Mechanism And Experimental Study Of Ultrasonic Vibration Assisted Polishing BK7 Optical Glass

At present,optical glass has been widely used and researched in aerospace,electronics,military and other fields due to its good performance,which has led to increasing demand for optical glass,and higher requirement for the surface quality of workpieces.Due to the high hardness and poor toughness of the optical glass,the optical glass is fragile and easily broken,making it difficult to achieve high efficiency and high quality processing.Ultrasonic vibration-assisted polishing technology is an emerging technology that uses high-frequency ultrasonic vibration to drive the abrasive particles in the polishing suspension to collide with the surface of the workpiece to achieve material removal and is suitable for polishing relatively complex surfaces.In this paper,BK7 optical glass is taken as the research object,and the material removal process in ultrasonic vibration assisted polishing process is deeply studied.The influence of polishing parameters on material removal rate and surface roughness Ra is verified by experiments.The specific content of the study is as follows:(1)Based on the ultrasonic theory,the impact velocity model of a single abrasive grain is established,and the threshold kinetic energy when the material is cracked is used to distinguish the material removal method caused by the abrasive impact.According to the plastic erosion theory,the mathematical model of the material removal volume in the ductility removal mode is established.Based on the indentation fracture theory,a mathematical model for the length and depth of cracks in brittle removal of materials is established.Analyze the effect of polishing parameters on the material removal volume and surface roughness Ra in the two removal modes.(2)The SPH-coupled FEM method was used to simulate the removal process of the material under the action of a single abrasive particle.The effect of two removal methods on the polishing result was obtained.On the basis of a single abrasive grain,the simulation of the wall surface polishing effect of multiple abrasive grains is carried out,and the surface quality of the workpiece after the workpiece material is removed is analyzed.On the basis of multiple abrasive grain simulations,the ultrasonic polishing process under the action of abrasive particles was simulated,and the surface quality of the polished workpiece was judged by observing the joint displacement of the workpiece surface.(3)Analyze the motion law of hollowed-out bubbles in ultrasonic vibration-assisted polishing process by ultrasonic cavitation theory,explore the influence of polishing parameters on cavitation effect,and establish the impact model of micro-jet.The process of cavitation bubble near the wall colliding with the surface of the workpiece is simulated.The effect of cavitation microjet at different speeds on material removal is explored to prevent the microjet velocity from causing damage to the workpiece material and promote the abrasive particles.The purpose of removing the material on the surface of the workpiece and reducing the residual stress on the surface of the workpiece.(4)Set up an ultrasonic vibration-assisted polishing test bench,and experiment according to the range of polishing parameters obtained from the simulation results,analyze the influence of various factors on the polishing effect,draw the concentration of the polishing liquid,the ultrasonic amplitude,the distance from the polishing tool head to the workpiece surface,and polish The time-to-line relationship between the material removal rate and the surface roughness Ra gives the optimal value of each parameter and the surface topography under the optimal value.The variance analysis is used to prove the significance of each parameter on the experimental results,and the surface topography of the workpiece under the optimal combination of parameters is obtained.