A secret that may not be known to those outside of the 3D printing industry is that an object 3D printed by means of fused filament fabrication (FFF) may not be as strong on the Z-axis as it is on the X- and Y-axes. While the filament is extruded in one continuous strand on the X- and Y-axes, layers on the Z-axis are only laid atop of one another. For this reason, FFF prints can crack along the Z-axis as one might snap a piece of wood.
To bring isotropic strength—that is, strength in every direction—to FFF 3D printing, a new partnership has developed between thermoplastic composites research company Essentium Materials and FFF printer manufacturer Cosine Additive. Together, the companies were able to create an FFF printer capable of achieving powerful levels of Z-axis strength.
The idea was thought up by C. Brandon Sweeney, the principal inventor and technology lead for the project, at the U.S. Army Research Laboratory three years ago. Using technology licensed from Texas Tech University and Texas A&M University, Sweeney developed a thermal welding device that attaches to the printhead of an FFF 3D printer. Once a number of layers are printed, the device applies an electric field to fuse the layers together.
In an interview with ENGINEERING.com, chief technology officer of Essentium, Blake Teipel, described the process, “When you lay down a layer with the FFF process, the polymer chains between layers aren’t talking to each other. They’re just resting on top of one another. But when you apply tons of heat energy, they start to melt together. That’s where our strength comes from.”
Essentium came into the picture about a year ago, when the Essentium team began exploring the drawbacks of FFF 3D printing. Recognizing the lack of isotropic strength as a main problem with the technology, the company went in search of potential technologies for addressing the issue, eventually coming across Sweeney and his work. Lending its materials expertise, the Essentium team then worked with the inventor to commercialize his technology.
Cosine Additive joined to develop the machine platform to leverage Sweeney’s device, modifying its existing AM1 3D printer. The new EM1 features a new set of electronics, the electric field emitter, and shielding on its sides to prevent the energy within from harming the operator.
Essentium provides the materials for the system, currently focusing on a PLA filament coated in carbon nanotubes. The EM1 3D prints this carbon PLA composite and, once an inch of material is laid down, the electric field gives the print a blast, fusing the material together.
Teipel elaborated on the power of the electric field involved, “Since it’s an electric field, you can penetrate all the way through the material. That’s the advantage over ultrasonics or lasers or other heat treatment technologies. It’s not limited to a surface treatment.” Parts printed with this technique have an interlaminar strength that is about 95 percent that of the bulk material, which is the pure material before it is fed into the machine.
Right now, the showcase application for the technology, according to Teipel, is the construction of load-bearing prosthetic devices. Though 3D printing has long been demonstrated as a powerful tool for creating low-cost, patient-specific prosthetic arms and hands, the ability to 3D print load-bearing, lower-limb devices has not seen as much progress.
Essentium’s sister company, TriFusion Devices, has begun 3D printing custom sockets for leg prosthetics. TriFusion, for which Teipel is the CEO, has developed its own thermal welding process that relies on microwaves to increase the Z-axis strength of FFF parts. With both the electric field and microwave technology, Teipel explained, “We can 3D print [load-bearing sockets] overnight. It’s no longer like a 4- to 8-week work cycle for a 3D-printed socket. It’s a 48-hour cycle.” As if to speak to the potential of 3D printing such devices, TriFusion won the Rice Business Plan Competition (RBPC) in April 2016 and took home nearly $400,000 to fund its startup.
Essentium and Cosine are currently looking for beta customers for the EM1, with plans of a commercial launch in less than a year. Those interested in becoming beta customers for the EM1 platform have been directed to email Teipel at Blake@EssentiumMaterials.com.