It’s an exciting time for additive manufacturing using PAEK or polyaryletherketone polymers, a relatively new industry sector, which has been developing for less than 10 years.
As in other areas of additive manufacturing (AM), the initial hype, enthusiasm and extensive claims around this PAEK family of high-performance polymers (HPP) preceded any realistic evaluation of materials and AM platform capabilities. The potential uses of these materials in AM have seen a similar trend of climbing the slope of a classic hype cycle before disappointment and ultimately a true assessment of the technology.
Due to the investment and research made by a small pioneering sector of the industry brave enough to take on the challenge of high temperature AM development, including the detailed examination of the strengths and limitations of the materials, we are now advancing developments towards mainstream adoption of high temperature AM with PAEK.
High-performance PAEK polymers such as VICTREX PEEK have been in use by the aerospace industry for decades due to their flammability performance and low smoke toxicity, exceptional heat and chemical resistance, strength and low weight. With the advent of AM, there were initial expectations that the combination of this process and materials, had the potential to create the new lightweight, bio-inspired, strong parts that the aviation industry was looking for, in its continuing search for increased fuel efficiency, simplified manufacture and long-term reliability.
A good choice for aviation
Advancements in AM using PAEK were initially limited due to processing issues related to the very high melting point of these materials (between 300°C and 380°C). In 2008, EOS launched the first high-temperature AM system for laser sintering of HPPs. The EOSINT P 800 has the ability to process temperatures up to 385°C. EOS also developed a new commercial grade material for the system. The EOS PEK HP3, based on Victrex material, also belongs to the PAEK family, with other members being PEEK and PEKK. PAEKs characteristics include flame retardance, low weight, high tensile strength and biocompatibility, making it a good choice for industries such as aviation.
The Centre for Additive Layer Manufacturing (CALM), at the University of Exeter, was one of the first to invest in the EOSINT P 800 and was ideally placed to investigate the system’s capabilities and properties of PAEK polymers. Established in 2010, CALM specialises in the use of high temperature and high-performance polymers and composite materials for AM.
The first generation of PAEK materials required nearly a full refresh of the powder before each build due to degradation at the high temperatures. HPPs such as PAEK are used for high value applications in extreme environments and throwing away large quantities of unused but degraded PAEK was not cost-effective or sustainable. Another area for improvement was processing temperature. PEEK and PEK are processed above their melting temperature of 343°C and 373°C respectively. These high temperatures limited the machines on which they could be processed and increased the challenges involved in controlling warp and shrinkage. PEKK on the other hand can offer melting points as low as 300 to 305°C but is completely amorphous in this form. These factors were limiting the potential development of these HPPs in AM and the research carried out by CALM focused on combating these to support new material developments, particularly researching the powder morphology, flow and recyclability and refresh rates.
Sensing an opportunity to drive the industry forward, in 2014 CALM hosted a conference on the European Strategy for Additive Manufacturing for High Performance Polymers with a particular focus on PAEK. The first conference on this topic, it was a chance to bring together a small but growing sector from manufacturers of PAEK HPP powder to potential end users. Research findings were presented and the challenges inhibiting industry mainstream adoption were discussed. These included a lack of process-specific high temperature materials, a need for enhanced recycling rates and lower overall production costs as well as more information about material properties. As a developing industry, it was important for this group to co-operate to identify how the current limitations could be dealt with collectively, so encouraging more investment.
As a result, a new consortium of eight organisations was formed, which brought together the entire materials and processing supply chain, including polymer makers/suppliers through to parts manufacturers and post-processors as well as end-users. At the same event, Victrex, a world leader in high-performance PEEK and PAEK polymer solutions, had presented some early-stage results on a new polymer with significant potential for AM. With funding from Innovate UK’s Aerospace Technology Institute (ATI), and led by Victrex, the consortium’s aim was to develop new grades of PAEK for laser sintering and free form fabrication as well as improving the recycle rate of powders to reduce cost. The new grades are particularly targeted at the aerospace industry to improve process reliability, contribute to production cost efficiencies and allow a common place fabrication route throughout the aerostructures supply chain.
PAEK products designed for AM
Now in 2018, the results of this collaborative research are about to be announced, including new VICTREX PAEK materials, which can contribute to production cost efficiencies. For example, the powder recycle work for laser sintering, using the new Victrex development polymer grades have gone well, with no measurable loss of properties when test components were made from 50% recycled powder. The company believes it will be possible to re-use all of the non-sintered powder that is recovered after a build run. This will result in a significant reduction in parts production costs compared to current HP3 PEK materials.
As part of this collaboration, CALM has also strengthened its methodologies and procedures of testing and analysis of PAEK HPP powders for AM, by creating rigorous protocols, ready to be used in new material developments.
In addition to recycling efficiencies, the surface finish of AM parts is an important aspect contributing towards its commercial viability. South West Metal Finishing (SWMF), a specialist in surface treatment of aerospace components and part of the consortium, developed the first known surface treatment process, which enhances all surfaces of additive manufactured PAEK components by chemically dissolving the material to remove semi-sintered powder particles and large undulations, leading to smoothing of the surfaces.
Furthermore, the melt temperatures of some of the new semi-crystalline PAEK materials are as low as 305°C, and the combination of the low melting point with crystallinity is unprecedented, combining the desirable properties of PEEK – wear, chemical, fatigue and creep resistance – with easier processing at significantly lower temperatures. The melt temperature improvements especially may contribute to running these materials on some of the newer machines with some additional development on machine process conditions, such as the announced EOS P500. These next-generation VICTREX PAEK materials for additive manufacturing mark a decisive step forward, having potential to transform multiple applications and allow PAEK AM, to achieve its potential to replace metals in applications such as airframe design and manufacture.