Advantages, available technologies and applications for 3D printing of composite materials

The processing of composite materials in 3D printers is a young technology that, however, possesses great potential that remains largely untapped. According to a report by SmarTech Analysis, 3D printing with composite materials will become a business of almost 10 billion US dollars within the next decade - to put it mildly, a significant growth opportunity. In today's article, we will examine the advantages of 3D composite printing, the key technologies and applications available on the market, to find out what is driving the growth of this exciting industry.

Composite materials or fiber-reinforced polymers typically comprise a core polymer material and a reinforcement material, such as chopped or continuous fibers. The composite material offers higher strength and stiffness compared to unreinforced polymers. In some cases, it can even replace metals such as aluminum. These improved material properties make composite materials highly desirable materials for tools and end-use applications across a range of industries such as aerospace, automotive, industrial goods, and oil and gas industries.

The ability to rationalize and reduce the costs of traditional composite manufacturing is one of the key factors for the growth of 3D composite material printing. In addition to 3D printing, there are numerous methods for manufacturing composite parts. However, most of them have a number of disadvantages: the need for manual layup of composite material layers and the use of expensive curing equipment and tools such as molds. This makes the process of traditional composite part manufacturing very labor-intensive, resource-intensive, and capital-intensive, which means that it can be difficult to scale it to large volumes. 3D printing, on the other hand, enables automation of the manufacturing process, since the entire process is controlled by software and only requires manual intervention in the post-processing phase.

In 3D printing, it is possible to print with two types of reinforcing fibers: discontinuous fibers and continuous fibers. With discontinuous fibers, small strands with a length of less than one millimeter are integrated into the polymer material. The percentage of fibers used and the base thermoplastic determine how strong the final part is. With continuous fibers, long fiber strands are mixed with thermoplastics such as PLA, ABS, nylon, PETG, and PEEK during the printing process. Parts 3D-printed with continuous fiber are extremely lightweight and yet as strong as metal. Regarding the types of fibers used, carbon fiber is one of the most popular, followed by glass fiber and Kevlar.

In 2020, the market for 3D composite fiber printing is still young and only a handful of companies offer 3D composite printing solutions. Most 3D printers that can process composite materials are based on the polymer extrusion process, referred to as Fused Filament Fabrication (FFF). In FFF, a nozzle moves over the build platform, extrudes a molten plastic filament, which is referred to as filament, and creates an object layer by layer. 3D printing of filaments containing discontinuous fibers is straightforward and requires only a hardened steel nozzle to withstand abrasive fiber strands. However, when it comes to continuous fiber printing, the FFF process requires a second nozzle to deposit a single, uninterrupted fiber strand separately.

The 3D printing process for continuous fibers was first introduced in 2014 by Markforged when the company launched the Mark One 3D printer. In the meantime, the second generation is available as the Mark Two 3D printer. While the Mark One was replaced by a new generation of 3D printers, the technology remains the same: the printer is equipped with two nozzles, one of which is used to deposit plastic filaments and the other to simultaneously deposit carbon fiber strands. Now, in 2020, Markforged offers a range of desktop and industrial 3D composite printers with primary applications for functional prototyping and the production of end-use parts and tools.

Desktop Metal is another company that has innovated FFF technology for printing composite materials. In a move that was quite surprising for a company that had previously focused exclusively on 3D metal printing, Desktop Metal launched the Fiber 3D printer in November 2019.

A new polymer desktop system combines traditional AFP technology (Automated Fibre Placement) with FFF for 3D-printed parts enhanced by continuous fibers. AFP technology is an automated manufacturing process for composite materials. Fiber reinforcements are heated and compacted on typically complex tool shapes to produce continuous fiber composite materials. Desktop Metal has scaled this process down to a desktop format and named its new technology Micro Automated Fibre Placement (μAFP). The μAFP functions like Markforged's technology but does not use fiber spools; instead it uses rolls of fiber tape. It can embed carbon fiber in nylon, PEEK and PEKK, and nylon can also be integrated with glass fiber. When manufacturing small composite parts, manufacturers still rely primarily on manual lay-up. Such labor-intensive processes require technicians, expensive tools and considerable time, which increases the overall cost of manufacturing a part. By combining μAFP with FFF in its new fiber systems, Desktop Metal aims to make manufacturing smaller composite parts simpler and more cost-effective. With the fiber, fixtures and jigs, various end-use parts, and all components where weight is a priority can be manufactured, such as racing equipment.

