Abstract: Based on the case study of air-conditioning plane frames, sink mark formation and evolutionary mechanism in a mold cavity were analyzed. Influence of bad thermal intersection and stress along the direction of wall thickness vertical to mold cavity on the formation of sink mark were achieved, and the vertical pressure difference between the both sides of cavity wall thickness was confirmed. It was found that the greater the pressure difference, the deeper was the sink mark. The studies indicated that, with a melt temperature of 191.5 ℃, a relative pressure maintaining pressure of 85.5 %, a mold temperature of 33.6 ℃ and injection time of 2.3 s, the optimum process parameters for the air-conditioning plane frame were achieved by using genetic algorithm and the minimum shrink mark index was calculated to be 1.352. Through a comparative investigation on injection experimental results and simulation values, and the exact value of sink mark depth and the sink mark index should be set to 0~0.05 mm and 0.38 %~1.43 % under the combination of optimized process parameters, respectively.

Key words: large thin-wall injection-molded part, sink mark, evolutionary mechanism, bad thermal intersection, combination of process parameter