TechView From Taboo to Trusted Method:
EDM Machining in Aerospace
Due to stringent regulations set by the FAA, the aerospace industry as a whole requires parts to be cut to the tightest tolerances. Until two decades ago, using an EDM to cut many aerospace parts was not a viable option because most EDM machines were unable to cut with the required level of precision. Te aerospace industry provides
another challenge for manufacturers in its use of unique materials. Since fuel economy is an ever-present concern for airlines, the materials used to make engine components need to be able to withstand extremely high temperatures and be incredibly strong while remain- ing lightweight. Tis has led to the use of newer materials such as Inconel, titanium 6AL and other aluminum al- loys—all of which can be very difficult to cut with high levels of accuracy. Prior to 1994, EDM machines caused
microcracking on the surface of cut parts due to electrolysis, which is the electri- cally enhanced corrosion of material in a water environment in a wire EDM machine. All DC power supply machines created rather deep corrosion craters in parts that create stress point and microfractures. Te recast layer, which included remelted brass wire and the ma- terial being cut, also created cracks that would continue into the parent material. Microcracking occurs when particles
removed from the piece are charged. Ten, behaving like a magnet, the chips would replate themselves to the parent layer, leaving imperfections on the surface of a part. Tis recast or “white” layer frequently displayed stress frac- tures, resulting in failure rates deemed unacceptable in the aerospace industry.
In 1994, Mitsubishi EDM devel-
oped a new technology that forever changed the relationship between aerospace and EDM. Mitsubishi ma- chines began using an antielectrolysis power supply as standard equipment after two years of having it as an op- tion in the 90SZ machines.
Manufacturers need to continue to adapt as new materials are developed.
With this new generator, chips were
no longer magnetically charged, and microcracking was almost completely eliminated. Finished parts were leſt with a smooth surface, devoid of a cracked white layer. Almost immediately, a major
airline began testing parts that were cut on the new EDM machines. Results showed that these parts were compliant with industry standards, and engine and turbine parts were quickly sent into production, starting an industrywide shift towards the use of EDM machines to cut engine and other aircraft parts. Since the tipping point in 1996,
antielectrolysis EDM technology has flourished in the industry, and over the course of the following decade, EDM has been adopted by aerospace compo- nent manufacturers the world over. Over the years, Mitsubishi’s antielec-
trolysis generator has evolved, each new generation improving upon the last in terms of eliminating problems with the white layer. EDM machines can now consistently machine difficult workpiec- es with unsurpassed accuracy.
Doug Maywald
Applications Engineer MC Machinery Systems Inc. Wood Dale, IL
Te latest addition to the MV Series
is the MV4800 Advance, which cuts substantially faster than EDM machines did in 1996, and a new, bigger tray allows manufacturers to machine larger parts than ever before—which is enormously important in aerospace. Te MV4800 Advance features an extensive travel of 800 × 600 × 500 mm and can machine workpieces up to 1349 × 1100 × 500 mm. Speed and table size are not the only
new features to the MV4800. It has the ability to thread at the breakage point in materials that have a lot of material movement. When machining certain types of materials—specifically high- stress metals—the gap will sometimes close up behind the cut. On previ- ous models, operators would have to rethread the wire at the initial thread point and retrace the gap to the break- age point. One EDM specialist company that
uses a Mitsubihsi FA30V and a new MV2400-ST is running 457-mm tall parts in both machines with the same 0.3-mm wire. Te new machine is run- ning 14–19% faster, depending on the material type. Tis is welcome news because the FA30V has a V500 power supply and the MV series uses the V350-V which one might assume to be slower. Te faster speed proves that the new technology with DMX-S works. EDM has gone from taboo to a
trusted method of machining parts for the aerospace industry. Although much has improved in the last two decades, there’s likely more change to come. Manufacturers will need to continue to adapt as new materials are developed and new regulations set in place. ✈
Aerospace & Defense Manufacturing 2014 53
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