Mark Two 3D Printer Makes Carbon Fiber 3D Printing Possible
Michael Molitch-Hou posted on December 23, 2016 |

As of this writing, Markforged is the only 3D printer manufacturer with a system on the market capable of 3D printing continuous carbon fiber. The company's flagship Mark Two 3D printer utilizes Markforged's patented continuous filament fabrication (CFF) technology to reinforce plastic and composite parts with carbon fiber or other materials, making it what may be the most affordable method for producing carbon fiber–reinforced plastic parts available.

The Mark Two from Markforged is a low-cost fiber composite 3D printer. (Image courtesy of Markforged.)
The Mark Two from Markforged is a low-cost fiber composite 3D printer. (Image courtesy of Markforged.)

After initially launching the Mark One in 2014, Markforged upgraded the system with the Mark Two, which was 40 percent faster than its predecessor and able to reinforce features 15 times smaller than possible with the Mark One.

The Mark Two's printbed features kinematic coupling so that it clicks into the proper location with 10-µm accuracy. As a result, it's possible to pause the Mark Two, embed a part and snap the bed back into its precise location before continuing a print. Custom precision components, a built-in touchscreen and Wi-Fi make the Mark Two a piece of modern manufacturing equipment.
Kinematic coupling ensures a level printbed. (Image courtesy of Markforged.)
Kinematic coupling ensures a level printbed. (Image courtesy of Markforged.)

What's more important than the machine's mechanical components is what it can do with these parts. While the firm’s new Onyx One and Onyx Pro machines can 3D print with Onyx filament, made up of chopped carbon fiber within a nylon matrix, the Mark Two offers the ability to actually fill Onyx and nylon parts with reinforcement material, including carbon fiber, Kevlar, fiberglass and high-strength, high-temperature (HSHT) fiberglass (discussed in greater detail below). This capability, not possible with traditional desktop extrusion 3D printers, gives users the ability to 3D print parts that are stronger and lighter than aluminum.

The Mark Two also has a build volume of 320 mm x 132 mm x 154 mm (12.6 x 5.2 x 6.1 in), which is large enough to print sizable components. Non-reinforced parts can be 3D printed with 100-µm layer resolution, as can parts reinforced with fiberglass and Kevlar. A layer resolution of 125 µm can be achieved when 3D printing with carbon fiber.

The Mark Two Enterprise Kit comes stocked with a complete assortment of Markforged materials, including 800 cm3 of Onyx, 800 cm3 of Nylon, 100 cm3 of carbon fiber, 100 cm3 of Kevlar, 100 cm3 of fiberglass and 100 cm3 of HSHT fiberglass filaments. The kit also contains three quick-change CFF and three quick-change standard extruder nozzles, as well as an additional printbed, Eiger software and premium software support.

How the Mark Two Works

The CFF process is a unique one that relies on two print heads. One print head features a specially engineered thermoplastic extruder built to handle the tough Onyx material, while the other is designed to lay down continuous strands of fiber reinforcement material.

To print fiber-reinforced objects, the Mark Two first prints a thermoplastic onto the printbed before the second print head lays down the reinforcement material to fill the interior cavity. A built-in cutting mechanism then cuts the fiber so that the next layer can begin. The printbed lowers after each layer is complete until the object is finished.
These prints demonstrate how carbon fiber is laid continuously throughout a nylon part before sealing the carbon fiber inside. (Image courtesy of Markforged.)
These prints demonstrate how carbon fiber is laid continuously throughout a nylon part before sealing the carbon fiber inside. (Image courtesy of Markforged.)

Essential to printing composite parts with the Mark Two is Markforged's cloud-based Eiger software. Similar to other print preparation software, Eiger begins with uploading an STL file; however, because Eiger runs in the cloud, the process is quick and agile.

Once one uploads a print file, the user can then determine the infill of the part, including density and pattern. When the “Use Fiber” option is switched on, Eiger automatically generates fiber reinforcement for the part. At this point, it's possible to get the internal view of the object and add more layers of fiber when required. One can also determine the way that the material is laid down, whether or not it should be printed in concentric circles or at a specific angle for optimized isotropic properties or both.

Markforged's Onyx material combines the benefits of nylon with chopped carbon fiber, making it 3.5 times stiffer than nylon, while retaining the toughness and wear resistance of nylon. The material also has a heat deflection temperature of 145 °C, as well as improved dimensional stability, making it possible to 3D print parts with larger, steeper overhangs. In turn, Onyx results in parts with 1) layers that don't warp, as seen with traditional thermoplastics, 2) sharper edges and 3) a matte black finish that requires less post-processing.

The Mark Two can build on the properties of Onyx with fiber reinforcement through the use of CFF. Continuous fiber reinforcement makes it possible to spread the reinforcement material evenly through an entire layer at a time, making it possible to carry a load throughout the part and resulting in greater overall strength.

For instance, carbon fiber reinforcement allows for the production of parts with a higher strength-to-weight ratio than aluminum and parts that are 27 times stiffer and 24 times stronger than ABS plastic. The carbon fiber reinforcement is 10 times stronger than Onyx alone.
This part reinforced with HSHT fiberglass allows for silicone injection molding without damaging the mold. (Image courtesy of Markforged.)
This part reinforced with HSHT fiberglass allows for silicone injection molding without damaging the mold. (Image courtesy of Markforged.)

