Until now, making aero turbine blades required investment casting, electrical-discharge machining, and multiaxis CNC milling. No longer. Researchers at the Fraunhofer Institute for Laser Technology (ILT) in Aachen, Germany, build aircraft-engine components using an additive method called selective-laser melting (SLM). The researchers are part of the 6.5 million euro, EU-sponsored Fantasia project, tasked with developing near-net-shape manufacturing methods and repair techniques for complex aero turbines. In operation, components must endure extreme pressures, rotate 1,000 times/sec, and withstand temperatures up to 2,000°C.
SLM resembles selective laser sintering (SLS) except that it fully melts the metal powder, while in SLS, the metal just comes close to the melting point. Similar to other additive manufacturing methods, SLM involves digitally slicing 3D CAD models into layers and using this data to construct physical parts layer by layer.
The SLM machine applies a 30 to 100-micron-thick layer of metal powder to the substrate, and a laser beam immediately melts the metal into place, forming a permanent bond with the already-completed portion of the object. The machine builds the entire component by continuing this procedure for each layer.
To date, SLM has worked well with titanium alloys and Inconel 718, building components difficult to make using conventional methods, says Fantasia lead Konrad Wissenbach of ILT. “For other fissure-prone aero materials, we are experimenting with preheating the construction platform and varying laser parameters to prevent cracking,” he says. “To increase the build speed by a factor of ten, we are combining a large-diameter beam for large surfaces with a smaller-diameter beam for contours. In the future, SLM should cut the amount of material needed by 50% and slash turbine repair costs by 40%.” | Copyright 2010 • Penton Media Inc. • All rights reserved.