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Research on the application of ultrasonic plasticization in the field of micro injection molding

the research and application of ultrasonic in polymer processing are booming. Combined with the research status of ultrasound in the field of polymer processing at home and abroad, this paper introduces the research progress of the application of ultrasound in micro injection molding in my laboratory, and prospects the future development direction of ultrasound in the field of polymer micro injection molding

basic principle of ultrasonic processing technology

ultrasonic is an elastic mechanical wave in a material medium with a frequency higher than 20kHz. Since the 1980s, with the popularity of power ultrasonic equipment, ultrasonic has been widely used in various industries

the physical basis of ultrasonic processing and processing technology is the four basic functions of ultrasound:

1) linear alternating vibration, that is, when ultrasound is used to spread in the media, it makes the media particles vibrate alternately, and causes the periodic change of stress or sound pressure in the media, thus causing a series of secondary reactions

2) when large amplitude vibration propagates in the media, it will form a periodic shock wave with sawtooth wavefront, causing a large pressure gradient on the wavefront, resulting in a series of special effects such as local high temperature and high pressure

3) the nonlinearity of vibration will cause the Bailey force close to each other, the DC average viscosity force caused by the periodic change of viscosity, etc. These DC forces can explain some mechanical effects such as orientation and condensation

4) cavitation, which is an important basic role of ultrasound in liquid media. In the sound field, the bubble of liquid may gradually generate and expand, and then suddenly burst. In the rapid collapse of the bubble, high temperature and high pressure appear in the bubble, forming a local strong shock wave in the liquid near the bubble, resulting in a series of secondary effects

the above four basic effects lead to five effects: mechanical effect, thermal effect, optical effect, electrical effect and chemical effect. At present, ultrasound is widely used in various industries, and it is the five effects of using it. With the mutual penetration of various disciplines, the research and application of ultrasound in the polymer industry is becoming more and more extensive

polymer ultrasonic plasticization and rheological testing device

research status of ultrasound in polymer processing

at present, domestic and foreign scholars have done many exploratory studies on the application of ultrasound in polymer processing such as extrusion molding, micro hot pressing, ultrasonic plasticization and so on

in the application of ultrasonic in extrusion molding, ultrasonic has been deeply studied on the properties of polymer melts. The State Key Laboratory of materials engineering of Sichuan University has conducted in-depth research on ultrasonic polymer degradation and polymer blending and extrusion. In the process of ultrasonic degradation, ultrasonic can reduce the molecular weight of polymer melt, increase the crystallization temperature, and reduce the apparent viscosity of the melt, resulting in the decrease of tensile strength; In the process of ultrasonic polymer blending and extrusion, ultrasonic can reduce the size of mixed particles, distribute more evenly, improve the mechanical properties of the blends, affect the nucleation growth behavior, increase the crystallization temperature and crystallinity, and significantly reduce the die pressure and melt apparent viscosity of the blends, so as to improve the flow properties

in terms of ultrasonic application in micro hot pressing, harutaka mekaru of Japan imprinted the microstructure by vibrating and heating the surface of plastic workpiece with ultrasonic tool head with microstructure mold core. It was found that ultrasonic vibration heating imprinted microstructure has excellent performance in improving the logistics performance of polymerization and weight reduction. The relevant departments of microstructure replication have held eight seminars on coal supply and demand in a short period of two months. The experiment shows that the precision of products formed by ultrasonic vibration heating and stamping is good

in terms of ultrasonic plasticization, the research on the plasticization quality of polymer melt by ultrasonic is still in its infancy. The IKv Institute of Aachen University in Germany introduced ultrasound into the micro Plasticization Process of polymers, which improved the plasticization quality of polymers and obtained polymers with good homogeneity; Hubei Institute of technology introduced ultrasound, mechanical vibration and high shear micro grinding into the plasticization process of polymers. It was found that ultrasound with a certain frequency played a positive role in the crystallization of polyolefins, and the plasticization effect of polymers was good

research progress of ultrasonic application in micro injection molding

the micro injection molding technology with part weight in milligrams or geometric size in microns began in the 1980s. With the advantages of easy realization of low-cost and large-scale commercial production, it has gradually become one of the key technologies for the promotion and application of MEMS technology. As an emerging technology, micro injection molding technology is facing many challenges in the development process, such as difficulty in filling micro cavities, uneven microstructure of micro products, and it is expected that the scrap market will be consolidated in a narrow range in the near future. In order to solve the difficulties encountered in micro injection molding technology, the Institute of mold technology of Central South University has done a lot of research on the application of ultrasonic in micro injection molding

