U.S. patent number 3,635,061 [Application Number 04/882,652] was granted by the patent office on 1972-01-18 for forming apparatus for hydraulic press.
This patent grant is currently assigned to Saab Aktiebolag. Invention is credited to Nils Folke Rydell.
United States Patent |
3,635,061 |
Rydell |
January 18, 1972 |
**Please see images for:
( Certificate of Correction ) ** |
FORMING APPARATUS FOR HYDRAULIC PRESS
Abstract
In a hydraulic forming tool of the diaphragm type, the punch and
the work holder or die member are rigidly mounted on separate
pistons that move in communicated cylinders, so that downward
movement of one effects upward movement of the other by reason of
displacement of fluid from the bottom of one of said cylinders to
the bottom of the other. Adequate forming force is assured by
metering outflow of fluid from the upper portion of the cylinder
having the upgoing piston.
Inventors: |
Rydell; Nils Folke
(Trollhattan, SW) |
Assignee: |
Saab Aktiebolag (Linkoping,
SW)
|
Family
ID: |
20302731 |
Appl.
No.: |
04/882,652 |
Filed: |
December 5, 1969 |
Current U.S.
Class: |
72/63 |
Current CPC
Class: |
B21D
22/205 (20130101) |
Current International
Class: |
B21D
22/20 (20060101); B21d 022/12 () |
Field of
Search: |
;72/63 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Herbst; Richard J.
Claims
The invention is defined by the following claims:
1. Forming apparatus for a press having a pair of jaws, one of
which is arranged for closing and opening motion toward and from
the other, said forming apparatus being of the type comprising a
pair of rigid tool parts carried by one jaw of the press and
cooperable with a resilient forming element carried by the other
jaw, one of said rigid tool parts being substantially annular and
in surrounding relation to the other, and said rigid tool parts
being movable relative to one another in the directions of closing
and opening motion of said jaw, said forming apparatus being
characterized by:
A. body means connectable with said one jaw of the press and
defining first and second cylinder means which are in substantially
concentric relation to one another and which are communicated with
one another near their ends remote from the resilient forming
element so that fluid can flow substantially freely between their
said end portions;
B. first piston means slidable in the first cylinder means and
rigidly connected with one of said rigid tool parts to be moved
toward said end of the first cylinder means upon closing motion of
the movable press jaw, thereby displacing fluid into the second
cylinder means from the first cylinder means;
C. second piston means slidable in the second cylinder means and
which is moved toward the resilient forming element by fluid
displaced into said second cylinder means;
D. means
1. providing a rigid connection between said second piston means
and the other rigid tool part and
2. cooperating with the second piston means to define, in the other
end portion of said second cylinder means, a chamber which varies
in volume with movement of said second piston means; and
E. means providing for throttled flow of fluid from said chamber to
yieldingly resist movement of said second piston means toward the
resilient forming element and concomitantly resist motion of said
one rigid tool part in the direction away from the resilient
forming element, thereby maintaining the resilient forming element
engaged under substantial force with a blank overlying both of said
rigid tool parts.
2. The forming apparatus of claim 1, further characterized by:
one of said cylinder means and its piston means being annular and
concentrically surrounding the other cylinder means.
3. The forming apparatus of claim 1, further characterized by:
A. one of said cylinder means comprising a plurality of cylinders
at circumferentially spaced intervals around the other cylinder
means; and
B. the piston means for said one cylinder means comprising a
plurality of pistons, one for each of said plurality of
cylinders.
4. The forming apparatus of claim 3, wherein said means providing
for substantially free flow of fluid between the first and second
cylinder means comprises means defining a plurality of passages,
one connecting each of said plurality of cylinders with said other
cylinder means, further characterized by:
means for selectively blocking at least certain of said passages,
for changing the effective volume of said one cylinder means and
thereby changing the relative strokes of the tool parts.
5. The forming apparatus of claim 1, further characterized by:
A. one of said cylinder means being located below the other;
B. the piston means of said one cylinder means being connected with
its tool part by a substantially elongated coaxial stem; and
C. the other of said cylinder means and its piston means being
annular and surrounding said stem.
6. The forming apparatus of claim 1, further characterized by:
A. said means providing for throttled flow of fluid from said
chamber comprising a flow-restricting device;
B. means providing a source of pressurized fluid; and
C. a flow-directing valve communicated with said chamber and
alternatively communicable with
1. said flow-restricting device and
2. said pressurized fluid source means to provide for refilling the
upper portion of the second cylinder means after a cycle of closing
and opening motion of the press jaws by which a workpiece is
formed, thus effecting return movement of the second piston means
and concomitant return movement of the first piston means.
