Note: Descriptions are shown in the official language in which they were submitted.
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Determinant Spar Assembly
Technical Field
This invention relates to a method and apparatus for
assembling wing spars and ribs to close tolerances, and more
particularly, to a method and apparatus for assembling wing
spars and ribs with extreme and unprecedented precision to
produce wing components having extremely close conformance to
the original engineering design, with significantly reduce
t:ooling expense.
E3ackground of the Invention
Conventional manufacturing techniques for assembling
airplane wing spars and ribs to a specified contour rely on
fixtured "hardpoint" tooling techniques utilizing floor
assembly jigs and templates to locate and temporarily fasten
detailed structural parts together to locate the parts
correctly relative to one another. This traditional tooling
concept usually requires primary assembly tools for each
subassembly produced, and two large spar assembly tools (left
and right) in which the subassemblies are assembled into an
assembled spar.
The tooling is intended to accurately reflect the original
engineering design of the product, but using the conventional
tooling concept in which the tooling sets the configuration of
the final assembly, there are many steps between the original
design of the product and the final manufacture of the tool.
It is not unusual that the,tool as finally manufactured
produces missized spars or wing components that would be
outside of the dimensional tolerances of the original spar or
spar component design without extensive, time consuming and
costly hand work to correct the tooling-induced errors. More
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seriously, a tool that was originally built within tolerance
can become out of tolerance from the hard use it typically
receives in the factory. Moreover, dimensional variations
caused by temperature changes in the factory can produce a
5"variation in the final part dimensions as produced on the
tool, particularly when a large difference in the coefficient
of thermal expansion exists between the tooling and the spar,
as in the usual case where the tooling is made of steel and
the spar components are made of aluminum. Since dimensions in
airplane construction are often controlled to within 0.005",
temperature induced dimensional variations can be significant.
Hand drilling of the part on the tool can produce holes
that are not perfectly round or normal to the part surface
when the drill is presented to the part at an angle that is
_slightly nonperpendicular to the part, and also when the drill
is plunged into the part with a motion that is not perfectly
linear. Parts can shift out of their intended position when
they are fastened in non-round holes, and the nonuniform hole-
to-fastener interference in a non-round hole lacks the
strength and fatigue durability of round holes. The tolerance
buildup on the spar subassemblies can result in significant
growth from the original design dimensions, particularly when
the part is located on the tool at one end of the part,
forcing all of the part variation in one direction instead of
-centering it over the true intended position.
Spar components are typically fastened together with high
interference fasteners and/or fasteners in cold worked holes.
Interference fasteners, such as rivets and lock bolts, and cold
working of a fastener hole, both create a pattern of stress in
the metal around the hole that improves the fatigue life of the
assembled joint, but a long line of such stress patterns causes
dimensional growth of the assembly, primarily in the longitudinal
direction, and also can cause an elongated part to warp , or
"banana" along its length. Attempts to restrain the assembly to
prevent such distortion are generally fruitless, so the most
successful technique to date has been to attempt to predict the
extent of the distortion and account for it in the original
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design of the parts, with the intent that the assembly will
distort to a shape that is approximately what is called for in
the design. However, such predictions are only approximations
because of the naturally occurring variations in the install'ation
.5 of fasteners and the cold working of holes, so there is often a
degree of unpredictability in the configuration of the final
assembly. A process for washing out the effects of the
distortion in the subassemblies before they are fastened into the
final assembly has long been sought and would be of significant
value in spar manufacturing, as well as in the manufacture of
other parts of the airplane.
Wing major spar tooling is expensive to build and maintain
within tolerance, and requires a long lead time to design and
build. The enormous cost and long lead time to build wing spar
tooling is a profound deterrent to redesigning the wing of an exist
model airplane, even when new developments in aerodynamics are
made, because the new design would necessitate rebuilding the wing
spar tools. One existing system for automatic drilling, fastener
installation and tightening is shown in U.S. Patent No. 5,664,311
-by lBanks et al. entitled "Automated Spar Assembly Tool". It
produces spars accurately, but is a costly system to build and
maintain.
The capability of quickly designing and building spars for
custom wings for airline customers having particular
requirements not met by existing airplane models would give an
airframe manufacturer an enormous competitive advantage.
