Punching holes in aerospace manufacturing theories

Figure 1A TRUMPF TruMatic 3000 punch-laser combination, like this one, is helping Unison Industries accomplish fabricating tasks, such as quickly making holes 0.125-in. thick in INCONEL, which wouldn't have been possible with the company's other tools.

Tin banging is not a term commonly used in aerospace manufacturing. The term—sometimes greeted warmly by metal fabricators, but derided by others in the field—is used to describe the general work of making parts out of thin sheet metal. Back in the day, that called for a lot of banging.

Banging is not necessarily a noise manufacturers of aerospace parts want to hear. It's more of a whiz and a whir sound as machine centers chip away to create metal parts with extremely high tolerances and that must meet stringent quality standards.

Times have changed on the fabrication shop floor as well. You might still hear the bang of an operator shaking out a sheet of parts, but that's lessening every year with the advent of more advanced material handling and part-separating systems.

However, not all in manufacturing know about the advances being made in fabricating technology. To them, tin banging is still the norm.

Chris Durnell found himself confronting that type of mindset as he tried to sell the idea of a new punch/laser combination machine to his co-workers at Dayton, Ohio-based Unison Industries, a manufacturer of metallic tubes, ducts, bellows, and manifold assemblies for gas turbine engines. Durnell, a value process engineer who had worked in sheet metal fabricating before coming to work for Unison five years ago, knew such a versatile fabricating tool would make a big difference in the fabrication of brackets for the hundreds of tubes that the facility produces, but the production team was a bit skeptical. Being an aerospace manufacturer, Unison has to meet the highest of quality standards, and adding an unknown variable to the manufacturing mix tends to make engineers a wee bit nervous. Ultimately, the benefits of a punch/laser combination would be too great to ignore.

The Big Bang: Seeing What It Can Do

Luckily, Unison did have experience with laser cutting. The facility has three five-axis lasers for cutting 3-D parts. It also had a flat-bed laser at one time that was later moved out to accommodate a waterjet, which was needed to cut parts that could not have a "recast" layer, which results from exposure to a thermal cutting source, according to Durnell.

In early 2008 Unison decided it needed to add capacity for cutting flat parts, which were expected to increase with an expected jump in customer orders.

"We wanted to go back to a laser. All they knew were flat sheet lasers," Durnell said. "So the ability to pick up the secondary operation on this [punch/laser] machine was totally new. As a matter of fact, some said it could not be done."

Durnell had experience with TRUMPF fabricating technology in the past, so he sought out the company's engineers for help. He needed evidence that a punch/laser combination could deliver on the elimination of secondary operations.

TRUMPF developed tools for the sample jobs and turned around the parts for the Unison engineer staff to examine.

"In this example, we were countersinking for the rivet, actually coining the rivet head to countersink the metal. So they actually produced some samples for us," Durnell said. "They sent a sheet full of countersinks, and there were still skeptics."

Seeing wasn't believing—at least not yet.

Aerospace manufacturers aren't so much resistant to change as resistant to the idea of quality processes being altered and risking poor quality output. Of course, one of the best ways to increase quality is to take human hands out of the equation, and that's what the punch/laser combination could do for some tasks.

"The bracketry that we make may be in orders of five or 10 pieces. On a sheet we may have 40 different part numbers. They take those off and go into a bay, and [the operator] has to manually countersink these," Durnell said.

"Now what side of the sheet is the countersink on? Some of the parts are near symmetrical," he added. "We even put tabs on the outside of the part to distinguish what is up on the part and what is down on the part."

That scenario spoke the language of the aerospace manufacturing veterans. Durnell had won buy-in.

In December 2008 the TRUMPF TruMatic 3000 punch/laser combination (see Figure 1) was delivered and installed. After a couple of months, the equipment was up and running at production speed.

It Punches, It Cuts

Since it's been in operation, the punch/ laser combination has been consistently running. Although job levels are not where they were expected to be as of early 2009, the equipment has been kept busy as the production team has moved as much work as possible from the waterjet cutting machine to the combination equipment.

Durnell estimated that the punch/ laser, with its 2,000-W coaxial flow laser resonator, runs six times faster than a waterjet. " That's just straight cut speed," he said.

Adam Hartley, the waterjet operator, was tapped to learn to run the punch/laser combination machine. Since he was familiar with flat-pattern programming because of his time running the waterjet and the laser that the waterjet replaced, he made a smooth transition in terms of learning about the new equipment, according to Durnell. In the months since the installation, he has transitioned to programming, which is done offline in an office right off the shop floor.

Hartley's not the only one getting familiar with the new machine tool. Everyone is learning about its capabilities.

"We are now punching 0.100-in.-diameter holes in 0.125-in.-thick INCONEL. Nobody does that," Durnell said.

How are they accomplishing this? Only with a punch/laser combination, that's how.

Unison Industries actually precuts an undersized hole in the INCONEL, and then the punch is used to shear the hole to size. Punching specifications for metal in the aerospace industry dictate that one-third of the nominal thickness must meet the drawing specified limits of size. By using the laser and then the punch, Unison is processing 0.125 in. thick INCONEL and getting 45 percent land in 0.100 in. diameter holes with only ±0.004 in. total tolerance.

"With a standard punch machine, you wouldn't do that, and with a combination punch/laser machine, you can hold ±0.002 [in.] diametrical tolerance on a 0.100 [in.] hole," Durnell said.

This newfound approach has eliminated another secondary process as well. All of those holes made in the INCONEL sheet—which could amount to thousands in one production day—previously had to be drilled out.

Talented Personnel and Their Tools

Those types of efficiency gains are possible with a combination of sophisticated machine tools and talented engineers and operators. It's just a matter of expanding one's mind in terms of what's possible in fabricating.

Unison is finding this out with its new TRUMPF press brake. Most of the company's press brakes are forming curved brackets; press brake operators don't bend a lot of right angles because the brackets have to hug the tubes snugly to the aircraft, all in the name of conserving space and weight.

The operators are able to execute these complicated bending patterns thanks to their own skills, ability to read complicated blueprints, and the six-axis backgauge on the press brake. In fact, they are capable of making these bends—some parts may have as many as 12—using TRUMPF's standard line of tooling.

These definitely aren't yesterday's tin bangers. Aerospace manufacturers are slowly learning this.