasonic vibration conditions.Comparison and Analysis of the variation trend of the equivalent mean contact pressure and the mean contact pressure in the indentation deformation region of K9 optical glass under two kinds of loading conditions.The results show that the mean contact pressure is close to the equivalent mean contact pressure without ultrasonic vibration.In addition,ultrasonic vibration reduces the equivalent mean contact pressure and the equivalent mean contact pressure under the removal of unit volume material.Then,the Vickersindentation experiment of optical glass under the condition of ultrasonic vibration is carried out to modify the middle crack model of the traditional indentation system,so as to obtain a more accurate model of the depth of the Vickers indentation crack under ultrasonic vibration condition.Finally,the ultrasonic vibration assisted grinding experiments are carried out to analyze the subsurface damage depth of different grinding feed depths,and the accuracy of the prediction model of ultrasonic vibration assisted grinding subsurface damage depth is verified.The relationship between the equivalent mean contact pressure and the Vickers indentation depth model of ultrasonic vibration and the subsurface damage depth of ultrasonic vibration assisted grinding are analyzed,and the mechanism of subsurface damage in ultrasonic vibration grinding is further revealed.It is of positive significance to promote the development of ultrasonic vibration assisted grinding technology.