Now, lightweight automobile structural parts made of carbon fiber reinforced SMC have been able to achieve mass production. A unique Daron® resin developed by AOC makes these parts have excellent mechanical strength, low density and emission, and can withstand the electrophoretic coating process while maintaining the unique design flexibility of composite materials.
AOC has developed a unique carbon fiber reinforced SMC technology
Using SMC made of AOC's unique Daron® resin and carbon fiber, it can stably produce parts with excellent mechanical strength, low density, electrocoating and maintaining the unique design flexibility of composite materials. Related personnel introduced how this new CF-SMC supported the research project TUCANA to successfully develop automotive structural components.
The sheet molding (SMC) molding process has been proven to be one of the most versatile production methods for composite parts. It has many advantages such as low production waste, high output, large design freedom, and functional integration. Therefore, SMC is widely used Ground is used for mass production of strong, durable and lightweight composite parts required by the transportation, electrical, construction and consumer goods markets.
SMC parts made of carbon fiber
"In recent years, the new SMC material based on carbon fiber has been commercialized and has now been fully industrialized. It is used to produce ultra-light structural parts that have better performance than similar aluminum and steel parts." Related personnel said, " Currently, there are several thermosetting resin systems that can be used in the SMC process, each of which has its own unique advantages and disadvantages."
Unsaturated polyester resins (UPRs) are the main resins suitable for SMC applications. UPR-based SMC compounds have good mechanical properties, allow the use of a high proportion of fillers (this helps reduce the cost of the compound) and are in type Good fluidity in the cavity. However, when used with carbon fiber, the UPR has incomplete infiltration of the carbon fiber and poor adhesion on the surface of the carbon fiber, which will result in low mechanical properties of the molded part.
The main advantage of vinyl ester resins (VERs) is that higher mechanical properties can be achieved in carbon fiber parts because the cured VER matrix provides higher mechanical properties. However, it is a big challenge to thicken VERs to the level required for SMC molding. In addition, the viscosity of VERs is usually so high that it cannot completely impregnate the fine carbon fibers, especially when using high volume percentage fibers.
Fine-tuned epoxy resins (EPRs) can bring high mechanical properties to SMC parts. However, it has been facing challenges to implement this process at low cost in mass production. The main disadvantage of the EPR SMC system is that the impregnation, curing and molding processes are difficult and require multiple time-consuming heating steps.
Perfectly compatible with carbon fiber
"In order to solve these problems, AOC has developed a unique SMC technology that can use UPR SMC and VER SMC to produce chopped carbon fiber molded parts with the mechanical properties of epoxy carbon fiber SMC." Related personnel said, "This breakthrough The technology is based on AOC’s Daron® polyurethane hybrid technology."
Daron® SMC technology provides unique advantages, including: extended storage time of the compound, which can be stored for 6 months at room temperature; it has good fluidity during the compression molding process, and can completely fill the cavity, including inserts and ribs. . Daron® SMC technology also uses styrene scavenging technology, which can achieve the best free radical polymerization reaction and greatly reduce the emission of volatile organic compounds.
"Based on the low viscosity of Daron® resin, the fine carbon fiber tows can be well infiltrated, so that high-volume carbon fibers can be used." The relevant person said, "In addition, Daron® SMC technology allows the curing of resin The ideal physical and chemical interaction between the matrix and the carbon fiber is realized."
These advantages, combined with the good fluidity during the molding process, mean that the molded parts can obtain extremely high mechanical properties, with a tensile modulus of up to 43 GPa and a tensile strength of more than 300 MPa.
OEM recognition
So far, the growth of CF-SMC technology in the industry has been relatively slow, which is usually due to the high system cost. To this end, carbon fiber manufacturers have developed a lower cost 50K split-tow carbon fiber. This kind of carbon fiber can be expanded during the SMC compounding process, and at the same time can provide the performance of small tow (about 3K) carbon fiber. When the 50K fiber is expanded into a 3K fiber bundle, the strength performance is improved, and the performance is significantly better than that of the 12K fiber.
The TUCANA project brings together the world's leading academic and industry partners to provide a stronger and lighter vehicle structure to improve the performance of electric vehicles. The TUCANA project will realize this vision through cost-effective and scalable carbon fiber composite solutions. As part of the project, split-tow fiber technology is being used in conjunction with AOC’s Daron SMC technology to produce a CF-SMC. So far, the CF-SMC produced meets all the specifications of the project. Including mechanical strength and molding properties.
In addition to mechanical properties and cost, another prerequisite for meeting the requirements of high-volume automobile production is that the composite parts produced must be able to withstand the test of the spraying process, including the electrophoretic coating step. Electrophoretic coating is usually carried out at a relatively high temperature, the temperature is as high as 200 ℃, and the whole process needs to last about 30 minutes. In the TUCANA project, the produced SMC body panels have passed the painting production line, and it has been proven that when processed with defined molding parameters, the SMC based on the Daron® resin system does not exhibit any delamination.
Not only that, Daron CF-SMC technology has a unique styrene removal function, so there is no styrene emission and the total VOC value is very low (much lower than the 100 μg/g required for interior applications). In the VDA 270 emission test, the odor level is evaluated as level 3. Therefore, Daron CF-SMC can also be used to produce interior parts.
Industrial production of high-performance products
By integrating the forces in the value chain, we have managed to produce CF-SMC on an industrial scale at a low cost. After Zoltek's split-tow fiber is unfolded by Astar, coupled with the application of AOC Daron® SMC resin, the produced CF-SMC can be used to produce the TUCANA project funded by the British government for research purposes The benefits of automotive interior structural parts are excellent mechanical properties, stable processing in mass production, low cost and component emissions, and high design freedom.
"Other potential applications of this new high-performance CF-SMC include dynamic load-bearing components, such as engine subframes and steering knuckles." The relevant personnel concluded, "This makes this material system an extremely good candidate for future automotive mass production applications.