Flow properties of polymer melt in longitudinal ultrasonic-assisted microinjection molding

Abstract

Microplastic parts are usually fabricated by microinjection molding (mIM) which is an effective and low cost method. But the defects, such as short shot, often appear during fabricating plastic parts with high aspect ratio structures or complex shapes. a longitudinal ultrasonic-assisted microinjection molding (LUmIM) method effectively improve the molding quality. In the paper, the mechanism that the ultrasonic vibration impacts on the polymer melt is investigated. Considering from the point view of energy effect, mechanical energy transmission, and mechanical energy conversion, which are divided from the energy of ultrasonic vibration, are analyzed. The model of energy transmission and a new rheological equation including the parameters of ultrasonic vibration are established to describe the rheological behavior of polymer melt in microcavity. The simulation results show that the ultrasonic vibration improves the viscosity field and the velocity field in complex shaped microcavity, and leads to a better filling capability and uniformity of the polymer melt. This research achievement can be used to guide the process flow and parameter selection of LUmIM. POLYM. ENG. SCI., 57:797-805, 2017.

Wall Slip of Linear Polymer Melts During Ultrasonic‐assisted Micro‐injection Molding

“…The experimental results show that when the wall slip does not occur, the apparent viscosity of the melt at the same shear rate is decreased with the increase of excitation voltage. This is mainly caused by the combined effects of ultrasonic vibration energy transmit and energy heating, which conforms to the results and discussion in preliminary work . Moreover, as shown in Fig.…”

“…In UμIM process, a longitudinal ultrasonic vibration is directly acted on the melt through the ultrasonic horn for improving the filling quality of the mold with micro structures such as high aspect ratio structures or complex structures without relying on higher parameter values and higher machine performance requirements [20]. Meanwhile, because of the enormous energy and high frequency vibration carried by ultrasonic, flow behaviors of polymer melts are greatly influenced by the effect of ultrasonic vibration, some changes in flow behaviors have been confirmed such as the flow rate in nano-flow process [21] and rheological properties in micro cavity [22]. However, as an important part of flow behaviors, the wall slip of polymer melts, which has been suggested to determine the molding quality of conventional microinjection molding in current researches, will show different performance under the effect of ultrasonic vibration that have not yet been clarified.…”

Micro-Ultrasonic Viscosity Model Based on Ultrasonic-Assisted Vibration Micro-Injection for High-Flow Length Ratio Parts

“…The simulation results of the microgroove filling experiment using the MU viscosity model at different injection pressures were compared with the experimental results ( Figure 4). In addition, the microgroove filling experiment was also simulated by using the ultrasonic viscosity model proposed by Gao et al (Gao viscosity model) [17] and the MCL microviscosity model [19]. When the flow length ratio of the microgroove was 3:1 (Figure 4a), the simulated values from the three viscosity models were very close to each other and were only slightly different from the experimental values.…”

“…Gao viscosity model [17] MU viscosity model MCL viscosity model [19] Experimental data (b) Flow length ratio 5:1…”

“…Isayev [16] analyzed the relationship between the shear rate and viscosity for low-density polyethylene (LDPE), polypropylene (PP), and polystyrene (PS) under different low-frequency oscillations. Gao [17] analyzed the mechanism of longitudinal ultrasonic-assisted microinjection molding (LUµIM). The longitudinal ultrasonic vibration energy was divided into transmission energy and conversion energy.…”