Abstract
The acoustic melt stream velocity field, total force, and trajectory of fluorescent particles in the plasticizing chamber were analyzed using finite element simulation to investigate the acoustic streaming and mixing characteristics in ultrasonic plasticization micro-injection molding (UPMIM). The fluorescence intensity of ultrasonic plasticized samples containing thermoplastic polymer powders and fluorescent particles was used to determine the correlation between UPMIM process parameters and melt mixing characteristics. The results confirm that the acoustic streaming driven mixing occurs in ultrasonic plasticization and could provide similar shear stirring performance as the screw in traditional extrusion/injection molding. It was found that ultrasonic vibrations can cause several melt vortices to develop in the plasticizing chamber, with the melt rotating around the center of the vortex. With increasing ultrasonic amplitude, the melt stream velocity was shown to increase while retaining the trace, which could be altered by modulating other parameters. The fluorescent particles are subjected to a two-order-of-magnitude stronger Stokes drag force than the acoustic radiation force. The average fluorescence intensity was found to be adversely related to the distance from the sonotrodes’ end surface, and fluorescence particles were more equally distributed at higher parameter levels.
Highlights
IntroductionMicro-injection molding has become a key technology for the manufacture of microand nano-devices due to its high dimensional accuracy and production efficiency [1]
Since the surface acoustic wave technique normally uses ultrasonic vibrations to produce a steady laminar flow motion [17,18], we speculate that there may be some kind of shear flow behavior of the melt inside the plasticizing chamber during the ultrasonic plasticization micro injection molding (UPMIM) process
The lack of relevant research has restricted the development of ultrasonic plasticization microinjection molding (UPMIM)
Summary
Micro-injection molding has become a key technology for the manufacture of microand nano-devices due to its high dimensional accuracy and production efficiency [1]. As an innovative variation of micro-injection molding technology, ultrasonic plasticization micro injection molding (UPMIM) has emerged as a new research hotspot thanks to its advantages of high material utilization [2] and low energy consumption [3–5]. Since the surface acoustic wave technique normally uses ultrasonic vibrations to produce a steady laminar flow motion [17,18], we speculate that there may be some kind of shear flow behavior of the melt inside the plasticizing chamber during the UPMIM process. Shear rate is a key design parameter for traditional micro-injection molding equipment that uses a screw plasticizing unit, and is often linked to the plasticizing rate and mixing efficiency [19]. As a screwless plasticization technology [22,23], the process characteristics of UPMIM differ considerably from traditional micro-injection molding techniques [24], but no relevant research was identified to reveal the shear flow behavior during the UPMIM process. Understanding the melt flow and mixing characteristics during the UPMIM process is critical for equipment design and process parameter optimizations
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