In a similar manner, Anisoprint, a Russian/Luxembourg start-up, has developed an extrusion-based process that the company calls Composite Fibre Coextrusion (CFC).

In contrast to the technologies of Markforged and Desktop Metal, CFC technology enables the reinforcement of plastic with continuous composite fibers directly during the printing process and not in the pre-print stage. With this approach, users can use any desired plastic (PETG, ABS, PC, PLA, Nylon, etc.) and change the fill density of the composite material.

Anisoprint's first device was a Composer 3D printer in desktop format. Recently, the company also introduced the Anisoprint ProM IS 500, an industrial machine for printing high-temperature thermoplastics with continuous fiber reinforcement. The Anisoprint ProM IS 500 features up to four interchangeable print heads for printing composite materials and pure plastic. With these, it is possible to reinforce different zones of the part with different composite materials (e.g. carbon/basalt), depending on the user's objective. When the system is officially launched at the end of 2020, this represents another step forward, both for 3D composite printing and for advanced polymer manufacturing.

In addition to FFF 3D printing, some companies have developed an approach that combines 3D composite printing with robotics. Such a combination offers greater flexibility with regard to geometry, since the robot arm can move along multiple axes, thus providing the ability to print larger parts. Arevo is one such company that has developed a laser-based method for 3D printing with carbon fiber. The process involves the deposition of layers of pre-impregnated continuous carbon fiber filament, which is simultaneously heated by a laser before a roller compresses it onto the build platform. The process is similar to the Direct Energy Deposition process, which is typically used with metals.

At Arevo, the print head is mounted on a multi-axis robotic arm, so 3D printing is possible in every orientation that best suits the design of the part.

"If you look at 3D printing, the majority of 3D printing is based on layers, and the layers are deposited in the X and Y plane. If you look at the properties of parts manufactured with this process, they tend to suffer in the Z direction," says Wiener Mondesir, CTO at Arevo. Thanks to the use of a robotic arm, Arevo "has eliminated the problem of strength in the Z direction that plagues other layer-based technologies, because they are able to deposit material in the Z direction".

Furthermore, robots offer "theoretically unlimited build size, since we can design our robots in gantry configuration to manufacture parts for aerospace. At the same time, the same robot can build a bicycle." Arevo has demonstrated the latter point by developing the world's first 3D-printed bicycle frame made from composite material. More on this application below.

Another company that combines 3D composite printing and industrial robots is Continuous Composites, based in the USA.

The method known as CF3D (Continuous Fiber 3D Printing) feeds a roll of dry carbon fiber into a print head mounted on a seven-axis industrial robot. Inside the print head, the fiber is impregnated with a fast-curing photopolymer resin and then extracted through the "end effector" and immediately cured with a powerful energy source. Like Arevo, the seven-axis robot arm enables the fiber to be oriented in all directions to produce a part that has high strength in all directions. Interestingly, curing the resin simultaneously with extrusion allows the CF3D process to print in the air without support material.

As shown above, parts that were 3D printed with discontinuous carbon fiber are weaker than those made with continuous carbon fiber. However, the Boston-based start-up Fortify has developed its DCM technology (Digital Composite Manufacturing), which demonstrates that this is not always the case. DCM is a novel version of digital light processing (DLP), in which a projector is used to harden a photosensitive resin in liquid state. In the case of DCM, the liquefied resin is mixed with reinforcement additives such as discontinuous carbon fibers, which are aligned during the printing process using a magnetic field. "We have developed a technique that allows us to magnetically align fibers in a liquid medium. The parts we print are essentially composite materials with the highest resolution ever produced. With the magnetic assembly, we can control multiple properties such as strength, stiffness and thermal conductivity in three dimensions in every voxel," explains Dr. Joshua Martin, CEO of Fortify, in an interview. One area that Fortify is currently focusing on is the development of tools using its composite technology.

"We are pushing strongly into the [injection molding] market because our tools can handle significantly more shots and cycles than competitive solutions."

In the past year, Fortify raised 10 million US dollars in Series A funding and established partnerships with two chemical companies, Royal DSM and Henkel. Given these milestones, Fortify is in a good position to advance its technology toward commercialization, which is planned for next year.

Impossible Objects is another company that is innovating in the field of 3D composite printing. Instead of using extrusion or robotics, the company has developed a completely unique approach.

