In March 2019, the JEC Organizing Committee, the world's top exhibition in the field of composite materials, awarded the 2019 Annual Additive Manufacturing (3D Printing) Innovation Award to the United States Continuous Composites Company, Air Force Research Laboratory, and Lockheed Martin team in recognition of its Innovative achievements in the development of continuous fiber 3D printing technology. Continuous Composites is a pioneer in continuous fiber-reinforced 3D printing technology, and in 2012 won the world's earliest process patent. Since the introduction of the first continuous fiber 3D printer in the United States in 2014, the technology has been developing rapidly and is gaining application in the aviation sector. With the gradual maturity and large-scale application of the technology, this technology may subvert the existing production model of composite drones and low-cost composite aviation structures.
Advantages of continuous fiber 3D printing technology
Continuous fiber 3D printing technology comprehensively utilizes industrial robots, 3D printed end effectors, in-situ detection, intelligent monitoring and machine learning to quickly transport and deposit continuous fiber reinforcements, as well as matrix resins, and impregnate and cure in situ. Compared with processes such as automatic wire-forming and fused deposition forming, the degree of automation and flexibility is higher. For typical carbon fiber / PEEK parts, the research and development cycle can be shortened to 1/30, and the production speed can be increased 100 times. Continuous fiber 3D printer can be composed of multiple robots with flexible units. Multiple 3D printing end effectors can be added to the robot. At the same time, the print head can support materials such as carbon fiber, Kevlar, glass fiber and even optical fiber and metal wire. It can be used for mass production of composite parts, and it can also print highly complex geometries or critical parts requiring extremely precise manufacturing at one time.
Development direction of continuous fiber 3D printing technology
Currently, US and European 3D printing technology developers and robot manufacturers have jointly developed a series of advanced continuous fiber 3D printing equipment and manufacturing processes. The main application directions and developments are as follows.
Mass production of low-cost composite structures
Arevo has developed a direct energy deposition (DED) process that prints thermoplastic prepreg tows into parts, and Airbus Capital has invested in the company. The DED work unit consists of an industrial robot, a laser-heated print head, and a rotating construction platform. Compared with traditional 3D printing, it can increase production speed by 100 times. In addition to drone fuselage, wings and other aeronautical parts, Arevo also produces bicycle frames similar to the drone frame structure. Continuous fiber 3D printing technology has shortened its development cycle from 18 months to 18 days. The company's new plant, which was commissioned in February 2019, has eight robotic work cells that can complete the printing itself, post-processing (such as drilling), and pre-grinding for painting, and can produce a total of eight large parts per day. The company is testing multiple printheads per robot and multiple robots per work cell to increase production speeds by a factor of three. In order to maintain quality and repeatability throughout the acceleration process, the company uses in-situ inspection and machine learning technology to equip the print head with multiple sensors (measurement of height, pressure, deformation, etc.), and the system software uses these sensor data. Adjust process parameters in real time as needed. In this way, when the work cell needs to run faster, it can ensure that the deposition rate, heating, curing and other parameters are optimally matched.
arevo 3D printing technology
American Orbital Composites has developed a highly customized 3D printing device consisting of a parallel robot and a modular coaxial extrusion end effector. The extrusion nozzle supplies the matrix material through its central hole and the fiber through the surrounding annular nozzle. Robots can speed up production through multiple collaborations, which can be up to 100 times faster than traditional 3D printing. The feature of this technology is that it can adapt to almost any composite material: dried and bonded fibers of 3-48K tow; plastic, ceramic or metal substrates including thermoset / thermoplastic and silicon carbide; and the ability to combine copper or aluminum wires, nanometers Materials, conductive inks, or other materials that help achieve multifunctional structures. This makes it particularly suitable for drone applications, where investment in one device can be applied to all structural and functional components.
3D printed products from American Rail Composites
The continuous fiber manufacturing process developed by the Italian company Moi Composites aims to solve the challenge of 3D printing using thermosetting resins and has successfully printed continuous glass fiber reinforced composites with epoxy, acrylic and vinyl esters. In addition to the curing mechanism suitable for carbon fiber applications, this process can also use UV curing, the curing time required is less than 1s. At present, the technology has begun to be used in the manufacture of aviation structural parts.
Moy Composites 3D printing process
Rapid development and small batch production of complex or precision structures
A research team at the McNair Aerospace Innovation and Research Center at the University of South Carolina has developed a fused filament manufacturing (FFF) process. The FFF system uses an industrial robot platform equipped with a continuous fiber deposition end effector, which provides 7 degrees of freedom. This technology is very suitable for three types of applications: first, the manufacture of small batch aviation structures with relatively high mold or mandrel costs, such as drones or small aircraft that only require a specific high-strength component; and second, the use of other manufacturing methods cannot produce Highly complex structures that require strength-to-mass ratio and stiffness-to-mass ratio, such as reinforced grids; third is overprinting, which is a technology that inserts components during the printing process and is thus fully embedded in the printed part, which can achieve part integration, such as Embed radio frequency identification chips or electronic sensors in printed parts. The traditional aviation structure with automatic tow placement has low integration. The highlight of this technology is that if a thermoplastic material is used to make a composite structure, each time it is re-melted through overprinting to add new components, eliminating rivets, fasteners and Adhesives can significantly improve these structures.
