为提高小口径非球面硫系玻璃镜片热压成型质量, 避免成型缺陷, 通过热压过程的有限元分析, 提出了一种新的非等温热压成型法。在上模仁和上加热板之间设置加热间隙, 对上、下加热板设置不同的加热温度, 以实现玻璃预形体的非等温加热。首先, 根据硫系玻璃高温粘弹性本构模型和热传递模型, 结合相关参数建立了镜片热压过程的有限元模型; 接着, 采用所建立的模型, 分析了非等温温差对玻璃预形体内部的温度分布、成型镜片最大残余应力分布及轮廓偏移量的影响, 以确定最佳的温差值; 最后, 进行了镜片的非等温热压成型实验, 并将仿真和实验结果进行了对比研究, 以验证仿真模型和结果的有效性。仿真与实验结果均表明, 最佳的非等温温差值为10 ℃。该条件下, 仿真获得的玻璃预形体内部温度差仅为2.6 ℃, 成型镜片最大残余应力可减至3.375 MPa, 成型镜片ASP1和ASP2的轮廓偏移量最大值分别为0.562 μm和0.615 μm; 实验获得的成型镜片ASP1和ASP2的PV值分别为118.2、194.0 nm, Ra值分别为17.0、37.8 nm, 轮廓偏移量最大值分别为0.583、0.644 μm, 均满足精度要求。仿真与实验结果具有较好的一致性, 采用合理的温差值进行镜片的非等温热压成型, 可有效降低玻璃预形体内部温度差及成型镜片最大残余应力, 避免粘连、气泡等成型缺陷, 提高成型镜片的精度。

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 lenses 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 μm and 0.615 μm, 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 μm and 0.644 μm, 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.