Experimental Study of Injection Molding Replicability for the Micro Embossment of the Ultrasonic Vibrator.

It is challenging to fabricate micro features on an injection-molded polymer product. Ultrasonic vibration induced into micro-injection molding is helpful for flow of polymer melt. In this paper, a micro-injection mold integrated with ultrasonic vibration was designed and fabricated, and micro embossment was machined on the surface of the ultrasonic vibrator. Poly(methacrylic acid methyl ester) (PMMA) was used for injection molding experiments, with four ultrasonic power levels (0, 300, 600, and 900 W), three injection speed levels (60, 80, and 100 cm3/s), two injection pressure levels (60 and 90 MPa) and a mold temperature of 60 °C. It was found that ultrasonic vibration perpendicular to the middle surface of the cavity is beneficial in forming transverse microstructure, but is not conducive to generating longitudinal microstructure. Increase in injection pressure can improve molding qualities for both the longitudinal micro groove and the transverse micro groove. Increase in injection speed is not conducive to forming the longitudinal micro groove but benefits formation of the transverse micro groove. When ultrasonic vibration is applied at the injection and packing stages, molding quality of the longitudinal micro groove becomes worse, while that of the transverse micro groove becomes better.

Investigation on Microstructures and Mechanical Properties of Isotactic Polypropylene Parts Fabricated by Different Process Conditions with Different Aging Periods.

Polymeric parts have been increasingly used in various engineering fields. The performance of polymeric parts is significantly affected by working-environment-induced aging. In this paper, an ultrasonic-vibration-assisted injection molding system was designed and utilized to fabricate polymeric parts from isotactic polypropylene (iPP) using different processing conditions. The natural aging experiments were performed to age the fabricated iPP parts for one year. The effects of key process parameters as well as ultrasound power on the microstructures and the mechanical properties of the iPP parts after aging were systematically investigated using X-ray diffraction analysis, Fourier transform infrared analysis, scanning electron microscope imaging, and tensile testing. It is found that both the microstructures and the tensile strength of the iPP parts deteriorate with the increasing aging time. In addition, the crystallinity and the tensile strength decrease with the increasing melt temperature but increase with the increasing mold temperature in a given range and holding pressure. The increase in ultrasound power leads to an increase in crystallinity. However, when the ultrasound power is over 200 W, the tensile strength of the aged iPP parts decreases, which indicates that high ultrasound power may not form optimal condensed microstructures with excellent anti-aging capacity.