Aerospace Components Maker Flies Through Production

David Steeber founded Accu-Tec with one customer back in 1988. As the aerospace industry strengthened, so did Accu-Tec's order intake, which saw a growth in turnover of more than 250% last year, mostly through referrals from their customer base. You don't get referrals like that without delivering high quality at a reasonable cost.

To keep up with its customers' demands for the extremely complex light metal air frame parts it produces, Accu-Tec has made shrewd investments in technology. Components include airframe, engine oil coolers, heat exchangers, etc., machined from aircraft aluminum and other high-tech alloys. Despite the increase in work, the company added only three employees, bringing the total to 15.

Moving up to 5-axis machining

Most of the machines in the shop are 3-axis Okuma vertical machining centers. Until recently at Accu-Tec, 5-axis work has been done by positioning and machining in three axes and then putting the parts on another fixture to put them in a new attitude. Now, the company is stepping up to true 5-axis machining because the parts it is seeing demand it: more complex surfaces and irregular shapes, requiring a highquality surface finish that needs to be completed in shorter cycle times at less cost.

Observes Steeber: "When we got into CAM software originally, we found out that the software was basically only machining in three axes. That's not good enough when you're trying to machine in five axes. So, our machine vendor suggested a couple of CADCAM companies; Delcam was one of them."

According to Steeber, "We found that Delcam was stronger on what we do, which is generating part code to produce a part, then have another piece of that software do the NC code to make it. Our part data comes to us in two ways. Some of the parts we do for maintenance are so old that we have to construct CAD models from blueprints. For newer parts, we may begin with native CATIA files and then build programs directly from those. We quickly saw that Delcam has a good import mechanism and data translator so we can take CAD files from any number of sources and smoothly create NC code."

Steeber explains that a Delcam rep came in and performed a demo and helped to develop the code on the first part, proving that the software worked as promised.

"We just ordered another, larger 5-axis horizontal machining center with pallet changer. The projections we did to justify that purchase has us reducing our cycle times by up to 66%. We can reduce our bench time (deburring) by 75% because the surfaces generated on the 5-axis machine will be that much better," Steeber says.

Five-axis machining has also simplified Accu-Tec's tooling requirements dramatically. For the last major 5-axis components contracts it won, it spent up to four months producing the tooling. They made good parts, but the 5-axis fixturing would have taken only three weeks to produce and less fixturing would have been required.

Glen Cotton, CNC programmer and Accu-Tec anchor man, uses Delcam software to design fixturing so that the parts can be completed by one machine rather than by two, including taking off the lugs or pads used to fixture the part.

PowerMILL can generate a 5-axis equivalent of any 3-axis toolpath, which can be necessary when a 3-axis approach is being used for most of a job, as at Accu-Tec currently, but where some 5-axis moves might be needed to avoid an obstacle or to machine as closely as possible to a steep face. Here, 5-axis roughing can also reduce the number of setups needed to machine many components. It can also be used to give a more efficient cutting angle that will allow more material to be removed with each pass.

According to Cotton, "The finish Accu-Tec achieved was better, eliminating the need for secondary operation or handwork, and improving our quality further, while avoiding the possibility of human error on the part. We put a bull-nose tool on the part and completed it with acceptable surface finish in minimum time."

Programming time for one complete part was in the range of 120 hours, Cotton says. "For this part, we were able to pull the programming I had done into the Delcam software. The process took a total of 250 hours to develop, including all the tooling and fixture designs for the four parts in the family. From there, we went into the sequence of machining operations."

Achieving better machining results faster

Most of the components are machined from solid blocks of 7050 aluminum plate. That provides the part integrity demanded by aerospace applications. The parts currently start on the 3-axis machining center, which roughs one side and puts in tooling holes. Then it is moved to the Okuma MU400 5-axis machining center to complete the part, beginning with roughing and finishing side 2, then the part is turned over and the first side is finished.

The operator then reclamps the part to finish the remaining edges and machine off the tooling lugs. Finally, the aircraft part requires only edge break and scotchbriting the surface, and then it can go to anodize, prime and paint.

"Our 5-axis process on this part is completed in half the time the 3D process took using the same machines. The difference is the dramatic positioning capability we now have with PowerMILL," says Steeber.

More efficient machining

"The Delcam software also helps to keep the tool on the part. If the tool is not on the part, it is not productive. This is another big advantage of the Delcam software, and it has helped us to reduce cycle times and produce high-quality surface finishes," Steeber says. There are several strategies in PowerMILL that help this to happen.

Three-axis swarf machining, for example, can be used to finish vertical walls. Using the side of the tool produces a better finish than cutting the wall in a series of operations at different Z levels. In addition, 3-axis swarf machining with tapered tools can be used to finish flat walls with a draft angle of the same value as the angel of taper on the cutter.

PowerMILL's "intelligent" programming methods make plunge milling pockets safe and effective, preventing damage to the machine spindle and cutter. The software updates the stock model after each pass so that each subsequent pass is based on the remaining material on the job. This ensures that an even amount of material is under the cutter before each plunge, and so keeps the load on the tool and spindle at safe levels.

The PowerMILL software provides better control over the point distribution within 5-axis toolpaths, taking advantage of the ability of the CNC to handle large amounts of data. Increasing the number of points in the toolpath permits more even machining with less vibration and more consistent tool loads. Both of these improvements give a better surface finish and less wear of the cutter, as Accu-Tec has found.

Error control saves time

Another Delcam feature allows Cotton to watch a complete part process simulation at his seat, off-line, and error-check the program. If the Delcam software detects an error, the simulation stops and an error message pops up, so Cotton can make a programming change. "From where I sit, that is a tremendous advantage to PowerMILL," he states.

"Previously, I would put in my best guess how far a tool should extend, but it may not work and I would not see it-until I got to the machining floor where they would find my errors while proving out the part," Cotton says. "If we had Delcam when we started the part, we could have saved two weeks by avoiding the trial and error on the floor. As it was, the machinists had to run the program in single blocks to check out each tool.

"Now, since the floor leader knows I'm using Delcam and can error-check before the part program goes to the floor, their confidence level in my programming has grown quite a bit," Cotton explains. "That's where the Delcam product helps a lot. It will tell and show if a tool is too long or too short to accomplish the task. It saves a lot of trial and error on the machine tools. We completely plan the process before we take it to the shop, so we can support the shop floor, should any questions arise."

According to Cotton, Accu-Tec intends to put another 7050 aluminum aircraft part on their new 5-axis machining center. "To help us justify the machine, Delcam's VAR helped us to do a time study of that machine with Delcam software machining that part," he says.

"We believe we will reduce the cycle time required by three-fold, with full 5-axis machining," Steeber says. "It will run faster and make a higher quality part. And in the aircraft industry, good surface quality means the absence of what is known as a stress-riser. Any point in the surface of an airframe part that has a scratch or knick, for example, or even a blend between cutters, is a stress riser. That's the place where failure is likely to occur because it probably would not handle the tension loads put on it in flight. The 5-axis machines can reduce this a lot because single clamping machining avoids mismatches on the parts or other nonconforming surfaces."

With 5-axis machining centers and Delcam PowerMILL, Accu-Tec looks set to serve the aerospace industry for years to come.

Accu-Tec is a provider of Commercial and Military Aircraft components that are precision machined and/or manufactured to the customer's drawings. For more information, visit www.accutec.biz.

Delcam plc is a developer and supplier of CADCAM solutions for the design, manufacture, inspection and reverse engineering of complex shapes and tooling. For more information on PowerMILL and other Delcam products, visit www.delcam.com