When will we start printing aeroplanes?

The aerospace industry is a longstanding pioneer in the use of Laser additive manufacturing. Nikolaus Fecht reports from the International Laser Technology Congress AKL'14, an event organised in Aachen by the Fraunhofer Institute for Laser Technology.
The timing was perfect: Only a day before the AKL'14 began, the laser manufacturer Trumpf Laser- und Systemtechnik and Sisma announced in Piovene Rocchette, near Vicenza they would form a joint venture that should develop the newest generation of manufacturing systems for the 3D printing of metal parts. Both companies are considered two of the long-standing pioneers of so-called additive manufacturing (AM).

The German-Italian joint company will concentrate on developing laser metal deposition (LMD), a process used in the aviation industry to maintain, repair and overhaul aircraft components. Trumpf's Dr Antonio Candel Ruiz from the Industry Management Laser Surface Treatment department in Ditzingen, Germany described the next steps in the development at the EU Innovation Forum ‘Laser Additive Manufacturing in Aeronautics,' a traditional meeting at the AKL'14. There, he mentioned new stronger machines, such as the TruLaser Cell 7040, which can clad layers up to 1mm thick at a speed of 2m/min, all thanks to its power of 4kW. In comparison to selective laser melting (SLM), LMD can work significantly quicker and lends itself to producing larger parts.

There is, however, only one real limitation regarding component size: the working cell of the LMD plant itself.
Currently, the cladding rates range from 5 to 40cm3/h (SLM 5 to 10cm3/h), but more than 100cm3/h can actually be attained. LMD would then be worth considering to directly manufacture metal components, for example reinforcement parts for existing aircraft components: bosses out of Inconel 718 for the landing gear.

To accomplish this, Trumpf is collaborating with aerospace companies and Fraunhofer ILT on the EU project AMAZE (Additive Manufacturing Aiming towards Zero Waste & Efficient Production of High-Tech Metal Products), which should increase the dimensional accuracy of the printed components, multiply the build rates ten-fold and reduce the rejection rate to under 5%. What is particularly interesting is the possibility of building LMD parts out of many layers. On an LMD plant (1kW power), Trumpf has generated a cube with a three-layer structure, comprising of Stellite, stainless steel and Inconel 718. All in all, the chances for the process look promising.
“With optimised processing conditions and tool path designs, near-net-shape full-scale parts can be successfully fabricated, featuring a range of wall thickness and lengths,” says Dr Candel Cuiz.

Pioneering the process

Among the pioneers of laser metal deposition are MTU Aero Engines, which has manufactured 200 different series-production parts out of polymers and metal. The company uses the process to manufacture mounting parts, tools and initial series-production components. The so-called borescope bosses count among these parts, which technicians use to look into the interior of the turbine to check the condition of the blades. Manufacturing the core of the drives should follow these component parts.

“There is an enormous potential,” emphasises Dr Karl-Heinz Dusel, head of rapid technologies. “And yet series production requires more than just a new AM machine. Rather, the complete process chain needs to be set up and improved.” In addition, conventional production processes need to be integrated into it.

Fraunhofer ILT's Professor Ingomar Kelbassa (pictured) is committed to getting the AM community to consider additive manufacturing anew. This way, when AM processes are applied, costs of final processing – for example, through the use of a 5-axis milling – could be significantly reduced, since the product no longer has to be milled from a solid; rather, a near-net shape component can be generated, which only has to be contoured. The specialist sees one special advantage of AM technologies, when compared to conventional production techniques, in that AM can keep manufacturing costs constant while complexity increases. Yet these advantages can only be used if AM processes also serve to generate completely new structures.

“Laser additive manufacturing is a completely new way of manufacturing components,” explains Kelbassa. “That's why I support a bionic design, for nature is a good design engineer.” An example can be seen in grid structures that consist of unit cells. Kelbassa continues: “The periodic combination of a unit cell results in an integral screen, which possesses a ‘swarm-like behaviour' of the individual cells under mechanical load.”

An innovation wonderland

Airbus Operations, Hamburg presented bionics in its most unadulterated form. “All of us in this room are living in an innovation wonderland, for we are providing the technology transformation,” states Bastian Schäfer, from the innovation department ‘Cabin Innovation Strategy & Concepts', as he tuned in the listeners of the EU Innovation Forum. “This is an opportunity we don't often have. For me as an engineer with his own projects, this situation is simply perfect.”

The euphoria is understandable, since Schäfer is working on the plane of the future. In his work on the Airbus Concept Cabin 2050, the engineer and his team were inspired by the bionic car from Mercedes Benz. Airbus used the body of a bird as a role model. To manufacture this structure, in which there will no longer be a single rectangular component, Schäfer is relying upon processes such as SLM, which with models of the aircraft of the future have already been made.

This sophisticated structure requires significantly more stable materials than what has formerly been used, such as CFRP or titanium. The idea of making completely new building blocks for the aircraft skeleton stems from bionics.

As Schäfer reveals: “Nature uses DNA, which contains all the information needed to build large, stable skeletons.” Instead of considering DNA, however, the Airbus researchers are thinking of tiny carbon tubes, so-called carbon nanotubes (CNT), which combine, as it were, into a swarm made up of quadrillions of CNTs to form a large skeleton. Large 3D printers should take over manufacturing these additive structures.
And yet AM processes are already changing the aircraft industry today. These Hamburg-based engineers are currently developing a new replacement parts supply.

“If we are not careful, the same thing will happen to us as happened to the music industry,” Schäfer points out. “Customers should be able to download our components virtually and manufacture them from 3D printers we have certified. Even now we have to get involved in a legal discussion on virtual building blocks.”

These visions from Hamburg indicate which directions additive manufacturing has inspired in aerospace industry pioneers: they point out the chances, but also the risks. Airbus' plans are a good example for Digital Photonic Production, the guiding topic of the International Laser Technology Congress AKL'14. As Professor Reinhart Poprawe, MA, head of Fraunhofer ILT puts it: “With this technology we can change production processes completely.”

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