Research On Ultrasonic Vibration Precision Grinding Process Of Low-expanding Glass Aspheric Surface

With the development of science and technology,people have higher and higher requirements for materials in the field of optics.Low expansion glass is a kind of material with very low expansion coefficient.Because of its hardness,good mechanical strength,wear resistance,electrical insulation,chemical stability,and the unique advantages of correction of spherical aberration,so is often used in extreme environment on the optical element of production,in the national defense science and technology and civil commercial products increasingly shows important scientific value and broad application prospects.As a kind of hard and brittle material,low expansion glass not only has low grinding efficiency in the process of aspheric surface processing,but also is difficult to obtain good surface quality,and its surface length will appear obvious grinding patterns.As an efficient machining method,rotary ultrasonic vibration was applied to the fabrication of aspheric surface of hard and brittle materials.With the adjustment of technological parameters,an efficient and high-quality grinding process route for aspheric surface components of low expansion glass was explored.Firstly,the relative position selection between the grinding wheel and the workpiece is compared.The same process parameters were compared between vertical grinding and parallel grinding with the aid of ultrasonic vibration.The experimental results were used to evaluate the surface quality from three aspects: surface texture,surface shape accuracy and surface roughness.It is concluded that the vertical grinding method is more suitable for the aspheric surface grinding of low expansion glass.After determining vertical grinding as the grinding relative position,the influence of ultrasonic vibration assistance on grinding force and material removal rate in the grinding process is investigated through the comparison experiment of rotation scratching with or without ultrasonic vibration assistance.It is concluded that ultrasonic vibration can greatly reduce the grinding force and increase the material removal rate.At the same time,a comparison experiment of aspheric vertical grinding with and without ultrasonic vibration was carried out to investigate the influence of ultrasonic vibration on grinding quality.It is concluded that ultrasonic vibration assistance can effectively improve the surface shape precision and surface roughness of the workpiece after grinding,and has little effect on the surface texture.Finally,according to the observation results of surface texture in various grinding experiments,combined with the theory of equal residual height and the theory of surface texture homogenization,a simulation model of aspheric surface grinding texture was established based on the grinding point position simulation and the interference trajectory of grinding points.An evaluation model of grinding point distribution characteristics was established based on the grinding wheel shape.According to the evaluation model of grinding point distribution characteristics,the process parameters in the grinding process were set in sections.The aspherical grinding texture simulation model was used to predict the surface texture of the workpiece after grinding.Combined with the results of the two models,the process parameter design guidance was provided for the subsequent process route improvement experiment.The grinding texture suppression and surface shape precision improvement are achieved without changing the grinding efficiency.