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Патент USA US2412731

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Dec. H7, 394%.
F. c. HQFFMAM
" EAEZJSI
STRETCH FORMING MACHINE
Filed May 10, 1944
4 Sheets-Sheet 1
,“
.wilu
'
AGENT
0 17,. R946.
2,412,731
‘ F. c. HOFFMAN
STRETCH FORMING MACHINE '
' Filed May 10, 1944
_4 Sheets-Sheet 2
IN VEN TOR.
P32235105" LT.’ 1%FFMN I
BY
AGENT
Ema
Pfum
F. C. HUFFMAN
2941129731!
STRETCH FORMING MACHINE
Filed May 10, 1944 ‘
4 Sheets-Sheet 3
kw
mm
lN VEN TDR.
mm
AGENT
Dec. 17, 1946.
2,412,?31
F. c. HOFFMAN
STRETCH FORMING MACHINE
Filed May 10, 1944
4 Sheets-Sheet 4
v:
00.
.
@m.
2
INVEN TOR.
Fkzzz?mzr L.‘ HUFFW
AGENT
Patented Dec. 17, 1946
2,412,731
UNITED STATES PATENT OFFICE
2,412,731
STRETCH FORMING MACHINE
Frederick C. Hoffman, North Hollywood, Calif.,
assignor to Lockheed, Aircraft Corporation,
Burbank, Calif.
Application May 10, 19 44, Serial No. 534,977
(Cl. 153-40)
16 Claims.
1
2
This invention relates to devices for shaping
or forming metal parts, and. has particular ref
erence to machines for stretch forming preformed
sections of aluminum alloys such as channels and
extrusions and other elongate parts.
Various devices and methods have been pro:
posed for stretch forming elongate metal parts.
Difficulty has been experienced in‘ obtaining sat
be readily adjusted to handle work parts having
wide ranges of proportions, curvatures, etc.
Other objects and features of the invention
will be readily understood from the following
detailed description of typical preferredforms
of the invention wherein reference will, be made
to the accompanying drawings in which:
‘
Figure 1 is a plan view of a stretch forming
machine of the invention;
isfactory uniform results ‘with such , machines
owing to the fact that the parts spring back to a,
considerable extent following the forming opera
tions. To compensate for this spring-back, it has
Figure 2 is a diagrammatic or schematic view
' of the machine illustrated in Figure 1;
Figures 3 and. 4 are‘ enlarged transverse de
10 .
been necessary to “scale” or proportion the form
ing surfaces of the machine in such a manner
that the formed part will have the desired di
mensions and contour subsequent to the spring
back. This scaling of the forming surfaces com
plicates the designing of the machine and ma
terially increases its cost.
1,5,
tailed ‘sectional views taken as indicated by lines
3-:3 and 4—4 respectively on Figure 1;
Figure 5 is an enlarged fragmentary vertical
section of a portion of the form block showing
provide a machine for stretch forming parts which
the pressure member in elevation;
Figure 6 is a fragmentary horizontal sectional
view taken as indicated by line B—6 on Figure 5;
Figure 7 is an enlarged fragmentary vertical
detailed sectional view taken as indicated by line
eliminates or minimizes the spring-back of the
1--'| on Figure 1;
parts. In the machine of the present invention,
Figure 8 is an enlarged fragmentary vertica
sectional view taken substantially as indicated by
, It is an important object of the invention to
2.0,
T
the spring-back is overcome or is reducedtothe
v
extent that it is unnecessary to compensate for 25 line 8-8 on Figure 1;
Figure 9 is a fragmentary vertical detailed sec
it in most cases in the design of the forming
tional viewtaken as indicated by line 9-9 on Fig,
block. As a result, a substantial saving is ef
ure 8; and
fected in the designing and manufacturing of the
Figure 10 is a diagrammatic plan view of an
machine.
Another object of the invention is to. provide
a machine of the character referred to embody
ing means for effecting a predetermined progres
sive rate of increase of stretch of the Work part
as the bending 0r forming occurs. This increased
stretching puts the entire cross-sectional area
of the, part under a tension exceeding the‘elastic
other form of the invention.
The embodiment of the invention illustrated
in Figures 1 to 9 inclusivemay be said to com—
prise generally a supporting structure H), a rotat
able ‘form block H, means l2 for associating the
workpiece W with the formlblocli ‘I I to be stretch
‘ formed upon rotation thereof,‘ means l3 for ro
limit, during the forming, so that substantially
tating theform block H, and'means I 4 for im
all the residual elastic stresses are eliminated and
posing an initial tension onthe workpiece. >
the resultant spring-back avoided. The tension
ing of the entire cross-sectional area of the part
also eliminates the tendency for the inner side
of the part to distort or buckle as a result of '
‘
‘
The frame or supporting structure It may vary
considerably in machines of different design, pro
' portion, “etc” and the invention is not to be con
sidered as limited to the particular frame struc
ture illustrated. A‘sfs‘h‘o‘wn, the supporting struc
ture‘ha's ‘an elongate track or .bed comprised of a
Another object of the invention is to provide
pair of horizontal beams l5 carried by longitu
45.
a stretch forming machine that is ‘operable to
dinally spaced‘pedestals or supports ‘ it. ‘The
stretch form particularly long workpieces through
beams [5 may be in the nature of I beams ar
compression.
substantially 366°. While not restricted, in its
ranged with their intermediate webs in spaced
application to the character or length of the
vertical planes and their lower flanges may be
work, the machine of the invention is particu 50 suitably secured to the supports it. The upper
larly. well suited to form the tension rings or
?anges of’ the beams I5 present broad supporting
or workingsurfaces. The form block H is ar
circumferential bulkhead rings of airplanes and
ranged adjacent one‘end of the elongate bed just
similar elongate parts of substantial length.
