Precise temperature calibration for visualized high-thermal-conductivity PPS in injection molding during filling process

Abstract

High-thermal-conductivity polyphenylene sulfide (PPS) is expected to be used to manufacture various products because of its light weight, strength, high heat dissipation, and low CO2 emissions during manufacturing compared with aluminum die casting. However, this has a unique filling behavior owing to rapid cooling during the filling process, and is likely to cause hesitation and short shots, which must be suppressed. To address this issue, simulations are used to accurately predict the filling behavior and optimize the product shape. However, the thermal behavior of the molten resin in the mold is complex and not yet fully understood, which limits the accuracy of the simulation. In previous research, we built a thermal imaging visualization system to understand thermal behavior. We selected sapphire glass as the transparent material for infrared transmittance, strength, and thermal conductivity. The sapphire glass was made thicker to withstand the high injection pressure and thermal stress during molding of the high-thermal-conductivity PPS, which resulted in a large interference due to infrared attenuation and radiation inside the sapphire glass, affecting the temperature measurement results. In addition, changes in reflectance caused by changes in the state of contact between the sapphire glass and resin due to shrinkage of the resin in the mold also affected the temperature measurement. In this study, we propose a new temperature calibration method to convert the radiance distribution acquired using the visualization system into an appropriate temperature distribution. The developed system successfully visualizes the temperature of the filling process. The temperature measurement results were verified by comparing with the results from thermocouple temperature measurements.