Study Of Two-Stage Injection Molding Optical Products

Improving the precision and performance of optical products is an important research direction of injection molding technology currently. This paper designed a two-stage injection molding machine, which characterized by plunger injecting after screw plastication for improving the injection precision. The machine was used to mold the flat and curved optical articles, the effects of molding process parameters on product weight repeatability, articles residual stress level and optical properties were studied, the main work and the results are as follows:1. A two-stage injection molding machine of screw plastication before plunger injection was designed, the theory injection quantity of which was 100g polycarbonate, the maximum clamping force was 100 tons, the maximum injection pressure was 250MPa, the maximum injection velocity was190mm/s, and the weight repeatability can up to 0.09%. The internal field of the injection unit in two-stage injection molding machine was simulated, the results show that the melt velocity, pressure and viscosity field were stable during the injection process, and the melt was homogeneous.2. An orthogonal experiment was designed to analyse the factor affecting the repeatability precision of product weight in the two-stage injection molding machine. The results show that the most critical factor is the melt temperature. Four materials of injection molding experiments, including PS, PC, PS/CaCO3 and PS/PP were launched for studying the linear quantitative relationships between product weight and the injection power in the two-stage injection molding machine. The results show that the product weight can forecasted and controlled by the injection power in the two-stage injection molding machine.3. The two- stage injection molding machine was used to mold the flat and curved optical articles, the residual stress of the flat optical articles was achieved by the photoelasticity experiments, and the optical angular deviation values were measured by the measuring instruments. The influences of the injection process on the residual stress and the optical angular deviation of the products were studied. The results show that the higher melt(290℃) and mold temperature(120℃), the larger injection velocity(100mm/s), the longer cooling time(24s) was favorable to reduced the residual stress, and the optical angular deviation was also excellent. Studies about PC curved articles show that the distribution of angular deviation influenced by geometric curvature radius presenting stepwise, while it appears parabola when influenced by azimuth and the pitch angle, the deviation appears minimum when the azimuth is zero, while it changes into maximum when the pitch angle is zero.