'A further object of the invention is to provide
described. In the particular machine illustrated,
an e?ective stretch forming machine that may 55 the ‘form. block II is horizontally disposed and
,
’
2,412,731‘
3
is positioned at one side of the bed. The support
the outer bolts 34 and their bushings 35 whereby
ing frame includes one or more beam members ll
projecting horizontally from the elongate bed ad
jacent one of its ends. The beam H is suitably se
the segments are secured to the form block [I
by the bolts 34. The outer edge surfaces of the
segments 38 are arcuate or curved so that the
cured to the adjacent beam l5 of the bed. and is
supported by spaced legs IS. A supporting pedes
tal i9 is.- arranged at the opposite side of the
elongate bedi'n alignmentwith the beam member
II. The pedestal l9 may be constructed of pipe
or tubular stock and has a lower horizontal arm .. 1.0 .
20 ?xed to a beam l5 of the bed. A second arm
2! is ?xed to the top of the standard or pedestal
I9 and extends toward the formblock H to pro
ject over the bed. The purpose‘of'the pedestal.
l9 will be later described.
The form block ll is the active work-shaping
or forming element of the machine. Theblock
ll may be horizontally arranged as illustrated,
series of segments presents a continuous surface
which is curved concentrically with the axis of
rotation, of the form block I I. The Opposite ends
ofi-the: segments 38 may be radial so that they
may have ?ush engagement one with the other.
The number of segments 38 employed depends
upon the length of the curvature to be formed in
theworkpiece'W. In the case illustrated, the
series. of__ segments I 38 extends well over 200“
aroundi'the-formmlock II.
It is to be under
stood'thatthesegments 38 are removable and are
' adapted to be'replaced by segments shaped to
form.a-.lcurvature: of any selected radius in the
workpiece.
The curved or arcuate active faces of the seg
or may, if desired, be mounted to occupy a verti
cal or inclined plane. In accordance with the 20 ments 38 are preferably prepared to receive the
workpiece-W. The formation or con?guration of
invention, the form block‘ I I is supported for free
thesegments 38 willdepend uponxthe character of
rotation, and" where the block is-horizontally ar
ranged, it is mounted‘for rotationabout a verti
the workpiece to- bestretch formed. The particu+ .
cal axis. 'The beam member i‘! above referred
lar workpiece WI'illustrated islsubstantially. z
to carries-an upstanding axle or~trunnion 22 for
shaped in transverse cross section having a broad
supporting the-form block H. The trunnion 22
Web and edge?angesextending inopposite di
is ?xed to a plate 23, which in turn, is secured to
rections therefrom. Slotsor grooves 46 are prothe beam l'l. One of a‘ plurality of spaced open
vided in the active edges of the segments 381to. re-.
ings 24 in the member [-1 receives the lower por—
ceive theworkpiece W.‘ The grooves 4050f. the
several‘segments 38Lare aligned-and register to
tion of the trunnion‘ZZ‘and the plate 23 is secured
to the beam member around the opening. The
constitute acontinuous peripheral'groove extend
ing throughout the. series. of.‘ segments. .The .
form block “has a hub 25<?xed to an elongate
cup-like bearing member‘ 26‘free1y rotatable on
grooves so are formed and proportioned sothat
the trunnion‘ 22. The end ‘of the bearing member’
the web of the workpiece may lie againstone
has a thrust'bearing Z'I'engaging with'the mount 35 side wall, with the inner workpiece?ange err-e
ing plate 23; If desired, suitable anti-friction
gaged with the bottomwall ofithe groove. The.
bearing means maybe'associated with the'trun
. outer ?ange. of‘ the; workpiece cooperates with
nion>22 and bearing member 26. The body 28 of
the arcuate outer faces of the segments 38 and
the‘, forn'r block H is a ?at disc-like element or
the faces of the segments mayzbestepped'at M
assembly reinforcediat its under side-by a chan 40 to receive the bead onthe outerworkpiece ?ange.
nel sectioned rim member 29. The form block
The inner or bottomwall of the groove tllis
ll may be large in diameter and it is desirable
curved concentrically With'th-e outer active..sur~
to support it against tipping or de?ection. One
faces of the segments38; Figure5 clearly illus
or more rollers 30 may be provided on the beam
trates the mannerin which: the workpiece W en.-v
member IT for engagement by the-under surface
gages in the grooves '40 :and :conforms‘to. the ‘outer,
of therim member-29 to aid int-supporting the
surfaces. of the segments 38. ,
form block and to prevent such tipping.' -_
Work partsof the con?guration illustrated; and
The body 28 of the form block ll has-a multi
workpieces of ' other. cross sectional. con?gurations:
plicity'of circumferentially spaeed- radial slots 3!.
may tend to distort or assume irregular cross
The slots 3'! extend inwardly from adjacent the 50 sectionalshapes as a result‘ of . the stretchform
periphery of the form block, and are preferably,
ing. operation; For; example, in the particular
equally spaced around‘ the block: Adjustable
case illustrated, the broad web oftthe. workpiece
strips or-blocks 32 carry spaced rods or bolts 33
W may tend to bulge, buckle‘ or wringlecwhen the‘
and 34‘ which pass vertically = through the slots
workis' stretch formed into-thev groove. Ml. In
3|.‘ As shown in Figures ,4 and 5, the two bolts 65 order to prevent this, I prefer ‘to employ a's'pacer
33'and 34 of each- block v32 extend through the
or ?ller 122. The ?ller 42. isadapted to'occupythat
respective slot‘ 3| of the block. Tubular spacers
portion of the groove 481 which" is notiilledl or
or bushingsSE extend through the'vertical open
occupiede by the workpieceW. In practice. the '
ings in the blocks ‘32yand washers 36, are provided
?ller dzmay be a strip; of wood'or other mate'- '
under'the heads and nuts 31‘ of the bolts; It will 60 rial having considerable ?exibility. Multiplicie
be seen‘ that‘ when: the nuts~3l are loosened‘ the
ties of spacednotches or slots 43=of substantial
blocks S'Z‘may' be adjusted‘radially on‘the‘form
' depth are formed in the inner‘edge of the ?ller
block H . As shown'in' Figures 4 and'5,‘ theouter
£2 to increase the ?exibility of the ?ller. 'Super
edges of 'the'adjustableblocks' .32 are adjacent ‘the
imposedstrips lid-of Wood, or the like, extend
rim or periphery of the form block; it being under- 65 along the outer edge of/ the i?ller 4-2 and-are
stood'that the blocks ‘may be‘. adjusted ' inwardly
as‘ required in‘ the particular’ stretchformingfop
eration.
