This paper discussed the mechanism of internal fogging in automotive lamp based on the principle of water vapor condensation, and put forward the concept of the critical fogging humidity of lamp according to the structure and engineering characteristics. It given out a simple way to judge lamp fogging on the base of lamp temperature field, and verified the existence of the critical fog humidity by the test. All of these are very meaningful on the evaluation of the lamp's structure and raise the level of lamp design

Due to large planar scale and small lateral scale of plastic drawing board, it was easy to cause warpage problem in injection molding. Optimization of injection molding process was taken to reduce residual stress and improve quality. Combining orthogonal experimental method and software Moldflow, analyzed the effect of mold temperature, melt temperature, hold pressure and injection velocity on warpage deformation. It changed multi-objective optimization to single-objective optimization by weighted method. Through range analysis obtained the influence trend between parameters and comprehensive optimal object. Lastly got the optimal combination of injection molding process parameters.