Online measurement of pressure, temperature, velocity, and viscosity of polymer melt within the injection mold is key to improving process control for quality assurance in injection molding. A multivariate sensing method has been introduced to enable simultaneous determination of the four parameters in injection molding using one single sensor package. Comparing with the method of measuring different physical parameters using separate sensors, the new method is advantageous in terms of system miniaturization and energy efficiency. This paper addresses the aspect of polymer melt velocity sensing based on the melt temperature measured by an Infrared (IR) sensing element integrated within the sensor package. From the Stephan-Boltzmann model, an analytical relationship between the melt front velocity and the ramping rate of the IR detector voltage output has been established. Using a Finite Element (FE) model, the process of polymer melt flowing over the IR sensor lens has been simulated. The result shows that the melt front velocity can be determined within an error of ± 0.25%, under a broad range of melt temperature and IR detector diameters. The result is experimentally confirmed by temperature measurement in a realistic injection molding machine instrumented with a reference IR sensor.

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