_’
‘secured: thereto. bynails. 135',’ or. the, ‘equivalent.
The strips.“ add strength’ torthe ?llerl?land
prevent it from cracking or breaking, by reason
of the deep slots 43. Itis p-referred‘to employ
‘
The ,form- block H is’further,‘providedwith
segments 38 for receiving orjacting on the work:
a minimum numberof nails 45 or ‘othersecuring
piece W. Thesegmentstii are’carried on the above
described blocks~32 ' and: are' capablejof ' limited
members .inthe outermost‘ strip .413. The ?ller
42 and .its reinforcing ‘strips .44' are" proportioned
radial adjustment with the block's; As'illustrated,‘
to completely" occupy ‘that, portion .of ' the groove
each segment ISBBis ‘sup-ported ;by‘_thr.ee‘ adjacent
. blocks 32.‘ Openings 39 in_ the segments 38 receive
7:5
li?'not'?lled bytheworkpiecev W and the'surface
ofv the outer' strip~ 44> may ‘lie substantially'?ush‘
5
2,412,731
with-the surface of the outer edge ?ange on the
' workpiece. This is clearly illustrated in Figure 5.
Itiwill be observed that the surface of the work
carry rotatable wheels or rollers 56 which engage
the under side of the upper beam ?ange to pre_
vent displacement of the carriage from the beam.
A plate 51 is secured to the upper side of the
carriage 52 and projects forwardly from the car
riage. The forward end of the plate 51 carries a
piece ?ange is free and exposed at the face of
the series of segments 38.
5)
The particular segments 38 illustrated are pro
portioned and arranged to impart a curvature of
grip 58 for releasably connecting the workpiece
maximum radius to the stretch formed work. In
W with the movable carriage 52. The grip 58
the event that it is desired to give the work a
may be of the self-energizing type, and may be
curvature of small radius the form block II is 10 similar to the above described grip 461, having
adjusted or moved to have its axis of rotation
a pair of wedges 59 for gripping the workpiece
closer to the elongate bed of the supporting means
when the assembly is put under tension.
10 and suitable segments of the required contour
The means for actively associating the work
are secured in the correct positions on the form
piece W with the form block I I, further includes
block: The bI‘OkBnrlinBS in Figure 1 show the 15 a ?exible element secured at one end to the form
form" block ll arranged with its axis of rotation ‘ ‘ block, to be wrapped thereon when the block is
relatively close to the elongate bed of the support- .
rotated, and secured at its other end to the car
ing structure, and illustrates a series of segments
riage 52, which in turn is connected with the free
on the :block presenting a forming surface of rela
end of the workpiece W. This ?exible element
tively small radius. ‘ The supporting bed ‘is cut 20 may be a rope, wire, cable or chain. In the par
away as at 8 to allow such adjustment of the
ticular embodiment of the invention illustrated,
form‘blo‘ck l I. There may be a plurality of form
the ?exible element is in the nature of a chain
block mounting stations comprising spaced open
60. The chain 60 has one end anchored or ?xed
ings24 in the beam member ii and the machine
to the form lblock II at El adjacent or beyond
may be equipped with several sets or series of 25 the trailing end of the series of segments 38 rela
segments 38 of graduated radii whereby the ma
tive to the ‘direction of active rotation of the
chine is adapted for the-formation of any stretch
form block‘ as indicated by the arrow A in Fig-ure
‘formed curvature within its extreme ranges of
l. The chain 60 is wrapped or trained about the
‘operation. In this connection, it is to be under
form block I! to cooperate with the‘forward
stood that the segments t8 are radially adjust
edges of its radially disposed plates or blocks 32.
able to some extent on the form block H, to give
The forward edges of the plates or blocks 32
the machine a substantial ?exibility of adjust
are shaped to have effective cooperation with
the chain 6!]. Chain locating notches 62 are pro
ment.
‘
'
i ‘The means !2 for associating the workpiece W
vided in the edges of the blocks 32 and lugs 53
with the form block I l for stretch forming there- ‘
on the walls of the notches are operable to ?t
within the links of the chain 60; see Figures 4
and 5. The engagement of the multiplicity of the
by includes a holding device or‘grip 46 for releas
ably securing the workpiece‘ to the block. This
grip .45 includes a housing having upper and
spaced blocks 32 with the chain 60 assures an
lower plates 4‘! which engage about the end por
adequate traction or drive relation between the
‘tion' of the segment 38 that is foremost relative 40 form block H and the chain 68. It is important
to the direction of active rotation of the form
to note that I have shown the effective chain
block ‘II. The grip housing plates 47 may be
engaging radius of the blocks 32 as being shorter
‘secured to the form block l I by the endmost bolts
than the e?ective radius of the Work-receiving
33 and 34 of the segment. A pair of blocks 48
. groove 40 of the segments 38. In Figure 2 the line
having opposing ‘convergent surfaces 49 is ?xed
B designates the effective chain-engaging radius
in ‘the grip housing. ‘Gripping wedges 5B‘ con
of the blocks 32 and the line C represents the
form to and slide on the ‘surfaces 49, and have
e?ective work-engaging radius of the segments
opposing surfaces 5! shaped to conform to the
38. The differential in radii as indicated in Fig—
workpiece W. Thesurfa'ces 5| may be serrated
ure 2 results in the portion of the chain 66 leav
or=roughened to effectively grip the same. The
ing the form block H being made increasingly
workpiece W is readily’ engaged‘between the
shorter in relation to the portion of the work W I
‘wedges 5B, and when tension is applied to the
work the wedges 56 are automatically actuated by
the convergent surfaces 49 to grip the work.
