Analysis of the current situation of the hottest m

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Analysis of the current situation of micro foaming injection molding technology

micro foaming injection molding technology can significantly reduce the weight of parts on the basis of basically ensuring the performance of products, and has the characteristics of small internal stress, not easy to produce surface defects, and special molding advantages for products with large wall thickness differences. Compared with conventional injection molding, structural foaming injection molding, chemical foaming injection molding and gas assisted injection molding, it has unique advantages in many aspects, and has become an important aspect of the development of injection molding technology in recent years

micro foaming polymer materials refer to porous polymer materials based on polymer materials with cell sizes ranging from less than one micron to tens of microns. Foamed plastics prepared by conventional physical or chemical foaming methods usually do not belong to this category because of their large pore size. Compared with the millimeter level pores of general foamed plastics, micro foamed polymers have much smaller pores and much higher cell density, so they are called micro foamed polymers

development overview

the manufacturing industry was the focus of encouraging foreign investment in the early 1980s. In 2013, it was a one-year field to strengthen the regulation of the rare earth industry. Massachusetts Institute of Technology (MIT) first proposed the concept of micro foaming plastics and developed the corresponding molding technology. This concept is proposed to introduce a large number of voids in the polymer matrix that are smaller than the original defect size of the polymer, so as to reduce the amount of material, improve its rigidity, and avoid obvious impact on the strength and other properties. The pore size of the micro foaming material prepared by this process is generally less than 10 microns, especially the high cell density, up to/cm3. The micro foaming process can be divided into three stages. First, the supercritical fluid (mainly carbon dioxide and nitrogen) is dissolved into the polymer to form a single-phase solution of polymer/gas; Then, the thermodynamic instability of the system is caused by temperature or pressure, which makes the solubility of the gas in the solution decrease; Due to the decrease of gas equilibrium concentration, a large number of bubble nuclei are formed in the polymer matrix, and then gradually grow to form tiny holes

many people think that the application of supercritical fluid in polymer processing is only in the laboratory. In fact, the commercial application of this method has long begun. Since the 1950s, supercritical ethylene has been used in large-scale manufacturing of low-density polyethylene. In the 21st century, trexel cooperated with MIT and first used this technology to realize the commercial application of micro foaming injection molding. It is reported that reedy international has also developed a similar extrusion micro foaming device

there have been a lot of literature reports on polymer micro foaming technology, and the research is mainly focused on the molding process of amorphous and semi crystalline polymer micro foaming materials, such as polyvinyl chloride (PVC), polystyrene (PS), polycarbonate (PC), polymethylmethacrylate (PMMA), polyethylene terephthalate (PET) and polysulfone. The research on processing technology mainly involves micro foaming extrusion, micro foaming injection molding, micro foaming blow molding and rotary molding. The units engaged in micro foaming technology research and achieved remarkable research results mainly include Massachusetts Institute of technology in the United States, University of Wisconsin Madison, Georgia Institute of technology, University of Toronto in Canada, GKSS research center in Germany, University of Twente in the Netherlands, etc

development status

in 1997, on the basis of cooperation with MIT, trexel took the lead in the industrialization research of micro foaming injection molding technology. The first injection molding machine used for research was Engel's 150 ton screw and piston injection molding machine, and later the reciprocating screw injection molding machine was used. Until 2000, trexel company first launched its commercial product of micro foaming injection molding machine at the International Plastics Expo in Chicago. At the same time, many companies in Japan, Europe and South Korea have also been committed to the development of micro foaming injection molding process. At present, the technology of preparing polymer micro foaming materials with supercritical fluid represented by MuCell of trexel company has been widely recognized. Many world-renowned equipment and raw material manufacturers have purchased the patent right to use this technology, including well-known companies and enterprises such as arbug, Demag, Engel, Milacron, husky, Krauss Maffei, Battenfeld, DuPont, JSW, Toshiba, etc. It can be said that micro foaming injection molding technology is changing from simple theoretical and experimental research to mature commercial development. Although this stage has experienced nearly 20 years, this mode of commercial development and its successful experience indicate that the industrialization of new processing technology will become easier and easier in the future. As Professor Nam P. Suh of MIT, the founder of micro foaming technology, said, this technology is by no means as simple as saving materials, and the benefits it brings will be gradually reflected in various applications in the future. The successful development of this technology can be said to be a model of cooperation between universities and industry. Practice has proved that as long as cooperation is carried out under a strictly demonstrated framework, research institutions and industry can benefit from such cooperation

