A TU Hamburg project shows that metal aircraft parts created in a 3D printer are much lighter and can be manufactured faster than conventionally produced ones. They help save kerosene and reduce the CO2 footprint of aircraft.

At first glance, it's not obvious what this workpiece is: It is round, open on both sides and there are many holes on the surface. What makes the curious piece special is that it is a metal part made in a 3D printer that is about a meter in diameter. "It's part of an aircraft turbine," says Dirk Herzog, solving the mystery. "And in fact, it is one of the largest individual parts that have been produced additively, i.e. by 3D printing, using a laser process to date," explains the engineer, who is responsible for the project for the Institute for Laser and Systems Engineering at TU Hamburg. But it's not just the size that's astonishing: "Switching from conventional casting to the additive process reduces costs and weight by 30 percent. And that means that its use can save valuable kerosene and thus CO2."

Down with emissions

It is an important step for aviation to comply with the EU's Green Deal. It stipulates that transport emissions should fall by 90 percent by 2050 compared with 1990 levels, and the aviation sector is expected to play its part. One research initiative to develop fuel-efficient aviation technologies was the Clean Sky 2 program funded by the European Commission and the European aerospace industry, which gave rise to the MOnACO project in 2018. In addition to TU Hamburg, which researched the printing process, project partners include Autodesk, which is taking care of design optimization, and TU Dresden. Their experts are building a test rig with state-of-the-art instruments that they will use to validate and measure the flow data after production. The consortium is working closely with the engine manufacturer GE Aerospace in Munich.

In principle, there are particularly stringent requirements in aircraft construction. This also applies to parts suppliers and leads to long lead times and high costs. These challenges and the fact that a turbine center frame is not a rotating part made it an ideal candidate for additive manufacturing. Dirk Herzog's team, which collaborates with the Fraunhofer IAPT in Bergedorf for 3D printing, makes it possible to manufacture the part in one piece, so that 150 individual parts no longer have to be joined together at the end - as is usually the case. This reduces the lead time for the manufacturer from nine to two and a half months.

Micrometer-thin layers

The printing itself takes place in a sealed-off large container. "In a layer of metal powder, in this case a nickel alloy, a laser beam fuses the individual parts of the powder at over 1,000 degrees Celsius," explains Herzog. "The layer is only 60 micrometers thin and sinks after the process. The metal powder is again evenly distributed and the laser exposure allows the next layer to form." The process repeats itself countless times until the turbine part is printed after quite a few days of construction. "A major advantage of additive manufacturing is the freedom in design. Depending on the specification, it can be adapted and rearranged at any time. Air diffusers, curves, channels or grid structures, everything is possible. At the beginning of the project, we mainly tried out how far we could reduce the wall thickness to save as much weight as possible," explains Herzog.

The process used is not limited to aviation. It has been used for medical implants, for example, for some time. But it is in aerospace that the financial benefits of weight reduction are greatest. This is shown by a simple "rule of thumb," which states that in aviation, 1 kilogram of weight saved can save 1,000 euros in fuel costs. Over the lifetime of an aircraft, this corresponds to around 25 metric tons of CO2. In other words, much more than in the automotive industry, where calculations are completely different due to higher unit numbers: Here, savings of 100 kilograms are needed to achieve the same cost effect. Since energy costs have risen across the board, weight reductions are likely to have an even greater financial impact. Herzog explains: "This is also the reason why such projects are often initially tested for the aerospace industry. 3D printing has already become established for individual, smaller engine components such as injection nozzles. But perhaps in the future, large-scale printed components will also be installed in aircraft as standard."

The MOnACO project consists of a consortium of Hamburg University of Technology (TU Hamburg), Technische Universität Dresden (TUD) and technology company Autodesk. It is supporting General Electric AAT Munich in the development and manufacture of a large additively manufactured metal component - the Advanced Additive Integrated Turbine Centre Frame (TCF).