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Патент USA US3093380

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June 11, 1963
Filed Nov. 20, 1957
2 Sheets-Sheet 1
Ma}, NJ“
June 11, 1963
Filed Nov. 20,’ 1957
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Patented June 11, 1963
edge portion on the cell walls. The method of effecting
a curve by making many cuts, each with a small displace
ment and/or angle differential, as related to the preced
ing cut, will not yield a smooth even curve unless much
Richard K. May, William O. Sunafrank, and Howard H. 5 time is sacri?ced to make a near in?nite number of over
Powell, Fort Worth, Tex., assignors to General By
lapping cuts. A smooth, uniform, burr-free surface rare
namics Corporation, San Diego, Calif, a corporation
ly results from these operations and deformation and
of Delaware
chipping of the ‘?ller material is Icommonplace.
Filed Nov. 20, 1957, Ser. No. 697,645
These defects ‘and disadvantages have been overcome
1 Claim. (Cl. 269—3€l9)
10 by the method and apparatus of the present invention
wherein the contour pro?les are made with planar cuts
This invention relates generally to improvements in
and wherein the milling ?xture provides for thermal
contour pro?ling land more particularly to a novel method
changes without bucklingwor warping. The milling ?x
and apparatus for machining icontour pro?les of cellular
ture is mounted to the support ?xture with a plurality
material with plane cuts with provision for holding the
workpiece during thermal expansion and contraction of 15 of longitudinally movable mountings, transversally mov
able mountings, and other mountings which will “?oat”
its support.
or move in either planar direction. The milling ?xture
The evolution of aircraft and missiles to their present
has its upper surface contoured such that the cellular
state where they are required to operate at very high
material is held in non-planar position. A plane cut in
speeds, great altitudes and over long ranges has neces
sitated many changes in manufacturing techniques and 20 the cellular material is then made. when released from
the milling ?xture, the spring-like elasticity of the ma
equipment. To achieve an aircraft or missile which will
terial returns it from deformation to its original position
satisfy the stringent operational demands made of it, the
and the plane cut surface then becomes the shape of the
structural components of such vehicles, particularly those
desired contour. The material may then be reversed and
components that are exposed to ‘aerodynamic flow, must
be capable of withstanding the very high temperatures
generated by air friction; have inherent insulating char
25 mounted on a second contoured milling ?xture so that a
second planar cut will contour the other side in a similar
acteristics and possess an optimum strength to weight
plates, is generally accepted by those skilled in the art
It is therefore ‘a primary object of the present inven
tion to provide for animproved method and apparatus
for machining contour pro?les in cellular core material.
Another object is the provision of apparatus for holding
a workpiece in deformed position while making plane
of aircraft structural design as being most conclusive to
The use of a structural composite type of mem
ber, usually designated as of cellular cored sandwich con
struction, and comprising a honeycomb-like cellular core
element, having two facings vof sheet material or face
the achievement of such design criteria. .The cellular
core element of said structural ‘composite is normally
manufactured in block or rectangular form and must sub
sequently be machine-pro?led to conform to the shape
Another object is the provision of a milling ?xture for
holding a workpiece wherein the ?xture is mounted for
expansion and contraction without buckling or warping.
Another object is the provision of a milling ?xture with
dimensions subject to thermal changes for immobilizing
a workpiece during a milling operation.
Another object is the provision of \a milling ?xture
for holding a workpiece during milling operations where
in the milling ?xture is positioned with longitudinal, trans
verse and freely movable planar mountings.
Another object is the provision of a milling ‘?xture with
of the aircraft component to which it is to be adapted.
Inasmuch as the structural integrity of such sandwich
panel structural components is dependent to a large de
g-ree upon the quality of the joint between the edges of
the cellular core and the inner surfaces of the facing
plates, it follows that the pro?le as de?ned by the ma
chined cellular core must conform precisely with the
design con?guration of the airframe or missile compo 45 an upper contoured surface for maintaining a ?exible
cellular core material in deformed condition.
nents of which it is to be an element, and therefore must
Another object is the provision of a milling ?xture
be dimensionally consistent to a very high degree. Con
having an upper contoured surface of such shape that a
sequently, said cellular core must be shaped by machin
plane cut through a flexible material de?ected thereagainst
ing to very close tolerances and be substantially free of
will provide a desired contour on one side of the material
burrs, deformations and other defects. It has heretofore
when it is restored to normal position.
been the common practice, in shaping curvate surfaces
Another object is the provision of a method of con
on cellular core material, to support the walls of each
tour pro?ling wherein the desired contour is made by
individual cell of the core material by ?lling the cellular
apertures thereof with solidi?able material and solidifying
the same, then machining the resulting high density mass
de?ecting the plane of the material, making a planar
cut and restoring the material back to its normal posi
with conventional contour mill cutters such as the stylus
and pattern type or the multiple pass type known to the
trade as “Keller” or “Hydratel” machines.
