Important Progress in Carbon Fiber 3D Printing: Remote Photothermal Assisted Curing To Achieve Floating, Unsupported Additive Manufacturing

Fiber reinforced composite materials are lightweight structural materials widely used in the transportation and energy industries.Current composite material manufacturing methods require expensive tools and long-term energy-intensive processing, resulting in high manufacturing costs, limited design complexity, and low manufacturing speed.3D printing of fiber-reinforced composite materials currently mainly has the following forms: staple fiber reinforced wire is extruded and printed with FDM/FFF, polymer powders such as staple fiber composite nylon are printed with SLS sintering or inkjet hot melt, tow co-extruded long fibers, and in situ impregnated long fibers and other technologies, each technology has its own application scenarios.

3D printing technology reference notes that the research team led by associate professor Mostafa Yourdkhani from Arizona State University in the United States has made new research progress in the field of carbon fiber 3D printing. Using this technology, high-performance composite materials can be manufactured quickly and scalable, and continuous and discontinuous fibers can be realized without tools, without support, and without post-curing. High-quality 3D printing, the fiber content of the material is as high as 70vol%, close to zero voids, and can be printed in mid-air.

Mostafa has won the Young Scientist Award from the iCANX Association, the 2024 PMSE Early Researcher Award, and was shortlisted for the CAMX Composite Material Excellence Award.The study was published in Nature Communications under the title “Additive manufacturing of carbon fiber-reinforced thermoset composites via in-situ thermal curing”, and the first author is from Colorado State University.Related comments pointed out that this technology may change the rules of the game in aerospace, national defense, energy and other fields.

The researchers' 3D printing of fiber-reinforced thermoplastic composite materials is based on the use of thermally responsive thermosetting resin as the matrix of the composite material, and the local remote heating of the carbon fiber reinforced material through photothermal conversion, so that the composite material can be quickly cured in situ without further post-treatment.After being deposited by the robot platform, the matrix thermosetting material immediately quickly solidifies and phases from a liquid or viscous resin to a rigid polymer. Discontinuous and continuous fiber reinforced composite materials can be manufactured with high fidelity and free forming without the use of support.

The developed polymer resin has adjustable viscosity and is a high-performance crosslinked thermosetting material, from low-viscosity liquid resin to viscous gel. It is an ideal choice for the development of additive manufacturing and processing methods for discontinuous and continuous fiber-reinforced thermosetting composite materials.It has a good combination of high modulus and strength, thermal stability, impact resistance, fracture toughness and chemical resistance, as well as low density, curing shrinkage and moisture absorption. These characteristics make it an ideal polymer for structural applications.

In terms of photothermal conversion, carbon fiber has good absorption characteristics and is used to convert the energy of the incident monochromatic blue laser (wavelength 450nm) and heat it locally within 100-200 ms to achieve effective photothermal energy conversion.The composite material is continuously and quickly heated during the printing process, and the heat generated is quickly transmitted to increase the temperature of the surrounding resin by using the high thermal conductivity of carbon fiber.

Combining thermal thermosetting resin with rapid photothermal heating of carbon fiber, it is possible to manufacture discontinuous and continuous carbon fiber reinforced composite materials at an unprecedented speed, solving the shortcomings of traditional manufacturing methods and commercial 3D printing processes.

In the 3D printing of discontinuous carbon fiber composite materials, the resin solution is first preheated at 30℃ for 1 hour to increase the viscosity, then 15vol% chopped carbon fiber is added, mixed with a centrifugal mixer for 5 minutes, and then continue to be placed at 30℃ for 20 minutes to make a printable ink with shear thinning behavior for extrusion through a small printing nozzle.

The prepared ink needs to use a thermoelectric refrigeration sheet to maintain the ink temperature at -5℃ to prevent the resin from crosslinking at room temperature.The ink is extruded in a predetermined trajectory under air pressure, and the blue laser locally heats the newly deposited composite material.Carbon fiber absorbs laser energy and quickly converts it into heat energy, causing the temperature of the surrounding resin to quickly increase to 220-240℃, which causes the resin to cure and realizes the rapid curing of composite materials, with a curing degree of up to 96%-98%.

In the in situ photothermal curing 3D printing of continuous fibers, the continuous carbon fiber tow is impregnated with resin on the print head of the robot platform, fed through the distribution nozzle, and placed along the printing path by adjusting the angle of the distribution nozzle or using a compaction roller.Due to the low viscosity and relative stability of the resin system at room temperature, the fibers are easy to be impregnated with resin and the controlled compaction of the composite material results in the composite material having little or no void content (0 to 1.5% by volume), which is quite challenging for the use of other composite 3D printing processes.

The researchers said that using a laser source with higher output power or a spatially aligned array of multiple laser sources can achieve higher printing speeds.At the same time, the concentration of carbon fiber will not significantly affect the photothermal conversion and curing rate of the composite ink. Carbon fiber can effectively convert the incident energy and transfer the heat generated in the filament at various concentrations.In the absence of carbon fiber, pure ink will not react to the incident laser beam, resulting in unsuccessful printing.

In stark contrast to traditional additive manufacturing methods, this additive manufacturing method does not require detailed control of the substrate or surrounding air temperature, thereby promoting the scalable manufacturing of composite structures.The multi-layer continuous composite structure is easily printed on a room temperature glass substrate through the automatic placement of impregnated fibers and rapid photothermal curing.At the same time, this additive manufacturing method simplifies the manufacture of customized composite components by reducing manufacturing time, eliminating the need for multiple processing steps and consumables, and minimizing manual intervention, and ultimately achieving faster production and lower costs.

In general, this newly developed additive manufacturing method can quickly, flexibly and energy-saving manufacture of fiber-reinforced thermosetting composite materials through the collaborative integration of thermosetting resins in thermal response and remote heating of carbon fibers through photothermal conversion.This method is suitable for a variety of thermal resins.At the same time, this newly developed additive manufacturing method will be able to quickly and scalable manufacture composite tools and complex parts, repair existing structures, and multi-material printing of multi-scale composite materials.