Research Of Evolution Rule On Microstructure In A Combined In-mold Decoration And Microcellular Foaming Injection Molding

Microcellular foaming product is promoting for the light weight,and dimension stability.However rough surface quality of microcellular plastic limits its application prospect in the industrial production.This article presents the combined In-Mold Decoration and microcellular foaming injection molding technology(IMD/MuCell),it can improve the the surface quality effectively,but based on the decorative film attached to the mold surface,the bubble grew up,bubble movement,bubble distribution and overall internal bubble structure have been influenced with the change of whole convection heat transfer system.In order to research the change of the bubble distribution inside the products with the combined In-Mold Decoration and microcellular foaming injection molding technology,the asymmetric melt temperature factors is introducted in the cavity,and then established the bubble growth and bubble migration model,the optimization method of bubble migration distance is came up,and bubble structure forming process is revealed,which indicates the evolution rules of the bubble.The growth model of bubble is built on combined In-Mold Decoration and microcellular foaming injection molding technology.The asymmetric melt temperature field mathematical model is brought in the melt,and based on the change of temperature field on physical parameters,the modification of classical crystal cell model is operated by melt viscosity model,diffusivity,surface tension and solubility.The the bubble size distribution is verified by the combination of simulation and experiment in a combined In-Mold Decoration and microcellular foaming injection molding technology,and the highest temperature appears near the film side,for the bubbles have more time to grow up,the biggest bubble location move to the side with film.The bubble movement rule is researched with combined In-Mold Decoration and microcellular foaming injection molding technology.Through analytic method,the mathematical relationship of asymmetric velocity field and non-isothermal melt is established in the mold filling process,maximum velocity position deviate to the film side,bubbles migrate to the film side by the lateral lift force.The motion trajectory of bubbles is investigated in asymmetric velocity field by the finite element method,and the lateral migration of bubbles is experienced in four stages: rapid migration,slow migration,fluctuating and stabilization.The migration process of bubbles is verified by physical experiments,the central bubbles migrate to the film side by lateral lift force.The effects of the offset distance are studied on technological parameters.The bubble migration distance is optimized by experiment design.By factorial experiment design: bubble position,bubble radius,initial bubble velocity have significant influence on bubble migration distance;the forecasting model of bubble migration distance on main effect factors is established based on composite design of experiment;Through build response surface analysis to receive the mutual interactions on the bubble position,initial bubble velocity.The optimal process parameter combination scheme is obtained to ensure the symmetrical distribution of bubbles in the cavity through genetic algorithm analysis.The formation mechanism of bubble structure is revealed to explore the fountain flow process in the melt front.Near the gate,the surface quality is better.Through the decorative film attached to the mold,it eliminates the surface bubble mark and improves the surface quality effectively.There is critical pressure stage in cavity injection molding process,the pressure in the cavity increases by the process of melt injection,when the pressure reach the critical value of bubble solubility in the melt,the melt in back-end filling is no longer foaming,until the melt filling get completed,and all bubbles grow up together.The average bubble diameter in film side is larger than the non-film side,and has little difference in bubble density.Aspect Ratio of bubble in film side less than the non-film side for the small shear action of melt.