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machine will unclamp, rotate about the tool point, reclamp,
recheck for normality before drilling the hole.
DRILLING FACETED SURFACES
The above example illustrates drilling holes on nonfaceted
surfaces on the wing, i.e. where the fastener’s
axis is normal to the wing surface. The GRAWDE also
has the capability to drill holes on faceted surfaces. For
these areas, the fastener is inserted normal to the wing
skin, but not normal to the exterior surface of the
reinforcing plate.
The rotating clamp nose on the GRAWDE makes it
possible to drill off normal on faceted surfaces with full
clamp load. As mentioned above, the clamp nose is
mounted on a spherical bearing. Because the clamp
nose pivots in a spherical bearing as it contacts the wing
skin, it will rotate normal to the exterior surface while the
drill axis is coincident with the wing skin normal vector.
The integrated normality sensors can be used to verify
that the theoretical facet angle agrees with the actual
facet angle.
INK MARKING
To aid in debugging programs and ensure proper hole
position, the GRAWDE has the functionality to ink mark
the part. This functionality is typically used for part
program try out. This allows the operator replace the
cutting tool with a marking pen and run the drilling
program while inhibiting drill feed. This paints dots on
the wing panel, which can be visually verified for position
prior to actual drilling.
JIG INTEGRATION
One of the greatest challenges of this project was the
integration of a precision CNC controlled drilling
machine into a wing assembly jig, while maintaining
access for manual assembly operations. To meet this
challenge, the GRAWDE was designed concurrently
with the assembly jig. Each jig is a 4 story steel
structure and is about 50 meters long. Manual worker
access is required from both sides of the wing in all
areas for fitting and fastening processes.
JIG CONSIDERATIONS
The jig was designed to provide a stiff structure for
supporting precision CNC machines, while maintaining
maximum manual access. Continuous floors are
required on each of four levels to extend to the surface
of the wing. The floors are moveable for part loading
and to provide machine access. The automatic drilling
machines need services such as air, power,
communications, and position feedback, all of which had
to be well integrated into the jig structure.
GRAWDE CONSIDERATIONS
Floor heights dictated by manual access requirements
determined the size of the GRAWDE working envelope.
To be a cost effective investment it is crucial that the
machine be portable and be able to move between
multiple wing surface zones. The tight working envelope
represents a challenge to provide a safe working
environment due to potential obstacles and tight
clearances between the machine parts and the jig,
creating shear points.
ACCESS
When operating the GRAWDE, the operators stand on a
moving platform 250 mm below factory floor and 500
mm above the machine beds. From the platform,
operators can reach the wing surface, operator controls
and quill box for changing tools. The platform has
handrails and a gate on two sides, to protect the
operator from falling and to protect from shear points
between the GRAWDE and assembly jig components.
Manual access can also gained by driving the GRAWDE
away from the immediate area and standing directly on
the machine bed. A drawing of the machine and
operator platform is shown below in Figure 3.
Figure 3 - Isometric view of GRAWDE and operator
platform
Integrated into the jig on the ground level are
hydraulically actuated bi-fold floors. When in the open
position, the floors allow access for the GRAWDE.
Because visual access is quite limited in the jig when the
floors are open, the doors are of a bi-fold design, which
provides a line of sight from the GRAWDE to the rest of
the ground floor stage 1 jig. When closed the floors
provide a working surface at factory floor height, which
provides optimal worker access to the rear spar area. A
pre-production image of the GRAWDE in the transfer
area with the bi-fold floors open is shown in Figure 4.
Figure 4 - GRAWDE bed and bi-fold floors
POSITIONING
Drilling, while a major portion of the assembly process,
is only part of building a wing. There is a significant
amount of part loading, fitting and fastening, which must
also take place. To maximize the usage of this asset,
the machine had to be able to be transferred between
jigs and work surfaces. One of the major challenges
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