Three‐dimensional modelling and simulation of sequential co‐injection moulding with application to a toothbrush handle

Sequential co-injection moulding (SCIM) is a promising technique in industrial production. Because of the complex hydrodynamic effect of air on polymer melts in a moulding process, it is difficult to accurately design and control the process. Corresponding theoretical investigations are very limited, especially for the transient free surface flows in the filling stage. In this paper, a three-dimensional (3-D) unified model is proposed for simulating fluids flow in SCIM. The melted polymer and air in the cavity can be regarded as a continuous fluid. The evolution of the melt front interface and skin/core melt interface are captured simultaneously at any moment by the level set method; this method has been widely-used in two-phase flow for its ability to track interfaces. The finite volume method is combined with a domain extension technique to deal with 3-D flows in an irregular cavity. The model is validated by simulating the SCIM process for a cavity with a block insert, and a distinct corner effect is observed. For a widely-used plastic toothbrush made by SCIM, the evolutions of transient free surfaces in the filling stage are investigated. All numerical results are consistent with corresponding experimental results, and demonstrate the capability of the model with the domain extension technique to simulate multiphase flows in SCIM.