3D Printing Ultra-Strong Polymers for End Production

Today, the 3D printing of polymers is limited to prototyping applications, with only a limited choice of low-performance materials, such as ABS (acrylonitrile butadiene styrene) and PLA (polylactic acid). The next leap forward, and the next challenge in this industry, is the ability to 3D print production-grade parts.

The aerospace, defense, oil and gas, and healthcare sectors have shown significant interest in this possibility. This is due to the promise of creating ultra-strong parts, along with an on-demand, software-driven, efficient manufacturing supply chain. The possibility of making parts with higher mechanical strength, unique functional properties, and geometries that cannot be achieved using traditional manufacturing techniques is driving a pent-up demand for 3D-printed polymer parts with a huge potential in functional use applications.

In order to realize this potential, three fundamental challenges need to be addressed. First, advances in 3D printing processes must occur to support high-performance materials, such as PEEK (polyether ether ketone) and fiber-reinforced polymers. Second, new testing methodologies must be created for the mechanical characterization of fiber-reinforced polymers. Finally, intelligent software must be developed that makes the properties of printed objects more deterministic. This article discusses both technical and non-technical hurdles of 3D printing production-grade parts from a process and qualification perspective. We also present general development efforts in this area, including Arevo Labs' own efforts to tackle these problems.

Polymers can be 3D printed using processes such as selective laser sintering (SLS) and filament fusion. We will focus on filament fusion, as this technique lends itself well to printing fiber-reinforced materials, and it also provides fine control over fiber orientation. 3D-printed reinforced polymer parts with fillers such as glass, carbon, and Kevlar fibers offer significantly higher mechanical properties than parts made with unreinforced polymers.

Materials choice and processing requirements
Aerospace, defense, oil and gas, and healthcare industries use high-performance polymers such PEEK, PAI (polyamide-imide), PPS (polyphenylene sulfide), PPSU (polyphenylsulfone), and PEI (polyetherimide). PAI, PPS, and PEI are examples of amorphous polymers, whereas PEEK and PPS are semi-crystalline materials.

Amorphous polymers are easily printed using filament fusion. This is why almost all filament fusion 3D printing systems today are limited to printing amorphous materials, the most common being ABS, PLA, and PC (polycarbonate). Printing high-temperature semi-crystalline materials such as PEEK is much more difficult due to their higher viscosities, which prompt a greater need for temperature management, and special considerations in material formulations and in deposition. For these materials, special formulations are needed to make them suitable for 3D printing using filament fusion.

The polymers' mechanical properties can be improved by adding reinforcing materials. For example, certain chopped carbon fiber-reinforced polymers shows an improvement in stiffness by a factor of five and an improvement in strength by a factor of two over unfilled versions. We have found a range of carbon fiber content between 10% and 20% to be an optimum choice for achieving a balance between the desired mechanical properties and the material's processability.

The reliable, consistent processing of high-temperature, high-performance materials for 3D printing requires understanding and solving two coupled problems. These are the correct design of printer heads, which involves both hardware and control software, and the problem of devising optimized material formulations.