Particle Shape and Flow behaviour in Laser Sintering: from modelling to experimental validation

Lead Research Organisation: University of Exeter
Department Name: Engineering Computer Science and Maths


This project proposes to investigate the way the polymeric powders of different shapes and sizes flow, interact and sinter in the Laser Sintering process, through modelling and experimental validation. Laser sintering is part of the additive manufacturing technology, known for its benefits in industries where custom made products, lightweight and complex designs are required. In laser sintering a polymer powder bed is heated to just below its melt temperature. A laser is then focused onto the bed which scans a raster pattern of a single layer of the final part. The bed lowers slightly and a new layer of powder is applied. The process is then repeated until the component is made and the additive layer process is complete.

The spreading and compaction of the powder is an important part of the LS process, a non-uniform layer of powder leads to high porosity and weaker bonding between layers and therefore a structure with poor mechanical performance. Similarly, the size and shape of particles can change the sintering process. Larger contact areas between particles lead to a good sintering profile and ultimately to a high density part and good mechanical properties. Surface area of particles, polymer viscosity and surface tension are characteristics which will be considered when modelling the flow and sintering process.

Planned Impact

The main direct beneficiaries of this project are: (i) companies delivering AM products; (ii) AM manufacturers, (iii) powder suppliers and (iv) mill manufacturers.

Companies delivering AM products will directly benefit from the guidelines on how to achieve better sintering product properties which can be further developed according to the research outcomes. The knowledge of how unconventional powders can be used in AM has high potential to broaden the use of AM technologies. Such effect will benefit all four sectors in that (i) could reduce production cost using low-cost powders, (ii) could expand their machine market, (iii) could have new users of certain powders from AM industry and (iv) could supply mills to AM manufacturers or AM users directly.

More specifically, AM manufactures will benefit from the understanding of the flow and sintering behaviour of certain shapes of particles and design and optimise AM machines for such powders. Powder suppliers will then benefit from catering to the new AM processes. Mill manufacturers will benefit from the knowledge about what particle shape and size distribution are required by AM and design milling processes suitable to produce such powders. Therefore, the project research outcomes will provide new impetus to prompt all four sectors to work together in a mutually benefiting "ecosystem".

The project will have also indirect benefits: (1) societal, a wider and more cost effective range of powders in the medical sector will lead to cheaper choices of materials for manufacture custom made implants (e.g. hip replacements) for the older population; (2) environmental, more flexibility in the range of materials leads to better designs, for more complex lightweight structures which ultimately lead to increased efficiency and lower fuel consumption.

The researchers and investigators will also benefit from the technical knowledge, team working and project management skills gained through the project.
Description The project provided in-depth knowledge of the powder flow and discovered new mechanism of crystallisation of PEEK a high temperature polymer with unique properties suitable for advanced applications.
Exploitation Route The outcomes of this project were used to feed in follow on research activities and collaborations with industry. The research highlighted through in-depth powder characterisation and modelling, the issue related with the existing powder materials and current grants are working to address these concerns.
Sectors Aerospace, Defence and Marine,Chemicals,Healthcare,Manufacturing, including Industrial Biotechology

Description The findings of this project together with the outcomes of the follow on projects are used by material manufacturers to design new high temperature polymeric powders suitable for additive manufacturing (AM) and subsequently to tailor performance and properties. The project showed the importance of powder properties and flow in AM, provided methods for characterisation of powders and modelled flow of particles with a high aspect ratio. These findings had been used and explored further in industrial collaborations which followed beyond this project. During this project, a new crystallisation mechanism of PEEK has been proposed and new crystal structures identified. As new PAEK polymer grades are being developed, understanding the crystallisation kinetics and crystal morphologies is important and will allow industry understand better manufacturing with these high temperature polymers.
First Year Of Impact 2018
Sector Aerospace, Defence and Marine,Chemicals,Energy,Healthcare,Manufacturing, including Industrial Biotechology
Impact Types Economic

Description Data and results for FDA
Geographic Reach North America 
Policy Influence Type Influenced training of practitioners or researchers
Impact The results we presented to the 2nd PEEK Conferences were very important to FDA community and the FDA experts to understand the future of PEEK materials and additive manufacturing process to medical implants.
Description White Paper on Needs and Recommendation on High Temperature AM sector - disseminated with the MTC which is part of the High Value Manufacturing Catapult and the National Additive Manufacturing Centre
Geographic Reach Europe 
Policy Influence Type Implementation circular/rapid advice/letter to e.g. Ministry of Health
Description Aerospace Technology Institute (ATI)
Amount £1,600,000 (GBP)
Funding ID 102362 
Organisation Innovate UK 
Sector Public
Country United Kingdom
Start 02/2016 
End 01/2018
Description IUK -Materials and Manufacturing Call
Amount £800,000 (GBP)
Organisation Innovate UK 
Sector Public
Country United Kingdom
Start 03/2018 
End 01/2020
Description EPSRC Impact accelerated account 
Organisation Victrex
Country United Kingdom 
Sector Private 
PI Contribution Understand molecular structure and behaviour in manufacturing of new PEEK grades
Collaborator Contribution Knowledge in PEEK
Impact Relevant information to PEEK structure
Start Year 2016
Description European Strategy for High Temperature Additive Layer Manufacturing ( September, 2014, September 2016, September 2018) 
Organisation Victrex
Country United Kingdom 
Sector Private 
PI Contribution This is an event organised by my research team. The aim of the event were to: - Bring together the entire supply chain; from material suppliers, system manufacturers, technology enablers and especially end users of High Temperature Laser Sintering technology. - Create a European Strategy (Technology Road Map) for Additive Manufacturing for high temperature polymers identifying key research themes and challenges. Produce a structured framework leading to a clear vision and direction - To create a community of experts within the field and to strengthen Europe's position within the area of High Temperature Laser Sintering of engineering polymers - Build a momentum within Europe to enable speed of TRL maturity ready for adoption and manufacturing. The event presented our group research findings, highlighted key areas where industrial collaborators and partners are keen to focus on in order to move the technology forward.
Collaborator Contribution The event included 40 industrial participants from 20 organisation. Key industrial players presented their strategy for development in this area: EOS GmbH- Germany; Airbus Group Innovation UK, Victrex, UK, Maplebird, Smiths Detection, 3T RDP and EIC group.
Impact The outcomes of the event are expected to develop and grow over the coming year, through setting up special funding arrangements/agreements and applying for funding through the current funding schemes, depending on the technology readiness levels. Currently, one clear collaboration had been identified between Victrex, Airbus Group Innovation and Exeter University, in progress of being set up. The project is focused on material development, and particle flow, morphology and structure is at the heart of the development. Last event, 2018, led to development of the High Temperature Polymeric AM strategy - for incorporation into the national UK strategy
Start Year 2014
Description Industrial Partnership between Centre for Additive Layer Manufacturing (CALM) and Victrex 
Organisation Victrex
Country United Kingdom 
Sector Private 
PI Contribution This is a joint multimillion partnership - funded 50-50% by the University of Exeter and Victrex Manufacturing Plc.
Collaborator Contribution
Impact The partnership is on track to deliver new commercial materials for AM.
Start Year 2018
Description European Strategy for High Temperature AM polymers (event - September 2016) 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Industry/Business
Results and Impact 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.
Year(s) Of Engagement Activity 2016
Description Event sponsored/organised and chaired by University of Exeter and Victrex Manufacturing Plc- "European Strategy for High Temperature Additive Manufacturing" - An industrial event at University of Exeter 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Industry/Business
Results and Impact The discussions are summarised in the article published in Aerospace Manufacturing magazine
Year(s) Of Engagement Activity 2016