Joel Gasca at the computer and Angel Diaz use and set up an API laser tracker and Verisurf software
to inspect the geometrical configuration of an aircraft skin subassembly before it is sent to final assembly.
They say a picture is worth a thousand words, but in the quality assurance department at Hawthorne, CA’s Vought Aircraft Industries, Inc., pictures have proven to be worth, not just words, but thousands of dollars in time and cost savings, too.
“We build some really big products, up to 60-feet in length, for some of the biggest names in the aerospace industry,” says Paul Evans, quality assurance lead and 34-year veteran at the company’s Hawthorne division. “We offer a full range of aerostructure fabrication and assembly capabilities to design and manufacture things like fuselage panels, empennage and flight control surfaces, nacelles, wings and doors. In nutshell, we’re a tier 1 subcontractor to companies like Boeing, Airbus, Gulfstream, Lockheed Martin, Sikorsky, Northrop Grumman, Bell Helicopter, Cessna and Embraer. As a result, everything we build has to meet stringent engineering specifications. But beyond that, we’re required to prove that we meet those customer specs. We’ve always met that challenge, but it hasn’t always been easy.”
Hierarchy of checks
Most of the products built at Vought are manufactured in sections that are assembled on complex holding fixtures designed to assure dimensional accuracy. Many of the completed products are then shipped to the customers on oversized rail cars.
“Because our products are so large, we inspect everything in stages,” says quality engineer Angel Diaz, a 23-year Vought veteran. “We can’t wait until assemblies are complete to check them. If we did that, we could find that major dimensional errors have accumulated, which, of course, is not acceptable to us or our customers.”
“The only sensible way to handle inspection of such large assemblies is to do it in sections as they’re built,” adds Evans, “what Boeing calls ‘a hierarchy of checks.’ So, we build a detail part, and that has one level of inspection. Then we might do some machining, which requires NC probing to check. Or we build things on a Cincinnati Pogobed gantry mill. We check that work. There’s a stringer drill cell, and another layer of engineering. Then all of the many subprocesses get put together into smaller assemblies, requiring further checks. Finally, it all comes together as a complete assembly on a large holding fi xture, which is where our laser checking systems come into play.”
“Most of our specifications come to us via Catia solid models,” says Joel Gasca, the newest quality engineer in the department. “They have local and aircraft coordinates, but we strip those down and give the product it’s own reference system to speed up the inspection and analysis. On these structures our average tolerance is plus or minus thirty thousandths, which doesn’t sound like much, until you realize you’re dealing with structures up to 60 feet long.”
“To make things worse,” says Evans, “we have to achieve those tolerances in changing temperature conditions, which can cause some pretty wild thermal expansion and contraction. Still, our engineers have always found a way to beat that problem and deliver products that are in spec.”
For years Vought has used a combination of laser systems and portable CMMs to measure it large products. The laser systems are used to measure the large structures, and Romer portable CMMs are used for constructions that can be measured with a 6’ long arm. But even with those tools hooked up to computers, analyzing the results and providing feedback to the production department, vendors and customers was at best a very diffi cult process.
“Think of it this way,” Evans explains. “We’re dealing with large sheet metal assemblies, which are very flexible. In the past we would take a measurement, then come back and analyze it on a desktop computer with a couple of different software packages. Then we would see that the product was out of spec and needed to be twisted this way or that to bring it into alignment. We might have to do several iterations like that before we got it right. It was a very timeconsuming process.”
“Sometimes it was tough to convince the production, or vendors or customers we were right,” says Diaz, “mainly because all we had to show them as ‘proof’ were a bunch of numbers on spread sheets. We really needed something that graphically illustrated the results of our analysis.”
A picture is worth a thousand numbers
“That situation changed signifi cantly in 2007 when our Hawthorne side decided across the board to switch over to Verisurf software to run our portable CMMs,” Evans says. “We evaluated several analysis software packages, and decided Verisurf was best suited for our needs.” Senior Measurement Engineer Joel Gasca says, “Verisurf is a very powerful software package. It resides within Mastercam and uses all the power of Mastercam’s design module. The whole system comes on a disk and installs on a computer as easily as Microsoft Office. Our computers are already connected to the lasers and the Romer arms, and since Verisurf recognizes most of the portable CMMs out there, it was ready immediately to go to work with our systems.”
Before joining Vought, Gasca worked for a company that was using Verisurf. “I used to call Ernie Husted, the president and inventor of Verisurf, and ask him to let me play with the software on the weekends to learn how to use it,” he says. “Then when I came here and saw what they were going through, I knew they would love Verisurf, first because it’s easy to use, and second, because they could get feedback instantly. No more running back and forth. We’ve had good service from Jim Edwards, the Verisurf representative ever since.”
Once Vought saw what the software package could do for their efforts, they didn’t go halfway. “Today we have fourteen seats around the plant,” Evans says. “We’re in a major model change right now, going from what was called the 747-400 series aircraft to what they now call the 747-8. This plane is going to be 220 inches longer than the previous version and will carry 455 passengers. It’s a big shift for us, and we bought the Verisurf packages to prepare for the ramp up.”
Advantages of Verisurf
The biggest advantage of the software comes from it’s graphics capability and it’s ability to yield instant answers, according to Angel Diaz. “The software is great at collecting all the data we need,” he says, “but in the past we had to take that data back to a desktop system, analyze on two different software packages, and then all we got was a spreadsheet with a lot of numbers.
With Verisurf, we set up our lasers or our Romers, take our measurements, and we get on the spot analysis. The software compares the real product against the solid model residing in Mastercam and gives us an instant and graphical error report.
It calls out the errors in little boxes and draws arrows pointing to the error location. Now we can send a graphic to our customers or our vendors or production and show them exactly where the error is. Where production used to groan when they saw us coming with our lasers, now they’re coming to us, wanting us to check things for them before they go too far. Verisurf has allowed us to become much more graphics capable then we ever were.”
“We’re now able to measure the product as it’s being built,” adds Gasca. “Previously we didn’t have that capability. All we could do was collect data and then go into some other room to analyze it. Now we’re able to take Verisurf down to the floor, call over the engineers and mechanics and show them exactly what’s wrong. They love it, because the longer an error goes before its found, the harder it is to fix.
I guess the bottom line for our department is that it used to take us sixteen hours to do an inspection on a large assembly, eight hours inspecting and another eight on the report. Now we can do the same job in six hours or less.”
Much like shops that have setup people and machine operators, Vought has Verisurf setup people and operators. “We find that Verisurf is very easy to learn and use, but to get the most out of it, it helps to have some knowledge about the Mastercam design software,” Evans says. “That’s
because you’re importing solid models into Mastercam and using Verisurf to compare the real product against the model. At present, in preparation for the 747-8 push, we’re training ten more people to setup and run Verisurf.”
And Evan’s bottom line on the software? “When it come to communicating with our customers, a Verisurf picture is worth a thousands words,” he says. “Even better, it’s worth thousands of dollars to Vought.”
C. H. Bush, editor, CNC-West,
First published in CNC-West, USA, February/March 2009 issue