| The results of simulations depend on the input parameters such as flow rate. When the flow rate was the product of injection velocity and cross-sectional area of the screw, there were significant differences between the measured and predicted flow rates. Correction of the measured flow rates for decompression time, overshoot of the injection ram, and actual velocity of the ram produced greater agreement between the measured and theoretical flow rates. Correction of apparent densities using the mass delivered per injection stroke made the measured flow rate equal to or less than the theoretical flow rate. A quasi-steady-state approximation for compressible flow was then used to estimate the losses in flow rates due to compressible flow and the remaining reductions of the measured flow rate were then attributed to leakage flow. After material and mold resistance were accounted for using a pressure-viscosity factor, the leakage flow rate depended on the machine and possibly on the compressibility of the material. In general, the mismatch between corrected measured flow rates and predicted flow rates increased with low melt viscosity materials, high resistance molds, and high injection rates. |