Currently, that capability does not exist because the cost of
the dedicated wing and wing spar tooling and the factory floor
space that such tooling would require make the cost of
"designer wings" prohibitively expensive. However, if the
samel tooling that is used to make the standard wing spar for a
particular model could be quickly and easily converted to
building spars for custom wings that meet the particular
requirements of a customer, and then converted back to the
standard model or another custom wing design, airplanes could
be offered to customers with wings optimized specifically to
meet their specific requirements. The only incremental cost
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of the new wing would be the engineering and possibly some
modest machining of headers and other low cost tooling that
would be unique to that wing design
The disadvantages of manufacturing processes using hard
tooling are inherent. Although these disadvantages can be
minimized by rigorous quality control techniques, they will
always be present to some extent in the manufacture of large
mechanical structures using hard tooling. A determinant
assembly process has been developed for airplane fuselage
manufacture, replacing hardpoint tooling with self-locating
detail parts that determine the configuration of the assembly by
their own dimensions and certain coordinating features
incorporated into the design of the parts. This new process,
shown in U.S. Patent No. 5,560,102 entitled "Panel and Fuselage
Assembly" by Micale and Strand, has proven to produce far more
accurate assemblies with much less rework. Application of the
determinant assembly process in airplane wing spar manufacture
should yield a better process that eliminates or minimizes the
use of hard tooling while increasing both the production
capacity of the factory and increasing the quality of the
product by reducing part variability while reducing the costs of
production and providing flexibility in making fast design
changes available to its customers. These improvements would be
a great boon to airframe manufacturers and their customers, and
improve the competitive position of the manufacturer in the
marketplace. The present invention is a significant step toward
such a process.
Summary of the Invention
Accordingly, it is an object of this invention to provide a
method of manufacturing long, large and heavy assemblies such as
airplane wing spars and ribs from flexible and semi-flexible parts
and subassemblies in accordance with an original engineering
design instead of the tooling.
Another object of the invention is to provide a method of
manufacturing airplane wing spars and ribs using intrinsic
features of the component parts to allow them to self locate
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and determine assembly dimensions and contours rather than
using conventional tooling to determine the placement of the
parts relative to one another and the contour of the assembly.
It is yet another object of this invention to provide a
5 system for manufacturing airplane wing spars that is
inherently more accurate than the prior art and produces
structures in which the parts are consistently located more
accurately on the structure with closer conformance to the
tolerance specified by the engineering design.
It is. yet a further object of the invention to provide a
system for manufacturing airplane wing spars that is faster,
more flexible, and less expensive than the prior art
traditional techniques and requires less factory space and is
less dependent upon the skill of workers to produce parts
within the engineering tolerances specified.
Still a further object of this invention is to provide a
method and apparatus which facilitates the manufacturing of
airplane wing spars with a precision and consistency that
enables airplane wings to be built within tolerance specified
in the original engineering design.
Another still further object of the invention is to provide a
method for building airplane wing spars having a sequence of
operations arranged to apply critical features to the detail
parts or subassemblies after the spar or spar component has been
distorted by operations, such as installation of interference
fasteners, that distort the spar or spar component.
These and other objects of the invention are attained in a
system for assembling wing spars and other long, large, and
heavy assemblies from flexible and semi-flexible parts using a
method that utilizes spatial relationships between key features
of detail parts as represented by coordination features such as
holes and machined surfaces drilled or machined into the parts
by accurate numerically controlled machine tools using digital
data from original engineering product definition, thereby
making the components and subassemblies themselves intrinsically
determinant of the dimensions and contour of the wing spar.
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Description of the Drawings
The invention and its many attendant objects and advantages
will become better understood upon reading the following detailed
description of the preferred embodiment in conjunction with the
following drawings, wherein:
Figs. 1-6 are sequential schematic diagrams showing the
major assembly steps performed on the spar web and other
components while they are supported on a line of stanchions,
shown in Fig. 8, during assembly of an airplane wing spar in
accordance with this invention;
Fig. 7A is a perspective view of a spar built in
accordance with the process and on the apparatus of this
invention;
Fig. 7B is an enlarged perspective view of the inboard end
of the spar shown in Fig. 7A;
Fig. 8 is a perspective schematic view of a wing spar
assembly cell in accordance with this invention;_
Fig. 9 is a plan view of the wing spar assembly cell shown
in Fig. 8;
Fig. 10 is a plan view of one side of the wing spar
assembly cell shown in Fig. 8, in the region of the bend;
Fig. 11 is a perspective view the portion of the spar
assembly cell assembly cell shown in Fig. 10;
Fig. 12 is a perspective view of one of the stanchions
shown in Fig. 11;
Fig. 13 is a perspective view of one of the stanchions
having a spar web support arm shown in Fig. 11;
Figs. 14 is a perspective view of a slightly modified spar
support stanchion showing the clamps of temporary chord
locators;
Fig. 15 is a view like Fig. 14, but showing the spar web
removed for purposes of illustration;
Fig. 16 is an enlarged view of a portion of Fig. 15;
Fig. 17 is a perspective view of the back right side of
the structure shown in Fig. 14;
Fig. 18 is,a,n enlarged perspective view of a portion of
Fig. 17;
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Fig 19 is an enlarged perspective view of the back left
side of the structure shown in Fig. 18;
Fig. 20 is a perspective view of chord locator tools
holding chords in place on the top and bottom edges of the
inboard portion the spar web;
Fig. 21 is a side elevation of a slightly modified form of
the chord locator tools shown in Fig. 20;
Fig. 22 is an enlarged side elevation of the top end of a
chord locator tool like the one shown in Fig. 21, but having
chord referencing surfaces set at a different angle,
corresponding to the angle of the chord at a different
position along its length;
Fig. 23 is a side elevation of the top end of a chord
locator tool having a chord locator reference surface on a
pivoted heel piece;
Fig. 24 is a side elevation of the structure shown in Fig.