While I have shown automatically energized me
chanical grip means, it is to be understood that
other suitable forms of grips may be employed
‘if desired. As shown in Figure 8 of the draw
ings, the grip 46 is located at the forward end
of the groove lit relative to the active direction
of rotation of the form block ii, and arranged
so ‘that the work extending from it immediately
.beingldrawn onto the form block and gradually
supporting structure IE! and extends along the top
enters the groove 40.
of the adjacent beam [5 teen idler or :a direc
increases the tension on the workpiece as the
stretch
forming
operation
progresses.’ This
action‘ and its purpose will be more fully de~
scribed. ‘ It is to be understood that the di?er
ential in the radii B and C may be varied‘to suit
different operations, and in some instances the
radii may be identical.
~ .The chain 60 passes tangentially from the form
block II at or adjacent the. elongate bed of the
tiOn‘ changing sprocket 64. The sprocket 64 is
Theend of the workpiece W which is remote
‘from the form block I l, prior to the stretch form 65 rotatably carried by a vertical shaft 65 project
ing‘ from the supporting bed. 'The chain 68
ing' operation, is operatively connected with a
engages substantially 180° around the sprocket
carriage‘ or traveler 52 movable along the elon
64? to continue longitudinally over the upper
gate horizontal bed of the supporting structure
Ill. "The carriage 52 is capable of riding or
?ange of the second beam l5. A suitable guard
moving along the upper ?ange of one of the 70 or safety housing 66 is preferably provided on the
beams l5 and comprises a horizontally disposed
beam l5 toenclose the major portion of the chain
body equipped with axles 53 carrying freely rotat
69. The chain 60 extends from the sprocket 64
able wheels 55. The pairsofwheels 54 roll along
toa second direction changing sprocket 6'! located
the top of the beam l5. Lugs or ears 55 depend
adjacent the opposite end of the ‘supporting bed.
from the opposite sides of the carriage 52 and
The ‘chain 60 ‘passes substantially 180° Tarouncl
end-"257m
.7
8
ablef'form'of- prime'imover or power means. C'In
the-.sprocket 81 toreturn over theltop :of .the
supporting bed to the‘ above describedtrcarriage
the-particular form‘ of ‘the invention illustrated,
52. The chain til is suitably secured to the car
this power-means comprises an electric motor
8| ‘mounted on a suitablesupport 82 on one side
riage at 63. ‘The sprocket 8'! is? supported by the
means ‘M to rotate. aboutv a generally. vertical axis
> as will be hereinafter described. . It is to beiob
of the elongate supporting‘bed. The motor shaft
carries- ordrives a worm 83. The-worm drives a
served that the chain 68, the workpiece W and
the intervening carriage 52 constitute. acontin
uous flexibleassembly havingits opposite ends
securedto the rotatable form :block H.- Upon
imparting axial movement to this tloop-like as
sembly, the form lblock H is rotated in the direc
tion-A to draw the work W onto it for forming
thereby. The means It, ‘to be later described,
sprocket‘ “carried by a'vertical shaft 85 mounted
on the support 82. The protective housing 66ifor
the chain 60 is interrupted at the sprocket 84 and
the sprocket has meshing‘ or driving engagement
imparts the longitudinalmovement to the chain -.
driving sprocket‘84. .It will be‘ understood how
the motor driven sprocket 84 operates "to advance
the chain 88 in the direction D to rotate the form
and workpiece linkage .or assembly.
.
,
:In order to assure proper contact of the. work
piece W‘ with the form block segments 38' and
to assure correct forming of the work to the con
tour of. the segments, it is desirable to employ .
a pressure foot or pressure member ‘l'il for acting
on the work as it moves onto the segments. The
with the chain. Spaced idler sprockets 86 are ro
tatably‘mounted on the supporting vbed to cooper
ate"with the chain 60 .at longitudinally spaced
points to hold it ‘in proper engagement with the
block H so that the‘ work W is drawn onto the
block. In this connection it will be noted that
the ‘differential in the radii .B s and C results -in
the work W being drawn onto the form block H
more rapidly than the chain 68 leaves the‘block.
pressure member
is carriediby 'a block ‘H,
which in turn is guided for horizontal movement
toward and away from thelform lblock H; see
Figure 4. The shiftable .block'll is directed. for
horizontal movement in .a direction radially with
respect to‘the form block H by a suitable guide
'12 on the under side of the pedestal arm 2 l. The
This differential in movement results in a gradual
‘increase in'the tension on the workpiece W, this
.pressuremember ‘iii is a generallyv cylindrical .‘
.erable. to maintain the initial tension or vary the
tension as conditions may require. during the
formingof'the work. The means I4 includes a
bracket or slide 81 carrying the above referred
roller-like part engaged in a correspondingly
shaped‘notch or recess T3 in the forwardend of
the. block ‘ii. The member "if? is supported. and
retained for partial rotation in the'recess. Discs
action continuing throughout the stretch form
ing. operation.
1
The" means I4 is operable to impose an initial
tension on the :work W preparatory to‘ the actual
stretch forming, operation and‘. is preferably-op
to sprocket 6'1; see Figure '7. The vertical shaft
‘M are. secured to the block H at the ends of the '; -88 of the sprocket-81 has‘ its opposite end por
tiOlls supported-by the slide 81 and the shaft pro
recess 73. and carrya shaft ‘£5 for retaining the
pressure member 13.. .‘The cylindrical‘ surface of
the pressure member ‘19 may directly bear on the
wall of the recess 13 and the shaft ‘l5 need not
assume the heavy active loads. The pressure
memlber ‘it has a chordal surface '56 for contact
ing the workpiece W. The. surface‘ 16 is capable
of automatically conforming to theexposed flange
of:the workpiece W even in situations where they
jects beyond the lower'side of the slide. The
.bracket‘or slide 81 is an open sided box-like struc
ture containing the sprocket-61 and the chain=60
enters and leaves its opposite open sides. A plate
.89 is ?xed to the beams 15 of the supporting bed
and the slide 81 is engaged on the upper surface
of the plate for free sliding movement longitudi
nally of the bed.