study on ultrasonic plasticization model and plasticization process of polymer

the plasticization quality of polymer is an important factor affecting micro injection molding. To apply ultrasonic to micro injection molding, we first need to study the melting and plasticizing process of polymer under the action of ultrasonic external field, analyze the influence of ultrasonic vibration force field on the viscoelastic properties and apparent viscosity of polymer, and the influence of ultrasonic cavitation field on the melting and plasticizing rate of polymer, and establish the physical model of ultrasonic melting and plasticizing of polymer on this basis

through the theoretical analysis and research of polymer melting and Plasticization Process under the action of ultrasonic external field, the research group developed a polymer ultrasonic plasticization and rheological test device, and carried out the relevant ultrasonic melting and plasticization experiments. The experimental results show that ultrasound can melt the polymer, and the melting process of the polymer under the action of ultrasound is proved. In the process of polymer ultrasonic melting and plasticization, the polymer solid particles at the end face of the tool head and around the tool head are violently rubbed and melted under the action of ultrasonic vibration to produce a molten film. As the melting process continues, all the solid particles near the end face of the tool head melt and form a cylindrical molten pool. Under the dual action of ultrasonic vibration and plasticizing pressure, the molten pool extends around the tool head, Until all plastic particles, such as battery heavy impact tester, battery ball impact tester, battery heavy impact tester, battery heavy impact tester, melt

Figure 1 physical model of polymer ultrasonic melt plasticization

study on the essential mechanism of ultrasonic plasticization

the essential mechanism of polymer ultrasonic melt plasticization is studied by theoretical analysis and simulation. The results show that there are three heat generation effects in the process of polymer ultrasonic melt plasticization, namely friction heat generation effect, viscoelastic heat effect and ultrasonic cavitation effect. The friction heating effect is proportional to the ultrasonic pressure amplitude, ultrasonic frequency and the friction coefficient of polymer; Viscoelastic thermal effect is proportional to stress, strain, phase angle of stress and strain and ultrasonic frequency; The ultrasonic cavitation effect is more intense under the conditions of low ultrasonic frequency (20 kHz), certain ultrasonic sound pressure amplitude (1.4 MPa), low plasticizing pressure (1.25 MPa) and appropriate polymer melt kinematic viscosity (1.2685 m2/s)

Fig. 3 SEM photos of the longitudinal section of the plasticized sample

study on the effect of ultrasonic plasticization on the micro morphology of polymer

the material of the experimental study is high density polyethylene. When high-density polyethylene crystallizes from the melt, it tends to generate spherulites without stress or flow. It can be seen from Figure 3 that the materials obtained by the two plasticizing methods have no stress or flow during natural cooling, so they both generate spherulites, but the size of the two spherulites is very different. The spherulites produced by heating, melting and plasticizing are relatively large, with a diameter of about 500, while those produced by ultrasonic plasticizing are relatively small, with a diameter of only about 200. Therefore, the polymer samples obtained by ultrasonic melting and plasticization have smaller and more uniform grains; It can also be seen from the figure that the microstructure of the polymer plasticized by ultrasonic is more uniform than that of the polymer plasticized by heating and melting, and the effect of ultrasonic plasticization is better than that of heating and melting

Research on energy consumption of ultrasonic plasticization

energy saving is the development direction of contemporary technology, and energy consumption has become an important indicator of new technology. Table 1 Comparison of energy consumption between ultrasonic plasticizing and injection molding machine

see Table 1 for the comparison of plasticizing rate, energy consumption per unit yuan of ultrasonic plasticizing and that with Arburg 370s injection molding machine imported from Germany. It can be seen that the plasticizing energy consumption of ultrasonic melting plasticizing method is basically the same as that of Arburg 370s injection molding machine, and ultrasonic plasticizing, as a new technology, has great room for improvement in energy consumption. And the polymer melt plasticized by ultrasonic melting has a more uniform microstructure

from the comparison between ultrasonic melting and plasticizing mode and heating melting and plasticizing mode, and the energy consumption of Arburg 370s injection molding machine, it can be seen that ultrasonic melting and plasticizing mode not only has great development potential in energy saving, but also has great advantages in plasticizing effect

development of ultrasonic plasticizing micro injection molding machine

due to the advantages of ultrasonic plasticizing in improving the crystalline morphology of polymers, reducing the apparent viscosity of melts, energy saving and so on, the development of ultrasonic plasticizing micro injection molding machine has become one of the important directions of the development of micro injection molding technology

based on the analysis of the screw plasticizing structure of the traditional screw injection molding machine, the Institute of mold technology of Central South University has designed and developed the ultrasonic plasticizing micro injection molding machine with reference to the latest micro injection molding machine at home and abroad, which has the following characteristics:

(1) the plasticizing part of the ultrasonic plasticizing micro injection molding machine transmits energy to the polymer melt through the vibration of the ultrasonic tool head, Complete the plasticizing work through the action of ultrasonic wave

(2) the single plasticization amount and injection amount are small（