22, with the clamp in its open position;
Fig. 25 is an enlarged side elevation of the bottom end of
a chord locator tool;
Fig. 26 is an enlarged perspective view of the bottom end
of the chord locator tool shown in Fig. 25;
Fig. 27 is a side elevation-of a tool for locating the
position,of the spar chords in the "X" direction;
Fig. 28 is a perspective view of the top end of the Chord-
X tool shown in Fig. 27;
Fig. 29 is a perspective view of a clamping, drilling and
fastener feed end effector shown in Fig. 8 to be carried by
the post mill and perform fastening operations; ,
Fig. 30 is a schematic view of a computer architecture and
process for converting data from a digital product definition
to instruction in a machine tool controller for perform
certain assembly operations;
Fig. 31 is a perspective view from the top of the pivoting
base plate shown in Figs. 8-11;
Fig. 32 is a perspective view from the bottom of the
pivoting base plate shown in Fig. 31;
a I I .
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a
Fig. 33 is a perspective view of the support arm shown in
Figs. 10, 11 and 13;
Fig. 34 is a perspective view of a positioning assembly at
the distal end of the support arm shown in Fig. 33; and
Figs. 35 and 36 are perspective views of the positioning
assembly shown in Fig. 34 in different stages of assembly.
Description of the Preferred Embodiment
Referring now to the drawings, like reference characters
designate identical or corresponding parts. The invention is
described as applied to a preferred embodiment, namely, a process
of assembling airplane wing spars. However, it is contemplated
that this invention has application to the assembly of parts into
major assemblies, generally, where adherence to a specified set
of dimensional tolerances and final product contours and
dimensions is desired. The invention has particular relevance
where some or all of the parts and subassemblies are flexible or
semi-flexible.
The embodiment of the invention described herein is the
preferred embodiment and the best mode contemplated by us
for practicing the inventive process. However, it should be
understood that the scope of this invention encompasses
these embodiments and other variations and modifications
thereof which will occur to those skilled in the art in view
of this disclosure.
The assembly process will first be briefly summarized as
applied in a wing spar assembly cell, with reference to a
sequence of schematic diagrams, Figs. 1-6, illustrating the major
process steps in the determinant wing spar assembly process
according to this invention. After this brief overview, the spar
assembly cell in which the process is performed will be described
and the process will be explained in further detail.
To provide context for the following description of the
process and apparatus of the invention, a representative airplane
wing spar will be described. Normally, an airplane wing includes
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two spars 30 extending lengthwise, or "spanwise", of the wing and
spaced apart in a"chordwise" direction. One spar, called the
"front" spar, lies adjacent the leading edge of the wing, and the
other spar, called the "rear" spar, lies adjacent the trailing
edge of the wing. Wing ribs extend chordwise between the spars
30 and are fastened to vertical rib posts 35, shown in Figs. 7A
and 7B, which are adhered and sealed to the spars 30 and fastened
thereto by numerous fasteners. Top and bottom chords 40 and 42
are adhered and sealed to top and bottom edges of a spar web 45,
and fastened thereto with numerous fasteners such as rivets,
bolts, lock bolts, Hi-Locks, and the like, which are widely used
in the aerospace industry, and are well understood and reliable.
These fasteners will be referred to herein as "bolts and/or
rivets" which is used herein to mean that the fasteners could be
all bolts, or all rivets, or a combination of bolts and rivets.
