Numerical Simulation of Polymer Flow Into a Cylindrical Cavity

In this paper, new finite-difference based detailed general methodologies are presented for numerical simulation of injection mold-filling during the production of a long cylindrical object. The polymer considered is low density polyethylene (LDPE) following power-law viscosity model for nonzero shear rate zone. However, where shear rate becomes zero, “zero-shear viscosity” value has been used. Three cases have been considered, namely; (i) isothermal filling at constant injection pressure; (ii) isothermal filling at constant flow rate and; (iii) nonisothermal filling at constant flow rate. For (iii), the viscosity of LDPE is also a function of temperature. The material of the mold is steel. For the nonisothermal filling, the concept of melt-mold thermal contact resistance coefficient has been incorporated into the model. The length and diameter of the body in all three cases have been taken as 0.254 m and 0.00508 m, respectively. The results show excellent agreement with the corresponding analytical solutions for the first two cases showing the correctness of the numerical method. The simulation results for nonisothermal filling are reported for the first time for this particular geometry and lend insight into various important aspects of mold-filling including injection pressure versus time, and effects of flow rates on melt temperature fields at various axial locations as well as on frozen skin layer.