Abstract
With the wide application of Micro-Electro-Mechanical Systems (MEMSs), especially the rapid development of wearable flexible electronics technology, the efficient production of micro-parts with thermoplastic polymers will be the core technology of the harvesting market. However, it is significantly restrained by the limitations of the traditional micro-injection-molding (MIM) process, such as replication fidelity, material utilization, and energy consumption. Currently, the increasing investigation has been focused on the ultrasonic-assisted micro-injection molding (UAMIM) and ultrasonic plasticization micro-injection molding (UPMIM), which has the advantages of new plasticization principle, high replication fidelity, and cost-effectiveness. The aim of this review is to present the latest research activities on the action mechanism of power ultrasound in various polymer micro-molding processes. At the beginning of this review, the physical changes, chemical changes, and morphological evolution mechanism of various thermoplastic polymers under different application modes of ultrasonic energy field are introduced. Subsequently, the process principles, characteristics, and latest developments of UAMIM and UPMIM are scientifically summarized. Particularly, some representative performance advantages of different polymers based on ultrasonic plasticization are further exemplified with a deeper understanding of polymer–MIM relationships. Finally, the challenges and opportunities of power ultrasound in MIM are prospected, such as the mechanism understanding and commercial application.
Highlights
In the last decade and even in the future, some electromechanical systems with special functions and personal electronic products will continue to maintain the trend of miniaturization and precision
Some representative performance advantages of different polymers based on ultrasonic plasticization are further exemplified with a deeper understanding of polymer–micro-injection molding (MIM) relationships
The results showed that when the ultrasonic power is flow behavior of molten polymer in the ultrasonic vibration injection-molding process, Jiang et al [43] developed a new visualization device for analyzing the filling velocity field in the injection-molding process
Summary
In the last decade and even in the future, some electromechanical systems with special functions and personal electronic products will continue to maintain the trend of miniaturization and precision. Due to the limitations of the process characteristics and material properties, when the micro-molded parts comprise cross-scale features or break through a certain volume/size boundary, MIM could be quite challenging in terms of replication fidelity, materials utilization, and energy consumption. In this context, power ultrasound was introduced to enhance the MIM performance. The simulation results of Gao et al [59] show that the ultrasonic vibration can obtain higher speed, lower viscosity, a more uniform viscosity field as Polymers 2021, 13, x FOR PEER REVIsEhWown, and better mold-filling performance, which makes the mold-filling qu aolfity of micro-plastic parts better, which is consistent with the experimental result before Qiu [45]. FFiigguurree66..((aa))VVisicsocosistiytyanadnd(b()bv)evloelcoitcyitdyisdtirsitbruibtiuotnioonf pofolpyomlyemr meremlt aellot naglotnhge tvheertvicearlticceanltceerlninteerolifntehoef ctrhoessc-rsoecstsi-osnecutinodnerudnidffeerredniftfceorenndtitcioonnsd[i5ti9o]n; Cs o[5n9d]i;tiCoonn1d—itwiointh1o—utwuiltthraosuotnuicl;trCaosnodniitci;oCno2n—dwitiiothn t2h—e fwlowithfrothnetiefrlovwibrafrtioonnt;ieCronvdibitriaotnio3n—; wCiothndthiteioflnow3—frownittiehr vthiberaftlioown afnrdonchtiaenrgvedibrrhaetioolnogaicnadl eqcuhaatniogne.d rheological equation
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