Naturally, the invention is not confined to the used of these
conventional fasteners and it should be understood that other
fasteners may be used as they are developed in place of these
conventional fasteners
The top and bottom chords 40 and 42 each have a vertical
flange that is secured to the spar web 45, and an angled top or
bottom flange to which a top or bottom wing panel is attached.
The vertical position of the chords 40 and 42 on the web 45 is
critical because it determines the spacing at the spars 30
between the top and bottom wing panels. Likewise, the position
of the rib posts 35 on the spar is critical because they
determine the position of the ribs which in turn determine the
contour of the wing panel. A bend or "kink" 46 at a "K" axis,
sho,Am in Figs. 7A and 7B, is found on most wing spars so that the
spars can conform to the designed position o-f the front and rear
outside edges of the wing box.
The space defined between the front and rear wing spars and
the top and bottom wing panels, that is, the outside structural
elements of the wing box, is normally used as the airplane fuel
tank, so the inside surfaces of the wing spars are commoniy
refered to as the "wet" sides and the outside surfaces are
refered to as the "dry" sides. That convention will be used
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herein. The rib posts 35 are attached to the wet side of the
spar and a multiplicity of vertical stiffeners 47 are adhered and
sealed to the dry side of the spar web 45 and fastened thereto by
a multiplicity of fasteners. A more complete description of the
5 construction of an airplane wing, and some additional components
attached to the wing spars, can be found in the aforesaid
Provisional Application 60/013,986 and in a corresponding PCT
Application filed concurrently herewith.
A spar assembly process in accordance with this invention for
10 assembling an airplane wing spar 30 begins with configuring a
reconfigurable assembly cell 50, shown in Figs. 8 and 9, for the
particular size and design of the wing spar to be assembled in the
cell 50. The assembly cell has a line of stanchions 52 mounted on
rails 54, as shown in Figs. 10 and 11, so the stanchions can be
moved in the "X" direction parallel to the plane of the spar 30 to
position them at the desired position lengthwise of the spar. Two
or more lateral positioning devices, such as the "pogo" devices 56
illustrated in Figs. 12 and 13, are mounted on each of the
stanchions 52 for establishing the lateral position of a spar web
45 in the "Z" direction in the cell 50. A support arm 60 is
atitached to selected ones of the stanchions 52 along the row of
stanchions, as shown in Figs. 10 and 11, to carry the weight of
the spar web 45. A primary index pin 64 in the end of one of the
support arms 60 is received in a coordination hole predrilled in
the spar web 45 to position the web accurately on the stanchions
in the "X" and "Y" directions, in an orientation that is
lorigitudinally horizontal and laterally upright, as shown in Fig.
14. Secondary index pins 66 on the other support. arms 60 are
engaged in coordination holes, also predrilled in the web 45, to
support the web vertically. The secondary index pins 66 are
horizontally compliant, as described in detail below, to
accommodate longitudinal growth in the spar web 45 caused by
fastener installation. Vacuum in vacuum cups 70 on the ends of
the pogos 56 draw the web 45 against front facing surfaces 72
within the vacuum cups 70 to hold the web in the lateral "Z"
position established by the extension of the pogos 56.
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A machine tool, such as a CNC post mill 75 shown in Figs. 8
and 9, is supported for longitudinal movement on rails 77 in the
cell 50. The post mill 75 has an elongated arm 80 that can be
driven in a self-parallel fashion on the body of the post mill 75
in the vertical or "Y" direction, and can also be extended
lengthwise. The body of the post mill 75 can be provided with
the capability to rotate about its vertical axis if, as described
herein, the cell has a line of stanchions on both sides of the
cell so the post mill can be performing operations on one side
while workers are installing parts, removing completed spars or
doing other manual operations'on the other side. Finally, the
arm 75 has a wrist that can rotate about the axis of the arm 75
and can tilt sideways. A gripping device at the distal end of
the wrist has mechanical and power connections for holding and
powering one or more end effectors 85 for performing the various
functions needed in the assembly cell 50. These axes of motion
permit the post mill 75 to position the end effector in any
desired position and orientation within the reach of the arm 80.
