Study On The Glass Microstructure Array Molding And The Interface Micro Friction

Optical microstructure array can be used for physical control of any wavelength light which is an important component in modern optical engineering.Precision Glass Molding(PGM)is the most effective solution to fabricate microstructure array on glass surface with high efficiency and low cost.Usually,the optical microstructure array has small periodic size and sharp structure,so it is a great challenge to guarantee the filling accuracy of the molded microstructure array.In order to increase the filling accuracy during the PGM,the creep characteristics of glass at high temperature was tested,and the viscoelastic model was carried out.The interface thermal resistance model was established.The FEM simulation in the heating stage was conducted to monitor the temperature rise during the PGM,and the process parameters of the heating stage were confirmed.The glass-mold interface friction model was established;the internal stress distribution inside the molded glass microstructure array was predicted.It was concluded that the main reason of the incomplete filling of glass during PGM is the interface friction resistance.The PGM experiments for microstructure array were carried out,and the phosphorus diffusion phenomenon was found.The scheme of using Rhenium-Iridium coating to isolate element diffusion and reduce interfacial friction was put forward and verified by experiments.In order to further improve the accury of molded glass microstructure array,a technical scheme of ultrasonic vibration assisted moding was proposed.The positive effects of ultrasonic vibration on reducing interface friction,improving the glass filling performance and reducing the surface defects of microgrooves were investigated.The research results provide theoretical and practical support for ultra-precision manufacturing of optical microstructure array.The main research contents and innovative results are as follows:1.The glass viscoelastic constitutive model and time-temperature equivalent model were established.The dynamic performance of the glass was analyzed.The creep model was verified by the FEM simulation.The influence of creep and stress relaxation at high temperature on PGM process were studied.2.The thermal resistance of glass-mold interface was built,and the effect of surface roughness and interface pressure on heating time was obtained.The glass-mold interface friction model was established.The influence of interface shear film coefficient on microgroove filling accuracy was obtained through FEM simulation adopting the glass-mold interface friction model.The relationship between the glass relaxation time and the attenuation of stress inside the glass was revealed.The scheme of reducing the stress concentration in the structural catastrophe zone was proposed.3.The influence mechanism of mold material and surface roughness on the roughness evolution of molded glass was investigated.A low cost manufacturing scheme for optical devices was proposed.The phenomenon of phosphorus diffusion inside the nickel-phosphorus(Ni-P)coating to the glass surface was found.It was proposed that the element diffusion increased the friction between the glass and mold,which increased the filling difficulty of microstructure.4.A scheme of using Rhenium-Iridium coating to isolate phosphorus from the surface of glass was proposed.The influence of the coating on the mold surface properties was also obtained.The results show that the thickness of Rhenium-Iridium coating is 400 nm,the mass percentage of Rhenium and Iridium in the coating is 1:3,the modulus of elasticity and yield strength of the mold surface were all significantly increased.The internal stress changes of Rhenium-Iridium coating after heating was studied.When the mold was heated to 580°C,the internal stress of the mold was 649 MPa,which was far below the yield stress of Rhenium-Iridium coating.The Rhenium-Iridium coating isolated the diffusion of phosphorus in the nickel-phosphorus(Ni-P)mold to the glass surface completely.5.The ultrasonic vibration assisted molding process for microstructure array was proposed.The effect of ultrasonic vibration on reducing the friction between the glass and mold interface was confirmed by the designed friction test experiment.The FEM simulation was applied to simulate the relative position of the glass and mold interface in several vibration cycles during the ultrasonic vibration assisted molding process.The phenomenon of periodic separation of the glass-mold interface caused by ultrasonic vibration was revealed.The effect of ultrasonic vibration on filling improvements during PGM was verified by combining the FEM simulation and experiments.The results show that the glass formability was directly proportional to the amplitude of ultrasonic vibration.The research results confirm that ultrasonic vibration has significant effect on improving the molding accuracy and reducing the molded defects of microstructure array.