Modified Theory of Welding Line and Optimal Design of Material Parameter for a Thin Part in the Injection Mould

Abstract

In this paper, based on thin-wall moulding under high processing pressure, we develop a theoretical model containing the pressure term by combining the Williams-Landel-Ferry(WLF) semi-experimental equation and the weld-line strength model of the molecular chains crossing the interface and self-diffusion. Then, the optimal theory is applied to find the optimal material. According to the theoretical model, high pressure would lead to a high viscosity and a low molecular diffusion to reduce the degree of bonding. The traditional weld-line theory cannot modify this fact, however. Therefore, it would be more accurate for a thin part to predict the degree of bonding by applying the theoretical model with the pressure term from the analytical result, it would be better for using a higher melt temperature in the moulding process. For thin-walled material, it is better to select a material with a lower density, lower plateau modulus, higher R 2 /M W ratio, lower molecular weight and lower glass transition temperature material with the allowable range of mechanical properties.