Pioneering
twin-gantry, 5-axis router uses POGO® Flexible Tooling System Technology and 30,000 rpm
HSK spindle to eliminate hard tooling, cut setup time by 2/3 and maximize part quality
HAWTHORNE, CA—"Configurable" tooling provided the right
figures for Northrop Grumman in expanding its productivity and capabilities at aircraft
skin processing. The Hawthorne plant ordered a new two-gantry, 5-axis Cincinnati Vertical
CNC Router with adjustable CNC fixturing to bypass build and setup costs for hard tooling.
Three adjustable beds of new POGO® Universal Holding Fixtures (UHFs) cut setup times by
about two-thirds on trimming and hole drilling operations on more than 100 different
fuselage skin parts.
Fixturing such a large variety of parts with traditional vacuum chucks and fiberglass
molds would have required not only lengthy setup burden, but also 75,000 sq ft (7000 m²)
of floor space to hold the master tooling dock and 60 pick-up stations needed to store and
retrieve so much tooling, said plant officials.
The pioneering approach
takes advantage of the new POGO® UHFs built into the 10 x 50' (3 x 15 m) work tables
under the company's new two-gantry, 5-axis vertical router. Consisting of hundreds of
individually programmable, variable-position vertical supports, a POGO® UHF can be
reconfigured for a new part in as little as two minutes—as easily as calling
up a new machine tool program.
Northrop Grumman's new router features three of the POGO® Flexible Tooling Systems,
allowing the separate gantries to machine different parts simultaneously. The router is
the first Cincinnati machine tool ordered with the new "soft" workholding
technology. Developed by CNA Flexible Tooling Systems (Redmond, WA), POGO® Universal
Holding Fixtures are sold exclusively by Cincinnati in the aviation, space and defense
markets.
"Flexible tooling is ideal for this application," says Northrop Grumman
industrial engineer Art McIntosh, who performed prove-out and "first article"
verification for the new machine. "We run these parts in units of one, so flexible
change-over between part numbers goes a long way toward streamlining our process."
First HSK Router
The Hawthorne plant produces the skins for a commercial aircraft
manufacturer. Covering the fuselage of a jumbo jet from behind the cabin to just before
the empennage, the aircraft skins are aluminum panels averaging 84" (2.1 m) wide, and
ranging from 220 to 260" (5.59 to 6.60 m) long and 0.049 to 0.500" (1.2 to 12.7
mm) thick.
The new twin gantry router complements existing fabrication operations performed by the
Hawthorne plant on the part to extend value-added benefits. The additional operations—periphery
milling and drilling holes for locating stringers and shear ties—allow
Northrop Grumman to deliver snap-together parts that minimize added labor during aircraft
assembly.
The Northrop Grumman fabrication area has used similar Cincinnati 5-axis machines for
profiling and pocket milling for over 20 years, McIntosh says. The new router addresses
evolving requirements in two areas particularly, he notes:
* Accuracy. "It's a high-precision machine," he says. Capable of
±0.002" (±0.050 mm) volumetric true position, the router easily holds Northrop
Grumman's ±0.015" (±0.40 mm) tolerance on milled surfaces and hole locations.
* HSK Spindles. "With HSK, we're able to take advantage of the full
30,000 rpm, and still hold our tightest tolerances," says McIntosh. The router is
Northrop Grumman's first machine tool accepting tools with the HSK taper, designed to
eliminate wobble up to the highest spindle rpms. The increased stability will let Northrop
Grumman drill at full speed, without leaving its 0.003" (0.076 mm) total tolerance
band on hole diameters.
Featuring 6000-30,000 rpm speed range on each of its two 17.5 hp (13 kW), No. 40 taper
spindles, the new router feeds at 650 ipm (16.5 m/min) and rapids at 1200 ipm (30.5
m/min).
880 Actuators
The router's three
POGO® UHFs look like beds of nails on the machining tables, where each "nail"
is a pneumatic actuator ending in a swiveling vacuum end effector cup. Interfaced with the
CNC, the POGO® actuators move to programmed heights with ±0.004" (±0.100 mm)
accuracy and ±0.001" (±0.025 mm) repeatability, across a vertical stroke as long as
30" (0.76 m). When hundreds of the POGO® actuators move independently to form a
pattern matching the contours of the part, the result is a support structure equivalent to
a hard-tooled fixture.
Northrup Grumman's UHFs each consist of 880 POGO® actuators, situated among 1320 pockets.
Though McIntosh believes his operation will allow them to remain stationary, he notes that
any POGO® actuator can be relocated to any pocket for added flexibility. "It's just
a four-bolt attachment," he says.
Saving
on Setup
With configurations for dozens of
parts stored in the CNC, one POGO® UHF can take the place of an entire inventory of
hard-tooled fixtures—eliminating not only the need to produce and store these
fixtures, but also to move them around. This relocation is the main source of the setup
savings, McIntosh says.
"All of the work associated with taking a fixture on and off the router's work table
is gone," he says. "No more bolting the fixture in place, squaring it, and
homing the machine to the tool. With the POGO® Universal Holding Fixture, most of the
setup remaining consists of just craning the part to the machine." |
