Performance polymers for performance parts

laser-sintered-pump-impeller
laser-sintered-pump-impeller

As high temperature polymer additive manufacturing moves from development to production, material understanding remains essential, explains Oana Ghita, academic lead at the University of Exeter’s Centre for Additive Layer Manufacturing (CALM).

The rapid advances in additive manufacturing (AM) and the use of high temperature polymers to create viable, cost-effective parts for demanding applications in the aerospace industry has meant that interest in this field has never been stronger. But how is this technology really developing?

To examine the latest developments and technical challenges, CALM has once again brought together the leading experts in the AM industry from the UK, Europe and the USA. Its second European Strategy for AM with High Performance Polymers Conference, supported by Victrex and the University of Exeter, included presentations from polymer manufacturers, right through to end-users and companies involved in post-manufacturing processing, as well as updates on latest academic research.

As a leading research centre, CALM collaborates with a wide range of organisations and academia to develop the next generation of high temperature polymers and composites used in AM processes. It is the only independent centre worldwide researching laser sintering of high temperature polymers using the EOS P800 platform.

In 2014, when CALM hosted its first European event, the challenges were easy to identify as the technology was still in its infancy. There was a need for more specific high temperature materials, lower material costs, better reprocessing rates, improved multi-functionality and greater knowledge of material properties.

Government backing

As a result of the first event, many of these issues are being addressed. With funding from Innovate UK, CALM and a consortium of seven other organisations led by Victrex, are exploring ways to create affordable, new high performance polymers and composite materials.

Victrex, a leading global provider of polymer solutions, is developing ground-breaking new grades of high performance polyaryletherketone (PAEK) polymers specifically designed for AM for use in the aerospace industry. The new Victrex PAEK materials will be tailored for laser sintering, filament fusion and new technologies. such as the Airbus patented AM process ‘ThermoMELT.’

PEEK and PEEK-CNT micro-gears
PEEK and PEEK-CNT micro-gears

High performance adaptable plastics such as those in the PAEK family and their engineered composites are of particular interest to airframe makers as metal replacements, being up to 70% lighter than steel, titanium or aluminium resulting in fuel efficiency and lower CO2 emissions. They are also chemically resistant and have excellent flame retardancy. The additive manufacture of PAEK polymers and composites is expected to become a standard fabrication route throughout the aero industry with defence, oil and gas and automotive industries also benefiting significantly from these developments.

The journey so far

Two years on, with a greater understanding of materials and their properties, industry representatives at the second Conference heard from Victrex about its commitment to support this growing sector and to satisfy end user requirements. Victrex is engaged in focused research in this area and investing in the construction of a dedicated polymer innovation centre to increase capacity to turn lab concepts – engineers’ dreams – into real-world solutions.

Airbus Group Innovations highlighted its advances in addressing recyclability and process reliability through its new ThermoMELT process, Versarien Advanced Composites presented its work with CALM on innovative new Graphene-PAEK nanocomposites, Indmatec, pioneers of extrusion deposition printers for PEEK, discussed its equipment manufacturing developments and CALM gave an update on recent research projects funded by EPSRC, Innovate UK and DSTL, demonstrating the rapidly growing knowledge now available about both materials and processes.

New research on encapsulated carbon fibre-reinforced high temperature polymers by laser sintering process specialist EOS, has shown significant improvement of mechanical properties and enhanced isotropy. The material was developed within a collaboration with Boeing, ALM and Stratasys and first parts were already used in Boeing’s ecoDemonstrator programme. Boeing also talked about its learning journey and findings of developing engineering polymers, while Eurocoating and Oxford Advanced Surfaces introduced innovations for PAEK surfaces, including titanium coating and adhesive bonding solutions.

Brett Lyons, from Boeing Commercial Aircraft, product development, material integration commented: “This size of event is great for discussions and networking and was a chance for me to meet people outside of the USA, working in the same area. It showcased a variety of different applications as well as the value of academic research in this field.”

The pace of material change

With new materials being developed, attention now is on tackling the remaining challenges and the events hosted by the University of Exeter have helped focus industry efforts.

A motorsport suspension mount manufactured from EOS PEK-HP3
A motorsport suspension mount manufactured from EOS PEK-HP3

Of these, robustness of the process is one of the major technical challenges still facing AM PAEK parts manufacture, with concerns around the variability of the process and quality of end product to meet the requirements for lightweight, stiffness, flammability and chemical resistance for aerospace applications. Delegates agreed that capturing data, further testing and research and the potential for real time process monitoring leading to a closed loop manufacturing process were essential next steps.

End users are also particularly interested in the long-term chemical, thermal and aging properties of high temperature AM components. Currently there is little data available on the stability of PAEK AM powders and parts. For many applications, a 30-years material performance forecast is desirable and more data and analysis is essential.

As Sybille Fischer, material & process developer at EOS observed: “I have come away with lots of new ideas, a big list of things to work on, and a better understanding of the future requirements of potential customers.”

The lower mechanical performance in z direction (high anisotropy) of AM parts is another area needing more research to create the ultimate isotropic structures. The use of nanomaterials with high aspect ratio, such as graphene and carbon nanotubes may be a possible solution to opening up new applications.

Recognising the need for process and long-term performance testing, these areas are likely to be the focus of investigations in the short-term, coupled with research to create the ‘tailored’ new materials the industry needs.

But with clearly identified applications now available and good knowledge of the materials and processes, the next few years are set to provide significant advancement with the aerospace industry positioned to capitalise on the growth of high temperature polymers for AM.

This was summed up by Uwe Popp, head of research and development at Indmatec: “Now is the right time for growth in the use of industrially relevant polymers in Additive Manufacturing. People are realising the significant opportunities that exist from using PAEK and although there are still many steps to get it into the market, innovations and developments in the field are moving very fast.”

At CALM, we are delighted with the outcome of the event. Engagement with industry is very important when working in the manufacturing research area. The ability to combine advanced materials knowledge with high temperature additive manufacturing capabilities places Exeter in a unique position within the UK manufacturing research landscape.

www.exeter.ac.uk

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