A longitudinal slot 90 in’the
flange is pitched or irregular. VRollers 9~may be .45 plate 89 receives the projecting lower portion of
the sprocket shaft 88 to assist in- guiding the slide
rotatably mounted in the member 18 to be ex—
8'5- and to limit its axial movement.
posed at the surface 1'5 to engage the work part.
The means 14 ‘further includes screw thread
The rollers 9 will'reduce the friction between the
means for‘ moving or advancing the slide 81 to
pressure member '58 and the work part W.
Means is provided for maintaining the pressure 50 tension the workpiece'W. This means includes
a threaded stud or screw 9| ?xed to the slide 81
member .78 in effective pressure engagement with
as by welding. The screw 9| projects from'the
the workpiece W as it moves onto the form block
end of the slide 8‘! and passes freely through an
ll. This means comprises'a cylinder and piston
opening 92 in=~a ?ange or block 93 ?xedron the
mechanism 'l'i secured to the standard I9 under
the arm iii. The piston rod ‘58 of the mechanism :55 end of‘ the supporting bed. .A nut 94 is thread
edly engaged on the screw 91 to react orbear
17 is operatively connected with the block ‘H.
vagainst the block 93. In practice a washer 95
Fluid pressure lines, 19 connect with the cylinder
maybe interposed betweenthe nut 94 and the
of the mechanism Ti and the mechanism is under
block 93. Radially projecting handles or levers
the control of a suitable manually operable valve
88. The mechanism 71 forces the pressure ‘mem P60 .96 are provided on the nut to facilitate its man
ual operation. It will be seen that when the nut
ber '10 against the workpiece under a constant or
.94 is rotated in one direction the slide 81 is drawn
uniform pressure during the stretch forming op
toward the block 93 to tension the workpiece .W
V eration.
connected between the chain 60 and .the form
The actuating means [3 is. operable to impart
axial movement to the‘ chain 68 tov produce: rota 65 block it and to incidentallytension the chain.
The screwill and nut 94 thus constitute a-means
tion of the form block II and to cause the work
for'initially tensioning the workpiece .prior to the
piece W to be drawn onto the block: for forming
thereby. As described above, the chain 60, the
workpieceW, and the carriage :52 constitute a
actual stretchforming operation; and if desired,
the nut v9d may be subsequently operated to in
continuous loop-like assembly . whose opposite 70 crease or reduce the tension on the workpiece as
desired during the vactual stretch ‘forming oper
ends are connected to the form block H so that
axial movement imparted to‘ the chain 60 in the
ation.
direction of thearrow D in Figure 2 produces'ro
tation of the form block H in the direction 'A.
The means l3‘maycompriseany-selectedor suit- ,
The 'tensioning means ' [4' also . preferably. 111-
‘eludes a ?uid pressure actuated mechan'lsmt'l
vfor imposing tension on the‘workpiece"W,."where.
I
2,412,713 1
10
by the tensile strain may be conveniently varied
at will during the stretch forming of the work.
ins reference to the axis of rotation of the form
block H. The invention automatically provides
The cylinder and piston mechanism 9'! is suit
for su?'icient tensioning of the ?bers of the inner
ably ?xed to the plate 89, or to other structure
zones of the workpiece without tensioning the
on the supporting bed l9, and. its piston or ram
outer ?bers beyond the maximum limit, thereby
98 may act directly on the inner end of the slide
eliminating wrinkling or other distortion of the
81. A pipe or line 99 carries the actuating fluid
inner sides of the workpiece, and more important,
pressure to the inner end of the cylinder and
completely eliminating or reducing to a minimum,
piston mechanism 91. A‘ manually operable valve
the spring-back that is often present in other
me controls the line 99 and is preferably such 10 stretch forming procedures.
that the pressure exerted on the ram 98 may be
In accordance with the invention, it may be
readily. and precisely controlled. A pressure
preferred that the tension on the workpiece be
gauge llJi may be connected in the line 59 to in
accelerated or continuously increased asthe op
dicate the pressure exerted on the ram 98 and
eration progresses; thus continuously increasing
thus disclose the tension being imposed on the 15 tension ‘acting to maintain thev fibers in ‘the inner
workpiece W.
zones of the workpiece under tension without
The invention preferably includes means for
unduly tensioning the ?bers in the o-uter‘zones.
restoring or returning the form block ll, chain
The continuously increased tension imposed on
50 and carriage 52 to their initial positions sub
the workpiece throughout the‘forming operation
sequent to the work forming operations. This 20 assures the maintaining of the ?bers in the inner
means comprises a pullback line or cable IE2 at
zone of the workpiece ‘under suf?cient tension to
tached to the form block H. Notches I03 in the
eliminate or minimize springeback. The increas
edges of the blocks 32 receive and guide the cable
ing elongation of the workpiece and the acceler
as it is wrapped on the form block during stretch
ated stretching of its inner ?bers are produced
forming of the workpiece; see Figure 5. The 25 by releasing the chain 69 from the smaller radius
cable Hi2 extends from the form block I! and its
B of the form block while simultaneously drawing
outer end is connected to the movable carriage
the workpiece onto the larger radius C. The
52. The cable is readily accessible at the top of
chain releasing radius B, being shorter than ‘the
the supporting bed to be grasped and pulled to
work forming radius C, causes ‘the portion of
restore the form block H, chain 69 and carriage
the chain 60 leaving the form block to be increas
52. A prime function of the cable M2 is to serve '
ingly shorter in relation to the unformed portion
as a safety means to prevent sudden rotation of
of the workpiece W being drawn onto the block.
the form block it in the event the work part W
Further, the portion of the tension'ed workpiece
breaks while under tension.