McNair 3D printing technology aims to produce highly complex and unique structures
McNair 3D printed complex parts
In November 2018, the Dutch CEAD Group launched its "Prime" large continuous fiber additive manufacturing 3D printer with a size of 2m × 4m × 1.5m, which is the largest 3D printer in Europe. During the manufacturing process, the printer first pre-impregnates the continuous glass fiber or carbon fiber with the required thermoplastic resin, and then the print head combines the continuous fiber with the molten thermoplastic resin particles, which can also include a certain percentage of chopped fibers, which is particularly beneficial for small batches. Produce large and complex products. It also has an intelligent heating / cooling system that monitors the process through thermal cameras and adjusts in real time as needed.
CEAD Group 3D printed autoclave mold
Russian startup Aniso Printing Co., Ltd. has developed a 3D printer based on the co-extrusion process of composite fibers. It is also pre-impregnated with reinforced filaments before they are sent to the printer. The matrix resin is usually a thermoplastic, which is said to be because thermoset polymers are easier to wet individual filaments than thermoplastics and can provide better adhesion, thereby improving the quality of cured parts.
Mass production of complex structures combining speed and precision
The continuous fiber system developed by American Mark Forging Company uses two print heads, one for the matrix resin and the other for the thermoplastic resin prepreg tow. The focus of technological improvements is reliability and repeatability. The company is committed to achieving a fully closed-loop process and is developing a range of features for this purpose, such as fully integrated material tracking and comprehensive automatic reporting capabilities. An important application of this system is printing tooling fixtures and components. Compared with machined aluminum components, 3D printed thermoplastic products are also strong but lighter, do not damage parts like metal components, and can be prepared in the same day. This can promote the development of aviation composite material manufacturing molds.
Dual robot continuous fiber 3D printer
The Continuous Fibers (CF3D) process, awarded by the American Continuous Composites company, uses fast-curing thermosetting resins (the process is also applicable to thermoplastics), impregnates the reinforcing fibers in the print head, and cures the composite immediately after the material is deposited. Thermoset materials enable this process to perform high-speed printing in free space, with fiber volume content that can reach 50% to 60%. Important developments in the award-winning project include more automated tool path generation; automated tool replacement, which enables high-resolution single-pass printing and high-deposit-rate multi-pass printing on the same part; and improved robot accuracy and precision. The company expects that this technology will be used to print the entire aircraft structure on demand-whether it is 10 or 10,000.
Continuous fiber 3D printing prints multiple structures as a single component. The picture shows an aircraft spar with embedded gussets. Printed using Continuous Composite's 3D process, followed by skinning by hand-deposited carbon fiber composite
The 9T laboratory in Switzerland has developed a "CarbonKit" system based on a continuous dot matrix manufacturing process. The system uses industrial-grade inexpensive materials to pull extruded composite rods. The rods enter the adjustable heat extrusion head through the traction unit. A series of thermoplastic matrix systems are used together, and the fiber volume content can reach more than 50%. Another important feature of this system is the ability to scale out different cross-sectional areas, so it can be adapted to high-resolution applications with small tows, and large-format additive manufacturing with large tows, such as stiffened wall panels. An ongoing project has confirmed that approximately 30,000 parts can be produced each year.
9T Labs 3D printed miniature drone frame
Inspiration suggestions
At present, there are two main problems with continuous fiber 3D printing technology: first, the fiber content is low, and the possibility of delamination between printed layers is high; the second is the lack of standardized continuous tool path generation business software. In the future, with the resolution of these problems, the technology will rely on the advantages of flexibility, openness, high speed, high efficiency, low cost, and full automation of production, and will certainly compete with traditional composite material manufacturing technologies. It is foreseeable that with the maturity and large-scale popularization and application of this technology, the aviation manufacturing industry will be further promoted to explore the mass production of 3D printing drones, complex aviation structures, and manufacturing tooling, which will open a new wave of aviation composite material development.
Faced with the rapid development of foreign technology, China should strengthen intelligence tracking research and judgment, and combine raw materials, robots, end-effectors, 3D printing software, sensors, machine learning, and numerical control system superior enterprises to develop and demonstrate as early as possible a series of independently controllable Process and equipment, forming a large-scale manufacturing process and equipment industry, supporting China's manufacturing industry to improve production efficiency and quality, in order to meet the high-speed and low-cost competition faced by the future aviation composite structure design and manufacturing, and meet the future represented by drones Demand for low-cost high-volume on-demand manufacturing of aviation equipment.