Students develop novel multi-metal 3D printing process
Students at ETH Zurich have developed a laser power bed fusion machine that follows a circular tool path to print round components, thereby being able to process multiple metals at once. The system significantly reduces manufacturing time and opens up new possibilities for aerospace and industry. ETH has filed a patent application for the machine.
Today, virtually all modern rocket engines rely on 3D printing to maximise their performance with tight coupling between structure and function. Students at ETH Zurich have now built a high-speed multi-material metal printer: a laser power bed fusion machine that rotates the powder deposition and gas flow nozzles while it prints, which means it can process several metals simultaneously and without process dead time. The machine could fundamentally change the 3D printing of metal parts, resulting in significant reductions in production time and cost.
The team of six Bachelor’s students in their fifth and sixth semesters developed the new machine in the Advanced Manufacturing Lab under the guidance of ETH Professor Markus Bambach and Senior Scientist Michael Tucker as part of the Focus Project RAPTURE. In a mere nine months, the students realised, built and tested their idea. The machine is particularly aimed at applications in aerospace featuring approximately cylindrical geometries, such as rocket nozzles and turbomachinery, but is also of broad interest for mechanical engineering.
Providing access to advanced technology
Project lead Tucker explains that the project came about from a very specific challenge: developing bi-liquid-fuelled rocket nozzles for ARIS, the Swiss Academic Space Initiative, that is building its own rockets with visions of reaching into space. Within the next few years, ARIS aims to reach the Kármán Line – the internationally recognised boundary of space set at an altitude of 100 kilometres, beyond which the atmosphere is too thin to support flight by aircraft without special propulsion.
In order to withstand the intense heat and pressure over an extended launch, rocket nozzles should ideally be made of multiple metals. For example, their interior can be made of heat-conducting copper with integrated cooling channels and their exterior of a heat-resistant nickel alloy. “For small players like our student rocket team, this sort of multi-material technology has up to now been too complex and too expensive, putting it out of reach,” says Tucker.
Rotational 3D printing
The heart of the new machine is a rotating platform that enables a high-speed printing process. Unlike conventional rectilinear laser power bed fusion machines, where a new layer of powder has to be applied after each layer is melted, the RAPTURE machine works non-stop thanks to its rotating platform. This means that powder is applied and fused by the laser simultaneously, which significantly enhances productivity. This reduces the manufacturing time for cylindrical components by more than two thirds.
“This process is ideally suited to rocket nozzles, rotating engines and many other components in the aerospace industry,” says Tucker. “They typically have a large diameter but very thin walls,” he adds. While the machine is also capable of producing non-axisymmetric or even arrays of parts, the rotating method is particularly effective for producing precisely this geometry.
Printing two metals simultaneously
The rotating machine can process two different metals in a single operation. Conventional systems require several steps and a much greater quantity of metal powder. As separation and recovery of mixed powder remains an open challenge, today much of this powder becomes waste. The new method only deposits the material where it is actually needed within the component, thereby reducing waste.
The machine features a mechanism that blows inert gas over the area where the powder is fused. This prevents the component from oxidising while it is being printed. Soot, spatter and other by-products are systematically extracted via an outlet. “At first we underestimated the extent to which the gas flow mechanism affects product quality,” says Tucker. “Now we know it’s crucial.” Thanks to the rotating architecture of the newly developed machine, the local gas flow conditions can be controlled much more tightly than with a conventional machine.
Customised rather than standard components
The students faced a number of technical challenges when developing the novel laser power bed fusion machine, one of which involved the synchronisation of the scanning laser with the rotation of the gas inlet and powder supply. In addition, as many of the parts needed for the machine are not commercially available, the team designed their own. These include a rotatable connection for the gas inlet and a system that automatically refills the powder during operation.
Nonetheless, the team of students has managed to build a machine that almost looks ready for industrial application. For Tucker, this was one of the highlights of the Focus project: “The fact that a team of students developed and built a functioning machine in nine months is pretty remarkable.”
Potential for aerospace, e-mobility and more
As well as concrete application for ARIS and for the aerospace industry in general, the team sees potential applications in other sectors, such as in aircraft and gas turbines, and for electric motors where ring-shaped geometries are the norm. Owing to its novelty and tremendous commercial potential, a patent application was filed by ETH covering the rotary multi-material laser powder bed fusion technology, which has since been nominated for the ETH Spark Award.
The components manufactured so far with the prototype have a diameter of up to 20 centimetres. The research team is now looking at scaling the process to higher speeds and larger diameters, and they are currently looking for industry partners to collaborate with them to further develop and deploy this revolutionary technology.
Source: ETH Zurich