The post mill 75 shown is supplied by Ingersol Milling
Machine Company, but other machine tools, such as a Henri Line
gantry mounted 5-axis tool, or an "Aeroflex"six-axis
positioner made by Pegard Products, Inc. in Machesney Park,
I1l. could be used. The required capabilities are precision
and repeatability in spindle positioning, which in this
application is about t0.005", and operation under control of a
machine controller that can be programmed to incorporate
digital product definition data originating from an engineering
authority for the wing and wing components, so that
coordination features specified by the digital product
definition can be placed accurately and repeatably by the
machine tool 75. These two capabilities enable the machine
tool 75 to apply coordination features, such as coordination
holes and machined coordination surfaces, to parts, components
and assemblies at precisely accurate positions specified in the
digital product definition. These coordination features are
used to position parts and components relative to each other
where they are pinned and fastened, thereby eliminating or
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drastically reducing the need for fixed hard tooling that
previously was used to located the parts and components
relative to each other. The coordination features thus
determine the relative position of the parts and components
that comprise the assembly, and thereby determine the size and
shape of the assembly, independently of most tooling.
After the cell is configured for the spar design to be built
that day, the upper and lower spar chords 40 and 42 are loaded,
as illustrated in Fig. 1, onto temporary chord locators 90
hanging on the pogos 56 for holding the spar chords adjacent to
the spar web position in preparation for transfer to the spar web
45. It should be noted that, for convenience, the spar 30 is
built in the inverted position because the lower edge of the spar
diverges where the spar becomes wider at the inboard end, so
building the spar in the inverted position reduces the reach of
the scaffolding that may be needed by workers to reach the upper
parts of the spar. Therefore, the drawings show the "upper"
chord 40 in the bottom position and the "lower" chord 42 in the
top position. The chords 40 and 42 are held in position on the
temporary chord locators 90 with over-center clamps 92 on the top
and bottom ends of the chord locators 90. Sealant is applied to
the vertical flange faying surface of the spar chords 40 and 42
where they will contact the spar web 45. The spar web 45 is
loaded onto the index pins 64 and 66 on the arms 60 and is drawn
against the facing surfaces 72 of the pogos 56 by vacuum in the
vacuum cups 70.
The position of the chords 40 and 42 in the "Y" direction
along the upper and lower edges of the spar web 45 is set by a
series of chord-Y tools 95, each of which is positioned on the
spar web 45 by way of a pair of indexing pins 100 and 102 in
chord tool coordination holes drilled with extreme positional
accuracy in the spar web 45 with a drill controlled by the CNC
post mill 75. As illustrated in Figs. 2 and 20-25, clamps 105
and 107 are attached to the top and bottom ends of each chord
tool 95. The clamps on the chord-X tools 95 shown in Fig. 20 are
slightly different from those shown in Figs. 21-25 to show that
different types of clamps can be used. The upper clamp 105 has
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reference surfaces 110 and 112, shown in Fig. 22, for precisely
locating the lower chord 42 at the correct vertical position on
the web 45. Likewise, the lower clamp 107 has reference surfaces
114 and 116 for precisely locating the upper chord 40 at the
correct vertical position on the web 45. The reference surfaces
112 and 114 may be on heel blocks 113 and 115 that are pivotally
connected to the chord-Y tools to conform to the angle of the top
and bottom flanges of the spar chords, as shown in Figs. 23 and
25.
The chords 40 and 42 are transferred from the temporary chord
locators 90 onto the chord-Y tools 95 and into position against
the chord tool reference surfaces and against the spar web 45 by
opening the chord tool clamps, as shown in Fig. 23, and sliding
the temporary chord locators 90 on the pogos 56 until the chords
contact the web 45. The clamps 92 on the temporary chord
l.ocators 90 are released and the chords 40 and 42 are positioned
accurately in the "X" direction by registry of index pins 118 and
120 in a chord-X tool 121, shown in Fig. 28, with coordination
holes predrilled in the chords 40 and 42. The chord-X tool 121
was previously attached to the web 45 by index pins 122 and 124
extending into coordination holes accurately drilled into the web
by the post miil 75 at the same time that the coordination holes
for the chord-Y tools 95 are drilled.
The chords 40 and 42, now indexed accurately in the "X"
direction with the chord-X tool 121, are pushed into position
against the reference surfaces 110-116 of the chord-Y tool 95 to
position the chords 40 and 42 against the top and bottom edges of
the web 45 accurately in the "Y" direction. The chords 40 and 42
are secured in place against the reference surfaces 110-116 by
the chord-Y tool clamps 105 and 107.
A probing routine is now performed to accommodate the
deflection of the stanchions 52 and support arms 60 under the
weight of the spar web 45 and chords 40 and 42. A probe held by
tYLe post mill arm 80 probes the primary index pin 64 and one or
more secondary index pins 66 to locate their actual position. A
suitable probe for this purpose would be a Renishaw contact
tactile probe Model No. MP6 made by the Renishaw Company in
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Onendagua, New York, although other probes available from other
sources could also be used. The machine controller for the post
mill 75 uses the actual positions of the index pins as located by
the probe to normalize the part program in the controller to make
it conform to the actual position of the parts on the stanchions
52.
