Experimental study on the penetration interfaces of pipes with different cross-sections in overflow water-assisted coinjection molding

The residual wall thicknesses (RWT) of the skin and the inner layers are important quality indicators of water-assisted co-injection molding (WACIM) parts. The influences of the shape of the cavity cross section and the processing parameters, including the water pressure, water delay time, inner melt temperature, and inner melt flow rate, on the penetration of the inner melt and water were explored via experiments. The results showed that the shape of the penetration section of the inner melt was closer to the cavity section with round corners, while that of the water ended up being round. Both the penetration ratios of the inner melt and the water increased proportionally with increasing circle ratio. Both the minimum values of the total RWT and the inner melt RWT increased with increasing circle ratio. Both the maximum values of the total RWT and the inner melt RWT increased with increasing Max-D, which is the maximum distance between the inscribed circle center and the wall. Both the penetration ratios of the inner melt and the water increased with increasing water pressure, decreased with increasing water delay time, and increased with increasing inner melt flow rate and increasing inner melt temperature.