Online measurement of polymer melt properties during an injection molding process is a key to provide a high quality plastic product. In-situ cavity pressure and temperature sensors are used to observe the polymer states in the mold cavity during an injecting molding process. A new multivariate sensor is introduced to measure pressure, temperature, velocity, and viscosity of polymer melt as the key parameters of the melt to improve the controlling process. This paper presents the viscosity calculating method based on melt velocity and the slope of melt pressure. The velocity is inferred using the melt temperature ramping rate; the new multivariate sensor detects melt temperature through the installed IR detector in the sensor, and the pressure is measured via the mounted piezoelectric rings. Injecting molding process of polymer melt is simulated under a range of melt velocity and temperature and the related viscosity values are inferred from simulation results and also from a set of experimental tests for a real injection molding process. Results are well matched with the expected rheological behavior of polymer.

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