Another object of this invention is to provide a novel
machining process that will effect a smooth, burr-free,
Many disadvantages are inherent in such processes, 60 evenly curved close tolerance contoured surface on ?ex
ible, low density material using conventional, existing
however, and deleterious effects often resulted therefrom.
For example, solidifying of the material was usually done
by freezing which also effected a temperature change in
evices for machining straight plane surfaces.
Other objects and features of the present invention
will be readily apparent to those skilled in the art from
the milling ?xture holding the core material. This pro
duced a dimensional change in the ?xture which would 65 the following speci?cation and appended drawings where
in is illustrated a preferred form of the invention, and
cause it to warp or buckle since it was rigidly secured
in which:
.to a support ?xture for immobilizing the core material
FIGURE 1 is a view of the preferred exemplary form
during the milling operation. Consequently the resultant
of apparatus that is adapted to’carry out one step of
contour of the core material when the milling operation
was ?nished was not within the exacting tolerances re
the process embodying the invention.
quired. Moreover, the large machines employed are
expensive, slow, and leave a rough, dented and deformed
FIGURE 2 is a perspective view of the work arrange
ment for the ?rst step of the preferred process for
machining a double convex rudder core from a block
or log of ?at aluminum honeycomb.
FIGURE 2a is a sectional view of the pro?led alumi~
num core after step one of the machining process is
completed and the core has been released from the mill
?xture shown in FIGURE 2.
FIGURE 3 is a view of the core, shown in FIGURE
standable with reference to other ?gures hereafter more
fully described.
An exemplary application of the method of the present
invention is its employment for the fabrication of a
double convex rudder core from a block of aluminum
honeycomb material. The initial step is illustrated in
FIGURE 2. Here a sheet of cellular material 15 having
2a, as it appears when inverted and ready for installa
parallel surfaces is ?exed downwardly against the curved
tion in the second mill ?xture.
upper surface of the concave mill ?xture. This may be
FIGURE 3a is a view of the work arrangement for 10 done, as explained in copending application, Serial No.
the second step of the preferred machining process, as
633,214, by ?rst holding down the material by use of
employed for shaping a double convex rudder core.
FIGURE 3b is a sectional view of the pro?led core
of FIGURE 3 after the second step is completed and it
has been released from the second mill ?xture.
FIGURE 4 is a diagram illustrating the preferred form
of milling ?xture or platen (used to control the heat
cycle of the mill ?xture), showing the points at which
a vacuum while the presence of small water droplets will
cause adherence of the core material to the milling ?x
ture when the droplets are reduced in temperature to
below freezing.
It is noted that in this ?rst step the
chord line 17 of the material is parallel with the contour
surface of the milling ?xture. A chord line is hereby
de?ned as the line of a straight edge brought into contact
it is a?ixed to the base of the milling machine.
with the lower surface of an airfoil section at two points.
FIGURE 4a shows the preferred fastening means, a 20 In the case of an airfoil having a double convex camber
T-shaped member, used to fasten the platen to the base
it is the straight line joining the leading and trailing
of the machine.
edges. While the chord line initially is in a plane normal
FIGURE 4b is a partial cross-sectional view of FIG
to the walls 16 of the material 15, as shown, it may be
URE 4 as taken at points 4b—-4b.
desirable to construct a panel in which the walls of the
FIGURE 40 is a partial cross-sectional view of FIG 25 cellular material are directed toward some greater exter
URE 4 at points 40-40.
nal force wherein it is desirable that greater rigidity be
FIGURE 4a’ is a partial cross-sectional view of FIG
effected in this particular direction. After the material
URE 4 at points ltd-4d.
has been de?ected to ?t the contour of the milling ?xture
and secured thereto, the milling operation may be made
An enlarged view of the preferred arrangement of
apparatus used in practicing the present invention is 30 in any suitable manner such as by straight or circular
cuts in a plane surface. After the core material has been
shown in FIGURE 1. Here a rotary mill cutter 10 is
released from the milling ?xture it ‘will characteristically
representative of any milling, cutting, grinding or other
spring back to its normal position as long as the contour
machine suitable to remove areas of metal as desired.
that has been machined did not exceed the elastic limits
This preferred cutting tool is the subject matter in co
pending application Serial No. 639,045, ?led February
of the core material. As shown in FIGURE 2a the core
material has been returned to its normal position with
no bending force acting upon it and the chord line 17
is substantially a straight line. FIGURE 3 shows the
used if desired. Here a concave milling ?xture 11 is
cellular material of FIGURE 2a in inverted position
mounted on a platen which consists of two pieces of
light metal 12, 13 bonded together in use. This platen 40 ready for contouring the other surface. The material is
then placed in a second milling ?xture 11a against its
in turn is supported on a base or support ?xture 14 in
8, 1957, for “Milling Cutter,” and now abandoned. How
ever, it is understood that other types of devices may be
a manner to be more fully described with reference to
other ?gures. A sheet of cellular honeycomb core mate
rial 15 is deformed and held in position with its lower
surface engaging the concave upper surface of the mill
?xture 11. This of course deforms the upper surface
of the material but the mill cutter 10 is used to make
contoured upper face in a manner previously described.