’
between the form block H and the outer grip 52
To prepare for the stretch forming operation, 35 is increasingly shorter as the operation progresses
the ends of the workpiece W are engaged in the
and this'further results in increasing the tensile
grips 46 and 58 in the position to correctly enter
strain on the workpiece. These two-factors or
the groove 40 of the form block segments 38. At
actions assure the application of sufficient ten
this time the pressure member "I0 is in the re
sion to the inner ?bers of the workpiece through
tracted position. The ?ller 42 is associated with 40 out the entire stretch forming operation to main
the workpiece and started in the groove 49. At
tain these ?bers under suiiicient tension to elim
this stage of the operation. the grip 46 on the
inate spring-back, or to reduce spring-back to
form block I i is adjacent the pressure member
an absolute minimum. In practice, I have found
10. With the workpiece engaged in the grips 46
that by employing a proper relation between radii
and 58, the pressure member 10 is actuated 45 B and C no, or only negligible, spring-back oc
against the workpiece by supplying fluid pressure
curs in many cases, and as a result it is unneces
to the mechanism 11 and the nut 94 is rotated
sary to take spring-back into consideration when
to impose the initial tension on the workpiece W.
designing the form block II.‘ This materially re
The automatic grips 46 and 58 are actuated by
duces the cost of designing and fabricating‘ the
this initial tensioning of the work. The actua 50 block. The machine of the invention assures
tion of the nut 94 may apply the full initial ten
uniform results even when handling work parts
sion to the workpiece or the mechanism 97 may
that necessitate designing or proportioning the
be utilized to assist in imposing the initial tension.
form block to compensate for spring-back. The
In either case, this initial tension while relatively
mechanism 91 and/or the nut 94 may be em
low is su?‘icent to put the metal of the workpiece
ployed to vary the‘tensile strain on the workpiece
in the plastic condition for ready forming to th
W at any phase of the operation. When the form
contour of the form block segments 38.
'
block H has been rotated to draw substantially
With the workpiece W conditioned as above
the entire workpiece W onto the segments 38, the
described, the motor 8| is put into operation to
motor 8i is deenergized and the formed work
advance the chain 69 and rotate the block II
piece is removed from the machine. The'cable
in the direction A. The tensioned work is drawn
H32 may then be employed‘to restore the parts
onto the rotating form block H to be shaped or
to their original positions for the neXt forming
formed to the contour of the groove 40,‘ which
operation. The machine when employed as just
in the instance illustrated, has a cylindrical
described, is operable to uniformly stretch form‘
curvature. It is to be understood that all ?bers 65 parts with no residual spring-back or with only
of the workpiece are in tension at the commence
negligible spring-back, and uniform results are
ment of the forming operation. The combination
of the bending and tensile forces effectively forms
the work to the active shaping surfaces of the
“form block segments 38.
;
.
.
Owing to the con?guration of the workpiece
W and the curvature being imparted thereto, the
?bers in the outer zones of the workpiece ‘are
more highly tensioned than the ?bers in theinner'
zones, the terms “inner” and “outer” here hav
consistently obtainable.
.
Figure 10 schematically illustrates another
form of the invention in which the continued in
crease in the tension on the workpiece W during
the forming operation is obtained by an auto
matic means supplementing or'replacin'g thedif
ferential radii B and C of the form block. ‘ The
differential in the radii B and C of the work
and chain receiving surfaces of the block I i may
2,412,731
ll?
12*
be maintained as Figures 1 to 9, maybe reduced,
mayappear to those skilled 'in the art. or‘ fal
or may be eliminated sothat the radii are equal;
The general construction of the machine may
be the same as above described. and correspond
ing reference numerals are applied to correspond
ing parts. In this form of the invention, the
screwv 9! at the outer vend of the slide, together
with its actuating nut 94, may be retained and
within the scopeof the following claims.
the cylinder and piston mechanism 91 may also
be included in the machine. A screw“ I I0 is held
against rotation by a sliding connection with the
ram 98 and its opposite end is slidably associated
with the'slide 81. A nut Ill threadedly engages
the screw H9 and is engaged between ‘spaced
?anges ! l2 secured to the pulley supporting slide
81. Upon rotation of the nut III, the screw Hi2
'
I claim:
‘
.
' -
-,
~
' 1‘; A stretch forming machine comprising a ro
tatable form‘ block having a curved formingsur
face and a second surface means closer to the
axis of rotation of-the block than the forming
surface, meansifor associating an elongated work
piece with‘ the'form‘ block to be drawn onto said
forr’ning'surface and formed thereto when the
block is rotated, and means for rotating the‘ form
block‘ and 'tensioning the workpiece as the block
rotates, including "an element connected between
the-{block and a part of the workpiece which is
remote from“ the block and trained over said sec
ond surface means to be unreeled therefrom as
the block rotates.
and slide 81 are moved longitudinally'of the sup
2. A machine of "the character described com
porting bed. The ram 98 of the mechanism 9?
prising a rotatable form block having a forming
may act against the inner end of the screw HE]
so that the mechanism may advance the pulley 20 surface and a second surface means closer to the
axis of rotation of ‘the block than the forming
slide 81 through the medium of the‘ screw. The
surface, means for engaging an elongated work
periphery of the nut l l l is in the form of a gear
piece to be formed with the forming surface, the
which meshes with a pinion ! 13.
block being rotatable to form the part, and means
Any suitable or selected means maybe em
ployed to drive the pinion H3 at a given rate 25 for tensioning the part operable to increase the
tension as the workpiece is formed by said sur—
relative to the rate of advancement of. the work
face, the last named means comprising a ?exible
W onto the form block ll. Ihave shown the
element wrapped on said second surface means
pinion 1 l3 keyed or ?xed toone'end' of a shaft
and connected with‘ the form block and a point
H4. A beveled gear ll5'is ?‘xed to the ‘opposite
on the workpiece remote from the block to be
end of the'shaft to mesh with 'amat'i'ng gear
unwrapped from said second surface means as
H6 formed on or ‘rotating with the sprocket 84'.
the block rotates.
