Ultrasonic Vibration Assisted Grinding Mechanism And Processing Technology On Low Expansion Optical Glass

Ultra-Low Expansion(ULE)optical glass opponents(including Zerodur)exhibit superb performance thanks to their ultra-low expansion coefficients while possessing denser structure,higher hardness and mechanical strength,better anti-wear and electrical insulation properties,as well as more chemical stability than normal optical glasses.In the application filed of space mirrors,astronomical telescopes,aeronautics and aerospace,integrated circuits,satellite navigation,space robots,mechanical equipments,optical instruments,the ULE optical components have been widely employed owning to their outstanding mechanical and optical properties.However,as the hard and brittle hard-to-machine materials,the manufacturing technology for ULE’s batch production to meet the demand for large quantities from different application field,is facing a big challenge ever since.However,the traditional machining technologies show their limitations on low expansion optical glasses in terms of batch production,high quality,short cycling time and low cost.Ultrasonic vibration assisted grinding features exerting vibration on either grinding tools or workpiece,is capable of modifying the single grain’s cutting behavior and trajectories,hence to affect the material’s removal mechanism,which is a so called new type of high efficiency,high quality grinding and low subsurface damage grinding approaches and can greatly shorten the following polishing allowance as well as the whole machining cycling time.This dissertation aims to study the ultrasonic vibration assisted grinding technology on Zerodur and ULE optical glasses in realizing the high quality and high efficiency manufacture.The research work is listed as follows.Firstly,through analyzing the characteristics of various vibration-assisted grinding,the axial vibration cylindrical grinding and axial vibration face grinding is experimentally compared.By introducing single grain’s kinematic analysis,the axial vibration cylindrical grinding method is determined as an optimized approach for fabricating Zerodur ULE optical glass in terms of high quality and high efficiency.Besides,the appropriate dressing method for axial vibration grinding is chosen via experimental trials,which can guarantee the grinding tool’s performance and stable grinding process.Secondly,the micro/nano indentation tests,normal scratching and axial scratching tests are performed on Zerodur and ULE glasses.In addition by means of indentation fracture mechanics the material’s intrinsic properties are calculated.Meanwhile,the material’s dynamic removal process and removal modes are observed.For single grain scratching,the effect of axial ultrasonic vibration,brittle-ductile material removal modes and material properties on the material removal mechanism is analyzed,laying a theoretical foundation for the following modeling of grinding quality.With regard to the indentation and scratching tests,a stress filed model is proposed correspondingly to deeply understand the initial position and propagating angle of three typical cracks from a view point of internal stress,hence presenting a microscopic description for the formation mechanisms of cracks.Thirdly,the modelling thought by introducing the material removal modes determined grinding force components is proposed,by which the generation mechanism of grinding forces as well as the effect of axial vibration are depicted.Besides,the ductile removal force,brittle removal force and friction force metadata models are created respectively.Through the created general grinding force models of normal grinding and axial vibration cylindrical grinding,the grinding force values and the effect regulations as well as the weight of the order of grinding parameters on grinding forces can be predicted,that is also verified through grinding experiments indicating that the model having a high prediction accuracy.Meanwhile,the grinding force model can also clearly explain the decreasing reason and the decreasing amplitude of grinding forces under axial vibration.By taking the surface roughness(Ra)and sub-surface crack maximized depth as the main characterizing indexes of surface integrity,the suitable prediction model for axial vibration cylindrical grinding is proposed on the basis statistics theory and indentation fracture mechanics respectively,which can directly link the ground surface integrity and grinding parameters through mathematical equations.The two prediction models’ prediction accuracy also are verified by the grinding experiments.This work not only could solve the key problems for optimizing the grinding parameters,also is able to provide the guidance for the following polishing process in determining the allowance.Finally,by combining the forwarded grinding force model to characterize the grinding quality,and the maximized subsurface crack depth as well as Ra predictionmodel to be as a comprehensive grinding quality prediction model,can predict the grinding quality in high efficiency,in addition to the material removal rate prediction,an optimized manufacturing solution for low expansion optical glasses can be presented featuring high quality,high efficiency and low surface/subsurface damage through ultrasonic vibration assisted peripheral grinding approach.This not only lays a theoretical foundation for optimizing the ultrasonic vibration assisted peripheral grinding technique,but also poses a significant meaning for batch production for low expansion optical glasses with high quality,short cycling time as well as low cost.