The chords are now fastened to the web 45 with the end
effector 85, shown conceptually in Figs. 1, 3-7 and 29. The end
effector 85 is carried and positioned at the locations along the
web 45 by the post mill arm 80, as shown in Fig. 8. A clamp 130
on the end effector 85 has a C-frame 132 with an anvil 134 on its
distal end that engages the vertical flange of the chords 40 and
42 on the "wet" side of the spar. A pressure_foot 136 is aligned
opposite the anvil on the other side of the C-frame 132 where it
engages the spar web on the opposite side of the web from the
anvil and is actuated with a pneumatic cylinder to exert a clamp-
up force on the order of 1000-1500 pounds to clamp the chords to
the web during drilling and fastener insertion. A frequency
controlled spindle motor mounted within the end effector 85
liehind the pressure foot 136 rotates and feeds a drill bit to
drill holes through an opening in the pressure foot 136 while
chips are vacuumed away through a vacuum hose 142. The drill
spindle retracts and a hole probe 144 mounted behind the anvil
134 probes the hole drilled through the web and chord flange
through an opening in the anvil 134_ If the hole quality meets
predetermined standards, a shuttle moves behind the pressure foot
to align a fastener feed holder with the newly drilled hole, and
an interference fit fastener is fed through a line 148 to the
holder. A.pneumatic hammer drives the fastener into the hole.
The pressure foot now unclamps and moves to the next fastener
location. Securing the fasteners with swage collars or nuts is
performed by workers on the outside of the cell 50 where there is
no danger of injury from the post mill 75 inside the cell 50.
The workers also remove the chord-Y tools 95 as the post mill 75
approaches their position on the spar 30.
After all the fasteners for the upper and lower spar chords
and 42 have been installed, the length distortion of the spar
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due to the radial and longitudinal compressive loading exerted by
the interference fasteners is substantially complete. There will
be additional fasteners installed when the rib posts and
stiffeners are fastened to the spar, but the length distortion,
5 if any, produced by those operations can be accomnrodated after
they are completed.
After both chords 40 and 42 have been attached, the post
mill uses the same end effector 85 or a separate drill-only end
effector to drill coordination holes for stiffeners and rib
10 posts. As described below, a master digital model 150 of the
spar in the engineering authority for the airplane manufacturer
specifies the location of the coordination holes for the rib
posts and the stiffeners, and the part program which controls
the movement of the post mill 75 is derived from that master
15 digital model 150.
Two different processes are used for attachment of the
stiffeners and rib posts, depending on where they are to
attached. As shown in Figs. 7A and 7B, the height of the spar 30
at the inboard end is considerably greater than it is for most of
its length. As shown in Figs. 5 and 6, the depth of the throat
of the clamp C-frame may be insufficient to reach the
longitudinal centerline of the spar 30. The weight of the end
effector 85 is affected by the depth of the C-clamp throat. A
deeper throat requires a heavier C-clamp. All post mills have a
weight limitation on the amount of weight they can carry on the
end of the arm 80. If an end effector 85 with a C-clamp throat
deep enough to enable the line of action of the end effector to
reach to the centerline of the spar at the inboard end would
exceed that weight limitation, then the inboard rib posts 35 and
stiffeners 47 could be attached by a semi-automated process,
described below.
The stiffeners 47 and rib posts 35 have coordination holes
predrilled when they are manufactured, or the coordination holes
are drilled in a separate dedicated fixture. The coordination
hole:s correspond to the locations of the coordination holes
drilled in the web 45 by the end effector 85. When the
coordination holes in the rib post 35 or stiffener 47 are aligned
.
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with the corresponding coordination holes drilled in the web 45,
the part is positioned with extreme accuracy on the web 45 in
accordance with the engineering design as represented by the
digital model.
For parts in the portion of the web that are within the reach
of the C-clamp throat, the flange of the rip post or stiffener
has sealant applied to its faying surface with the web 45 and is
temporarily fastened to the web with clecos or some other
removable temporary fastener. With the part thus temporarily
fixed accurately in position, the end effector 85 is positioned
by the post mill arm 80 to clamp the part flange to the web,
drill a fastener hole and insert a fastener as described above
for the chords 40 and 42. The clamp-up force is sufficient to
squeeze out excessive sealant so the drill chips do not have
-sealant on them which could foul the chip vacuum system, and
prevents interlaminar burrs from intruding between the part 35 or
47 and the web 45.
