Innovative MuCell micro-foaming injection molding technology

Development overview and principle of MuCell
At present, MuCell micro-foaming technology has become a very mature innovative injection molding technology, which is widely used in the world. Its use began in the United States and Europe, and then extended to Japan and Southeast Asia; Although it has just started in China, users are growing rapidly after more than a year of development. Trexel, the patent holder of this technology, has established a complete technical support service system and spare parts library in China. After years of mass production and use by different users in various products such as commercial equipment, auto parts, electronic appliances, etc., many world-famous OEM manufacturers have designated MuCell to be applied to their products. At the same time, Trexel has also established close cooperation with many famous injection molding machine brands around the world, such as Nissei, Arburg, Engel, Milacron, Husky, Krauss Maffei, Sumitomo, Demag, JSW, Toshiba, etc.
The micro-foaming process can be divided into three stages:
First, the supercritical fluid (carbon dioxide or nitrogen) is dissolved into the hot melt adhesive to form a single-phase solution and maintained at high pressure;
Then, the mold cavity with low temperature and pressure is injected through the switch nozzle, and a large number of bubble nuclei are formed in the product due to the molecular instability caused by the reduction of temperature and pressure,
Finally, these bubble nuclei gradually grow and form tiny holes. From the section of the product, we can clearly see that the surface layer is still an unfoamed solid layer. This is because the mold temperature is low during the filling process, the resin on the surface cools rapidly, and the nucleus has no time to grow.
Basic principle
When using MuCell, special screw and barrel must be installed on the injection molding machine:
1. The screw has a special thread design - after the supercritical fluid is injected into the mixing zone, special threads are needed to cut the supercritical fluid to fully dissolve it with the hot melt adhesive to form a single-phase melt.
2. Single-phase fusion body must be kept at a certain high pressure to prevent segregation. Trexel's barrel is designed with one-way check valve and on-off nozzle to form a closed high-pressure section in the ejection section at the front of the barrel. When injection, the switch nozzle is opened, and the single-phase melt body is injected into the mold cavity immediately and starts foaming.
MuCell hardware system diagram
Users can upgrade the existing injection molding machine, replace Trexel's special equipment, such as screw and barrel, add syringe and injection interface system, and connect a supercritical fluid controller. In addition, these special parts can also be directly integrated in the injection molding machine manufacturer when purchasing new injection molding machines of some brands. The screw and barrel of MuCell are customized parts. Generally, the screw diameter corresponding to the specification of the injection molding machine is selected. The length-diameter ratio is usually 22:1 or 24:1, which is slightly longer than the ordinary ones. The injection molding machine equipped with MuCell can easily switch back to traditional injection molding, enabling users to flexibly arrange production.
Common application areas and case sharing
At present, almost all thermoplastic materials can adopt the micro-foaming injection molding technology. However, considering the economy and product quality requirements, MuCell micro-foaming products are mainly concentrated on products with high quality requirements and expensive materials. The above table lists some commonly used products. Of course, many users have successfully applied this technology in different fields of other industries.
MuCell micro-foaming molding mainly relies on the growth of cells to fill the product, so it is carried out under a low and average pressure. Unlike traditional injection molding, which depends on the constant pressure of the machine, the internal stress of the product is greatly reduced, and the shrinkage of different positions becomes very average.
The formation of single phase melt reduces the viscosity of the resin. Because the decrease of resin viscosity makes the fluid flow faster, it can reduce the melt temperature, mold temperature and injection pressure, make the plastic parts stable and the molding window larger.
MuCell micro-foaming technology can solve the following common problems of traditional injection molding: uneven shrinkage of parts leads to dimensional instability and internal stress problems, shrinkage marks, poor flatness, insufficient concentricity or roundness, poor dynamic balance, difficult filling, etc. The use of MuCell injection molding technology can improve the quality of parts. The following are some application examples.
Typical application fields of MuCell micro-foaming technology
Electronic socket
Due to uniform shrinkage, the size of the product is extremely stable. In the early stage of mold development, the stability and consistency of size reduced the repeated modification of mold design and manufacture, and the Cpk value was very good in production, greatly reducing the defect rate. The left figure shows an electronic socket of Tricon. The material PA66 plus 33% glass fiber can achieve 8% weight reduction and 48% cycle reduction, and the locking force can be reduced by 40%. The Cpk value in production can reach 1.66, and the mold temperature can be reduced by 28 ℃.
The car dashboard
Because of the low injection pressure and melt temperature, MuCell is widely used in IMD products, which effectively solves the phenomenon of "film punching" and "edge penetration" which are easy to occur in traditional injection molding, and also solves the appearance problem caused by shrinkage, improves the stability and straightness of dimensions, thus greatly reducing the defect rate and the locking force.
Car cooling box
Traditional injection molding to solve the warping and distortion of parts usually depends on extending the injection molding and pressure holding time, and at the same time, it uses special fixtures to shape, which greatly reduces the production efficiency. MuCell makes the parts not only very flat during production, but also can be maintained after heat treatment. Many applications show this advantage, such as car cooling box, printer paper rack, etc.
New Technology Development of MuCell Microfoam Injection Molding
MuCell is not suitable for direct use in products with high appearance requirements, but it can be combined with surface spraying and IMD (in-mold injection molding decoration technology) to produce products without shrinkage marks, more straight and more beautiful appearance.
In order to meet the needs of some users who want to directly apply MuCell to appearance products, Trexel and Rhodia have jointly developed nylon materials TECHNYL XCell 6.6 and 6 that are suitable for MuCell micro-foaming technology, and can also carry out fiber or mineral modification according to customer requirements. This material has been certified by WEEE and RoHS. The products processed with it under the MuCell process have excellent appearance performance while ensuring the mechanical properties and other characteristics of the products.
The components made with Rhodia Technyl XCell MuCell 6.6 have excellent appearance
In addition, Trexel is also developing the mold cavity thermal spraying technology, and the products made with this treated mold combined with MuCell also have good appearance performance.
It is believed that Trexel's continuous efforts to optimize and improve these auxiliary technologies can bring MuCell micro-foaming into a broader application field and allow more users to enjoy the advantages of MuCell micro-foaming injection molding.