Continuous Fibre Reinforcement (CFR) can revolutionise engineering workflows by enabling the substitution of machined components with carbon fibre 3D printing.
CFR offers advantages over traditional FFF, such as increased stiffness, impact resistance, improved heat resistance, and extended durability.
CFR harnesses FFF technology but introduces a secondary nozzle that feeds in a continuous strand of composite fibre, such as carbon fibre.
It is impossible to print these strands of composite material through normal FFF processes because they are applied to the internal layers with the assistance of a fibre nozzle. Simply put, you need a Markforged 3D printer.
Markforged CFR 3D printers let you reinforce Nylon and a proprietary carbon fibre-filled nylon called Onyx with strands of carbon fibre, fibreglass, and Kevlar.
This opens new opportunities for designers and engineers to quickly produce complex parts made from reliable, durable, heat and chemical-resistant materials for jigs, fixtures, fittings, prototypes, and end-use parts.
What is CFR?
CFR is an augmented 3D printing process that works alongside FFF by injecting continuous fibre with a second nozzle.
FFF (Fused Filament Fabrication) works by heating thermoplastic until it nears its melting point and then extruding it from the nozzle. The nozzle traces the cross-section of the part, and the process repeats layer by layer until the model is complete.
With CFR, a composite – such as carbon fibre, fibreglass, or Kevlar – effectively reinforces the part’s perimeter, features or entire layers, creating a stronger part than one printed purely from plastic. Parts can be as strong as machined aluminium.
The final mechanical characteristics of CFR printed components depend on the core and composite material and the level of reinforcement, including whether you place continuous fibres within each layer of the part.
How is this superior to filled filaments?
Continuous fibres are reinforced through a process called Continuous Fiber Reinforcement (CFR), which is an additional step when compared to filled filaments.
FFF filaments infused with carbon fibre contain short carbon fibres, typically 100 microns long and printed like standard filaments. The short carbon fibres can improve a material’s mechanical properties, flowability, and surface finish.
CFR is different because it introduces continuous strands of carbon fibre. These are comprised of long carbon fibres encased in thermoplastic, with the fibre tows fused to the part by melting the material through a heated nozzle.
The effect is simple – the strength of parts reinforced with continuous carbon fibre is equivalent to that of parts produced via traditional composite fabrication techniques.
CFR parts show superior mechanical properties compared to filled filaments due to tensile and flexural loads applied to long fibre tows rather than the matrix polymer. This reduces loading on the matrix polymer and increases the reinforcement of the parts, enabling them to withstand high-stress loading conditions better.
Another advantage of CFR as a process is it supports fibreglass and Kevlar, making it more versatile and suitable for more applications.
How does CFR work?
Continuous Fibre Reinforcement (CFR) has a two-step process on the print bed.
The first extruder prints nylon or Onyx – a thermoplastic reinforced with short-strand chopped carbon fibres – to form the shell and fill in the parts. The second nozzle is used to inlay CFR into the part’s perimeter and select features or entire layers.
You can adjust the fibre content in parts dynamically by changing the fibre content in each layer and specifying the number of layers that are reinforced. This changes the part’s mechanical characteristics.
The benefit of using Onyx over nylon is it already contains chopped carbon fibre strands, making it stiffer than nylon. Continuous fibres further increase part strength, with strength levels sometimes exceeding aluminium.
While the extrusion system utilises a standard FFF process to construct a base material, the second extruder deploys long and continuous fibres into the layer to create composite reinforcement.
This unique process creates stronger, stiffer, and more durable parts than standard plastic parts while retaining the heat resistance, chemical resistance, and print quality of the thermoplastic matrix material.
Markforged is the first company to offer this advanced 3D printing process, enabling the creation of composite parts that can replace machined metal.
What are the materials?
CFR 3D printers print a core material and a composite material.
Core materials include:
- Nylon. A non-abrasive material perfect for ergonomic surfaces. Compatible with the Mark Two, FX20, and X7.
- Onyx. A carbon fibre-filled nylon with excellent stiffness. Compatible with the Mark Two, Onyx One, Onyx Pro, X3, X7, and FX20.
- Onyx FR. A flame-retardant version of Onyx. Compatible with the X3, X7, and FX20.
- Onyx ESD. An ESD-safe version of Onyx. Compatible with the X3, X7, and FX20.
Composite materials include:
- Carbon Fibre. It can yield parts as strong as 6061-T6 aluminium. Compatible with the FX20, X7, and Mark Two.
- Carbon Fibre FR. A flame-retardant version of CF. Compatible with the FX20 and X7.
- Aramid Fibre (Kevlar). It can yield impact-resistant parts that are nearly immune to catastrophic failure. Compatible with the FX20, X7, and Mark Two.
- Fibreglass. It can yield parts 10x stronger than ABS. Compatible with the Onyx Pro, Mark Two, X7, and FX20.
- Fibreglass HSHT. It can yield parts over 20 x stronger than ABS. Compatible with the Mark Two, X7, and FX20.
Common material combinations include:
- Nylon or Onyx with Carbon Fibre. This is ideal for high-strength tools and fixtures.
- Onyx with fibreglass. This is ideal for soft jaws and medium-strength tools and fixtures.
- Onyx and Kevlar. This is ideal for end-of-arm tooling, wear stops, and stanchions.
- Onyx with Fibreglass HSHT. This is ideal for polymer moulds and high-temp prototyping.
Of all the materials, carbon fibre is arguably the most interesting.
Carbon fibre is ideal for advanced fabrication due to its superior mechanical properties and chemical and heat resistance over plastics. Its high stiffness and tensile strength, combined with its relative light density compared to steel or aluminium, make it a top choice for the aerospace and automotive industries.
Find out more
To find out more about CFR 3D printing, call us on 01765 694 007 or email team@additive-x.com.
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Top image credit: Markforged.