The semi-automated process mentioned above uses the same
coordination hole drilling process for establishing the location
of the rib posts 35 and stiffeners 47 described above. However,
since the C-frame throat of the end effector clamp 132 is not
deep enough to enable the centerline of the end effector to reach
the inner fastener locations, the holes must be drilled without
clamp-up, so interlaminer burrs are likely to occur. Therefore,
the parts are temporarily fastened to the web 45 with clecos or
the like and the fastener holes are drilled with the end effector
85 or another drilling-only end effector. The clecos are then
removed and the parts and web are deburred. Sealant is applied
to the faying surfaces and the parts are again temporarily
fastened to the web 45 with clecos or the like. Interference
fasteners are inserted with pneumatic drivers and the fasteners
are secured with swage collars or nuts in the same manner as
described above. With the lengthwise growth of the spar because
of insertion of interference fasteners substantially completed,
the position of certain critical features may now be probed and
the part program updated with the actual dimensions of the
assembled spar. Using the updated part program, coordination
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lioles are drilled with extreme precision, entirely unaffected by
the growth during assembly, for two fittings for connection of a
inain landing gear beam and certain other fittings such as flap
support fittings and aileron hinge line brackets. The spar is
tiow complete and is removed from the cell by crane and
transferred to the wing line for installation in a wing.
The digital product definition or digital model 150 is the
ultimate engineering authority for the product, in this case, a
particular model airplane. It exists on a master computer 152 in
a computer-aided design program as the digital model 150 which
includes all the dimensions, tolerances, materials and processes
that completely define the product. The dimensional data from
the model 150 is provided in a file to an NC programmer or an
automatic translator where it is used to create a dataset 154 and
machine instructions, such as cutter type and size, feed speeds,
and other information used by a controller of the post mill 75 to
control the operation of the arm 80. The dataset and machine
instructions are launched in a post processor 156 where they are
converted to a machine readable file 158 that is transmitted to a
data management system 160 where it is stored for use by the
controllers 162 of the post mill 75. On demand, the file 72 is
transmitted over phone lines 164 or other known means of
communication to the machine tool controller 162 for use by the
controller in operating the post mill 75.
Referring back to Figs. 7A, 9 and 10, the bend or kink 46 in
the spar is at an angle that is unique to each model airplane.
To enable wing spars of several different model airplanes to be
made on the assembly cell 50, the stanchions 52 on the inboard
side of the bend 46 are mounted on a plate 170 that is pivotally
mounted for rotation about a vertical axis 172 that is set to
coincide with the "K" axis of the bend 46. The upper surface of
the plate 170 has a pair of parallel grooves 174 to receive the
tracks 54 on which about six stanchions 52 are slidably mounted.
A spherical socket 176 on the end of a wing 178 projecting from
the front inner corner of the plate 170 has a receives a '
spherical bearing ball which enable the plate to swivel about the
axis 172 when lifted by air bearings on the underside of the
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plate 170. A tab 180 projecting from the rear distal end of the
plate 170 has a precision index hole 182 for receiving an index
pin by which the plate can be indexed to a precision hole in a
plate fixed in the floor. Configuring the cell 50 for assembling
a spar of a particular model airplane is a simple matter of
mobilizing the plate 170 with its air bearings and moving it to
the position specified at which the index hole 182 in the tab 180
aligns with the index hole in the floor plate, and turning off
the air bearing to allow the plate 170 to settle into hard
contact with the floor. The plate 170 is an aluminum casting
about 27 feet long and 6 feet wide. It weighs on the order of
5000 pounds, even with an X-brace construction on its underside,
shciwn in Fig. 32, so its weight and the attachments at the tab
182 and the wing 178 anchor it securely to the floor.
Initial Cell Set-Up
When the cell 50 is first built and ready for operation, a
series of index holes 185, one for each model airplane spar to be
built on that cell 50, is drilled for each stanchion, as shown in
Figs. 12-15. The position of the stanchions 52 along the rails
is then easily set by inserting an index pin 187 in a tab 190 of
the front of each stanchion 52 in the proper index hole 185,
which are suitably labeled to facilitate quick and sure
identification by the workers for that purpose.
The vertical position of the pogos 56 are set by adjusting
servomotors 192 which drive ball screws threaded into a slide
mounted on vertical guides in the stanchions 52. The post mill
75 probes the pogos to confirm that the correct vertical position
has been attained and issues a correction to the servomotors if
the vertical position is incorrect.
