A numerical simulation of the cavity filling process with PVC in injection molding

Abstract : In this work a numerical simulation of the mold cavity filling process was attempted. The mold filled in this simulation is a disk which hot polymer melt enters through a tubular entrance located at the center of the top plate. The tube is 2.54 cm. long and has a radius of 0.24 cm. The plate separation and outer radius of the disk cavity may be varied. A constant pressure applied at the entrance of the tube causes the flow. The cavity walls are kept at various low temperatures. The reported results are for rigid PVC. Continuity, momentum, and energy transport equations for a constant density power law fluid are used to solve the flow problem. It is assumed that the outer radius of the disk is very much greater than the plate separation, that there is axisymmetry, that only one of the viscous terms in the momentum equation is significant, and that in the flow direction heat conduction is negligible compared with convection. Constant values for the thermal conductivity and heat capacity of the melt are used. The resulting differential equations are transformed into difference equations explicity, except for the energy equation. In this case a Six Point Crank- Nicholson implicit differencing technique was necessary to assure thermal stability of the solution. The difference equations were solved by using a Fourth Order Ruhge-Kutta integration formula for the velocity profiles and the Thomas method for the temperature profiles. Convergence to the differential solutions is guaranteed but since a lower limit was imposed on the time increment by the core storage limit of the computer facilities (27K) and long execution times, all results are semi-quantitative for the problem as stated. (Author, modified-PL)