The BMW Group manufactures functional prototype parts for test vehicles by means of laser deposition welding. For example, the developers modify existing parts, altering their shape or thickening the material when components are required to withstand higher strains, for instance.
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Lufthansa Technik is the leading manufacturer independent provider of maintenance, repair, overhaul and modification services for civil aircraft. The six business units of Lufthansa Technik (Maintenance, Overhaul, Component Services, Engine Services, VIP Services and Landing Gear Services) serve customers worldwide.
The BMW Group consists of the brands BMW, Mini and Rolls-Royce. The company is one of the world’s most successful premium manufacturers of automobiles and motorcycles as well as a provider of premium services for individual mobility.
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“It used to be that we would manufacture a tool for every prototype,” says Maximilian Meixlsperger, project manager for advanced development of additive manufacturing processes. “That could sometimes cost six-figure sums and take up to half a year. And then, as soon as the next redesign came along, the tool was obsolete. With 3D LMD, we have the first prototype within a week.”
The BMW Group’s strategy is to use the best method for the job at hand according to the following general scheme: They create prototypes of small components, using the powder-bed-based SLM method. From a certain component size upward, they opt for additive laser deposition welding to modify existing components — where those components are available, of course. In the case of extensive alterations or if engineers need the parts in larger volumes, it becomes more economical to make a new tool. Meixlsperger explains: “We weigh what the right course is on a case-by-case basis. And sometimes it turns out to be laser deposition welding.”
Laser metal deposition reairs blades
Lufthansa Technik also employs additive laser deposition welding and, beginning in 2014, it will use the method to repair the high-pressure compressor blades in aircraft engines. As well as having to withstand extreme tempera ture differentials, these blades suck in ash, sand, and water during flight. That soils and damages them at the edges of the air inlets and exhaust outlets and on the leading sections of the blades.
To achieve optimum performance, the blades have to be overhauled again and again. Dr. Stefan Czerner from the engines division at Lufthansa Technik explains: “Working with material which in some cases is just 0.2 millimeters thick is beyond even our best manual welders. We need high-precision positioning — accurate to a hundredth of a millimeter — and precisely metered energy input. The only way to do that is with a laser.”
Aviation engineers grind or mill the damaged areas to a defined geometry. Then the laser gets to work, all around the part, and builds the missing volume back up again with powder — near-net-shape and up to a depth of two millimeters. The laser machine uses the same material the blades are made of: a nickel alloy specially developed for aviation, containing chromium, aluminum, and other substances. The whole operation takes just a few minutes. Finally, everything is given a quick polishing, and the blade is returned to the engine.
“The process is so good that we can repair the blades more often — with longer intervals between repairs,” says Czerner. He and his colleagues expect a significant drop in costs for the components affected, for each engine overhaul.
Research on portable LMD-methods
Another person expecting many new repair applications from additive laser welding is Prof. Michael Rethmeier, head of joining and coating technology at the Fraunhofer Institute for Production Systems and Design Technology (IPK) in Berlin.
Rethmeier’s team is currently working on a portable method for bringing the machinery to the workpiece: “What we have in mind are things like the huge turbine blades in power stations, which we could reconstruct on site. Or take the boilers in chemical plants, where we could turn cracks into shaped grooves and then fill them in by means of laser deposition welding.”
Rethmeier wants to teach his students to think about the possibilities afresh. “Today, deposition welding lets us repair things that the text books say are unweldable. If we want to repair a workpiece with great susceptibility to thermal cracking, then we mix the ideal metallurgical material from the powders where possible. Then it’s no problem.” The heat input during laser deposition welding is so low that the structure remains intact, even with heat-sensitive materials.
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