Gate design for injection molds

Generally, the model developed in this investigation predicted quite well the values of the parameters measured experimentally. In certain cases, deviations were observed, but these were due to known factors which have been described in the previous section.

This model represents the first link in a chain that is just beginning. The end use of the program will be in DOC feed-forward control applications for injection molding cycles.

Several improvements can be made on this model. First, a more detailed analysis should yield a better relationship between the volumetric flow rate and the pressure at a given point. This is necessary because the volumetric flow rate should be smoothly decreased in order to keep the runner entrance pressure at the constant preset injection pressure. In this investigation, a power law relationship was used. This exponential relationship proved to decrease the volumetric flow rate faster than it should have. This caused some oscillations in the predicted temperature and pressure values. It was observed from the experimental data that a linear relationship could do the job, and that the volumetric flow rate should be decreased at each time interval as the pressure increased, instead of waiting until the preset injection pressure was reached as it was done in this investigation. Second, a non-linear regression fit should be performed on the experimental data available for heat capacity and thermal conductivity. The regression equations could be used in the model. This will reduce the consistently high temperatures predicted by the model.

Third, the model should be extended to take into account the heat transferred to the wall of the channels. In this investigation a constant wall temperature was assumed in order to simplify the initial development of the model. At this point the finite difference grid used in the model could be extended to include the metal containing the cooling channels where the temperature is known. The inclusion of this feature could be accomplished with a small programming effort.

Finally better packing and cooling models could be developed. The cooling model proved to be the poorest of the proposed models. An extra effort to develop a better cooling model was not considered to be necessary, because this investigation was more concerned with the filling and packing stages, which are the critical stages for gate design purposes.