One of the aspects I love the most about the 3D printing industry is that it is transforming boring, complex, manufacturing machines into something amazing and fascinating. New additive manufacturing (AM) technologies are rapidly and constantly changing the face of the manufacturing industry, making it better, quicker, more sustainable and more capable of addressing specific individual needs. Everything we have taken for granted for decades — such as injection moulding for mass manufacturing — can be challenged and sometimes (actually most of the time) it turns out that there are those who have already found a new way of doing things. One of the most radical shifts in this sense was announced just a few weeks ago, when we reported about the University of Sheffield Department of Mechanical Engineering’s Professor Neil Hopkinson’s newly funded FACTUM study on patented HSS (High Speed Sintering) technology. Leveraging £1.5 million in both public and private financing it may prove that, for certain small and complex geometries, additive manufacturing could be more affordable than injection moulding for any number of parts. I caught up with Professor Hopkinson, whose background shows an amazingly long list of studies on sintering technologies and achievements in additive manufacturing development, to find out if, when and, most of all, how, HSS will change the face of global manufacturing.
“I get asked that a lot,” Professor Hopkinson admitted. “It all began about ten years ago when my supervisor, Prof Phil Dickens, and I conducted a cost-cross analysis study to find out which would be the cut-off volume for sintering compared with injection moulding, starting from the idea that you use sintering for a single part and injection moulding for millions of the same part. The result was that for a very complicated part the theoretical cut-off volume was set at 144,000 units. Most, at the time, did not think it was ever going to happen. Now, ten years later, it is happening: some companies are using sintering for series production in the low thousands.”
So, as a manufacturing engineer, Hopkinson set out to achieve the next goal, finding out if additive manufacturing could be used for producing volumes in the order or hundreds of thousands and even millions of units. One of the aspects that is driving up the costs of making laser sintered parts is machine depreciation: a cheaper and quicker machine would thus be a good place to start. The first step in developing HSS was to replace the laser with inkjet technologies and infra-red lamps. The first prototype HSS machine allowed Hopkinson to predict that with a 1x1x1 meter print volume, it would allow a production rate of 0.67 seconds to make a finger sized part. A production rate that would allow direct competition with the injection moulding market.
HSS is not only faster than the SLS (selective laser sintering) process but is also capable of producing parts with higher mechanical properties because, in fact, the heat source sinters each single part more slowly than a laser. “It seems like a paradox,” explains Hopkinson, “but the production rate is faster because we can produce lots of parts by simultaneously sintering material. Think about two particles sitting next to each other: it takes a certain time for them to sinter when you melt them, a bit like two drops of water coalescing on a smooth surface like a window. Polymers do the same but much more slowly: the ideal sintering time for a polymer particle is somewhere between one and 10 seconds.”
“A laser heats the polymer particle in a tiny fraction of a second, something in the order of 0.1 milliseconds,” Hopkinson continues. “It applies that heat in a tiny amount of time and the particle sinters thereafter – this is not a very efficient way to sinter particles. In our process – even though it is quicker in terms of throughput – the infra-red lamp will go past at a much lower speed, applying the heat to the particle for around one second, which is much closer to the ideal sintering time.” To clear up the concept Hopkinson suggested thinking about cooking a chicken: the ideal time is two hours while what the laser does is like trying to cook it in less than one second. Applying the heat more gently results in much better properties for certain materials.
The HSS process is particularly efficient for certain geometries that are small and complex but still possible to injection mould. “We think that by having an open supply chain for materials, this technology will be used for high volumes, [thus] driving down the costs. In fact we now think there are some geometries that are complicated to the point where it will be more convenient than injection moulding for any number of parts.”
The first possible application of HSS looks like it might be in the enclosures on packaging for fast moving consumer goods (which is why Unilever got involved) but also on certain targeted accessories such as sports footwear. A previous project Hopkinson worked on with New Balance involved laser sintering footwear for elite athletes but HSS technology means it could be possible to start making personalized inserts for anyone. “Imagine this: you would just go to the store, run on a treadmill, register your foot pressure distribution and then generate the data to print out the correct left and right foot heel structure,” he explains. “It just gets printed and bonded to your new shoe and then you pick it up an hour or so later.”
Because the fixed cost of a printhead heat based machine is much lower than a laser powered one, Hopkinson envisions a smaller version of the HSS printers to be present right in the store. It may seem like something still very far away but the speed of development has increased tremendously in the past months and the newly funded FACTUM study will probably accelerate it further, although there are still no official forecasts on the dates for a commercial release of the first HSS based industrial 3D printers.
One heat-based 3D printer that has already hit the markets is Blue Printer. The technology it uses is quite different but Professor Hopkinson thinks the two are synergic and could offer reciprocal support. “I am big fan of Blue printer, I think it is a really good idea and an excellent low-cost technology. I am certain there will be lots of them in schools. It works by using a thermal print head to press down with heat onto the powder. The physics is different from HSS technology: Blue Printer uses conduction to heat up the particles which is a slow process, while HSS uses radiation which is much quicker. I personally think that Blue Printer is going to be restricted in terms of scalability but nevertheless I think it is a great entry level technology.”
So, things continue to move apace across the 3D printing industry and developments are increasing exponentially now. We will definitely keep you updated on the developments with HSS and, it seems, we should keep an eye on BluePrinter too.
All Images Courtesy of Xaar
