Study On Material Removal And Surface Quality In Ultrasonic Vibration Mill-grinding Of Optical Glass

Optical glass is an isotropic high-tech material. With the excellent chemical durability, mechanical properties, optical properties and thermal properties, optical glass is widely used in the production of components of optical instruments and apparatus. Optical glass is a typical brittle material and the fracture, chippings and cracks of the conventional process make the surface quality difficult to be guaranteed, so further applications are limited. With the processing characteristic of intermittent contact between abrasive cutting edges and the workpiece, ultrasonic vibration mill-grinding is particularly suitable for the processing of brittle materials and has great advantages compared with conventional machining. Brittle-ductile transition mechanism of material removal in ultrasonic vibration mill-grinding of optical glass was investigated. Meanwhile, ultrasonic vibration parameters and mill-grinding parameters on the material surface roughness and subsurface damage were studied to provide technical support for low damage machining of optical glass.Based on the analysis on brittle-ductile transition mechanism of material removal in ultrasonic vibration mill-grinding, brittle-ductile transition model of optical glass was established. Microscopic indentation experiment and single grain scratching experiment with ultrasonic vibration on BK7 and JGS1 were conducted respectively. Then the surface morphology of indentation areas and scratching grooves was detected. The indentation sizes of the two kinds of optical glass were measured and the influence of loads on hardness and fracture toughness was studied. Besides, the influence of ultrasonic vibration amplitude on critical load and critical depth was studied with the measurement of critical force and critical scratching depth.To investigate the influence of ultrasonic vibration parameters and mill-grinding parameters on the surface roughness in ultrasonic vibration mill-grinding of the optical glass, single-factor experiments with the parameters of spindle speed, feed rate, cutting depth and vibration amplitude were carried out in this paper. The influence of different parameters on surface roughness was obtained and surface roughness prediction model in ultrasonic vibration milling of optical glass was established. The results laid a foundation for the preferences of process parameters in precise machining of optical glass.Based on the experiment of different parameters in ultrasonic vibration mill-grinding of optical glass, the machining workpieces were processed with HF acid etching after being polished. Milling areas were observed by a scanning electron microscope(SEM) and sub-surface crack type and size were detected to obtain the forms and characteristics of the subsurface damage in ultrasonic vibration milling of optical glass. Meanwhile, the influence of different parameters on the degree of sub-surface damage was studied to lay foundation for the reduction of subsurface damage in the machining of optical glass.