Advantages, available technologies and applications for 3D printing of composite materials
The processing of composite materials in 3D printers is a young technology, but one with huge, largely untapped potential. According to a report by SmarTech Analysis, 3D printing with composite materials is set to become a nearly $10 billion business within the next decade - a significant growth opportunity to say the least.
In today's article, we will look at the benefits of composite 3D printing, the key technologies and applications available in the market to find out what is driving the growth of this exciting industry.
What is a composite?
Composite materials typically comprise a core polymer material and a reinforcing material, such as chopped or continuous fibers. The composite material offers greater strength and stiffness compared to non-reinforced polymers. In some cases, it can even replace metals such as aluminum.
These improved material properties make composites desirable materials for tooling and end-use applications in a range of industries including aerospace, automotive, industrial goods and oil and gas.
What are the advantages of 3D composite printing?
The ability to streamline and reduce the cost of traditional composite manufacturing is one of the key factors driving the growth of composite 3D 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 to manually lay up the layers of a composite material and the use of expensive curing equipment and tools such as molds. This makes the process of traditional composite part manufacturing very labor, resource and capital intensive, meaning it can be difficult to scale up to large volumes.
3D printing, on the other hand, enables the automation of the manufacturing process, as the entire process is controlled by software and only requires manual intervention in the post-processing phase.
Continuous fibers vs. interrupted fibers
In 3D printing, it is possible to print with two types of reinforcing fibers, interrupted fibers and continuous fibers. With interrupted 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 filament, long strands of fiber 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 yet as strong as metal. In terms of fiber types used, carbon fiber is one of the most popular, followed by fiberglass and Kevlar.
3D printing technologies for composite fiber materials on the market
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 known as Fused Filament Fabrication (FFF).
In FFF, a nozzle moves over the build platform, extruding a molten plastic filament called a filament and creating an object layer by layer.
3D printing filaments containing interrupted fibers is straightforward, requiring only a hardened steel nozzle to resist abrasive fiber strands. However, when it comes to continuous fiber printing, the FFF process requires a second nozzle to deposit a single, uninterrupted strand of fiber separately.
Markforged: Pioneer of 3D printing with composite fiber materials
The continuous filament 3D printing process was first introduced by Markforged in 2014 when the company launched the Mark One 3D printer. The second generation is now available as the Mark Two 3D printer.
While the Mark One has been replaced by a new generation of 3D printers, the technology remains the same: the printer is equipped with two nozzles, one for depositing plastic filaments and the other for simultaneously depositing carbon fiber strands. Now, in 2020, Markforged offers a range of desktop and industrial composite 3D printers with main applications for functional prototyping and the production of end-use parts and tooling.
The Micro Automated Fiber Placement technology from Desktop Metal
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 previously focused exclusively on metal 3D printing, Desktop Metal launched the Fiber 3D printer in November 2019.
A new polymer desktop system combines a traditional Automated Fiber Placement (AFP) technology with FFF for 3D printed parts enhanced by continuous fibers. AFP technology is an automated manufacturing process for composite materials. It involves heating and compressing fiber reinforcements on typically complex tooling molds to produce continuous fiber composites. Desktop Metal has scaled down this process to a desktop format and named its new technology Micro Automated Fiber Placement (μAFP). The μAFP works like Markforged's technology, but instead of using fiber spools, it uses rolls of fiber tape. It can embed carbon fiber in nylon, PEEK and PEKK, and nylon can also be integrated into glass fiber.
Manufacturers still rely mainly on hand lay-up to produce small composite parts. Such labor-intensive processes require technicians, expensive tooling and a lot of time, which increases the overall cost of producing a part. By combining μAFP with FFF in its new fiber systems, Desktop Metal aims to produce smaller composite parts more easily and cost-effectively. The fiber can be used to make jigs and fixtures, various end-use parts and any component where weight is a primary concern, such as racing equipment.
Anisoprints composite fiber coextrusion technology
Similarly, Anisoprint, a Russian/Luxembourgish start-up, has developed an extrusion-based process that the company calls Composite Fiber Coextrusion (CFC).
In contrast to Markforged and Desktop Metal technologies, CFC technology enables the reinforcement of plastic with continuous composite fibers directly during the printing process and not in the pre-print. With this approach, users can use any desired plastic (PETG, ABS, PC, PLA, nylon, etc.) and change the infill density of the composite material.
Anisoprint's first device was a desktop-format Composer 3D printer. 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 has 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 goal.
When the system is officially launched at the end of 2020, this will be a further step forward for both 3D composite printing and advanced polymer manufacturing.
3D printing with composite materials and robotics
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 in terms of geometry, as the robotic arm can move along multiple axes, offering 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 depositing layers of pre-impregnated continuous carbon fiber filament, which is simultaneously heated with a laser before a roller compresses it onto the build surface. The process is similar to Direct Energy Deposition, which is typically used for metal.
At Arevo, the print head is mounted on a multi-axis robotic arm, allowing 3D printing in any orientation that best suits the design of the part.
"If you look at 3D printing, most 3D printing is based on planes, and the planes are placed in the X and Y planes. If you look at the properties of parts made 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".
In addition, robots offer a "theoretically unlimited size, as we can build our robots in a gantry design to produce parts for the aerospace industry. 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 composite bicycle frame. More on this application below.
Continuous composites
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. As with Arevo, the seven-axis robotic arm allows the fiber to be oriented in all directions to create a part that has high strength in all directions. Interestingly, curing the resin simultaneously with extrusion allows the CF3D process to be printed in the air, without support material.