With atselected pitch of the threads on the screw
3. A machine of the character described com
Ill ‘and a selected ratio in the gearing, the slide
prising a form block having a forming surface,
8'! may be moved at a speed to produce the de
sired gradual'increase in the tension in the work 35 means for engaging an elongated workpiece with
the block, the block being rotatable to cause said
piece W. When the sprocket 84 is motor driven
surface to ‘form the workpiece, and means for
during thestretch forming operation, the nut l l i
tcnsioning the workpiece and operable to increase
is rotated'through the medium of‘the gearing,
the tension as the workpiece is formed by said
and rotation of the nut produces translation of
the slide 81 in an‘ outward direction. This out 40 surface upon rotation of the block, the last named
means comprising a second surface on the block
ward travel of the slide 87 ‘increases the tension
substantially coaxial with the forming surface
on the workpiece. The unformed portion of the
and closer to the axis of rotation of the block
workpiece between the form block II and the
than the’forming surface, and a ?exible element
grip 58‘ becomes increasingly shorter as the op
connected between the block and a portion of
eration progresses. . This factor, coupled with. the
the workpiece remote from. the block and wrapped
automatic outward movement of the tensioning
on the second. surface to unwrap therefrom at
sprocket 61 ‘and the optional actuation of" the
a rate slower ‘than the rate at which the Work
mites and mechanism 91 ampli?es the tensile
piece is formed on said surface. ‘
strain‘ imposed on the workpiece ‘and maintains
4.. A machine of the character. described com
theiinner ?ber 0f the workpiece under tension '
prising a rotatable form block having a curved
throughout the entire forming operation to pre
forming surface and a second curved surface, said
vent spring-back. The cylinder and piston mech
surfaces being substantially concentric with the
anism ii? may be employed to supplement ‘the ac-‘
axis of rotation of the block, the radius of curva
tion of the gear and screw thread means or may
be utilized‘ independently of the gear and screw ' tureof the second surface being shorter than the
radius of curvature of the forming surface, means
thread ‘means to obtain a constant, variable or
for connecting an elongated part to‘ ‘be formed
increasing tension on the workpiece during the
with the-block to be drawn onto and formed by
stretch forming operation. ‘The mechanism 9'!
thev forming surface upon rotation of theiblock,
may-be readily operated or governed by the valve
60 and'means for‘ tensioning the part and operable‘
IE0 or other suitable valve mechanism.
to. increase the tension thereonas the block ro’ During operation of both forms of the inven
tates
to form the part, the last namedmeansin
tion herein disclosed sufficient tension may be
eluding a ?exible element connected with the por
imposed on‘the part being formed or bent to
tion of said part remote from the block, secured
maintain its entire cross-sectional area under - to the block and wrapped on the‘ second surface
a tensile strain exceeding the elastic limit of the
of the block‘ to be unwrapped therefrom as the
material to bring about the permanent “stretch
part is drawn onto the forming surface.
.
forming” ofthe part and: the accelerated or in
5. A machine of the characterdescribed ‘com
creasing tension operating, as above ‘described
prising arotatableform :block having aacurved
eliminates, orv ‘reduces to a . minimumthe. undesir-~ 70 forming surface and a seco-ndcurved surface, said
able spring-back;
'
surface being‘ substantially concentric with the
Having described only typical formsof the ‘in
axis of rotation of the block, the radius of cur-va
ture of the second surface being shorter than. the
radius of curvature of the forming surfaceim'eans
to myself any-variations or- modifications. that 75 for connecting an elongated part to beformed
Vention, I do not wish to be limited" to the spe
ci?c details herein set forth, but wish. to reserve
2,412,731
13
to increase the tension thereon as the block ro
tates to form' the part, the last named means in
cluding a ?exible element connected with the por
drawn onto and formed by said surface upon ro
tation of the block and means for rotating the
tion of said part remote from the block, connected
block and for tensioning the part‘during such
with the block and wrapped on the second sur
face of the block to be unwrapped therefrom as
the part is drawn onto the forming surface; and
14
‘9, ‘A‘machine of the character described com
prising a rotatable form block having a ‘curved
forming ‘surface substantially concentric‘ with the
axis of rotation,‘ means for connecting an elon
gated part‘ to be formed with the block to be
with- the block to be drawn onto and formed by
the forming surface upon rotation of the block,
and means for tensioning the part and operable
10
means for acting on said element to impose an
initial tension on the part.
i 6. IAmachine of the character described compris
ing a rotatable form block having a curved form
ing surface‘and a second curved surface, said sur
faces being substantially concentric with the axis
of rotation of the block, the radius of curvature
of the second surface being shorter than the
radius of curvature of the forming surface, means
rotation including a ?exible element connected
between the block and the portion of the part
remote from the block, means for exerting a lon
gitudinal pull on the element to rotate the block,
and means acting on the element to tension the
part comprising surface presenting means on the
block“ substantially concentric with the axis of
rotation of the block on which the element is
wrapped and having an effective radius which is
shorter than the effective radius of said forming
surface, the element being unwrapped from said
for connecting an elongated part to be formed 20 surface means as a result of said pull:
10. A machine of the character described com
with the block to be drawn onto and formed by
prising a rotatable form block having a forming
the forming surface upon rotation of the block,
surface curved generally about the axis of rota
and means for tensioning the part and operable
tion of the block, means for connecting an
to ‘increase the tension thereon as the block ro~
elongated part to be formed with the block to be
mesa form the part, the last named means in
drawn onto and formed by said‘surface upon ro
cluding a flexible element connected with the
tation of thevblock and means for rotating the
portion of said part remote from the block, con
block and for tensioning the part during such ro
nected with the block and wrapped on the second
tation including a second surface means on the
surface of the block to be unwrapped therefrom
as the part is drawn onto the forming surface, y; block closer to the axis of rotation of the block
than the forming surface and curved generally ‘‘
and means for acting through the medium of the
about said axis, a ?exible element connected be
element to impose an initial tension on the part
tween the block and the portion of the part re
and operable to vary the tension on the part as
mote from the block and reeled on said second
it is drawn onto the forming surface.
