Vibration Assisted Injection Molding: An Innovative Energy Efficient Processing Technique for Poly-Lactic Acid (PLA) with Enhanced Properties

P. Gao, A. Duhduh, A. Kundu, J. Xing, J.P. Coulter
Lehigh University,
United States

Keywords: injection molding, PLA, efficient manufacturing

Summary:

This work is focused on the development of time and energy efficient injection molding processing strategies to fabricate semi-crystalline plastic components with enhanced properties. A Vibration Assisted Injection Molding (VAIM) process was devised for this purpose. In VAIM, an oscillatory motion is introduced to the injection screw in addition to the forward motion during the injection stage of injection molding process. The frequency, duration and amplitude of the oscillatory motion can be individually controlled precisely by a separate instrument module that seamlessly interfaces with the control unit native to the injection molding machine. The processing parameters such as injection time, cooling time, melt temperature and cooling temperature can be controlled via the built-in control system. This research was focused on understanding the effect of processing parameters such as vibrational frequency and cooling time on the mechanical and structural properties of semi-crystalline grade poly-lactic acid (PLA). It was observed that VAIM can reduce the cycle time for fabrication of PLA by 40% from 35 seconds for traditional injection molding process to 21 seconds for vibration assisted injection molding. Furthermore, the VAIM samples had enhanced ultimate tensile strength by 50% more on average, even with the reduced cycle time as compared to the traditional injection molded samples. The VAIM samples developed higher crystallinity and larger ratio crystalline domains of α phase than traditional injection molded samples. It was concluded the enhanced crystallinity was the primary contributor for enhanced properties and efficient fabrication.