It is noted that in pro?ling convex surfaces a concave
surface of the milling ?xture is provided. In the second
milling ?xture 11a, as shown in 3a, allowance must be
made for the previous curvature since the under surface
of this material no longer was a planar surface but in
stead has been milled previously to its desired contour.
a planar cut on the upper surface in the manner shown.
Therefore, the second contour surface must combine
The cellular honeycomb core material 15 is of low
density and is ?exible to permit its deformation to ?t the 50 and total the desired curvatures of both sides of the
double convex part. As previously described the top
contour of the mill ?xture 11. As shown the normally
surface is then planed or milled to a ?at surface in some
parallel walls 16 of the core material when the material
convenient manner. When the milling operation has
is deformed are no longer in parallel relationship. Other
been completed the cellular material is then released
types of cellular core material may be used which is
from the second ?xture. The resiliency of the material
capable of de?ection within its elasticity characteristics.
restores it to its normal position such that the chord 16
The cells may be ?lled with a solidi?able material, such
is again straight and the double convex part is complete
as water frozen to ice, if desired, although with the cutter
as shown in FIGURE 3b. The next step would be to
shown this is not necessary. The preferred method of
apply the outer skin panels in the manner well known
maintaining the cellular material in its de?ected position
in the art such as by bonding, brazing, welding, etc.
on the surface of the mill ?xture 11 is by the use of
freezing liquids as taught in copending application, Serial
Double-convex core elements with mild contours may
No. 633,214, now U.S. Patent No. 2,937,437, ?led Janu
be effectively milled by eliminating step one of the above
ary 9, 1957, for Method and Apparatus for Holding a
Workpiece, although, of course, other suitable hold-down
process. A single operation evolving the double con
tour in a single ?xture is here employed. The limit of
techniques are known and may be used. The freezing 65 degree for this type contour is usually determined by
the relative ?exibility of the core, and the core must be
with a solidi?able material while superior in some re
acted upon by some outside force, such as the edge clo—
spects to other techniques, presents the problem of main
sure members of a sandwich panel construction, to cause
taining the mill ?xture 11 and hold-down platen 12, 13
it to retain its desired double-convex contour.
securely connected to the base or support ?xture 14 in
Due to contraction of metal during the freezing proc
a non-buckling and non-warping condition. This con
ess, such as in ?lling the cores or as a means of securing
dition results from the manner in which the platen is
the core to the ?xture, the milling ?xture, when bolted
secured when provision has not been made for expansion
in the conventional manner to a support ?xture, will
and contraction due to thermal changes. This problem
contract unevenly resulting in buckling or warping. This
has been overcome in the manner more clearly under
may cause variations in the ?nished honeycomb parts
liquid hold-down technique and for the ?lling of holes
beyond the tolerable limits of the ?nish requirements.
Therefore the preferred means for attaching the mill ?x
ture to a base ?xture to avoid these undesirable effects
is shown in FIGURES 1, 4, 4a, 4b, 4c, and 4d.
Referring back to FIGURE 1 there is shown an over
all view of the preferred means of attachment of mill
This permits the platen to expand and contract in both
transverse and longitudinal directions. This arrangement
is adaptable to any size base and platen. Such fastening
system renders every point on the platen free to move in
its plane except mid point 29 with center lines 25 and 27
movable only in an axial direction.
The invention thus described exempli?es a novel ma
?xture 11 to its base or support ?xture 14 through a
chining method and apparatus for effecting contoured
temperature controlling platen 12. As previously men
surfaces on ?exible material, adapted particularly for
tioned this platen d2, 13 consists of two pieces of like
use in connection with aircraft, whereby the desired con
metal bonded together. The top piece of metal 12 con 10 ?guration of the core normally consists of relatively mild
tains a preferred means for uniform temperature control,
such as disclosed in copending application Serial No.
633,214, and the bottom piece 13 is divided at small
intervals by longitudinal T slots 18. Mill ?xture 11 acts
as an over-platen, in this case, and is held down by con
ventional locating pins and vacuum grid, not shown, or
by the freezing liquid method previously mentioned.
contours that are within the elastic limits of the core.
