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are sometimes referred to as half templates as they are
used in pairs to place alternating holes.
The manual drilling technology is not suited for
accurately and efficiently cutting large holes in a single
pass. One hole may require as many as five tool
changes. The hole is started with a small pilot and then
stepped up to the final size. The hole is finished with a
final ream and countersink pass. Table 1, below, shows
a sample drill sequence for a .871-inch diameter hole.
Each drill size uses a dedicated drill motor, which
represents a significant cost element. As shown in the
table below, several types of drill motors may be used
for a single hole. Figure 2 shows a sample drill motor
and template. Drilling these large holes manually can be
a time consuming process and may sometimes require
rework.
Table 1 Example drill step sequence
Hole - .871 Stack - 2.6
Step Tool Description Machine Type
1 DRILL - NON / PILOTED Positive Feed
2 CORE DRILL - NON / PILOTED Positive Feed
3 REAMER - NON / PILOTED Positive Feed
4 BACK SPOTFACE CUTTER RACKFEED
4 SPOTFACE ARBOR
5 COUNTERSINK - FORWARD / PILOTED RACKFEED
6 COUNTERSINK - FORWARD / PILOTED Pistol
6 ARBOR - COUNTERSINK CUTTER
7 GAUGE, PLUG
WORKER ACCESS
The gear rib area has limited access in the assembly jig.
It is located on the first floor with the lowest part of the
trailing edge below factory floor level. From an
ergonomics perspective, this requires manually lifting jig
plates and drill motors into positions, which range from
below floor level up to 2 meters above the ground. The
ideal working range is approximately 1.1 to 1.3 meters
above ground. Work below that range requires workers
to be on their hands and knees and above that requires
an elevated platform.
AUTOMATED PROCESS
The GRAWDE is a CNC controlled five-axis, precision
drilling machine designed to replace the manual drilling
process. The head consists of a single spindle with an
integrated pressure foot. The 22kw spindle spins at up
to 8000 RPM. It uses HSK 80 hydraulic holders
complete with through-bit starvation lubrication. The
spindle provides sufficient stability and power to
accomplish one shot drilling and countersinking of the
large diameter holes present in the A380 gear rib area.
The headstone or pressure foot on the GRAWDE is
fitted with a spherical nosepiece with integral normality
sensors. This permits the GRAWDE to be driven to a
precise location on the wing skin, sense and adjust to
the local normal vector by rotating the drill about the tool
point. The Z-axis drive (parallel the spindle axial feed
axis) is fitted with a force sensing load cell. Allows the
GRAWDE to clamp or press up against wing skin with as
much as 2000 lbs of force for added process stability
and rigidity.
DRILLING
The drilling process starts with CNC programs or tapes.
Airbus programmers develop programs, which define
nearly all aspects of the drilling process. The machine
runs under five-axis CNC control in each the wing
surface zones. The machine operator calibrates the
machine using test coupons, synchs the machine to the
proper zone using a camera target and runs the CNC
tape.
Coupon stands are located in the inboard area of the
assembly jig. Multiple coupons, representative of the
wings skin are used for setup. The coupon stands also
have a re-synch target used for establishing machine
position and calibrating for normality. The re-synch
target consists of a flat plate with a precision hole whose
position and orientation in the coordinate system are
known. Calibrating involves using the re-synch camera
to establish the machine position and then clamping up
to calibrate the normality sensors.
Holes are usually drilled in the coupon prior to drilling the
wing in order to prove the cutting tool and establish
plunge depth for the counter sink. Once the machine is
calibrated, the tape will drive the head to a position easy
for the operator to access the drill head and prompt the
operator to install the appropriate cutting tool. A Balluff
tool identification system is used to verify that the proper
cutter is loaded into the machine. The NC tape drives
the machine to the appropriate position and rotates the
U-axis to the theoretical normal vector. The machine
head then drives along the theoretical normal vector in
force sensing mode.
When the pressure foot engages the wings skin with the
programmed force, the program verifies the actual
normal vector, as measured with real time sensors, is
within a set tolerance of the theoretical vector. If not, the
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