The hot ticket of high speed sintering

Last week I wrote about Xaar’s efforts to sell its printheads into the 3D printing market, much as every other printhead manufacturer is quietly trying to do. But Xaar also has another trick up its sleeve in the form of high speed sintering, which should give the company a real edge in the additive manufacturing market.

Neil Hopkinson, director of 3D printing at Xaar

High Speed Sintering or HSS was developed at the University of Loughborough by a team of researchers led by professor Neil Hopkinson, with the original patent filed back in July 2003. Sintering normally involves using heat to bond materials together without actually melting those materials. There are several 3D printing technologies that are based on some form of sintering, typically using a laser to generate the heat in a specific pattern that can produce complex shapes. But lasers are very expensive so Hopkinson looked for a cheaper alternative, eventually hitting upon the idea of using an inkjet printhead to jet an infrared absorbing fluid to direct the heat.

The process uses polymer powders, which are first spread across the bed. Then the print shuttle passes over the bed, jetting the infrared absorbing inks in the first pass, and then passes back over it to cure the ink with an infrared lamp. The ink absorbs the heat from the lamp and melts the powder particles directly beneath to form a single layer, currently 100 micron thick. More powder is deposited on top and the process repeated to build up an object one layer at a time.

The unused powder can be recycled afterwards with no waste whatsoever and no limit as to how often it can be put through this process. The part itself is put through a cleaning stage – blasting beads at it to get rid of any excess powder. There’s a choice of materials, with some being quite rigid while others are based on elastomers and can be used to create flexible parts such as hinges.

The main difficulty is that HSS produces a great deal of heat, far more than most printheads can withstand under normal operating conditions. Hopkins says that he approached several printhead vendors and only Xaar was willing to work on this problem. To be honest, I’ve met a fair few people from Xaar over the years and they’ve generally been pretty open to trying new ideas and to pushing the boundaries around their technology.

Xaar has been involved with this since 2005, when the company worked with Hopkinson’s team to fit Xaar 380 printheads to a selective laser sintering machine. Xaar went on to research inks suitable for the HSS process.

Xaar’s Adam Ellis demonstrates the Little Blue 3D printer.

Hopkinson later moved to the University of Sheffield but the intellectual property rights remained at Loughborough. By 2011 a dedicated HSS machine, affectionately known as Little blue, had been developed at the University of Sheffield, initially using Xaar Proton printheads. These were upgraded in 2015 to the 1002 printheads giving better resolution at higher speeds.

Around this time, the Factum initiative was set up to exploit both laser sintering and high speed sintering technology and develop commercially attractive additive manufacturing products. It was a consortium of various interested parties, including the Universities of Loughborough and Sheffield as well as Xaar. This project also helped to convince Doug Edwards, Xaar’s CEO, that 3D printing was an opportunity that Xaar should invest further in. This lead directly to the Nottingham facility being established at the beginning of 2016. Edwards persuaded Hopkinson to set up and to lead its 3D printing business unit, where he has been able to continue to refine the HSS technology that he originally developed. He explains: “I was ready for a new career after 20 years in academia.”

For now, Xaar is working with the Little Blue machine, which has been moved to its Nottingham base. This machine has a very small print area that is perfectly suited to testing different materials, which is the main activity at the Nottingham facility.

Last year Xaar picked up the remnants of the Danish team behind BluePrinter. This company had developed a large desktop 3D printer that gathered some interest, and was even shown at the last Drupa, but ultimately was too slow to be competitive. However, Hopkinson says that BluePrinter had useful know-how in maintaining thermal control, which is crucial to high speed sintering, and so added this team based in Copenhagen to the R&D mix.

The Copenhagen team is in the process of building a new machine with a much bigger build area though Hopkinson won’t talk about this beyond a vague promise to share more details later this summer. Although this machine will be bigger, the HSS process is best suited to small complex parts rather than large pieces mainly because of the difficulty in controlling the temperature so the idea is to use a large bed to produce many parts in a single cycle.

Hopkinson explains: “The machine we are developing, we see it as intended for industrial part production. It will benefit from the high viscosity printing that we can achieve. We will have machines going out to selective partners in the second half of this year.” Xaar’s plan is to partner with companies that can offer sales and support, leaving Xaar free to concentrate on developing the machine itself and the materials. The initial target markets are aerospace and sport and leisure though Hopkinson believes that automotive will be the biggest market in the long term.

3D printed samples at Xaar.

Xaar claims that the HSS process can be up to 100 times faster than laser sintering, depending on the size of the bed and the complexity of the part geometry. Hopkinson says that the biggest opportunity is to replace injection moulding where this approach can be much more cost-effective because it’s easy to print many thousands of parts.

The key to this lies in the range of materials that can be used with the HSS process, which is where Xaar is currently focussing. The materials are all polymer-based but Hopkinson says that polymer would be suitable in some cases to replace metal for production parts. He explains: “Polymer is harder to cut than metal but easy to print. Aircraft have lots of machined aluminium but if you can just print without machining then polymer would be good.”

It’s impossible to draw any real conclusions about Xaar’s HSS venture until the company is a little more forthcoming about the machine it’s developing. There are quite a few other industrial-scale 3D printers, either already shipping or in development and just about to become available. Most of these use a relatively large build area to produce large numbers of small, complex parts in a single cycle. We are currently in a period where we are seeing many new machines appear after years of development, which is good news both for manufacturing industry and for journalists. Over the next few years we’ll see a shake-up as the market decides which of these machines are most useful.

Xaar clearly has a massive opportunity here, both through the high speed sintering technology and its printheads as well as the work that it is doing in developing suitable materials. Only time will tell what Xaar makes of this opportunity though we will all have a much better idea when it reveals its first production HSS machine later this year.

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