As ‘described, the preferred hold down method is by
means of freezing a liquid which necessitates special
clamping to compensate for the expansion and contrac
tion of the milling support while ‘maintaining the ma
terial in a ?xed position. Thus it is possible to provide
a smooth, burr-free, evenly ‘contoured surface on the
These three pieces, i.e., mill ?xture -11 and the two parts
material which will effect a stronger, more efficient bond,
of platen 12, 13, are made of the same type metal and
braze, or weld when the material is used as a component
therefore will expand and contract uniformly. Base ?x
part of a composite sandwich panel construction.
ture 14 is insulated from platen part 13 to increase
While certain preferred embodiments of the invention
temperature controlling efficiency. Thus, the expansion
have been speci?cally disclosed, it is understood that the
differential is between base 14 and platen part 13 and
invention is not limited thereto as many variations will
provision for this must be made in connecting the two
be readily apparent to those skilled in the art and the
members. Base 114 is divided at small intervals by trans 25 invention is to be given its broadest possible interpreta
verse inverted T slots 19.
tion within the terms of the following claim.
FIGURE 4 shows a gridded pattern formed by the
What we claim is:
longitudinal and transverse T slots. Here the longitudinal
Apparatus for holding material being machined in
dashed lines 18 represent the longitudinal T slots 18 in 30 cluding a ‘base ?xture and a platen for ?xedly holding
the platen 13 in FIGURE 1 and the transverse dashed
said material during expansion and contraction of said
lines 19 represent the transverse inverted T slots 19 in
platen, means for securing said platen to said base ?x
the base ?xture 14.
ture, said securing means comprising a plurality of spaced
The preferred construction of fastening means is
T slots in the bottom surface of said platen extending
shown in FIGURE 4a. Here a T-shaped slidable mem 35 in one direction, said spaced T slots including a centrally
ber 21 is adapted to engage and slide in slots 18 and slid
located slot, a plurality of inverted T slots in said base
able member 22 is adapted to engage and slide in slots
?xture extending at right angles to said slots in the bot
19. When positioned at points ‘of intersection of the
tom of said platen, said inverted T slots including a
transverse and longitudinal slots 18, 19, they may be
centrally ‘located slot, and elements :slidable within said
secured together by a bolt (not ‘shown in FIGURE 4a)
slots and engageable therewith, each of said elements
inserted in the apertures through their respective centers.
comprising two sections secured together, one of said
FIGURE 4b is taken along the line 4b—4b in FIG
sections engaging a platen slot and the other of said
URE 4 and shows the preferred manner in which the
sections engaging a base ?xture slot at points of inter
platen ‘12 is secured against movement in ‘a transverse
section of said slots, at least a pair of said elements with
direction because of some external force. Here bolt 23 45 sections positioned and secured in said centrally located
is seated within the base aperture 24 to prevent transverse
slot on said base ?xture, and at least a pair of said ele
movement of the lower slidable member 22 in slot 19‘ yet
ments having sections positioned and secured in said
this does not prevent longitudinal movement of the
centrally located slot on said platen. l
platen over upper T member 21 due to its expansion and
contraction with temperature changes. Since line 4b-4b 50
is taken ‘at each end of longitudinal center line 25', the
platen may also expand and contract transversely in
both directions from this center line. In other words
longitudinal center line 25 may expand or contract in a
longitudinal direction but otherwise will not move.
FIGURE 40 is taken along the line 4c——4c in FIG
URE 4- and shows the preferred manner in which the
platen is secured against movement in a longitudinal di
rection because of some external force. Here bolt 26
References Cited in the ?le of this patent
Bosworth ____________ __ Ian. 26,
Hertner et al. ________ __ June 20,
Mershon _____________ __ Mar. 2,
Heuze ______________ __ Nov. 21,
Soderberg ___________ __ Dec. 4,
Perry et al, __________ __ May 25, 1937
Harrington ___________ __ Apr. 4, 1939
Leary _______________ ___ July 25, 1939
is extended upwardly beyond the upper slidable member 60 ‘2,152,801
21 to engage platen 12, 13. This will permit transverse
movement only of the platen due to its expansion and
Since line 4c——4c is taken at each end of
transverse center line 27, the platen may also expand
and contract longitudinally in both directions from this
center line. In other words center line 27 also may ex
pand and contract but otherwise does not move. The
free ?oating type of fastener is shown in FIGURE 4d
with the bolt 28 engaging the two slidable members only
and neither engages the lower platen or the base ?xture.
Stackpole ___________ __ Apr. 12, 1885
Bailey ______________ __ June
Remington __________ ___ Nov.
Remington __________ __ May
Lewis _______________ __ Feb.
Dougherty __________ __ Mar.
Gri?ith et a1. ________ __ Oct.
Nielson _____________ ___ Sept.
Cole et a1. ___________ __ May
24, 1960
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