The micro-foam injection molding process is an innovative precision injection molding technology. The micro-foam injection molding process breaks through many limitations of traditional injection molding, can significantly reduce the weight of parts, shorten the molding cycle, and greatly improve the warping deformation and dimensional stability of parts. Micro-foam injection molding technology has great advantages in producing precision products with high quality requirements. In the field of injection molding, Trexel's MuCell micro-foaming molding process has performed particularly well and is also one of the fastest-growing and most widely used molding technologies in precision molding technology.

Technology Demand

The soaring prices of raw materials have brought a huge impact on the Asian market where manufacturing is relatively cheap. Many processors have begun to realize that even China is no longer the source of cheap products. But on the other hand, in order to gain a favorable market advantage, suppliers in Vietnam, Indonesia and some other countries have to adapt to consumer demand by cutting prices.

However, as products become more and more complex, the tolerance requirements and surface appearance quality requirements of parts are also getting higher and higher. The use of traditional injection molding technology to produce these parts often leads to a variety of quality problems, such as large internal stress in the products, product deformation due to uneven shrinkage, etc., which cannot meet the required quality or cost requirements. It can be said that plastic processors have encountered unprecedented challenges and they urgently need to seek new processing technologies to change the predicament.

Precision injection molding technology is attracting more and more attention. Micro-foam injection molding process, this technology can control the production size accuracy of parts between 0.01 and 0.001 mm, sometimes even below 0.001 mm. Compared with traditional injection molding processes, the parts produced by this technology have good mechanical properties and dimensional stability, and the dimensional accuracy and repeatability of the parts are high, and the tolerance range is small.

Due to its own multiple performance advantages, coupled with the "mutation" in the field of plastic processing, this technology has a broad space for development. In the medical and electronic fields that have very high requirements on product specifications, precision injection molding has developed into a very mature and complete injection molding process. With the rapid development of the automobile market, drivers are looking for cars with lower fuel consumption, and they also need to configure high-precision automobile accessories and trims. The production of these precision parts is also inseparable from the precision injection molding process.

Principle

The MuCell micro-foaming process mainly relies on the expansion of pores to fill the product and completes the molding of the product under a relatively low and even pressure. Micro-foam molding can be divided into three stages (as shown in Figure 1): First, the supercritical fluid (CO2 or N2) is dissolved into the hot melt adhesive to form a single-phase solution, and then maintained at a certain constant pressure; then, the single-phase solution is injected into the mold cavity with lower temperature and pressure through a switch nozzle to form a micro-foam product. The decrease in temperature and pressure triggers molecular instability, thereby forming a large number of bubble nuclei in the product, which gradually grow and generate tiny holes. The enlarged cross-section of the foamed product is shown in Figure 2. It can be seen that the surface layer of the product is still an unfoamed solid layer. This is because the mold temperature is low, the surface resin cools quickly, and the cell nucleus has no time to grow.

Development Prospects

The traditional injection molding process requires a relatively high in-mold pressure to complete the injection molding. However, the higher pressure point at this time often causes the product to rupture due to the large and uneven pressure. In contrast, the MuCell micro-foaming molding process does not need to rely on the machine's continuous pressure maintenance to achieve smooth filling of the melt, thereby greatly reducing the internal stress of the product and ensuring the average shrinkage of different positions of the product, effectively improving the dimensional stability of the product, and significantly reducing the weight of the product and eliminating flash. In addition, the molds used in this process do not require repeated fine-tuning, and the quality of injection molding can be guaranteed as long as they operate normally.

The MuCell micro-foaming molding process speeds up mold filling and cooling, while eliminating the pressure holding process, effectively improving the molding cycle of the part. At the same time, this process also enables injection molding production to develop in the direction of automation, which is more conducive to improving production efficiency.

Advantages

1. Precise size control

The MuCell micro-foaming molding process can control the tolerance of the parts within the required range to ensure the dimensional stability of the parts. For the early stages of mold development, this can also reduce repeated modifications to mold design and save production costs.

Take the production of a mold with a height of 32.43cm, a width of 87.33cm and a length of 191.50cm as an example (as shown in Figure 3), the mold is produced by using traditional injection molding process and MuCell micro-foaming molding process respectively, and thus a group of solid parts and a group of micro-foamed parts are obtained. The two groups of parts were measured in length, width and height. Through comparison, it was found that MuCell parts have smaller dimensional deviations in all directions and have stronger process capabilities for controlling dimensions. This can also be seen from Figure 4.

Japan has already produced a small printer bracket using the MuCell process. This is a very lightweight part that moves back and forth on the surface of the printer, so the weight and tolerance requirements of the part are very high. The process improves the part's cost, precision, weight and molding cycle time. Furthermore, the tolerance of the component is only 30¦Ìm.

2. Improve warpage

Warpage is one of the common and difficult-to-solve product defects in traditional injection molding production. It is mainly caused by uneven stress and shrinkage of the product. This problem is solved because the part is always under average pressure during the entire MuCell micro-foam molding process, ensuring uniform shrinkage at different positions. Taking the paper guide as an example, the degree of warping deformation of the solid part obtained by the traditional injection molding process is 0.807mm, while the degree of warping deformation of the part obtained by the MuCell foaming molding process is only 0.429mm, which is 47% higher than the former.

Another typical application example is the use of this process to produce traction control connector housings on automobiles. The component is made of PBT material reinforced with 30% glass fiber. After reinforcement, the shrinkage rate of the material in the horizontal and vertical directions is inconsistent. Therefore, when using the traditional injection molding process for production, it is very easy to warp and deform. The deformation degree of the solid part is 1.1cm, while the warping deformation of the part obtained by MuCell micro-foaming molding has been significantly improved, and its warping deformation degree is only 0.27cm, which is about 75% lower than the former.

3. Weight reduction

The advantages of MuCell technology in weight reduction are also obvious. Different resin materials such as PBT, filled nylon and ABS are selected to produce parts. This process can reduce the weight of the parts by 10% without greatly changing the structural strength. It can be seen from Table 2 that the weight of micro-foamed molded parts made of different materials is lower than that of solid parts made of the same material.

Different from structural foaming, the micropore structure of MuCell is more regular and the distribution of micropores is more uniform. For small thin-walled products, the injection speed of the MuCell micro-foaming molding process is very fast, and the crystal nuclei are formed instantly. Therefore, these micropores will not experience the undesirable micropore fusion phenomenon. ¡±

It is worth mentioning that although polycarbonate materials can be micro-foamed well, the impact strength of parts made from this material will decrease, so it is not suitable for this process.

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