AOCwill showcase its unique Daron ® The combination of resin and carbon fiber makes SMC components with excellent comprehensive performance, including high mechanical strength, low density, low emissions, and online coating, while maintaining the unique design flexibility of composite materials. AOC European technical experts introduced how this new carbon fiber SMC can be used for the development of automotive structural components in the Tucca project (funded by the UK government).

The sheet molded compound (SMC) process has been proven to be one of the common production methods for composite material components. It combines the advantages of low waste in the production process, large-scale production, and functional modularization, making SMC widely used in the mass production of sturdy, durable, and lightweight composite material components, applied in transportation, electrical, construction, and consumer markets.

Manufacturing SMC components using carbon fiber

AOC European R&D scientist Ron Verlege explained, "In recent years, new types of SMC materials based on carbon fibers have been commercialized and have been applied on an industrial scale. The ultra-light structural parts made from these materials have better performance than similar products such as aluminum and steel." The SMC process can use several thermosetting resin systems, each with its specific advantages and disadvantages.

The commonly used type of SMC is unsaturated polyester resin (UPR), as UPR SMC has good mechanical properties, allows for a higher filling amount (thereby reducing product costs), and the material still has good flowability in the mold. However, when used with carbon fibers, resin infiltration is incomplete and adhesion to the surface of the carbon fibers is poor, resulting in poor mechanical properties of the molded parts.

Vinyl ester resin resin (VER) used for carbon fiber molded parts can obtain higher mechanical properties. However, thickening vinyl resin sheets to the required platform is a challenge. In addition, the viscosity of vinyl resins is usually too high to fully immerse carbon fiber filaments, especially when the proportion of carbon fibers is high.

The optimized epoxy resin (EPR) can also be used for SMC parts and achieve high mechanical properties. However, the disadvantage of the EPR SMC system is that it is difficult to infiltrate, and the maturation and molding processes require a considerable amount of time-consuming heating steps, which makes the EPR SMC system difficult to produce on a large scale and lacks competitiveness in cost.

Compatible with carbon fiber

AOC Strategic Project Manager Luuk Groenewoud added, "AOC has developed a unique SMC technology that enables short cut carbon fiber SMC to have the excellent processability of UPR SMC and VER SMC, as well as the high mechanical properties of epoxy resin carbon fibers. This breakthrough technology is based on AOC's Daron ® Polyurethane hybrid technology.

Daron ® SMC technology has unique advantages, such as long storage time (up to 6 months at room temperature), good fluidity during the molding process, and the ability to completely fill the mold cavity, including inserts and reinforcing ribs. Daron ® SMC technology also has a unique free radical curing system, resulting in abnormally low emissions of volatile organic compounds during the production process.

Ron Verleg said, "Daron ® The resin viscosity is very low, and even high volume carbon fiber bundles can be well wetted. In addition, Daron ® SMC technology creates ideal physical and chemical interactions between the cured resin matrix and carbon fibers.

These advantages, combined with the good fluidity of the forming process, endow the components with high mechanical properties, with a tensile modulus of 43GPa and a tensile strength greater than 300MPa.

Obtaining OEM recognition

The industrialization process of carbon fiber SMC technology has been relatively slow due to high system costs. Carbon fiber manufacturer Zoltek has developed a low-cost 50K split bundle carbon fiber that can be opened during the SMC molding process, and the performance of the opened carbon fiber can reach the small bundle level (about 3K). When 50K fibers are divided into 3K bundles, the strength increases, significantly exceeding that of 12K fibers.

The Tucana project, funded by the British government and initiated by Jaguar Land Rover, aims to develop a harder and lighter vehicle structure to improve the performance of electric vehicles. The participants include academic and industry partners. The main focus of the Tucana project is to seek cost-effective and scalable solutions for carbon fiber composite materials. As part of this project, Astar combines Zoltek's bundle splitting fiber technology with AOC's Daron SMC technology to produce a CF-SMC that meets all the specifications of the project to date, including mechanical strength and mold performance.

In addition to mechanical performance and cost, another prerequisite for mass automotive manufacturing is that composite parts can withstand the coating process, including online electronic coating. The latter is carried out at relatively high temperatures, up to 200 ° C, for about 30 minutes. In the Tucana project, the template has been run through the production line painting workshop and has been proven to be based on Daron ® The SMC of the resin system will not exhibit any delamination when processed using the specified molding parameters.

In addition, Daron CF-SMC technology includes a unique free radical curing technology that significantly reduces styrene emissions during the production process, with a very low total VOC value (far below the 100 µ g/g threshold set for indoor applications), and the odor is rated as Level 3 in the VDA 270 emission test. Therefore, DaronCF-SMC can be used for the production of internal components.

Industrial scale provides high performance

By integrating the power of the industrial chain, Zoltek, AOC, and Astar have found a cost-effective solution for the industrial production of CF-SMC. Zoltek's bundle splitting fiber, Astar's fiber opening technology, and AOC's Daron ® SMC resin, combined with the advantages of the three, forms CF-SMC for the engineering design and production of automotive interior components in the Tucca research project. It has a series of advantages such as strong mechanical properties, process robustness for large-scale production, favorable cost efficiency, extremely low VOC emissions, and design freedom.