Pressure-dependent switchover

Depending on the cross section of the molded part and the corresponding flow resistance of the melt, a pressure increase is measured during mold filling. After switch over to holding pressure, the melt is compressed, and there is a rapid pressure increase. Because of the pressure transfer in the polymer melt from the flow path end up to the sensor position near the gate, it takes some time for the increase in pressure to be measured, and that is why a cavity pressure-dependent switchover to holding pressure tends to be too late. 

To make sure the stable state of resin in the process optimization test, the process monitoring system (PMS) was applied in a wide range in this study. For each critical step of the test, the way to utilize the PMS dq ended upon the phenomenon in the mold and the purpose of the test. The dependent variables such as switchover point and holding time were properly set with the aid of the PMS. Based on the relationship of the state of the resin with pressure and temperature, a new PMS index was proposed. The index showed the best correlation with the part weight among various indices through the correlation analysis. 

The process optimization includes the initial condition search. In order to optimize the process, the control variables should be selected properly. When the control variables are poorly selected, the process optimization may end up with unexplainable result. For the best result, the characteristics of the process variables should be carefully understood. The process variables can be classified as machine variables and material variables, as shown in Table 1. The state of the resin in the mold is closely related with material variables such as resin temperature, resin pressure and viscosity, etc. However, the material variables are hardly measured and controlled directly. The machine variables can be classified as independent, dependent and restrictive variables. The control variables for the process optimization should be chosen among the indepmdait variables. The depmdmt variables such as switchover point and holding time are to be properly found. These variables can be set in the initial condition searching stq>. For the purpose, the PMS provides the detailed information in the mold. 

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