Abstract: Polymer water-assisted co-injection molding is a new and innovative advanced molding technology of molding inner surface smooth, dense, high-performance multi-layer composite hollow plastic products, and may make up for the inner surface porosity defects of gas-assisted co-injection molding products which leads to decline in the mechanical strength of products. The melt shear –thinning effect characteristics is the key control parameters of controlling the penetration process of water or core melt, and the inner quality of water assisted co-injection molding products. Therefore, the influencing rules of the melt shear –thinning effect characteristics on the penetration process of water or core melt and the front moving interface flow stability for water-assisted co-injection molding process were systematic studied by means of the established the full three-dimensional unsteady and non-isothermal finite element numerical simulation algorithm and technology of water-assisted co-injection molding process, and the influencing mechanisms were finally revealed by theoretical analysis. Research results show that with the increase in the shear-thinning effect characteristics of core melt, the water and core melt penetration depth increase, which is conducive to water-assisted co-injection molding process of slender plastic products, but the increase in the shear-thinning effect characteristics of core melt make the front moving interface between water and core melt tend to be unstable, which affects seriously the inner surface quality of water-assisted co-injection molding products.

Key words: water-assisted co-injection molding;formation mechanism, numerical simulation;shear-thinning effect characteristics