Precision compression molding is an important technology in lens processing. Diffractive optical elements (DOEs) have special optical and temperature characteristics and are of great application value in infrared optical systems. They are widely used in the field of infrared detection and infrared imaging technology. DOEs are widely used in modern optical systems because of their small size and light mass. Of all processing technologies, PGM technology can be used to manufacture optical elements of various wavelength levels. The rapid manufacturing of DOEs with chalcogenide glass can be achieved by precision molding technology, which meets the mass production requirements of infrared DOEs. The influences of the diffractive structure filling and the maximum stress on the surface precision of the lens are studied in this paper to improve the diffraction efficiency and reduce the surface precision deviation of the DOE in the compression molding process.

In this paper, simulations and experiments are used to study the influences of the diffractive structure filling and the maximum stress on the surface precision of the lens. Firstly, the finite element simulation method is used to analyze the molding process so as to study the filling condition and stress distribution of the diffraction structure under different process parameters. The diffraction structure is too small compared with the size of the whole lens, and hence, the filling effect of the diffraction structure cannot be accurately judged from the simulations. Therefore, a simulation model for the local diffraction structure is built to analyze the effects of molding temperature, pressing velocity, and friction coefficient on the filling and maximum stress of the diffraction structure. Then, the molding experiment of the chalcogenide-glass diffraction surface is carried out. The mold used in the experiment is made of microcrystalline aluminum RSA905, and the glass preform is IG6. Since the friction coefficient of the mold cannot be controlled, the changing process parameters during the molding experiment are temperature and pressing velocity.

The simulations indicate that with the increase in the molding temperature, the filling of the diffraction structure shows no obvious change (Fig. 4), and the maximum stress of the lens decreases first and then increases (Fig. 5). A smaller pressing velocity means a more complete diffraction structure (Fig. 6) and smaller maximum stress of the lens (Fig. 7). A larger friction coefficient is accompanied by a more complete diffraction structure (Fig. 8) and larger maximum stress of the lens (Fig. 9). The experimental results (Table 6) show that when the pressing velocity is unchanged, the surface precision deviation of the lens is the smallest at the molding temperature of 230 ℃. When the molding temperature is constant, a smaller pressing velocity means a smaller surface precision deviation. The comparison of the simulations and experimental results shows that there is no significant change in the diffraction structure filling when the temperature changes in the simulation; when the molding temperature is 230 ℃, the maximum stress of the molding lens is the minimum. This indicates that the smaller maximum stress of the lens means a smaller surface precision deviation of the lens. When the molding temperature is fixed, a smaller pressing velocity is followed by a smaller surface precision deviation. The simulations demonstrate the same variation trend as the experimental results. The optimum process parameters are 230 ℃ and 0.01 mm/s. Under these parameters, the surface precision deviation is 0.3053 μm, and the surface roughness R_a is 2.95 nm.

For the molding process of infrared chalcogenide glass IG6, the microcrystalline aluminum RSA905 is used as the mold to carry out the simulation analysis and experimental research. This study simulates the influences of temperature, pressing velocity, and friction coefficient on the filling and stress of diffraction elements during the molding process of the local diffraction structure of chalcogenide glass. On this basis, the optimal process parameters are obtained by experiments. The results show that the optimal temperature of IG6 is 230 ℃ when the microcrystalline aluminum RSA905 is used as the mold die. The filling of the diffraction structure does not change greatly when the temperature is the variable in the simulation, but the maximum stress of the molding lens reaches the minimum at 230 ℃. When the molding temperature is fixed, a smaller pressing velocity means a smaller surface precision deviation, which conforms to the variation trend that a smaller pressing velocity is accompanied by better filling of the diffraction structure. The optimum process parameters are 230 ℃ and 0.01 mm/s. Under these process parameters, the surface precision deviation is 0.3053 μm, and the surface roughness R_a is 2.95 nm. This surface precision deviation meets the requirements of most infrared DOEs. The method is of great significance for promoting the mass production of infrared DOEs at a low cost.