Roughing it 5x faster: special process chips away Inconel blanks into aerospace blisks.

Position:ECDM strategies

GE Aviation of Evandale, OH, had a vision of a machine that would rough out blisks (bladed disks) from an Inconel blank--and that it would use a process combining Electro Chemical Machining (ECM) and Electrical Discharge Machining (EDM), called ECDM.

It is now roughing material out five times faster, and the ECDM time is one-half as much as before.

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KRC Machine Tool Services of Independence, KY, made it happen. The company built two Blue Arc machines, named after the color the electrode glows as it removes the tough metal at 40 ipm.

While on a trip to China to see the GE research center, Scott Ashworth, president of KRC, and one of his partners saw a prototype version of a blisk machine.

"You couldn't actually see material removal because everything was taking place submerged," Ashworth said.

The submersion process was primarily to maintain consistent heat in the heat-affected zone, he said. In addition, it helps with smoke by dampening it into the liquid, and since the process is noisy, the liquid helps dampen noise.

Constant arc crucial

GE developed this new process to ECDM material--to "rough" it off. It takes a copper electrode, 7mm in diameter; a variable power supply to control voltage from 0 to 70 volts; and current from 0 to 500 amps. What makes this process unique is the switching power supply, a fast pulse power supply, and GE's software that communicates between the control and the power supply.

The real process is in monitoring the voltage, the current and the feed rate, and continually manipulating those to maintain a constant arc, which is essential to precise material removal.

"We originally thought about building our own machine," Ashworth said, "but we ended up talking to our friends at Mazak (Florence, KY). They agreed to sell us two-thirds of the machine, and we finished the rest.

"What we got is a well-designed base, ballscrews, linear guide system, and a tool changer," he said. 'We looked at it, got the drawings from Mazak, and realized we could modify and elevate the tool changer to be able to handle a 30"-long rod, which is being consumed during the machining of the blisks.

"Not only are you 'machining' very tough Inconel, you're consuming the tool in the process."

Ashworth said GE wanted to be able to load the tool changer (30 tools) and run it for hours, non-stop, which meant that KRC had to modify the way the tool changer was mounted, but not the tool changer itself.

A unique machine

"What we...

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