Fortify: Combination of 3D composite printing with digital light processing
As shown above, parts 3D printed with interrupted carbon fiber are weaker than those made with continuous carbon fiber. However, Boston-based start-up Fortify has developed its Digital Composite Manufacturing (DCM) technology that proves this is not always the case.
DCM is a novel version of digital light processing (DLP) that uses a projector to cure a photosensitive resin in a liquid state. In the case of DCM, the liquefied resin is mixed with reinforcing additives such as interrupted 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 composites with the highest resolution yet produced. With the magnetic assembly, we can control multiple properties such as strength, stiffness and thermal conductivity in three dimensions in each voxel," explains Dr. Joshua Martin, CEO of Fortify, in an interview. One area that Fortify is currently focusing on is the development of tooling with its composite technology.
"We are pushing hard into the [injection molding] market because our tools can handle many more shots and cycles than competitive solutions."
Last year, Fortify raised USD 10 million in Series A funding and partnered with two chemical companies, Royal DSM and Henkel. Given these milestones, Fortify is in a good position to advance its technology to commercialization, which is planned for next year.
Impossible Objects
Impossible Objects is another company innovating the field of 3D composite printing. Instead of using extrusion or robotics, the company has developed a completely unique approach.
In the process known as Composite-Based Additive Manufacturing (CBAM), films made of fiber-reinforcing material such as carbon fiber are fed under an inkjet print head, which applies a liquid solution to the film in the corresponding cross-section of the layer.
A layer of polymer powder is then applied to the film. The powder adheres to the areas where the liquid has been deposited. The excess powder is blown off or vacuumed off. 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, which melts the thermoplastic powder, resulting in a fiber-reinforced thermoplastic composite. Due to inkjet printing, the CBAM process is much faster than extrusion processes, and there is also the possibility of printing large parts. Impossible Object's latest 3D printer, the CBAM-2, launched 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 of carbon or fiberglass. Other materials, including nylon 6 and elastomers, are under development.
Applications for 3D printing with composite materials
Applications for 3D composite printing range from prototyping and tool manufacturing to the production of final components. In the aerospace industry, manufacturing tooling can be a long and expensive process. To overcome these challenges, American aerospace manufacturer Bell Helicopters turned to Thermwood to produce large molds for helicopter blades.
Thermwood is a US-based manufacturer that has developed LSAM (Large Scale Additive Manufacturing) technology, which can be used to print large composite tools. One of the unique features of Thermwood's LSAM 3D printer is its hybrid approach to manufacturing parts, combining additive and subtractive technologies. Returning to Bell, the company required a very large composite tool with good surface finish, tight tolerances and the ability to withstand autoclave processing - a technique that can be used to reinforce composite parts that are subjected to elevated pressure and temperature.
LSAM was ideal for such an application for two main reasons. Firstly, the 6m long tool could be made from a high performance carbon-reinforced PESU material that can withstand high pressures and temperatures. Secondly, as LSAM is a hybrid technology, a part can be 3D printed and finished on a second machine without the need for machining, which further accelerated the production process.
These advantages allowed Thermwood to produce the tool in just a few days, as opposed to the months that conventional processes would take. This achievement points to the new possibilities that large-scale 3D composite printing opens up for large and technically complex aerospace components.
Wärtsilä 3D prints composite lifting tool
Wärtsilä, a company specializing in marine and energy markets, used an X7-3D composite printer from Markforged to produce a lifting tool. The tool is a customized piece of hardware that allows the team to move immensely heavy engine parts such as pistons.
The company machined such tools from solid steel, but found the process too expensive and opted to 3D print a polymer lifting tool reinforced with carbon fiber. The resulting tool was 75 percent lighter and could lift 960 kg. Wärtsilä estimates that the switch to 3D composite printing alone saved 100,000 euros in tooling costs.
This example also demonstrates the possibility of replacing metal components with lighter but equally strong composite materials.
Bicycle frame made of composite material
Bicycle frames are one of the most successful applications of 3D composite printing in the production of end parts. Carbon fiber bicycle frames are becoming increasingly popular as the material properties lend themselves well to frame construction. The material is strong, durable and lightweight, making it a desirable 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 drawbacks: The material is extremely expensive and the manufacturing process is labor-intensive. Arevo overcomes these challenges with its robotic 3D printing process. The company's approach creates a frame that is equally strong in all three dimensions. This feature differentiates Arevo's technology from traditional filament 3D printing, where 3D printed parts are anisotropic when first printed, meaning they are not equally strong in all directions. Thanks to this technology, Arevo says it can produce carbon fiber bicycles at a competitive cost of 300 US dollars, compared to similar traditionally manufactured bicycles with an average price range of between 1000 and 2000 US dollars. The start-up is already working with a number of bicycle manufacturers, including Franco Bicycles and Pilot. As 3D printing of composite bicycles becomes more widespread, Arevo's technology adds a new dimension to the field of bicycle manufacturing.
Composite 3D printing: pushing the boundaries of composite manufacturing
Although it is a young technology, composite 3D printing is gaining traction in the manufacturing industry. It offers a faster and more automated approach to producing composite parts that have long been made by hand.
Composite 3D printing helps to rethink material selection for certain applications, allowing manufacturers to replace metal with durable, cheaper plastic. Finally, it helps make the process of manufacturing composite parts more cost-effective.
Taken together, these benefits suggest that composite 3D printing will grow and mature to become a standard method of manufacturing.