Simulation and experiment of non-isothermal hot pressing of small-diameter aspherical chalcogenide glass lens

Based on the finite element analysis of hot pressing process, a new non-isothermal molding method was proposed for improving hot pressing quality of small-diameter aspherical chalcogenide glass enses and avoiding pressing defects. A heating gap was set between the upper mold core and heating plate, and the upper and lower heating plate were heated by using different temperatures to realize non-isothermal heating of the glass preform. Firstly, based on the high temperature viscoelastic constitutive and heat transfer model of chalcogenide glass, the finite element model of glass lens on hot pressing process was established by using the relevant parameters. Then, according to above FEA model, the influence of non-isothermal temperature difference on the temperature, maximum residual stress distribution and contour offset was analyzed, and the optimal temperature difference was also determined. Finally, the experiments of non-isothermal hot pressing were carried out, and the results of simulation and experiment were also compared to verify the validity of the simulation model and results. Both simulation and experimental results show that the optimal non-isothermal temperature difference is 10℃. Under this condition, the internal temperature difference of the glass preform obtained by simulation is only 2.6℃, the maximum residual stress of the pressed lens can be reduced to 3.375 MPa, and the maximum contour offsets of the formed lenses ASP1 and ASP2 are 0.562 m and 0.615 m, respectively. The actual PV values of the pressed lenses ASP1 and ASP2 are 118.2 nm and 194.0 nm, Ra values are 17.0 nm and 37.8 nm, and maximum values of contour offset are 0.583 m and 0.644 m, respectively, which meet the accuracy requirements. The simulation results show good agreement with experimental results. By using the reasonable temperature difference, the new method of non-isothermal hot pressing can effectively reduce the internal temperature difference of the glass preform and maximum residual stress of the pressed lens, avoid the defects such as adhesion and bubbles, and improve the lens precision.