Overview of Microcellular Foam Technology Development
In the 1980s, the Massachusetts Institute of Technology (MIT) first proposed the concept of micro-foaming, hoping to produce high-density closed cells in the product, so as to reduce the amount of material while increasing its rigidity, and to avoid such problems as strength Impact on performance.
Trexel was established in the mid-1990s and obtained all MIT patents. It commercialized the microfoaming technology and continued to develop vigorously. Now it has obtained more than 70 related patents around the world. MuCell has now become a very mature and innovative technology that is widely used around the world.
The use of MuCell micro-foaming technology began in the United States and Europe, and then extended to Japan and Southeast Asia. Although it has just started in China, after more than a year of development, users are growing rapidly.
From the above description, we can roughly know that micro-foaming is to produce high-density closed foam in the product. How are these closed foams generated? What is its basic principle?
Fundamental
Microcellular Foaming refers to closed micropores with a thermoplastic material as the matrix and dense layers of the product ranging from ten to several tens of micrometers. The micro-foaming molding process can be divided into three stages: first, the supercritical fluid (carbon dioxide or nitrogen) is dissolved in the hot melt to form a single-phase solution; and then the injection cavity is injected into the mold cavity with a lower temperature and pressure Due to the instability of the molecules caused by the decrease in temperature and pressure, a large number of bubble nuclei are formed in the product; these bubble nuclei gradually grow to form tiny holes.
Microbubble forming process
Compared with conventional injection molding, structural foam injection molding, chemical foam injection molding, and gas-assisted injection molding, micro foaming technology has unique advantages in many aspects and has become an important aspect of the development of injection molding technology in recent years.
Technical characteristics and advantages
Compared with conventional molded products, in addition to purchasing licenses and increasing investment in equipment, the average cost of microfoamed molded products can be reduced by 16% -20%. This is mainly achieved through the following six aspects:
1.Product weight is reduced by about 10-20%
The advantages of the microfoaming technology in reducing weight are obvious. Using different resin materials such as PBT, filled nylon, and ABS to produce parts, the process can be used to ensure that the structural strength of the part does not change greatly. Reduce weight by 10%, reduce material cost of products. This technology is different from structural foaming, the microstructure is more regular, and the distribution of micropores is more uniform. For small thin-walled products, the injection speed of this process is very fast, and the crystal nuclei are formed instantaneously, so the phenomenon of micropore melting does not occur.
2. Shorten the injection cycle
Because the filling of microfoam is relatively fast and does not require dwelling, time can be saved in filling and dwelling, thereby reducing processing costs. Generally, the cycle can be shortened by 15% to 40%, depending on the product and mold design.
3. Reduce mold cavity pressure and extend mold life
Cavity pressure is the pressure established after the plastic fills the cavity. For plastic product designers, the pressure inside the mold cavity is the "number one enemy" that causes them headaches. Due to the pressure, the mold will deform due to heat, and even some parts will break. Micro-foaming technology can effectively reduce the cavity pressure by 57%, thereby extending the life of the mold.
4.Reduce warping
Because there is almost no residual stress inside the product, warpage and deformation of the product can be well suppressed.
5.Improve dimensional stability
The micro-foam molding process greatly reduces the internal stress of the product and ensures the average shrinkage of the product at different locations, effectively improving the dimensional stability of the product, and also significantly reducing the weight of the product and eliminating flashing, thereby improving product quality And price increases provide more room.
6. More flexible product design
Automotive applications
Almost all current thermoplastic materials can use micro-foam injection molding technology. However, considering the requirements of economy and product quality, MuCell micro-foam products are mainly concentrated on more expensive products such as commercial equipment, automobiles and interior decoration materials, electronic and electrical products, such as printers, copiers, and automotive interior parts. , Safety box, electrical switch, thin-walled container, etc. The following table lists some commonly used products for micro foam applications in the automotive field.
Practical applications in the automotive field
1) Door interior panel
Johnson Controls was one of the first users in Europe to use the MuCell process. With extensive experience, the company has newly designed a door trim panel for the Mercedes W212 4-door sedan that was launched in 2009. According to reports, this SPE award-winning product was successfully designed based on the application of the MuCell process.
Using the MuCell process, Johnson Controls designed an improved door trim panel. The door interior trim panel includes a three-layer structure: an ABS skeleton, a PU reactive foam intermediate layer, and a fabric layer with a stretch film as an upper layer material. Due to the lower viscosity of the material when using the MuCell process, the wall thickness of the product can be designed to be thinner. In addition, since a rib / wall ratio of 1: 1 can be used, no sink mark defect is generated. In addition, the inherent injection pressure of the MuCell process is low, so that foamed materials can be injected on the back of the PP film. For the production of the door trim panel with integrated storage box, all the structures on the door can be molded in a single injection process, thereby avoiding the secondary operation process and the waste and repair caused by it. Edge processing, in addition to avoiding sink marks and warping defects.
2) Engine cover
Ford's engineers took inspiration from bubble chocolate to reduce the weight of the body by filling air bubbles during the manufacturing of plastic parts. They use MuCell micro-foam injection molding technology to fill the air bubbles during the part forming process to form a very fine honeycomb structure. These fine voids not only save plastic materials, but also reduce weight without affecting the parts. Any performance. Within a few years, MuCell technology will first be used in the engine cover of Ford vehicles. The first type of application vehicle is the 2012 Fox. In addition, the application models include C-MAX, Grand C-MAX, S-MAX, Mondeo and Galaxy.
3) Fan guard
Fan cover for automobile (Chrysler RS Car), the material is nylon 6 (PA6) with glass fiber, supercritical fluid micro-foam injection molding, compared with traditional injection molding, in addition to reducing deformation and increasing fatigue life, the product (1850g ) 8% lighter than before, cycle time (45 seconds) 20% shorter than before, and clamping force required to be reduced from 800 tons to 400 tons (50% reduction).
Prospects of microfoaming technology
1. Micro-foaming is a technology proven by different products in various industries around the world. It has a broad market, but its application in China is still new.
2. Micro-foaming can provide higher quality (reduce deformation, improve flatness, roundness and dimensional stability, no shrinkage) and lower cost (weight, molding cycle and molding tonnage reduction, more material-saving product design ).
3. Microfoaming can create new business opportunities-high-end applications and cost savings.
4. Not all products are suitable for micro-foaming technology, and need to cooperate to find suitable products.