Greyscale adjustments optimise 3D printed parts

Dubbed high speed sintering (HSS), the process has the potential to produce parts at a rate that could challenge a substantial portion of the injection moulding market.

HSS uses an inkjet and infrared lamps instead of a laser and an advanced optics system to help form 3D printed parts.

’We feel we’re in a good place, particularly with the higher end polymer products’

‘Its like other 3D printing approaches whereby where we design a part and slice it into lots of discrete layers,’ explained HSS pioneer Neil Hopkinson, a Professor of Manufacturing Engineering at Sheffield University.

Each layer of the 3D CAD design is then uploaded onto an HSS machine, which deposits a layer of engineering grade powder approximately 100 microns thick onto the machine’s part bed.

Hopkinson said: ‘We then print ink onto that powder and that ink is specially designed so that it absorbs infrared energy.

‘We then irradiate the bed surface with IR energy, [which] is particularly suited to be absorbed by the ink that we print but not by the powder that the ink is printed on.

‘The ink gets hot and heats up the particles that lie underneath it and those particles melt and join together which creates a single layer of the part we’re creating. The process is repeated many times over, depositing a fresh layer of powder on top and printing again the next shape that we want to melt, so that we start melting powder together within layers and also between layers.’

As well as nylon 11 and nylon 12 the team process a range of elastomer materials for applications where they see a lot of potential for impact absorption.

‘Anything from making running shoes through to perhaps damping on automotive systems,’ said Hopkinson.

Up until recently, the Sheffield team has printed always printed 100 per cent black but they’ve found that they can control the density and strength of the final product by printing the ink at different shades of grey and that the best results are achieved by using less ink than is standard.

‘To date we have been using old Proton print heads from Xaar, which require the dithering approach to create greyscale,’ Hopkinson said via email. ‘However in future will use Xaar’s 1001 series print heads that give us the true greyscale option without dithering - I expect this will allow us to improve properties even more.’

In the long term , HSS could produce parts with varying properties but that are relatively simple to recycle as they do not require multiple materials. The process has also the potential to challenge injection moulding as a viable means of mass production as lead times are shortened and customers have the flexibility to change their designs without having to create new moulds.

Hopkinson said: ‘We feel we’re in a good place, particularly with the higher end polymer products.

‘We have a very compelling case to compete with injection moulding for the manufacture of a substantial range of products and I think that is our unique selling point in terms of how we’re moving forward.

‘But its not something we can do in isolation, its really important that we are working with a range of companies from different sectors - from FMCG through to aerospace - and also their supply chains in order to take the technology forward.’