Additive manu­facturing in engine production

Additive manufacturing is the technology of the future. Used to build up dental crowns and orthopedic implants, industrial tools, complex, lightweight car parts and even pieces of jewelry layer by layer, additive processes are rapidly spreading from one industry sector to the next. In aviation, too, they are playing an increasingly important role. In the field of engine construction, MTU Aero Engines has achieved a breakthrough: The long-established Munich-based company is among the first engine manufacturers in the world to use additive processes to manufacture production parts.

05.2014 | Text: Martina Vollmuth

Dr. Rainer Martens, MTU Chief Operating Officer, explains: “We’ve been making bore­scope bosses for compliance and production engines using additive processes for sev­eral months now, and have been very successful in doing so.” This makes Germany’s leading engine manufacturer one of the first companies in the industry to use additive processes in production. While other manufacturers are also working with the new technology, most of their products are still in the prototype stage. This is what sets MTU apart: Its bore-scope bosses made by selective laser melting (SLM) form part of the production low-pressure turbine case the company is making for the PW1100G-JM engine to power the A320neo. “With this move, MTU has reaffirmed its leadership in de­livering innovation; for we are using one of the most advanced technologies there is to produce parts for one of the most advanced engines in the world, the Geared Turbofan™,” Martens emphasizes.

Borescope bosses are attachments that allow the blading to be inspected for its con­di­tion and for potential wear and damage at regular intervals. They are riveted to the case and serve as access ports for borescopes. “We used to make these parts by cast­ing or by milling them from the solid,” explains Walter Gieg, Integrated Product Team Leader, Stator, PW1100G-JM at MTU in Munich. The low-pressure turbine for the PW1100G-JM geared turbofan (GTF) will be the first production turbine to come equipped with borescope bosses manufactured using an additive process. MTU sent its first PW1100G-JM compliance module to Pratt & Whitney at the end of last year for installation in the first compliance engine. In June, this engine will be delivered to Airbus, where it will undergo a comprehensive compliance program under which en­gine and airframe will be tested and certified as an integrated system.

Germany’s leading engine manufacturer began looking into options to use additive manufacturing about ten years ago. “We started off making tools and development parts with a simple geometry,” says Dr. Karl-Heinz Dusel, Senior Manager, Rapid Technologies. In a second phase, SLM parts were produced as substitutes for con­ven­tion­al ones, such as injection nozzles and grinding wheels for use on the shop floor. At around the same time, work on the borescope bosses for the GTF engine to power the A320neo began to pick up speed. This brought about significant changes for the com­pany. “By becoming a manufacturer of blanks, MTU was venturing into completely new territory,” explains Prof. Dr. Thomas Uihlein, Consultant, Technology Transfer Man­age­ment at MTU.

“In the past we simply bought the blanks we needed rather than producing them our­selves. So we had no prior experience to draw on, and there were no processes, methods or structures for the manufacture and certification of these blanks,” says Uihlein. “We had to build everything up from scratch.” It took two years just to gen­er­ate the required standards and specifications and to compile the necessary data. Suddenly confronted with challenges they had never faced before, MTU’s engineers had to get to grips with the materials and equipment for this new production method. “For example, we had to perform new analytical calculations for components we had been familiar with for decades,” says Uihlein. The specialists also encountered non-conform-ances that cannot be detected using conventional inspection and test methods. That’s why the process proper must be closely monitored to ensure early de­tection of departures from specification requirements. At MTU, an online system is used for the purpose.

Further improvements to facilities, processes and methods are in the pipeline. For ex­ample, the parts MTU produces have to undergo an extra processing step because otherwise their excessive surface roughness would compromise their structural-mechanical properties. “We need surface finishes that match those of castings, which only require rework of the mating surfaces,” Uihlein explains.

The process of direct metal laser sintering (DMLS) allows components to be built up layer by layer.

The process of direct metal laser sintering (DMLS) allows components to be built up layer by layer.

The process of direct metal laser sintering (DMLS) allows components to be built up layer by layer.

“Additive manufacturing is particularly suitable for producing parts in materials that are difficult to machine, as, for example, nickel alloys,” according to production expert Dusel. MTU sees great potential for the technology in engine construction. The com­pany expects additive manufacturing methods to prove a boon especially with com­plex components, such as bearing housings and conceivably also turbine airfoils. Says Chief Operating Officer Martens: “We are currently pressing on with SLM, giving its further development top priority in numerous technology projects and programs, as the technology opens the door to entirely new designs, cuts production and lead times and brings down production costs.” As part of its activities under Clean Sky, the largest aeronautical research program ever launched in Europe, MTU is manufacturing a seal carrier using the SLM technique. The inner ring with integral honeycombs will be installed in the high-pressure compressor and contribute to a weight reduction, lighter-weight designs being one of the key objectives in engine and aircraft construction. Another advantage: It takes much less time to produce this seal carrier, as multiple work steps can be completed in one go.

For Martens, this much is clear: His strategy has worked out pretty well. “We didn’t start with complex components right away, but began with relatively simple engine parts, such as borescope bosses. We kept moving forward step by step, gathering more and more experience in the process. This approach is now paying off, for we are among the first to use SLM in production.” And Uihlein confirms: “Working on the A320neo engine, we’ve learned how additive manufacturing technology works. We developed the process from scratch and tested it to the point of mastering it. That’s our advantage, because we can now adopt the process for other components and en­gine types as well, the basic structures being the same.”

Inside MTU Selective laser melting at MTU

The first step in selective laser melting is to use a computer to slice up a 3D CAD model of the component to be produced. A laser then builds the solid equivalent of the model layer by layer on a building platform using powdered material, the layer thick­ness being 20 to 40 micrometers. In the process, the powder particles are locally melted and fused together.

This process allows the almost tool-free production of complex components that are extremely difficult, if not impossible to manufacture using conventional methods. In addition, the technology substantially reduces the amount of material wasted. The flexi­bil­ity of the process makes it particularly suitable for low-volume production and for one-off components. MTU in Munich has six direct metal laser sintering (DMLS) facilities made by EOS that replace conventional casting and milling machines. Five of them are used to produce components, while the sixth is reserved for development pur­poses. At present, the only materials processed are Inconel 718 nickel alloy as well as steel. Plans are to also use cobalt-chrome and titanium alloys at a later date.

“In the SLM chamber we are using a 400-watt laser that melts the metal powder at temperatures of over 1,000 degrees Celsius,” explains Dr. Karl-Heinz Dusel, Senior Manager, Rapid Technologies.

The process permits the production of several borescope bosses at a time on one building platform, and takes about two days. Once finished, the components are sep­ar­ated from the carrier material, heat treated, finished and inspected for cracks. The entire manufacturing process is subject to strict process control.

GeFe_Metall-Schmelzen

Within fractions of a second, the material is melted.

GeFe_Metall-Schmelzen

Within fractions of a second, the material is melted.

Rohling-Rueckseite

Das PW1100G-JM is the first production engine to be equipped with borescope bosses manufactured using an additive process.

Rohling-Rueckseite

Das PW1100G-JM is the first production engine to be equipped with borescope bosses manufactured using an additive process.

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