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Pushing simulation software to attack problems in new, innovative ways at the company’s Nashville manufacturing plant.
One of the sites, located in Nashville, TN, produces individual parts and sub assemblies for Airbus, Gulfstream, Cessna, and Lockheed. With approximately 900 employees spread over two million square feet of work space, the Nashville site has 10 large CNC gantry mills, nine large assembly riveters, and a variety of smaller CNC equipment. In the machining area, there are more than 35 CNC spindles making chips.
“The Nashville facility focuses on parts that are ‘long and large’. Most everything we do is longer than 30ft,” said Numerical Control (NC) Manager Kevin Chandler. “In the past, we made thousands of small parts – parts you could hold in your hand, but those are gone. So too are many of the programmers. At one time Nashville had a staff of 32 programmers, now four remain. We don’t have the luxury of multiple try-outs anymore. That’s where Vericut has been a life saver – and a job saver.”
Part Verification
Despite changing ownership several times, the facility has a long history of using NC simulation software. It first began using VERICUT software for material removal simulation in 1991, when it was Textron Aerostructures. In 1996 it was purchased by The Carlyle Group and in 2003 it became part of Vought Aircraft Industries. Vought Aircraft Industries, Inc. was acquired by Triumph Group, Inc. in June 2010 and was renamed Triumph Aerostructures – Vought Aircraft Division.
Chandler and Gwinn are two of the most experienced Vericut software users in the world. Combined, they have more than 35 years experience using VERICUT. “Experience has shown us that the more we can simulate on the screen, the less problems we will have down the road. We both agree on the advantages provided by machine simulation,” Gwinn said.
Before VERICUT was implemented, the Nashville facility was using Catia V4 and programming in APT, which had a slow check process using a flat-bed plotter. Then they machined the first few parts out of foam, or some other non-production material.
Gwinn added, “When a program is ready, we don’t even go out in the shop anymore. Once it’s passed through VERICUT, there is nothing major that can go wrong. We know it will be cut correctly.”
For example, a new high-speed 5-axis Handtmann PBZ milling machine is being employed to machine stringers that are over 60 feet long. To hold the stringers in place during machining, the Triumph Aerostructures Numerical Control (NC) group designed dovetail-shaped fixtures that they refer to as “scuff plates.”
NC Program Optimization
The Triumph Aerostructures NC group recently had a two-fold challenge: they needed to quickly update legacy programs for the new Handtmann UBZ panel milling machine, while in the process of upgrading from Catia V4 to V5. By using VERICUT and its NC program optimization feature, OptiPath, the NC group was able to create NC programs for the new machine — without re-programming them in Catia V5. First, they re-processed the Catia V4 programs for part location and cutter changes, then re-posted the resulting APT source files for the new machine. Next, they simulated them in VERICUT to ensure they would be collision-free, and finally used OptiPath to update the feeds and speeds for the target machine.
“Rather than re-invent the wheel, we took some of our old programs and ran them through OptiPath to get more out of them,” said Chandler. “In addition to shortened machining times, we also saved several hundred hours that would have been required to re-program the parts in the new CAM system.”
OptiPath optimization software works by analyzing the NC program (G-codes or native CAM output) and cutter contact with the ever-changing workpiece. It then divides the motion up into smaller segments to determine what conditions would benefit by increased feed rates, and where the feed rate needs to be reduced to protect the cutter. Since the software knows exactly how much material is being removed at each segment, it is able to determine the ideal feed rate. The toolpath trajectory is never altered.
Optimized feed rates maintain a more consistent chip load, which reduces wear on the cutters. Cutter wear is also minimized due to the reduced amount of time required to cut each part. NC programs with optimized feed rates maintain a more constant cutting pressure between the NC machine tool and the workpiece. The machine is subject to less wear and tear not only because of the reduced machining time, but also because of the more constant load. An optimized tool path also produces a better finish because constant cutting pressure causes little or no variation in cutter deflection. Work piece finishes in corners, edges, and blend areas are improved significantly.
Another major benefit for the Triumph Aerostructures NC group has been VERICUT’s Auto-Diff feature, which enables the programmer to compare a CAD design model to a VERICUT simulation model and automatically detect differences. According to Gwinn, “All new programs, especially those generated from Catia V5, have solid models. We didn’t always have those in the past using Catia V4, but now we try to make sure all new programs start with solid models, and we use those same models to compare against our NC tool path. We have a slang saying around here that has stuck and holds true: ‘VERICUT don’t lie!’ We have come to trust that what you see on the screen in VERICUT is what you will get on the machine. It is virtual reality!”
