Engineers from Trinity College Dublin are leading a four-year, half-million euro European Space Agency (ESA) project to hone ‘Cold Spray’, a revolutionary technology that allows mechanical structures to be made and coated with different materials. The results of the project will be seen on spacecraft in outer space, as well as on a variety of household applications and transport vehicles. While a number of national companies will collaborate with the Trinity team on the technical side of the project, there are an array of space science missions that would avail of Cold Spray, including the ExoMars, Juice, Euclid and Solar Orbiter missions as well as the James Webb Space Telegraph and the International Space Station. Prof Rocco Lupoi, an assistant professor in the university’s Department of Mechanical & Manufacturing Engineering, is the leading Cold Spray expert in Ireland. He will head the project along with Dr Shaun McFadden and Dr Anthony Robinson, who are assistant and associate professors in mechanical and manufacturing engineering. “This is the largest ESA research project awarded to Trinity and we’ll bring cold spray to the next level,” said Prof Rocco Lupoi. “The project is starting in the next few months and I’m in the process of recruiting the team. It will include a post-doctoral researcher, a PhD student and two more lecturers from Trinity College,” he added. The project team has identified two key areas: reducing the cost of the manufacturing process through innovative solutions and improving efficiency and precision. “Not only will we bring down its cost through the development of innovative solutions, but we’ll also enhance its technical capabilities for use in additive manufacturing, which was recently ranked as a top-10 breakthrough by Massachusetts Institute of Technology,” said Prof Lupoi.

Cold Spray properties

[caption id="attachment_18528" align="aligncenter" width="634"]Trinity Cold Spray Cold Spray schematics[/caption] He explained that the Trinity Cold Spray works by applying layer after layer in a matter of seconds to build up a shape. It accelerates powders of material at supersonic speeds – some 1,000m/s – before firing them onto structures via a nozzle. It can build coatings or simple geometrical components made out a wide range of materials around 1,000 times quicker than any other additive manufacturing or 3D-printing technologies allow. Helium gas is used as a carrier of the metallic particles to be applied. “We accelerate the gases to supersonic velocity and, when you inject particles into the gas, they’ll also reach supersonic speeds,” he explained. The particles move so quickly that they penetrate the surface and bond almost instantly, so that it is possible to build up 5mm of material in just seconds, The process does not require heat, which is an advantage because it means there are no heat-affected zones, microstructural changes or distortions to worry about on the end product. It is not polluting and it does not rely on toxic materials to make it work, only pure non-toxic helium. One disadvantage is that Cold Spray is currently expensive and inefficient, so part of the Trinity team’s work will be to reduce costs. The high costs, despite the simplicity of the working mechanisms involved, are due in part to the use of helium gas to carry the metallic particles that are applied to objects. “The technology is simple in terms of its working mechanisms. But it is, for the vast majority of cases, expensive to run because it uses helium and helium is a very expensive gas,” explained Prof Lupoi. Due to these high costs, as yet there is no large-scale industrial implementation of this type of technology. However, he went on to explain how the four-year project aims to address this hurdle. “There is not really yet a big industrial implementation of this process because it’s expensive. We’ll try to fix this through a very detailed programme which is going to last about four years. We will try to bring down the costs to see if we can justify the industrial implementation of this process, firstly for space applications but also for terrestrial conventional applications.”

Cold Spray and 3D printing

[caption id="attachment_18530" align="aligncenter" width="640"]Trinity Cold Spray Ti64 aerospace component made of two halves and joined with Ti64 CS deposition (leak tight) - ongoing work in collaboration with the University of Twente, Lab of Design, Production and Management[/caption] Up until now, Cold Spray has been used predominantly for making coatings. Yet, the technology has the potential to be a revolutionary improvement on current 3D printing techniques. A key difference between conventional 3D printing and Cold Spray is that with the latter technology, the components are metal and engineered to a very high standard. There are numerous applications in space which would benefit significantly from access to this technology. With the right level of automation and robotic stage design, this technique could also produce 3D components with low manufacturing costs. The concepts being brought forth in this project will specifically target these technological bottlenecks. “We want to see if we can use it to make 3D objects. The advantage of trying to make components in 3D using Cold Spray is that this process is exceptionally quick. You can really build up volumes at a rate that nobody else can do out there. However, apart from the high costs involved, the precision by which these things get built up is very low,” said Prof Lupoi. It is not always possible to immediately attain the complex geometrical properties required with cold spray at an affordable price. Part of the project would be to address this problem. Additive manufacturing with cold spray is new, so a cost-effective process is required to achieve the high precision expected by the space industry for use in spacecraft. While the space industry is very much the target, Prof Lupoi foresees a range of everyday applications of this technology, if it can be made more cost effective. He offered an example of how Cold Spray is already in use in an everyday domestic situation in Japan.

Alternative uses

[caption id="attachment_18531" align="aligncenter" width="640"]Trinity Cold Spray WC in-house 200mm long nozzles with CFD prediction of carrier gas velocity (m/s) with nitrogen at 30bar, room temperature[/caption] “In Japan, there are some domestic applications already for which people use Cold Spray. For example, depositing copper onto steel – that’s a very challenging operation,” he explained. “It doesn’t sound so [complex], but it is because the two materials are not metallurgically compatible. So it’s very difficult with conventional processes to do that kind of deposition – pretty much impossible, in fact. “With Cold Spray, however, due to the way it works, you don’t need metallurgical compatibility, so you can easily add copper on top of steel. The deposition of copper on to steel has important implications for heat applications in Japan. It’s probably one of the few situations whereby Cold Spray is really used as yet. Copper has very high thermal connectivity and steel doesn’t really, so depositing copper around the steel will help carry the heat,” he concluded. Funding Body

FP7 - Marie Curie Actions (CIG), Industrial Collaborators, Enterprise Ireland