Wire EDM can replace broaching for fir tree slots

As aerospace OEMs and supply chain companies face increasing pressure to produce more fuel-efficient aircraft, wire EDM (WEDM) is emerging as a key machining technology, reports GF Machining Solutions. According to a body of evidence generated by David Welling at the Laboratory for Machine Tools and Production Engineering (WZL) at RWTH Aachen University (Germany), WEDM has the potential to replace broaching as the technology of choice for the manufacture of fir tree slots for found in high-pressure compressor and turbine disks.

“Broaching tools have obvious limitations; one of these is the high tool wear that results from the increased toughness of aerospace materials,” says Welling. “Also, broaching machines require a lot of floor space, have a high initial investment cost and offer low flexibility.”
Until about 10 years ago, WEDM was not considered a viable process for full fir tree slot production due to the recast white layer left on components by earlier generator technology. But Welling’s research has shown that WEDM now, with the advent of sophisticated digital generator technology, compares well to broaching in terms of surface integrity and part tolerances – both important in fir tree slots.
So far, Welling’s research has shown through component high cycle fatigue studies that WEDM compares with broaching in terms of component fatigue life, and that WEDM is actually capable of machining fir tree slots with the required accuracy. In addition, Welling says that WEDM offers an advantage when it comes to automation since it offers the process monitoring capabilities necessary to ensure machining quality.
“Furthermore, WEDM does not present the tool wear challenges inherent in broaching,” he adds. “In WEDM, since the tool is the wire that is being unwound from the spool, there’s a new tool being used for every process second.”
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