The Mark Two 3D Printer: Carbon Fiber on Your Desktop
Michael Molitch-Hou posted on July 15, 2016 |

When Markforged unveiled its continuous filament fabrication (CFF) technology at SOLIDWORKS World 2014, the Massachusetts-based start-up shook the manufacturing industry with what was the only desktop 3D printer capable of continuous fiber reinforcement. The implications were that labs and businesses could create custom, low-cost parts reinforced with carbon, fiberglass and, later, Kevlar and high-strength, high-temperature (HSHT) fiberglass.

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.)

The Mark Two is the most recent upgrade of the company’s CFF 3D printer. Markforged describes the system as being 40 percent faster than the Mark One. It is also capable of laying down fiber reinforcement material for features 15 times smaller than the previous model. Improvements were made more generally to the hardware and software of the machine, as well. Additionally, the Mark Two is a modern piece of equipment, featuring a built-in touch-screen and Wi-Fi capabilities.

As the Mark Two is capable of reinforcing nylon and carbon fiber-nylon composite parts with carbon fiber, Kevlar, fiberglass and HSHT fiberglass, it offers a number of capabilities not possible with traditional desktop extrusion 3D printers. Carbon fiber reinforcement, for instance, results in parts stronger and lighter than aluminum. More information about these materials is listed in the section below.

Kinematic coupling ensures a level printbed. (Image courtesy of Markforged.)
Kinematic coupling ensures a level printbed. (Image courtesy of Markforged.)

The Mark Two is capable of 100-micron layer resolution when printing without reinforcement, as well as with fiberglass and Kevlar, and 125 microns for carbon fiber—all with a relatively substantial build volume of 320 mm x 132 mm x 154 mm (12.6 in x 5.2 in x 6.1 in). Due to the use of kinematic couplings, the printer’s printbed will remain level within 10 microns once first adjusted.

How the Mark Two Works

The Mark Two is the first 3D printer of its kind to lay down continuous strands of fiber reinforcement material into a 3D printed object. The machine utilizes two printheads: one for a traditional 3D printing filament and one for the continuous fiber. A layer of the traditional filament is printed before the reinforcement material is used to fill the inner cavity of a part. The printbed lowers with each layer and the process is continued until the part is complete.

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.)

While there are a number of chopped carbon fiber filaments on the market, these materials may only be about twice as strong as the base material due to the chopped nature of the reinforcement material. CFF’s greatest quality is the continuous nature of the reinforcement material, which sees thousands of continuous fibers spread evenly through an entire layer and allows a load to be carried throughout a part. This results in strengths five to ten times stronger than a nonreinforced part.

Carbon fiber reinforcement allows parts printed on the Mark Two to have a higher strength-to-weight ratio than aluminum and to be 27 times stiffer and 24 times stronger than ABS. The material also maintains high thermal conductivity. As a result, users can 3D print lightweight, high-strength parts, which is impossible with most other 3D printers.

Fiberglass, in contrast, is more cost-effective with the same strength as carbon fiber, but with twice the weight and a stiffness 40 percent less than that of carbon fiber. HSHT fiberglass is a stronger and more temperature-resistant material with twice the flexural strength and the ability to withstand temperatures of over 221 °F (105 °C). While the former might be used in place of carbon fiber, but with a reduced price tag, the latter might be implemented to create molds injected with hot silicone.

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.)

Kevlar is the most flexible reinforcement material offered by Markforged and offers the highest abrasion resistance. For this reason, it is best used for printing parts needing great impact resistance, such as the landing gear to a quadcopter or for components that might be tossed around in the field of duty.

Up until recently, Markforged used nylon as the base material for 3D-printed parts; however, the company has developed its own chopped carbon fiber-nylon composite filament called Onyx. This makes parts 3.5 times stiffer while maintaining the toughness and wear resistance of nylon. The material also has a head deflection temperature of 293 F° (145 °C).

Other qualities of Onyx include, according to the company, improved dimensional stability for less warping, steeper overhangs and sharper edges; improved appearance; and less post-processing.

The Mark Two in Action

Autometrix Precision Cutting Systems produces textile cutting equipment and software for a number of industries, from sailmaking to medical device manufacturing. The equipment is made from CNC machined aluminum parts and Autometrix has often relied on computer numerical controlled (CNC) milling to evenly produce the prototype components for this equipment—a costly and time-intensive process. To speed up time to market at a reduced cost, Autometrix looked to 3D printing. Initially disappointed with traditional thermoplastic 3D-printed parts, Autometrix Chief Technical Officer Jonathan Palmer, explained, “You can’t compare a standard printed plastic part with the behavior, the performance you would get out of a machined aluminum part.”

Fabric cutting equipment featuring parts 3D-printed with CFF technology.
Fabric cutting equipment featuring parts 3D-printed with CFF technology.

The company finally came across CFF technology from Markforged, recognizing it as an alternative to low-quality 3D printers, as well as more costly CNC machines and metal 3D printers. After testing sample parts from Markforged, the company ultimately decided to bring the technology in house, finding that CFF could create stronger parts more quickly and at a reduced price compared to other processes.  

As a result, Autometrix was able to produce such components as a complete cutting head, which was determined to be a half-pound lighter than an aluminum equivalent. Moreover, the team has been able to iterate designs more quickly, as new concepts can be 3D printed in house, rather than outsourced to a service bureau. The company estimates that a part made by a machine shop from aluminum would cost about $629.20 and take 96 hours to produce, plus shipping, whereas 3D printing the component with CFF only costs about $45.50 and requires 42 hours to produce.

Palmer explained to ENGINEERING.com what he saw as the benefits of CFF, “From our perspective, it all came down to wanting to prototype parts that will ultimately be made out of aluminum in production runs. We needed reasonable structural strength to see if the parts would build a system stiff enough, strong enough, etc., for our end product. We're not just testing form and fit—we have to test function!”

Palmer added that CFF has the “unique ability to reinforce nylon parts with composites is what made the difference for us and has allowed us to test ideas quickly and affordably without paying the high price (both money and time) for one-off machined parts.”

In terms of disadvantages, Palmer said, "The only limitation we've found is just in part size. The parts have to have a minimum size before they can fit fiber reinforcement into the layers.  So, small parts simply can't be reinforced. It's a frustrating limitation at times, but a completely understandable one. They've got to be able to route fibers, and if there isn't enough room, that's just the way it is. I will say that some of the samples I've seen from upcoming versions are working to minimize this limitation!"

Manufacturer: Markforged

Model: Mark Two

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

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

Layer Thickness: 100 microns (.004 in) nonreinforced, fiberglas, HSHT, and Kevlar; 125 microns (.005 in) reinforced

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

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

Machine Price: Standard Package, $5,499; Professional Package, $8,799; and Enterprise Package, $13,499

Who Should Use the Mark Two:

Product developers, engineers and manufacturers may be excited about the ability to manufacture strong, light parts in house. The Mark Two is particularly adept at replacing CNC milled aluminum parts.

Why You Wouldn't You Use the Mark Two:

The Mark Two is not capable of the full geometrical complexity offered with other 3D printing technologies. Therefore, if creating intricate or geometrically intricate parts is more important than advanced physical properties, such as strength, abrasion resistance and temperature resistance, then another machine may be more appropriate. A metal 3D printer may be capable of achieving both, but will cost much more.


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