Related Glossary Terms
Enlarging a hole that already has been drilled or cored. Generally, it is an operation of truing the previously drilled hole with a single-point, lathe-type tool. Boring is essentially internal turning, in that usually a single-point cutting tool forms the internal shape. Some tools are available with two cutting edges to balance cutting forces.
- gang cutting ( milling)
gang cutting ( milling)
Machining with several cutters mounted on a single arbor, generally for simultaneous cutting.
Machining operation in which material is removed from the workpiece by a powered abrasive wheel, stone, belt, paste, sheet, compound, slurry, etc. Takes various forms: surface grinding (creates flat and/or squared surfaces); cylindrical grinding (for external cylindrical and tapered shapes, fillets, undercuts, etc.); centerless grinding; chamfering; thread and form grinding; tool and cutter grinding; offhand grinding; lapping and polishing (grinding with extremely fine grits to create ultrasmooth surfaces); honing; and disc grinding.
Tooling usually considered to be a stationary apparatus. A jig assists in the assembly or manufacture of a part or device. It holds the workpiece while guiding the cutting tool with a bushing. A jig used in subassembly or final assembly might provide assembly aids such as alignments and adjustments. See fixture.
- machining center
CNC machine tool capable of drilling, reaming, tapping, milling and boring. Normally comes with an automatic toolchanger. See automatic toolchanger.
Machining operation in which metal or other material is removed by applying power to a rotating cutter. In vertical milling, the cutting tool is mounted vertically on the spindle. In horizontal milling, the cutting tool is mounted horizontally, either directly on the spindle or on an arbor. Horizontal milling is further broken down into conventional milling, where the cutter rotates opposite the direction of feed, or “up” into the workpiece; and climb milling, where the cutter rotates in the direction of feed, or “down” into the workpiece. Milling operations include plane or surface milling, endmilling, facemilling, angle milling, form milling and profiling.
Minimum and maximum amount a workpiece dimension is allowed to vary from a set standard and still be acceptable.
Workpiece is held in a chuck, mounted on a face plate or secured between centers and rotated while a cutting tool, normally a single-point tool, is fed into it along its periphery or across its end or face. Takes the form of straight turning (cutting along the periphery of the workpiece); taper turning (creating a taper); step turning (turning different-size diameters on the same work); chamfering (beveling an edge or shoulder); facing (cutting on an end); turning threads (usually external but can be internal); roughing (high-volume metal removal); and finishing (final light cuts). Performed on lathes, turning centers, chucking machines, automatic screw machines and similar machines.
The Bell Helicopter Drive Systems Center (DSC) in Arlington, Texas, can never be confused with anything “little.” It’s a huge facility, filled with the latest milling, drilling, and boring equipment, and operated by 600 machinists, programmers, operators, engineers and technicians. In fact, some newly installed equipment is making some of the company's biggest components in its history.
The DSC does resemble a small job shop is in its agility, flexibility and responsiveness, which was critical as the company tried to operate during the challenges of today’s world.
According to Mark Rudeseal, vice president of the DSC, during the previous four years the DSC had been under siege as the economy affected orders. When the U.S. government said the V-22 Osprey twin tiltrotor aircraft had been green lighted, and the Marine Corps had committed to a four-year program, the DSC was already a year behind on capacity.
Rudeseal explained that when the V-22 project was approved, work in the DSC had been in flux. While demand for Bell helicopters was still high, real-world factors meant that cancellations were high as well.
“We had all of the year sold out,” Rudeseal said, “but then customers began saying, ‘We really need the helicopter, but we can’t get financing.’ So, we had quite a few customers who walked away at the last minute, saying they really wanted the aircraft, but couldn’t find the money to buy right now.”
When the V-22 program was given the go ahead, the company realized not just that project plans had to be adjusted, but that the machine tools that had successfully built helicopters (four-bladed Hueys and Cobras), Jet Rangers gunships, and other projects in the past, would not be hefty enough for the V-22 work that included large castings and forgings for gearboxes, adapters, fittings and components.
The Starrag 5-axis STC 1250 machining center was big and rigid enough for production, and was able to hold tight accuracies in all axes, said Gerald Henderson, director, manufacturing support. He said that Starrag guaranteed 0.002” (0.0508 mm) true position on multiple bores.
The V-22's proprotor gearbox requires a number of bores along multiple access. A bore test was designed in which 36 holes were drilled into a 2” x 3” (50.8 x 76.2 mm) piece of aluminum. After drilling, the B-axis was rotated 90°, and another series of holes was drilled.
“What we were looking for was not only could they hold the tolerance in a linear motion, but could they hold that tight tolerance while we rotated the B-axis?” said Henderson. “By doing this they were able to hold less than 0.0004” (0.01016 mm) error. Which was well within what we were looking for.”
Other features that appealed to the DSC experts was the trunnion size table that was needed for the V-22’s big transmission adapter and the proprotor gearbox. In addition, Starrag standardized on Siemens 840D controllers for all their machines, meaning jobs and operators could fluidly move from one machine to another.
In addition, the DSC also wanted to reduce set-up and cycle times while increasing throughput. “With the old method,” Rudeseal noted, “it took us more than 200 days to do a gearbox.”
That changed after the DSC installed new equipment including large 4-and 5-axis SIP jig bores, 4-axis CWK 800s, and 4- and 5-axis SIP 7000s. The heart of the new equipment is the Large Case Cell featuring twin 5-axis STC 1250s and a multi-story Fastem pallet loader/unloader that was dubbed The Monster.
“We reduced planned cycle time down to a little less than 100 days,” said Rudeseal. “We cut it (cycle times) in half. We were able to achieve a 30% productivity output increase with all these new machines and combining operations. We went from around 300 boxes to 400 boxes a year, therefore, we probably did 40-45 percent more boxes.”
Henderson said the twin STC 1250s run at 6,000rpm even though they have the capability of 10,000rpm. “The program is written at 6,000rpm because engineering doesn’t want us to run the spindle too high. They worry about the residual stresses on the material, the heat buildup.”
When machining castings or forgings, the company removes 0.0015” or 0.0016” (0.0381 or 152.4 mm) material. “We really are a precision shop — very high precision,” Henderson said. “Our gears are AGMA Class 13. The only people who build a better gear is NASA (Class 14), and we’ve built a number of their gears.”
Starrag Group is a global technology leader in manufacturing high-precision machine tools for milling, turning, boring and grinding workpieces of metallic, composite and ceramic materials. Its North American headquarters can be reached at 859-534-5201 or visit them at www.starrag.com.