the main feature of micro foaming injection molded products is to reduce the weight on the basis of basically maintaining the original mechanical properties of the products. At the same time, there is almost no residual stress inside the product, so the warpage and deformation of the product can be well suppressed. Moreover, because it can effectively prevent shrinkage marks, the requirements for the uniformity of product wall thickness are greatly reduced, which provides more space for product design

theoretically, almost all non structural plastic products and some structural plastic products can be prepared by micro foaming injection molding process. However, considering the market demand, economy and other factors, at present, the micro foaming injection molding products developed by the United States, Japan and other countries are mainly concentrated in the fields of automotive and interior decoration materials, electronic and electrical products, medical products and other fields, such as automotive intake manifold, fuse box, hood, electrical switch, electrical control module, thin-walled container, medical syringe and so on

characteristics and advantages

comparison with conventional injection molding products

based on the analysis and relevant data comparison of the existing micro foaming injection molding machine using trexel's patent abroad, it can be seen that compared with conventional molding products, the average cost of micro foaming molding products can be reduced by 16%-20% except for the purchase of licenses and the increase of equipment investment. This is mainly achieved through four aspects:

1 The cycle time of micro foaming injection molding can be reduced by 50%, thus reducing the processing cost. At the same time, the proportion of leftovers of injection molding products is reduced, and the energy consumption of the equipment is also lower

2. For the same type of products, the micro foaming injection molding process can use smaller and fewer machines, and the mold cost is lower, thus reducing the investment cost

3. Because the density of micro foaming injection molded products is reduced, products with more thin-walled structure can be designed to reduce the material cost of products

4. Due to the reduction or elimination of the internal stress in the mold caused by conventional molding in the process of mold closing and pressure maintaining, micro foaming injection molding can prepare products with flatter, straighter and higher dimensional accuracy, thus providing greater space for the improvement of product quality and price

comparison with other injection molding processes

many other injection molding processes also use or involve gases or foaming agents. These processes mainly include structural foaming injection molding, gas assisted injection molding and chemical foaming molding

micro foaming injection molding and structural foaming injection molding

Structural foaming injection molding is usually used to mold larger products. The most common is to use special low-pressure injection molding machine to process high-density polyethylene (HDPE) raw materials. The weight of its products can be reduced by 10% or more. Micro foaming injection molding has more advantages than structural foaming injection molding in some aspects. For example, for most materials, including commonly used engineering plastics, the reduction of materials and the reduction of injection cycle time are more significant. Micro foaming injection molding can form both thin-wall and thick-wall structures. The product designer should have greater flexibility in the verification surface of the machine with an annual cycle. However, micro foaming injection molding does not have many advantages for products with large aspect ratio and thick wall (more than 6mm) products

micro foaming injection molding and gas assisted injection molding

gas assisted injection molding can mold products with very high surface quality. Through special design of molds and products, gas assisted injection molding can be realized by designing cavities in the interior of thick wall products. Micro foaming has no advantage for the molding of thick wall products, and the surface quality of its products cannot be very perfect

however, gas assisted injection molding is usually only used to eliminate the shrinkage marks of products, so in this regard, micro foaming injection molding may be a better choice, which can reduce the weight of products more, form in a shorter cycle time, and reduce the warpage of products, and eliminate the shrinkage marks at the same time

micro foaming injection molding and chemical foaming molding

chemical foaming agent decomposes at a specific temperature to produce gas foaming agent. Different types of foaming agents are suitable for decomposition and foaming at different temperatures. It is usually used for forming thick wall products to eliminate shrinkage marks, and at the same time, it can also reduce the density of products. The use of chemical foaming agent for thin-walled products will degrade the surface quality and significantly reduce its mechanical properties. Moreover, from the economic point of view, chemical foaming can not significantly reduce the density

the advantage of micro foaming injection molding is that many endothermic chemical foaming agents will generate water (also CO2 gas), so it is necessary to add water absorbent to prevent the degradation of polymer melt due to the presence of water. The different batch numbers of gas blowing agents make it necessary to adjust the production process at any time in the production process. In addition, due to the poor thermal stability of chemical foaming agents, it is difficult to process high-temperature resins. Chemical blowing agents usually remain in the resin or produce by-products. Resins with by-products or undissolved chemical foaming agents usually reduce the aging resistance of products and may cause blockage of mold exhaust holes. Moreover, the leftovers produced in the processing process are difficult to be recycled on site

of course, micro foaming injection molding technology is not perfect. For products requiring strong transparency and very high surface quality, the use of micro foaming injection molding technology needs to be more careful

the patterns or elements are designed in nano scale or 1 billionth of a meter scale

source: China Plastics and rubber heyadong, Beijing University of Chemical Technology

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