Carbon fibre joins the 3D printing revolution

However, the nature of these applications also highlights the major issue with carbon fibre – namely its expense. The reason it is largely used in high-end applications is that only they can afford it. Someone who had first-hand experience of the difficulties posed by carbon fibre was Greg Mark, who co-owns Aeromotions, a company that builds computer-controlled racecar wings. To make those wings both strong and lightweight, it uses carbon fibre. Here, though, the problem is that making custom parts out of carbon fibre is extremely challenging, costly and time-consuming. With these problems foremost in his mind, Mark sought alternative methods in the form of 3D printing. To his frustration, however, nothing on the market could print the material, and no available materials could print pieces strong enough for his purposes. This led him to devise his own solution: the MarkForged Mark One, the world's first carbon fibre 3D printer. Says Mark: "The expense in composites has traditionally been in both the material and the hand layout process. You have to lay out all the fibre in the moulds, you infuse the resin; you trim it, you cut it, you glue it together. It's a lot of labour. What we did was we took that idea of laying up composites and then we took the mechanics of a 3D printer and we put it together. So essentially you push the button and it does all the labour for you." This, of course, sounds deceptively simple, but – needless to say – it is not. The machine has two print heads. One head is capable of printing composite filaments (CFF) in carbon fibre and the other, traditional thermoplastic filaments (FFF). Parts may be printed either by a single head or a combination of the two. "We had to do two things," says Greg Mark. "We had to make this new material and then we had to make the machine that printed it. Instead of just printing plastic, we reinforce the plastic with carbon fibre and make it 10 times stronger than plastic has ever been before." What this means is that the main structure of an object can printed in a material like PLA or nylon, and then carbon fibre added as a thick layer just below the surface. The company reports that the carbon fibre filament is twice as stiff and five times stronger than ABS plastic, which is a bit less rigid than PLA plastic. What makes the Mark One different from other 3D printers is that it uses a new 3D printing process referred to as CFF (Composite Filament Fabrication) in combination with traditional FFF. Parts made with CFF are reinforced by continuous strands of fibres embedded in a thermoplastic matrix. Fibre-reinforced composite parts have many excellent structural qualities. The parts printed on the Mark One are up to 20 times stiffer and five times stronger than similar parts 3D printed using ABS plastic. Their strength depends on the type, orientation, and volume fraction of the reinforcing fibres. As well as carbon fibre, the Mark One can 3D print a range of other materials to help professionals design and iterate quickly. It is possible to make tough parts with Nylon Filament or load low-cost PLA filament for quick form and fit prints. And if you need the best cost-to-strength solution, it is possible to a print using MarkForged's exclusive Fibreglass Filament, which uses the same patented Continuous Filament Fabrication. The Mark One does not print with a weave, instead depositing layers of unidirectional composite in a user-defined orientation that can be specified by layer. In general, unidirectional composites have a higher strength-to-weight ratio in the preferred fiber orientation than composites made with woven fabrics. Quite how significant this development could prove to be is emphasised by Jon Hirschtick, founder of SolidWorks, who describes it thus: "This is a significant advancement in materials science. For the first time you can 3D print a part that is as strong or stronger than metal." Says Mark: "People have been trying to do this for at least 18 years... We knew we had something special the first time we took a part off the print bed and went to bend it and, instead of feeling like plastic and giving, it had the resistance and stiffness of carbon fibre." The machine also features It features an anodised aluminum unibody and a translucent printing bed. Kinematic coupling makes it simple to level the bed (indeed, the bed clicks into the same place every time within 10 microns). The printer itself is compact and elegant looking, measuring 574mm x 361mm x 323mm, making it a genuinely desktop unit. Ultimately, of course, the really exciting thing about this technology is that it puts custom carbon parts within reach of all sorts of other industries and allows intricate shapes to be formed that would be very difficult to create using traditional carbon fibre manufacturing techniques. This, according to the company, has already meant a great deal of interest from a number of new markets. One market that has shown particular interest is the medical prosthetics sector, where the ability to produce parts easily and less expensively in carbon fibre could prove revolutionary. Indeed, speaking at SolidWorks World recently, Hugh Herr of Biom (see cover story) specifically pointed to the Mark One, saying: "To be able to 3D print composites is very exciting. Biological tissues are essentially composites and composites have many extraordinary properties. They're very lightweight and strong, so to be able to print such 3D structures is very exciting." The printer is in a prototype stage at the moment, but will sell for about $5000 when it hits retail. Pre-orders for the printer have started, with shipping in the second half of 2014.