Virginia Tech
When Chris Williams – the L.S. Randolph Professor in Mechanical Engineering at Virginia Tech – started out as a professor 15 years ago, he couldn’t envisage that his lab would ever build bespoke additive manufacturing (AM) equipment. Instead, his lab would devote their efforts to studying how existing processes affect novel material properties and the new design spaces such capabilities would afford.
Fast forward to 2023, though, and Williams finds himself working alongside several students with experience in building 3D printers at home, working with microcontrollers as a hobby, and a strong drive to push the boundaries of AM.
This capability is coming to the forefront as Williams’ DREAMS Lab – Design Research and Education for AM Systems – develops a new tyre retreading method through a 1.5 million USD research project. Funding comes from a 1:1 cost share between Virginia Tech and the REMADE Institute, which has been established by the US Department of Energy to accelerate the country’s transition to a circular economy. Arizona State University and industry partner Michelin will also be involved as they attempt to address the waste generated by retreading and the fuel efficiency of road vehicles.
In the US alone, 14.5 million tyres are re-tread every year. Conventional tyre re-treading methods use a buffing process to remove the remaining tread and sidewall rubber from the casing before new tread material is stitched to the casing and the built tyre is heated up to around 155°C during a curing process. This workflow sheds a significant amount of excess rubber and affects the performance of the tyre, which in turn can see more energy exerted.
“There’s an opportunity with additive to selectively re-tread,” Williams tells TCT.
“In the cases of uneven wear, instead of throwing away the entire tread, can we only re-tread a portion of a tyre? With traditional manufacturing, selectivity is not really something we can achieve, but with additive we can. The focus is reducing material waste, number one, and number two, is that when we retread tyres, currently there’s an increase in rolling resistance, which translates to reduced fuel economy.”
The retreading process being imagined by Williams and his team is one whereby a little buffing is required, but then only the worn-down section on the tyre’s cushion rubber is printed upon, with a traditional tyre tread being laid on top. To achieve this vision, Williams and co are midway through a two-year project that is seeing significant ongoing developments across polymer science, 3D printing and industrial robotics.
Working with Tim Long, formerly of Virginia Tech and now the Director of Arizona State’s Biodesign Center for Sustainable Macromolecular Material and Manufacturing, Williams says two materials have been developed that perform as well as the conventional material. One is a ‘direct rubber’ material and the other is a ‘new age’ formulation, with the team suggesting it has found a way to ‘reduce the viscosity of rubbery material so that it is easily printed’ while still getting all the required properties. Key to these developments is the DREAMS Lab’s multi-stage printing process, which sees material selectively deposited through a nozzle, with a curing step coming later. This is facilitated by a robotic work cell that allows material to be conformally and precisely deposited onto a tyre surface with the support of 3D scan data and rapid toolpath changes.
Get your FREE print subscription to TCT Magazine.
Exhibit at the UK's definitive and most influential 3D printing and additive manufacturing event, TCT 3Sixty.
“If we want to advance the state of the art, we can’t only treat AM as a singular standalone manufacturing solution,” Williams suggests. “So, [we’re] taking AM literally out of its box and using it as one of many tools that our robot can use. [That’s] what has got my attention right now - with robotic AM, we can print in true 3D, no longer just in stacks of 2D layers. We can change between both additive, subtractive, and pick-andplace tools. This project is a great opportunity to demonstrate this vision for the future of AM, and its for the cause of a more sustainable future.”
If the DREAMS Lab is successful, Williams estimates it could result in annual reductions of around 90 metric kilotons of tyre waste and 800 metric kilotons of C02 emissions across the retreading industry. In the next 12 months, one material from the two options will be selected, before testing with partners is carried out and a lifecycle assessment is performed to gauge the process’ economic and environmental impact.
The re-treading technique may then be taken forward by an industrial partner. That is somewhat out of the control of Williams and co, but in the technology they're developing, there is confidence that the potential goes beyond just the tyres on the wheels of our cars.
“It’s not just about tyre repair. One key aspect of this project is focused in automatically generating toolpaths from in-situ 3D scan data. And that’s applicable to every other additive and repair process,” Williams says. “In addition, the way in which we’re now printing elastomers is generalisable to any other kind of elastomer system, not just this one type of rubber. Our hope as scientists is that our work is something that will provide a foundation for other people to build on and take it where they think it needs to be.”
“It’s not just about tyre repair. One key aspect of this project is focused in automatically generating toolpaths from in-situ 3D scan data. And that’s applicable to every other additive and repair process,” Williams says. “In addition, the way in which we’re now printing elastomers is generalisable to any other kind of elastomer system, not just this one type of rubber. Our hope as scientists is that our work is something that will provide a foundation for other people to build on and take it where they think it needs to be.”
