Turn out the lights on wire EDMing

Of all machining processes, wire EDMing is perhaps best suited for lights-out manufacturing. No chips get in the way. There are no worries about cutting tool wear or breakage. And if a wire breaks or shorts out, the machine tries to rectify the problem before notifying a human that it needs help. This allows tool and die makers and an increasing number of traditional machine shops—especially those serving the aerospace and medical industries, where wire EDMing is used to cut otherwise unmachinable part features—to significantly boost available machine time while reducing labor costs.

Tap, Tap

Unfortunately, the one thing that can go wrong might actually break the machine tool. When a slug comes loose, it can fall into the lower nozzle and cause damage or become jammed between the head and workpiece. One inelegant solution is so-called slugless EDMing, in which the wire vaporizes the slug, but this eats up huge amounts of time, wire and electricity. Small metal tabs can be left to support the slug until the next morning, but removing them requires additional processing and human intervention.

GF Machining Solutions’ ASM system uses compressed air to lift and remove just over a ½-lb. slug, which then is deposited into a basket at the side of the machine. Image courtesy of GF Machining Solutions

Steve Raucci, EDM product manager at Methods Machine Tools Inc., Sudbury, Massachusetts, offers a solution. He said the Core Stitch function on FANUC RoboCut α-CiB series wire EDMs retains slugs in the workpiece via a reverse discharge “brass adhesion” process, leaving small islands of soft material that hold slugs in place. After roughing, a few light taps with a plastic or brass hammer are enough to separate a slug, whereupon the operator can return the workpiece to the wire EDM for final machining if necessary.

A hammer helps achieve lights-out machining because, for starters, Core Stitch eliminates the need to stop a machine and apply electrically conductive glue or magnets to hold slugs, automating what was once a manual function. As Raucci explained, the tapping function itself also can be automated.

“We have an aerospace customer that’s using a FANUC robot as part of a machining cell,” he said. “The robot removes a jet engine component from the EDM and sets it on a slug removal station. It then exchanges its grippers for a brass punch, knocks out the slugs and places the part back into the machine for a final skim pass.”

Slugging It Out

GF Machining Solutions LLC, Lincolnshire, Illinois, takes a different approach to wire EDM slug management. EDM Product Manager Eric Ostini said the company’s AgieCharmilles Cut P series wire EDMs can be equipped with an automated slug management mechanism that uses a Venturi-style vacuum to basically suck slugs out of a workpiece.

FANUC America’s Core Stitch function uses a reverse discharge process to retain slugs in the workpiece. They then can be removed with a few light taps from a hammer. Image courtesy of Methods Machine Tools

“As the slug breaks free, it’s supported by the lower head while the upper head lifts up and out of the way, allowing the attached ASM mechanism to move into position,” he said. “The ASM uses compressed air to generate enough suction to lift and remove just over a ½-lb. slug, which is then deposited into a basket at the side of the machine. The upper head then returns to its previous position and either finishes the cavity or moves on to the next one, all completely lights out.”

An unattended machining strategy, however, requires more than automated slug removal. Flawless automatic wire threading is also needed. FANUC America Corp., Rochester Hills, Michigan, addresses this with its revamped AWF3 automatic wire feed system. Raucci said the new threader includes an integrated air supply that runs the length of the annealing tube, allowing the machine to thread while fully submerged, even at the maximum 20″ Z-height.

“It’s very accurate,” he said. “We can thread a 0.01″ wire, for example, through a 0.015″-dia. hole and are able to feed the wire through much taller kerfs than the previous generation. Couple that with the machine’s automated probing, coordinate rotation, remote management features and extreme reliability, and it means you can load it up with a 66-lb. spool and come back 100 hours later to a pile of finished parts.”

Trust, but Verify

Because robust threading is important, Ostini said GF Machining Solutions created its Threading-Expert and automatic wire changer systems. But just as important is knowledge of wire breaks and other process-related events. That is why the company has developed eTracking software that constantly monitors and records the spark condition related to specified norms, generator parameters and maintenance and alarm status, providing full traceability of mission-critical components.

“It also provides an area where step-by-step work instructions are presented to the machine operator, which will not allow the machine to start unless the operator verifies that each step was performed,” he said.

Makino’s UP6 Heat wire EDM boasts 1μm precision across its entire 25.6″×18.5″ working area. Image courtesy of Makino

Makino Inc., Mason, Ohio, is another wire EDM builder that recognizes the need for efficient, predictable lights-out machining. Brian Pfluger, EDM product line manager, noted that his equipment easily checks the dependable threading box thanks to a jetless threading system, which is reportedly able to thread through 4″ of kerf with 100% reliability. He also said smaller slugs are manageable with Makino’s dual-pump, independently programmable flushing system. Yet he’s quick to point out that shops must have several other critical functions in place before turning out the lights.