Markforged offers a fiberglass filament as a more affordable reinforcement option that is 5 times stronger than Onyx alone. It is not quite as light or stiff as carbon fiber, however, weighing about twice as much at about 40 percent less stiff.

HSHT fiberglass is an upgrade to the standard fiberglass option. Designed to withstand higher temperatures—over 302 °F (150 °C)—than its traditional counterpart, HSHT fiberglass is better suited for high-temperature applications like injection molding.

Markforged is also the only company that has made it possible to 3D print with Kevlar, which is known for its extreme abrasion resistance. This might be necessary for printing such items as a landing gear to a quadcopter or military components that would be handled in the field of duty.

The Mark Two in Action

Due to the strength of parts printed by the Mark Two, it is not uncommon for the printer to be used, not just for producing end parts, but for 3D printing components that are used in a larger manufacturing process. At Dixon Valve & Coupling, for instance, a Mark Two is used to 3D print custom jaws for industrial robotic arms.
Dixon Valve & Coupling’s pipe fittings in the factory aligned with 3D-printed fixtures. (Image courtesy of Markforged.)
Dixon Valve & Coupling’s pipe fittings in the factory aligned with 3D-printed fixtures. (Image courtesy of Markforged.)

While manufacturing fittings for fluid transfer industries, Dixon Valve & Coupling relies on a large robotic arm to transfer parts between two vertical turning centers. Due to the huge variety of valves, gauges and fittings that the firm produces, it's necessary to also use custom tooling and grips while manufacturing different parts. Typically, these parts would be machined in-house or through a third party, which is a time-intensive process.

A two-jaw gripper set for a pipe fitting 3D printed with Onyx on the Mark Two. (Image courtesy of Markforged.)
A two-jaw gripper set for a pipe fitting 3D printed with Onyx on the Mark Two. (Image courtesy of Markforged.)

To tackle this issue, the firm turned to the Mark Two, 3D printing grippers on demand. Given the fact that Dixon Valve & Coupling deals with volatile chemicals, the firm has a preference for Markforged's Onyx material for its chemical resistivity and strength. As J.R. Everett, an automation technician at Dixon Valve & Coupling said of the material, “Onyx is one of my favorite materials because it combines stronger composite material with the chemical resistivity of nylon. It hits the sweet spot for us in chemical resistance and strength.”

With the Mark Two, Dixon Valve & Coupling is able to retool a robotic gripper in less than 24 hours. Whereas having parts CNC machined by a third party would cost the company $290.35 and at least three days plus shipping to turnaround, it costs only about $9.06 and nine hours and 20 minutes to print in-house.

As Everett added, “I would say Markforged is a critical company; [the Mark Two] is a critical component in our design process and is really changing the way we work, to the point that we are actually altering our procedures and plans to accommodate this ground-breaking product.”


Manufacturer: Markforged

Model: Mark Two, Enterprise

Material: Carbon fiber, Kevlar, fiberglass and HSHT fiberglass reinforcement material; nylon and chopped carbon fiber-nylon composite base material

Build Envelope: 320 x 132 x 154 mm (12.6 x 5.2 x 6.1 in)

Layer Thickness: 100 µm (0.004 in) nonreinforced, fiberglass, HSHT and Kevlar; 125 µm (0.005 in) reinforced

Printer Dimensions: 575 x 322 x 360 mm (22.6 × 12.7 × 14.2 in)

Recommended Uses: Ideal uses include rapid prototyping and producing end parts with high strength, thermal resistance and abrasion resistance

Machine Price: Mark Two Enterprise, $13,499

 

Who Should Use the Mark Two Enterprise:

Those looking to produce end parts, prototypes or secondary manufacturing components, like jigs, tools and fixtures, will find that the Mark Two Enterprise is up to the task. Because it comes with a complete set of materials, it will be particularly valuable for those with a diverse set of needs or those interested in experimenting. The Mark Two is also great for manufacturing strong, lightweight parts in-house and replacing CNC milled aluminum parts. The company's Eiger software also makes it possible to network an entire suite of Mark Two 3D printers for scaled production of end-use parts, lending itself for use with large manufacturers, as well.

Why You Wouldn't Use the Mark Two:

The Mark Two is not engineered with multiple colors for finely detailed miniatures or toys in mind. And, unlike photopolymer 3D printers, it is not meant for creating jewelry or dentistry models for casting.

Those requiring less powerful reinforcement materials can also turn to Markforged's Onyx Series of printers. The Onyx One and Onyx Pro are available at a lower cost than the Mark Two and feature different levels of strength and reinforcement.  The Onyx One prints with a single print head for the Onyx material and is easily upgraded to the Onyx Pro that contains a second print head for fiberglass reinforcement for 5 times the strength. These systems can both be upgraded to the Enterprise Kit, if need be.

Markforged has sponsored ENGINEERING.com to write this article. It has provided no editorial input. All opinions are mine. —Michael Molitch-Hou

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