surface means to unreel‘therefrom upon rotation
“ '7‘. A machine of the character described com- '
of the block in a direction to draw said part onto
prising a rotatable form block having a curved
the forming surface, means acting on the element
forming surface and a second curved surface, said
to rotateithe block in said direction, and means
surfaces being substantially concentric'with the
acting‘ on the element to tension the part com
axis of rotation of the block, the radius of curva
prising a ?uid pressure actuated part movable
ture of the second ‘surface being shorter than the
to tension the element and part.
radius of curvature of the forming surface, means
11. A machine of the character described com-‘
for connecting an elongated part to be formed
prising a rotatable form block having a curved
with the block to be drawn onto and formed by
forming surface curved generally about the axis
the forming surface upon rotation of the block,
of rotation of the block, means for connecting an
and means for tensioning the part and operable
elongated part to be formed with the block to be to increase the tension thereon as the block ro
drawn onto and formed by said surface upon ro- i
tates to form the part, the last named means in
tation of the block and means for rotating the
cluding a ?exible element connected with the
block and for tensioning the part during such
portion of said part remote from the block, con
rotation including a second surface means on
nected with the block and wrapped on the sec
the block closer to the axis of rotation of the
ond surface of the block to be unwrapped there
block than the forming surface and curved gen
from as the part is drawn onto the forming sur
face, and screw thread means for exerting an
initial tension on the part.
8. A machine of the character described com
prising a rotatable form block having a curved
forming surface and a second curved surface, said
surfaces being substantially concentric with the
erally about said axis, a ?exible element con- ,
nected between the block and the portion of the
part remote from the block and reeled on said
second surface means to unreel therefrom upon
rotation of the block in a direction to draw said
part onto the forming surface, means acting on
the element to rotate the block in said direction,
axis of rotation of the block, the radius of curva
ture of the second surface being shorter than the 60 and means acting on the element to tension the
part comprising a sprocket for driving the ele
radius of curvature of the forming surface, means
ment and means for moving the sprocket.
for connecting an elongated part to be formed
12. A machine of the character described com
with the block to be drawn‘ onto and formed by
prising a, rotatable form block having a curved
the forming surface upon rotation of the block,
forming surfacecurved generally about the axis
and means for tensioning the part and operable
of rotation of the block, means for connecting an
to increase the tension thereon as the block ro
elongated part to be formed with the block to be
tates to form the part, the last named means in
drawn onto and formed by said surface upon ro
cluding a ?exible element connected with the por
tation of the block and means for rotating the
tion of said part remote from the block, con
block and for tensioning the part during such
nected with the block and wrapped on the second
surface of the block to be unwrapped therefrom
as the part is drawn onto the forming surface,
and screw thread means acting through the me
dium of said element for imposing an initial ten
sion on the part.
. rotation including a second surface means on the
block closer to the axis of rotation of the block
than the forming surface and curved generally
about said axis, a ?exible element connected be
75 tween the block and the portion of the part re
15
aeiarsl
16
mote. fromthe block and reeled on; said second
surface means to unreel therefrom upon rotation
of the‘ block in a direction to draw. said partonto
on the block curved generally‘ about. the-axis of
rotation. of the block, onwhich the element is
to'rotatel-the block in said direction,- andmeans
wrapped and having an effective radius which is
shorter than the effective radius of said forming
driven by the‘ last named means, and actingon
the element to tension the part.
13. ;A machine of the character described com.
prising' a‘ rotatable form block, having a curved
surface, and means acting on‘the element for
varying the tension on the workpiece during ro
forming surface curved generally about the axis‘ 10
blockand for tensioning the part during‘such r0
tation- including’ a second surface means on the
block closer to the axis of rotation ‘of the block
than the forming surface and curved generally
about said axis, a ?exible element connected be
tween the block and the portion of the-part re
mote from the block and ‘reeled’ on said second
surfacemeans. to unreel therefrom» upon rota
tion: of the-block in a direction to draw said part
ontovthe forming surface, means ‘acting on the
element-torotate the block.‘ in said direction, and ,
means acting. on the element to tension the part
comprising a movable sprocket engaging the ele- '
ment,. and screw thread means actuated by' the
block: rotating means for moving the sprocket.
1.4;‘; A'machine of the character described‘com- .
prising a rotatable form: block having a forming
surface curvedv generally about the axis of rota
, tion. of the block, means :for connecting an
an elongated workpiece with the block to be
drawn onto'and' formede'by said surfaceupon ro
tationof the block and ‘means for rotating the
block and: for tensioning, the workpiece during
such’rotation‘including a .?'exible element con
nected -' between the, block and the workpiece,
means acting on the element to rotate the block,
'
workpiece comprising, surface presenting means
theifor-ming surface,~means acting on‘ theelement
of rotation‘ of. the block, means for connecting an
elongated. part to beformed with the block ‘to be
drawn onto and formed by said surface upon ro
tation- of- the block and means for rotating the
V
and‘ means acting on the element totension the
tation
of the block.
‘
'
'
_
_
-
V 15. A machine of the character described com
prisingaa rotatable form block having a forming
surface and a second surface, the surfaces ‘being
curved about the-axis of rotation of the block, a
?exible element having'one end connected with
the form block and being wrapped on said second
surface, means for connecting the other end of
the element with one end portion of an elongated
workpiece, means for connecting the other end
portion of the workpiece with the form block-so
that the workpiece is drawn onto the forming
surface upon rotation of the block, and means as—
sociated with the element for rotating the block
to cause the workpiece to be formed by theblock.
16. A machine of .the character described com-.
prising a rotatable form block having a forming
surface and a second surface, the surfaces being
curved about the axis of rotation of the block, a
?exible element having one end connected with
the form block and being wrapped on said second
surface, means for connecting the other end of
the element with one endportion of an elongated
workpiece, means for connecting the other end
portion of the workpiece with the form block so
that the workpiece is drawn onto- the forming
‘ surface upon rotation of the block, means for roe
tating the block to draw the workpiece onto the
forming surface, and means associated with the
element for tensioning the workpiece as itv is
formed.‘
FREDERICK C; HOFFMAN.
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