There has been a lot of hype about the potential of using 3D printing to manufacture all manner of products, and footwear is no exception. While short-run high-end products such as running shoes have been made, many more advances will be needed for more mainstream uptake. Sarah Houlton reports.
Additive manufacturing – or 3D printing – is moving on from being a niche novelty technique and becoming a practical tool for industrial production. Not only is the technology for the printers themselves moving forward apace, but material manufacturers are embracing its potential, and creating novel material grades to use with the machines.
Footwear, in particular, has the potential to become a sizeable market for 3D printing. Shoes made in this way have already reached consumers, albeit very specialist short-run products such as the Futurecraft 4D running shoes from Adidas. These were made via a collaboration with 3D printing specialist Carbon using its dynamic light synthesis method.
But it’s still early days. ‘There is still a way to go before 3D printing is routinely applied to all components in the shoe, and they get integrated into mass production,’ said David Pascual, global commercial lead for 3D printing at Lubrizol Advanced Materials. ‘There are a few examples, and I expect other shoemakers will launch small-run products, too.’
Lubrizol, for one, is embracing the prospect of 3D printed shoes and components. ‘Footwear could be a very good example of how 3D printing can change the traditional way things are manufactured,’ Pascual said. ‘Today, it is still at the prototyping stage. I believe that to be useful in mass production, several things need to happen.’
Material requirements
First and foremost, Pascual believes we still lack the materials and post-processing solutions that will allow the move to be made from what is, essentially, prototyping and into large-scale production. ‘Whether the printing technology is stereolithography (SLA), multi-jet fusion or selective laser sintering (SLS), we need to come up with production-grade materials,’ he said. ‘If they need to be ground, will there be grinding capabilities? It makes no sense at all to think about making a million midsoles if we cannot provide a material that is scalable and can be ground without issues.’
BASF is also very active in the 3D printing space, having set up Heidelberg-based Forward AM in 2017 to exploit its capabilities for 3D printing materials. ‘Most of our material is coming from BASF, but not all,’ said Florian Fischer, its business development manager. ‘We are free to make other formulations or take other raw materials from other suppliers, but most of them are BASF. We take granulates or other raw materials and make them into 3D printing materials. For example, we might make filament.’
Forward AM uses thermoplastic polyurethane for two printing technologies, Fischer said. ‘The first is filament printing, in which you heat a thermoplastic filament and draw a part in 3D,’ he said. ‘For the second technology, we would go from granulated TPU and make a powder out of it which can be used in a multi-jet fusion machine from Hewlett-Packard, or selective laser sintering technologies like the Eos printers.’
Both of these use TPU, but the PU traditionally used for foam is not so amenable to 3D printing because it is a thermoset which reacts to make the foam, Fischer said. ‘In this case we use the base chemistry BASF owns for our photopolymer resins. And that is our third technology. This uses light to cure layer by layer of a liquid resin.’
Flexible materials can be diffcult to work with in the 3D printing world, and may need to be adapted to ensure good layer adhesion ‘As you are printing layer by layer, you have to optimise the grades to have a better adhesion in between the layers,’ Fischer said.
‘You can see huge warpage in those kind of materials, and we optimise our formulations so they are printable without warpage. That way you can get a get really a fl at sheet for example, and not more like a banana-like shape.
All three technologies have their pros and cons, Fischer said. ‘For example, fi lament technology is quite easy to start out with because you have a cost-effective printing system, the machine itself is not too expensive and, you can be quite fast, but the accuracy is not the highest,’ he said. ‘You don’t get the most detailed surfaces, so it’s more for structural parts or prototyping.’
Powder technology represents a bigger investment: the printers themselves are very expensive, he said, and will require more specialised applications and larger volumes. But printing with powder gives better resolution than filament technology. Better resolution still is seen with photopolymers. ‘Those give really high resolution, good-quality surface parts, with the high fi nish requirements of the surface.’
Pascual believes that if materials suppliers like Lubrizol want to promote 3D printing as an option to the footwear industry, it will need to create an appropriate value network. ‘We still work in silos, with raw materials suppliers, software and hardware providers, post-processing experts and designers,’ he said. ‘If we don’t look at these on a shared profit model, it will not work. Yes, we sell raw materials and want to run a successful business, but if we don’t consider the other partners in the whole value chain, the shoes remain several hundred dollars a pair, and we will not be able to challenge the current traditional way of making shoes.’
All of these ecosystems will need to work together to minimise the cost, and offer the shoemaker a better alternative to traditional manufacturing methods. ‘We want to be part of this ecosystem,’ he said. ‘It’s not just us talking with the OEM or the shoemaker; we are in conversations with Tier 1 and Tier 2 suppliers. Lubrizol has had a solid footprint in the footwear industry for many years, and we are trying to show our customers what we can do differently in order for 3D printing to be adopted in the most economical way, to make sure it could be integrated as part of the footwear value chain. We want to bring in the best performance of our current TPUs, for example, but can we scale it and the technology up?’
And scaling up will be a significant challenge. While 3D printing is great for short runs and prototypes, the realities of commercial-scale production are stark: huge farms of 3D printers will be required to make them, representing a substantial investment in costly machinery. ‘Are we midsole, shank or upper, and make thousands of them using 3D printing, while keeping the costs viable?’ Pascual said. ‘Widespread use is only going to happen if the costs are viable for the industry.
However, while printing whole shoes on a large scale seems a distant dream, he reports defi nite customer interest in making shoe components. ‘We show them what can be done through 3D printing, with uniqueness and customisation, whether for midsoles, shanks or upper parts, the features and benefits that are possible and can be transferred into the real world,’ he said.
