Additive manufacturing: Laser sintering
Laser sintering is a powder bed process that uses a laser as a power source to sinter powdered material. Understanding the material at a microstructure level is critical to the development of materials for laser sintering. We use in-house designed methodologies and test to investigate how the size and morphology of particles, crystallisation kinetics, and subtle changes in chemical structures influence powder flow, spreadability and sintering. This is combined with statistical and mathematical methods to predict powder properties and performance.
We use a range of analytical equipment to assess materials before putting them in one of our laser sintering machines, which currently includes 2 high temperature systems (EOS P800 and EOS P810), as well as an EOS P100 and a Sharebot SnowWhite system, with the group working closely with material manufacturers to develop tailored grades for AM processes and specific applications.
Research projects include:
Combining nano-particles with PAEK polymers, this project is looking to develop new bespoke lightweight multifunctional materials that can be 3D printed using powder bed fusion technology and FFF. PAEK polymers are temperature resistant, tough, and corrosion resistant. They are increasingly being used for metal replacement within aviation and military application.
Boron nitride and graphene have been selected as the nano-materials most suited for the intended applications here. These new materials will offer multifunctional capabilities including lightweighting, thermal and electro-magnetic properties. Incorporation of nanomaterials with different particle sizes and shape which will significantly affect powder flow, polymer viscosity and subsequently sintering mechanisms are very important to the success of this project.
The project will study the surface chemistry of the nanoparticles for good interface bonding with PAEK; fabrication of the composite powder (encapsulation of the nanoparticles either on the surface or within the bulk of the PAEK particles) and laser sintering of these new powders. Powder properties (bulk density, compaction, shape - roundness and circularity, aspect ratio, viscosity, surface tension) are key parameters for a good sintering process,
Funded by: Innovate UK
Partners: Qioptiq Ltd, Thales UK Ltd, Victrex Manufacturing Ltd, Hosokawa Micron Ltd, Airbus Operations Ltd, 2-DTech Ltd, Haydale Ltd
The University of Exeter is part of a consortium of 8 organisations, led by Victrex, to develop PAEK for various 3D printing processes. This project was conceived and the team established following the conference held by the University of Exeter – European Strategy for Additive Manufacturing with High Temperature Polymers.
A key objective is the improvement of the recycle rate for powders used in laser sintering. This would significantly reduce polymer wastage in this type of additive manufacturing process and reduce costs. The project will also address unpredictability of inter-layer adhesion and parts surface finish in filament-based printing.
Funded by: Innovate UK (Aerospace Technology Institute)
Partners: Victrex Manufacturing Limited, E3D-Online Ltd, 3T RPD, South West Metal Finishing Limited, Airbus Group Limited, EOS, HiETA
The aim of this project is to develop novel high performance, nanocomposite feedstock powder materials and filament for two processes: Laser Sintering and Fused Deposition Modelling (FDM). It will examine the potential use of inorganic fullerene-like tungsten disulfide (WS2) as nanofillers for high value, PAEK (Poly Aryl Ether Ketone) based products.
The incorporation of these nanomaterials has been shown to improve thermal, mechanical and tribological properties of various thermoplastic polymers. It reduces wear and the coefficient of friction as well as offering processability benefits with dispersion characteristics that are superior to 1D and 2D nanoparticles. They are also the best shock absorbing cage structures known to mankind and importantly, they are non-toxic and thermally stable.
Funded by: EPSRC
Partners: University of Exeter and Ulster University. Supported by Victrex Polymer Solutions, Laser Prototype Europe, Bombardier Aerospace, Daido Metals Co. Ltd.
This project investigated the way the polymeric powders of different shapes and sizes flow, interact and sinter in the laser sintering (LS) process, through modelling and experimental validation. 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 mechnical properties. Surface area of particles, polymer viscosity and surface tension were characteristics which were investigated when modelling the flow and sintering process.
Findings
It was a highly innovative project and its findings have the potential to help unlock the materials limitations for polymeric laser sintering. This allows rapid expansion into a wider range of higher value applications due to lower powder costs, wider choices and better understanding of their behaviour within the manufacturing process.
Funded by: EPSRC
Partners: University of Exeter and University of Edinburgh. Supported by Victrex Manufacturing Ltd and 3T RPD
Reference https://doi.org/10.1016/j.powtec.2016.11.002
Arkema and CALM are working together on optimising Poly Ether Ketone Ketones (PEKK) for the EOSINT P 800 powder bed process. The PhD aims to gain a deep understanding of the material at the microstructure level in order to optimise it for the manufacturing process.
Arkema is a European chemical company leader in the field of high performance polymer materials, one of which is PEKK, invented in the 1960s as part of the Apollo space program.
PEKK Kepstan®, one of Arkema’s PEKK materials, has a very high melting point (300°C to 360°C depending on the grade) and provides excellent resistance to chemicals and abrasion. Reinforced with carbon fibres, it is as rigid as some metals, but very much lighter and it is non-flammable without releasing any toxic fumes.
Funded by: University of Exeter and Arkema
High temperature laser sintering is an additive manufacturing technique enabling the highest level of design freedom currently achievable. High customisation, multi-functional integration and design optimisation are the most outstanding characteristics of this process.
However, the small number of polymers currently available constitute a significant drawback for many engineering applications, especially in the automotive and aerospace industrial sectors, where only one grade, PolyEtherKetone PEK HP3, can meet the material performance required.
In an attempt to expand the choice of materials for laser sintering manufacturing, this research project has focused on the investigation and implementation into laser sintering of a new high temperature polymer, Poly Ether Ether Ketone (PEEK). This research work has examined some of the key requirements needed for the successful development of new materials in laser sintering at experimental and theoretical levels and led to the manufacture and testing of some medical applications using a medical grade of PEEK.
Supported by: Victrex, Invibio Biomaterial Solutions