The pogos 56 are all fully extended by pressurizing air
cylinders 194 in which the pogo rods 196 are mounted. The
cylinders are vented and the post mill. 75 extends its arm 80 into
contact with the facing surface 72 of the pogo to push each one
back to the desired position, whereupon a pneumatic lock 200 is
actuated to lock the pogos 56 in the desired position.
The support arms 60 are indexed to the stanchions 52 by index
pins 202 and secured by fasteners 204. As shown in Figs. 33-36,
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an end plate 206 on the end of each support arm 60 carries a
positioning assembly 210 for the index pins 64 and 66. The first
step in setting the position of the index pins 64 and 66 is to
"face off" or mill the face of the end plates 206 so they lie on
a vertical plane and at the correct lateral position in the cell
50. A vertical dovetail groove plate 212 is positioned on the
end plate 206 by index pins in coordination holes predrilled in
the vertical dovetail rabbet plate 212 and aligned with
corresponding coordination holes drilled in the end plate 206 by
the post mill 75. As best shown in Fig. 36, a dovetail tenon
plate 215 having a vertical dovetail tenon on its back surface
and a horizontal dovetail tenon on its front surface is mounted
for vertical adjustment on the vertical dovetail rabbet plate
212, with the vertical tenon on the plate 215 in the rabbet of
the plate 212, and is locked in place by a top plate 216 when it
is at the correct height in the "Y" direction, as verified by the
probe on the post mill arm 80. A horizontal dovetail rabbet
plate 218 is mounted on the horizontal tenon of the dovetail
tenon plate 215 for horizontal adjustment parallel to the "X"
axis. A pin 220 attached to and protruding forwardly from the
dovetail tenon plate 215 is received in a lock block 222 to which
a mounting plate 224 for the index pins 64 and 66 are attached.
The lock block 222 has a vertical hole opening in its lower edge
for receiving a ball lock pin 226 which passes up through a
corresponding vertical hole in a base plate 230, in turn attached
to the lower edge of the dovetail tenon plate 215. The lock
block 222 can be locked in position against horizontal movement
while it s position is being probed for position by the tactile
probe held by the post mill arm 80 during the probing routine,
and then can be freed for horizontal movement in the "X"
direction during longitudinal growth of the spar 30 by virtue of
therr.nal expansion and installation of interference fasteners.
The ball lock pin 226 on the positioning assembly 210 on which
the primary index pin 64 is mounted will be retained in its
locked position to establish the reference "X" position from
which "X" axis growth occurs.
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A system is thus disclosed which is usable for assembling
airplane wing ribs and spars to a high degree of precision. The
determinant assembly concept embodied in this disclosure utilizes
the spatial relationships between key features of detail parts
5 and subassemblies, as defined in the digital design and
represented by coordination holes and other coordination features
put into the parts and subassemblies by a numerically controlled
tool, using original part design data from the engineering
authority, to control the relative location of detail parts in
10 __subassemblies and the relative relationship of subassemblies to
each other, making the parts and subassemblies self locating.
This concept eliminates the need for traditional hard tooling
used for decades in the air frame industry and for the first time
enables assembly of large, heavy, flexible and semi-flexible
15 mechanical structures wherein the contour ofthe structure and
the relative dimensions within the structure are determined by
the parts themselves rather than the tooling.
Freed in this way from dependence on fixed tooling, the
wing spar can now be built to accommodate distortion created by
20 manufacturing processes, such as interference fasteners and
cold working, so that attachment of critical features on the
wing at precisely accurate positions specified by the
enclineering design can be scheduled in the manufacturing
process after distortion by the upstream processes which would
_have affected their position or orientation on the wing. The
factory can now manufacture wing spars of any shape and size
for which engineering data is provided, within the physical
rarige of the CNC machine tools, and do so faster and with far
greater precision than was possible with fixed tooling. The
cost of building and maintaining the conventional wing spar
tooling, and the factory floor space for such fixed tooling, no
longer need be amortized and factored into the price of the
airplane, and it is now possible to build spars for wings
customized to meet the particular requirements of particular
customers.
Obviously, numerous modifications and variations of the
system disclosed herein will occur to those skilled in the art
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in view of this disclosure. Therefore, it is expressly to be
understood that these modifications and variations, and the
equivalents thereof, will be considered to be within the
spirit and scope of the invention as defined in the following
claims, wherein we claim:
