Effects of ultrasonic injection molding conditions on the plate processing characteristics of PMMA

Polymer processing is a crucial and diverse field in the manufacturing industry. We investigated the process characteristics and effects of injection molding using ultrasonic vibration. An ultrasonic device was installed in an injection mold; polymer was directly vibrated during injection. An ultrasonic oscillation device 45 mm in diameter was placed in the cavity and used to vibrate a poly(methyl methacrylate) melt at 19 kHz. The amplitude of the acoustic unit was set at 15 mu m for the measurements. Moreover, cavity pressure sensors were positioned at the front and rear sides of the vibration region to determine the melt flow behavior under ultrasonic-assisted injection molding conditions. Because of the absorption of ultrasonic energy, local heat was generated inside the resin, thus improving the flow characteristics of the melt. Moreover, the melt flow behavior around the skin layer was changed; the molecular orientation and high shear effect were reduced. Furthermore, the freezing rate of the melt was reduced; thus, the amount of melt pressure lost through the cavity was decreased and the residual stress inside the injection-molded component generated during the photoelastic stress analysis was lower.