Understanding Carbon Fiber 3D Printing: Types and Techniques

Carbon fibers are rarely used alone. They are often combined with other materials to form so-called composite materials, in this particular case called carbon fiber reinforced materials. Carbon fiber 3D printing achieves the perfect combination of light weight and high strength by compounding carbon fiber with a matrix material, which can give plastic parts metal-level strength as well as heat resistance, chemical resistance and corrosion resistance. More and more 3D printing companies are beginning to offer carbon fiber reinforced materials or technologies used with this composite material for industries such as aerospace, automotive manufacturing, and construction engineering. This article will introduce the definition and types of carbon fiber 3D printing.

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Technical principles and material types

In FDM 3D printing, carbon fibers are usually embedded in thermoplastic filaments in the form of chopped or milled fibers. These fibers act as a reinforcing "skeleton" to enhance rigidity, dimensional stability and heat resistance. Unlike continuous carbon fiber materials (such as Markforged's proprietary technology), FDM carbon fiber relies on short fibers dispersed in a polymer matrix.

According to the fiber morphology and processing methods, it is mainly divided into three types:

Grinding carbon fiber materials

Mixed with micron-level carbon powder and plastic, although it can achieve a matte surface effect, it will significantly reduce the strength of the material. This type of material is inexpensive (such as ABS mixed material for $30) and is only suitable for appearance prototypes or non-load-bearing parts.

Chopped carbon fiber composites

Industrial-grade materials are reinforced with 0.5-1mm chopped carbon fibers and are divided according to the application scenarios:

General-purpose: with engineering plastics such as nylon to improve impact resistance

Aviation-grade: combined with high-performance polymers such as PEEK and PEI to meet high temperature resistance requirements

This type of material can be used to manufacture functional prototypes, production jigs and terminal parts in harsh environments, while maintaining 85% of the basic material properties and significantly improving dimensional stability.

Continuous carbon fiber technology

The continuous fiber process represented by Markforged obtains mechanical properties close to metal by layered deposition of continuous carbon fiber bundles. Its product strength can reach 30 times that of ordinary plastics, the strength-to-weight ratio is 3 times that of aluminum, and the density is only 1/7 of steel. Although it requires special equipment and higher costs, it has significant advantages in replacing load-bearing structural parts.

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Material processing and process control

Chopped carbon fiber

Carbon fiber 3D printing uses short carbon fiber reinforced thermoplastics. These short fibers are usually less than 1 mm and are evenly mixed in the base material (such as PLA, PETG, ABS) to enhance the strength and stiffness of the material. Although carbon fiber filling materials can significantly improve the mechanical properties of parts, their high hardness and wear resistance will cause rapid wear of the nozzle, so stainless steel, hardened steel or tungsten carbide nozzles are recommended to prevent rapid loss. In addition, too high a carbon fiber content may affect the surface finish of the print, so the appropriate carbon fiber ratio should be selected according to the needs.

In terms of printing settings, the temperature setting of carbon fiber reinforced materials is usually similar to that of their base materials. For example, CF-PLA can refer to the printing parameters of ordinary PLA, but since the addition of carbon fiber may affect the melt fluidity, it is recommended to appropriately reduce the printing speed (such as 30-50mm/s) to improve the interlayer bonding. After printing, carbon fiber particles are likely to remain inside the nozzle, so it is recommended to use 15-20cm of pure PLA filament for cleaning after printing to prevent nozzle clogging. In addition, the high abrasiveness of carbon fiber accelerates nozzle aging, so regularly checking the nozzle wear and replacing the wear-resistant nozzle in time will help maintain good printing quality and equipment life.

Continuous carbon fiber

Unlike fiber-filled filaments, continuous fibers are achieved through an additional process of continuous fiber reinforcement (CFR). CFR allows users to flexibly implement continuous fibers in their parts; therefore, users can better control the amount of carbon fiber to be added to the part, and strategically arrange the fibers according to load requirements to achieve the best effect. Optimized parts can also reduce manufacturing time and manufacturing costs. Markforged(https://markforged.com/ ) said that when considering the use of continuous fibers, adjustments are made through two key methods: 1. Determine whether to place continuous fibers in each layer of the part 2. Determine the reinforcement strategy for each printed layer that needs to be reinforced. Examples of common continuous fiber technologies for parts include:

Sandwich panels

Similar to the manufacture of traditional composite layups, sandwich panels only add continuous fibers to the top and bottom of the part. Under most bending load conditions, the stress on the surface of the part is the highest. Sandwich panels are used to resist forces in the Z-axis direction.

Shells

Skins are similar to sandwich panels, but use closed loops of continuous fiber within the walls of each layer. For shell reinforcement, continuous fiber is placed around the periphery of each layer to resist forces along the XY plane.

Strip

Strips follow the style of sandwich panels, but with “strips” of continuous fiber added in some critical areas of the part. Strips can be used in taller sandwich panels to spread the load, reducing the risk of infill buckling.