In the process referred to as Composite-Based Additive Manufacturing (CBAM), films made from fiber-reinforcing material such as carbon fiber are fed under an inkjet print head, which applies a liquid solution in the corresponding cross-section of the layer onto the film.

After that, a layer of polymer powder is applied to the foil. The powder adheres to the areas where the liquid has accumulated. The excess powder is blown off or vacuumed away. This is repeated layer by layer until the object is complete as a stack of sheets. This stack is then compressed and placed in an oven that melts the thermoplastic powder, resulting in a fiber-reinforced thermoplastic composite. Due to the inkjet printing process, the CBAM method is much faster than extrusion methods, and there is also the possibility of printing large parts. Impossible Object's latest 3D printer, the CBAM-2 introduced in 2019, can 3D print parts with sheets of approximately 30 cm x 30 cm (12 inches x 12 inches). The CBAM-2 can currently work with PEEK and Nylon 12 thermoplastics and long fibers made of carbon or glass fiber. Additional materials, including Nylon 6 and elastomers, are in development.

Applications for 3D composite printing range from prototyping to tooling to the production of end-use parts. In the aerospace industry, the manufacturing of tools can be a long and expensive process. To eliminate these challenges, American aerospace manufacturer Bell Helicopters turned to Thermwood to produce large molds for helicopter blades.

Thermwood is a US-based manufacturer that developed LSAM technology (Large Scale Additive Manufacturing), which enables the printing of large composite tools. One of the unique features of Thermwood's LSAM 3D printer is its hybrid approach to part manufacturing, which combines additive and subtractive technologies. Returning to Bell, the company needed a very large composite tool with good surface finish, tight tolerances, and the ability to withstand autoclave processing - a technique used to reinforce composite parts that are exposed to elevated pressure and elevated temperature.

LSAM was ideal for such an application for two main reasons. First, the 6 m long tool could be manufactured from a carbon-reinforced high-performance PESU material that withstands high pressures and temperatures. Second, since LSAM is a hybrid technology, a part can be 3D printed and finished without the need for machining on a second machine, which further accelerated the production process. These advantages enabled Thermwood to manufacture the tool in just a few days, in contrast to the months that conventional methods would require. This achievement points to the new possibilities that large-scale 3D composite printing opens up for large and technically complex aerospace components.

Wärtsilä, a company specializing in marine and energy markets, used a Markforged X7 3D composite printer to manufacture a lifting tool. The tool is custom hardware that enables the team to move extremely heavy engine parts such as pistons.

The company machined such tools from solid steel, but found the process too expensive and decided to 3D print a carbon fiber-reinforced polymer lifting tool. The resulting tool was 75 percent lighter and could lift 960 kg. Wärtsilä estimates that switching to 3D composite printing alone saved 100,000 euros in tool costs. This example also demonstrates the possibility of replacing metal components with lighter but equally strong composite materials.

Bicycle frames are one of the most successful applications of 3D composite printing in the manufacturing of end parts. Carbon fiber bicycle frames are becoming increasingly popular because the material properties are well-suited for frame construction. The material is strong, durable, and lightweight, making it a sought-after alternative to metal bicycle frames.

Arevo uses robotic materials and software to enable product designers and manufacturers to create strong, lightweight composite parts using 3D printing. However, carbon fiber frames have two main disadvantages: the material is extremely expensive and the manufacturing process is labor-intensive. Arevo addresses these challenges with its robotic 3D printing process. The company's approach creates a frame that is uniformly strong in all three dimensions. This feature distinguishes Arevo technology from conventional filament 3D printing, in which 3D-printed parts are anisotropic upon first printing, meaning they are not equally strong in all directions. Thanks to this technology, Arevo can reportedly manufacture carbon fiber bicycles at competitive costs of $300, compared to similar traditionally manufactured bicycles with an average price range between $1,000 and $2,000. The start-up is already working with several bicycle manufacturers, including Franco Bicycles and Pilot. As 3D printing of composite bicycles becomes increasingly widespread, Arevo's technology opens a new dimension in bicycle manufacturing.

Although it is a young technology, 3D composite printing is gaining increasing importance in the manufacturing industry. It offers a faster and more automated approach to the production of composite parts that have long been manufactured by hand. 3D printing with composite materials helps to reconsider material selection for specific applications, allowing manufacturers to replace metal with durable, cheaper plastic. Finally, it helps to make the process of manufacturing composite components more cost-effective. Taken together, these advantages suggest that 3D composite printing will grow and mature and become a standard method for manufacturers.