Lubrizol is seeing is interest from both Tier 1 and Tier 2 suppliers, as well as the shoe companies themselves. ‘They are trying to bring new technologies into the marketplace, and while there is some way to go before some of them will be convinced that 3D printing can replace existing technologies, some customers are thinking about launching short run productions for specific campaigns,’ he said. ‘Now it may be more from a marketing standpoint than large production, but we do see a lot of customers approaching us to ask what we could do, for example, to make an individual part in TPU.’
Unique opportunities
But it’s not all about replicating existing shoe components and simply making them in a different way. Take the midsole, for example. These components have very demanding performance requirements: they need to be light, give good foot control, and be both stable and durable. ‘Injection moulding was the best we could do in the past, but now 3D printing can produce very complex lattice structures,’ Pascual said.
He believes that technologies such as fused filament fabrication and powder bed fusion could be used for several parts within the final shoe, like midsoles, insoles and upper parts. ‘This is a starting point for showing the market that we are able, through design, to make reality some of the concepts that are seen on paper,’ he said. ‘We have already proved we can get lightweight solutions with very good foot control stability, and which can be customised to the individual foot. Complex designs are a strong winning point for the 3D printing industry. This was not possible before. From a performance standpoint, it is not just marketing. It is truly down to the benefits, and the material can give lightweight, energy rebound, durability and stability. We need to be able to translate these from a marketing approach. I think this is crucial for the industry to believe in 3D printing.’
Multi-jet fusion technology, such as that pioneered by Hewlett-Packard, offers the enticing prospect of being able to fuse different materials together in a single manufacturing process. It does this by printing materials on top of a component that has already been printed using another material.
The advantages for footwear are clear, and the company has been working with companies such as Nike on prototyping new products, and also shoe manufacturer New Balance and insole specialist Superfeet to make customised orthotic insoles. This is unlikely to be the last example of this strategy, and as the technology develops and matures, we can expect many more companies looking to fuse different materials together seamlessly.
Fischer reports a huge increase recently in the use of 3D printing to make moulds and other tools, speeding up the development cycles of new products. ‘We are also seeing a huge increase in the use of 3D printing for fashion shoes, from high end brands such as Balenciaga and Philipp Plein,’ he said. ‘These tend to be low volume, maybe only 1000 or 2000 pairs. But their adoption of 3D printing I think is the way to go towards later mass production, or at least higher volumes.’
Many companies are also thinking about delocalised production that moves manufacturing closer to the markets, but Fischer is not sure whether the big shoe companies think this is a viable model. ‘What we do see is start-ups thinking about starting somewhere small and using different service bureaus all over Europe and the US to build their shoes, rather than having one big factory which is more the norm in Asia,’ he said.
And this highlights the question of where it would make sense to put big 3D printing facilities. Most shoemakers routinely produce large volumes of shoes in Asia, particularly in countries such as China and Vietnam. ‘What might make sense would be 3D printing production centres, where components such as midsoles or outsoles could be made up and then assembled,’ Pascual said. ‘Cost-wise, this would make sense. I think we are working in this direction, with production centres around what are today the industry’s Tier 1 suppliers.’
Of course, to make a million midsoles would require a very big farm of printers to be installed. ‘I don’t think there will be widespread conversion from existing traditional manufacturing to 3D printing any time soon, although perhaps for small runs and maybe for some campaigns, it might,’ Pascual said.
There are some people who think the sector is going in the direction local shoe retailers producing customised shoes for individual customers in the shop, Fischer said, but he thinks this is unlikely. ‘When you can get a package from Amazon overnight, I don’t see a 3D printer as a production machine in every shoe shop’s basement,’ he said. ‘I think that every big city, region or state might have a manufacturing location. The customer would go into a store, get their feet scanned and send the data to the factory, and then the next day or the day after their shoes would be delivered.’
The future’s bright?
It is still, of course, early days. Yes, 3D printing is certainly ideal for customisation and personalisation, and the sort of short runs that create highly sought-after training shoes, and Pascual believes that the big shoe brands will be convinced of the feasibility of switching from existing manufacturing technologies such as injection and extrusion in the medium-term for this type of short-run product. But he still doesn’t see a widespread change any time soon, unless there is a massive breakthrough in technology or market demand.
‘But maybe thinking about 1% of the total footwear industry, I am positive that as we bring more technology and more materials that can show the same performance, in the immediate future there will be a lot of evolution in this segment,’ Pascual said. ‘Like other raw material suppliers, part of our responsibility is to bring more robust solutions that can have the same or superior performance. But I want to believe that it will be new technologies, materials that will make it more attractive to the current footwear industry, and Lubrizol will be leading this journey using a partnership model.’
3D printing can play a big part in improving sustainability, Fischer believes. ‘Many companies want to reduce waste, and reduction of stock is a big thing, especially in the fashion world,’ he said. ‘3D printing can be an enabler to reduce logistics, reduce flying parts all over the world or stop making more than needed. They might produce a whole bunch of parts and six months later only half or a third of them were sold, and the rest has to be destroyed. 3D printing is a way to produce just what’s needed.’
Forward AM is also working with some partners on recycling 3D-printed TPU parts. ‘We can even try to do upcycling because 3D printing material waste is often quite high grade,’ he said. ‘The volume of 3D printing today is almost too small to recycle material back into the same process. So we would like to upcycle material into injection moulding to make different parts. In a few years, we hope the volume of 3D printing will be big enough to recycle back into 3D printing.’
