The ASTECH Engineered Products Division of GKN Aerospace is a company used to solving the big, tough engineering and production problems found in manufacturing lightweight, high-strength, heat-resistant and noise-suppression structures for advanced technology aerospace applications. Its two main products, Stresskin© and Soundwich©, are honeycomb materials that consist of flanged ribbons resistance spot-welded to face sheets, creating a unique, high-strength panel material with superior heat, sound and other performance characteristics.

Located in Santa Ana, CA, the more than 40-year-old company has produced exhaust nozzles and other components for use in space and for aircraft ranging from the F117A stealth fighter to the Airbus A330. Thousands of Boeing and other aircraft use the company’s honeycomb materials in engine nozzles and thrust reverser systems. Thousands more use its sound-absorbing structures to help meet stringent noise reduction requirements.

Big Problems, Little Problems

But like most advanced technology aerospace companies, in order to solve the big engineering and manufacturing problems as required by its customers, it also has to find solutions to countless smaller ones.
One such problem occurred in the manufacture of special copper electrodes used in resistance welding its honeycomb panel materials.

“We use thousands of thin copper electrodes to manufacture our honeycomb panels,” says Michael Stites, component fabrication manager. “The electrodes are 2.2” wide, two to three hundred thousandths thick and range in length up to 50 inches.”

“The electrodes are used to create paths for currents in the welding process,” adds Nick Skrobot, program manager for the company’s Rolls Royce Trent 1000 core fairing project. “They carry 8,000 amps of electricity, and we consume them in large quantities. They’re intricately designed and have to be machined to close tolerances.”

“Up until about a year ago, we produced the electrodes on an old CNC machine using manual set up for each electrode,” says Stites. “We produced aluminum fixturing in house to hold the electrodes. Unfortunately, because of the fixturing limitations, up to four setups were required per part. As a result, our lead times on the electrodes were averaging 45 days.”

“When I joined the company two and a half years ago, before becoming a program manager, I worked as a business improvement facilitator,” says Skrobot. “Part of my job was to look at the manufacturing processes and introduce lean to the business. One of my tasks was to take hours out of the process and reduce the lead time for electrode production.”

“Nick did the research to find a faster machine and a better workholding solution,” says Stites. “He finally recommdended that we buy a 15,000-rpm, 3-axis, Haas VF-4 mill, which has a 50” x 20” x 25” work envelope. He also found a totally different approach to workholding which allows us to produce the electrodes in one set up.”

Vac-U-Lok Workholding System

The workholding solution Skrobot recommended was a vacuum workholding system from a company called Vac-U-Lok.

“We bought most of the Vac-U-Lok subsystems,” says Skrobot, “which consisted of a heavy-duty vacuum system, a multi-station vacuum chuck, a coolant return system, and a vacuum safety system. The safety system shuts down the CNC mill if something goes wrong with the vacuum.”

“We bought the multi-station chuck,” explains Stites, “so, if necessary, we can place up to seven different length electrodes on the chuck at one time, and program the machine to machine them all.”

“The good thing here is that there is no fixturing to interfere with the machining process,” adds Skrobot. “The vacuum holds the electrodes flat, so we can finish machine the parts in one set up.”

Actually, setup couldn’t be easier now,” Stites says. “We use tooling pins located in the vacuum chuck. We just drop the electrodes over the pins, give them a tap to make sure they’re flat, and that’s it. The operator flips a switch applying the vacuum. When the machining is done, the operator shuts off the vacuum and that’s it. He just lifts the finished parts out and starts over again.”

Flexible Workholding System

The ASTECH workholding problem was relatively easy to solve, because the electrodes are flat, says Skrobot. But vacuum systems can be used on a variety of shapes.

“A vacuum system can be used to hold round or odd shapes, as well,” he says. “But that requires special fixturing. The chucks have to be machined to match the contours of the parts being held. You probably could do the machining yourself, but in our case we had Vac-U-Lok do the basic

machining on the chuck for us. They’re very experienced and made the whole process relatively easy for us.”

“The system was installed by Vac-U-Lok,” Stites says. “We showed them our workholding problem and they designed the vacuum chuck for us. We can now modify the chuck, put in new undercuts and spaces, to suit our changing product needs.”

Lead time for the Vac-U-Lok system, was about 14 weeks, according to Skrobot.

“Once the system arrived at our plant, it took only a day for them to install it,” he says. “But we had some work to do to get the vacuum chuck ready. They had prepared the base and some of the rudimentary cuts in the plate for us, but we had to cut in the part-specific details.”

Major Savings

How has the new vacuum workholding system paid off so far?

“Savings in lead time and production costs have been major,” Stites says. “We had as many as four setups per part in the past. We were manually bolting down the fixtures for each setup and then taking them apart and cleaning everything for the next operation. It was tedious and time consuming, very costly.”

“The bottom line for us is in lead time reduction, though,” says Skrobot. “We’ve gone from 45 days for the parts down to about seven days,

including all the paperwork and other procedures required. Machine cycle time for a finished electrode is down to 15 to 20 minutes. Elapsed machine time to produce a part in the past was as high as 54 minutes.”

“I’m happy with the system,” Stites says, “because I’m getting the parts needed out the door. And with the new system, I’m also getting the quality parts we need.”

“I’m happy with the system, too,” says Skrobot, “because we have freed the old CNC for more suitable applications and have drastically reduced lead times on the electrodes. 
 

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