7. The forming apparatus of claim 6, further characterized by:
A. first control means connected with the flow-directing valve and
operatively so associated with a part connected with the forming
apparatus as to cause the flow-directing valve to be communicated
with said pressurized fluid source means in consequence of movement
of said one press jaw away from the other to its fully open
position; and
B. second control means connected with the flow-directing valve and
operatively associated with a part that moves in unison with one of
said piston means for causing the flow-directing valve to be
communicated with said flow-restricting device when the first
piston means attains a predetermined position in its return
motion.
8. The forming apparatus of claim 6, further characterized by:
A. a pressure-responsive transducer in the upper portion of the
second cylinder means for producing an output which is a function
of fluid pressure therein;
B. a rate-responsive transducer operatively associated with one of
said tool parts for producing an output which is a function of the
rate at which said tool part moves; and
C. said flow-restricting device being connected with said
pressure-responsive transducer and with said rate-responsive
transducer and being responsive to their outputs.
9. The forming apparatus of claim 1 wherein said resilient forming
element comprises:
A. a substantially cylindrical pressure chamber member having a
bore therethrough and which is carried by said other jaw of the
press for limited motion toward and from the same in the directions
of opening and closing motions of the press;
B. a plunger fixed to said other jaw of the press and sealingly
slidably received in said bore in the pressure chamber member to
close one end portion of the same;
C. a resilient diaphragm extending across the bore in said pressure
chamber member near the other end thereof and cooperating with said
member and the plunger to define a pressure fluid chamber; and
D. means yieldingly biasing the pressure chamber member in the
direction toward said other jaw to maintain fluid in said fluid
chamber under pressure.
10. Forming apparatus for a press having a pair of jaws arranged
for relative closing and opening movement, said forming apparatus
being of the type comprising a resilient diaphragm carried by one
jaw of the press and a pair of relatively movable rigid tool parts
carried by the other jaw for cooperation with the diaphragm, one of
said rigid tool parts being substantially annular and in
surrounding relation to the other, said forming apparatus being
characterized by:
A. a substantially cylindrical pressure chamber member having a
bore therethrough and which is carried by said one jaw of the press
for limited axial motion toward and from the same in the directions
of jaw motions, said diaphragm extending sealingly across the bore
in said pressure chamber member near the end thereof remote from
said one jaw;
B. a plunger fixed to said one jaw and sealingly slidably received
in said bore to close the other end thereof;
C. means yieldingly biasing the pressure chamber member in the
direction toward said one jaw to maintain fluid in said bore under
pressure;
D. means providing a motion-transmitting connection between said
rigid tool parts whereby the force which the diaphragm exerts upon
them through a blank to be formed, upon closing motion of the jaws,
effects motion of one of said rigid tool parts in the direction
toward said other jaw and motion of the other one in the opposite
direction; and
E. means for yieldingly resisting motion of the rigid tool parts in
their said directions, to thereby maintain a substantially high
pressure in the fluid in said bore and concomitantly maintain
forming force upon a blank interposed between the diaphragm and the
tool parts, the last-named means comprising:
1. a plunger rigidly connected with one of the tool parts to move
in unison therewith,
2. means in fixed relation to said other jaw cooperating with said
plunger to define a variable-volume pressure chamber, and
3. means providing for throttled flow of fluid out of said
variable-volume pressure chamber.
11. The forming apparatus of claim 10, wherein said rigid tool
parts have normal positions from which they are displaced in
consequence of closing motion of the jaws, further characterized
by:
F. pump means connectable with said variable-volume pressure
chamber in bypass relation to said means providing for the
throttled flow of fluid therefrom, for effecting return motion of
the rigid tool parts to their normal positions upon completion of a
cycle of closing and opening motion of the jaws.
Description
This invention concerns hydraulic forming tools used with presses
for the forming of sheet metal blanks; and the invention is related
more particularly to hydraulic forming tools of the type comprising
a body which defines a pressure chamber that is closed at its
bottom by a resilient diaphragm, a rigid blank holder beneath the
body that cooperates with the diaphragm to clampingly confine
marginal edge portions of a workpiece, and a central punch which is
movable relative to the blank holder and which cooperates with the
diaphragm in forming the central portion of the workpiece.
Forming tools of the general type to which this invention relates
are disclosed, for example, in U.S. Pat. No. 3,392,563, to H.
Moller, and U.S. Pat. No. 3,115,858 to C. L. Mitchell. Such a
forming tool can be built into a press as an integral part thereof
or can comprise a separate attachment for use in conventional
presses.
Particularly where a forming tool of the character described is
designed as an attachment, it has often happened heretofore that
either the stroke of the press or the space between the press jaws
was insufficient, when the attachment was received between them, to
leave room for withdrawal of formed parts from between the
diaphragm and the rigid tool members that cooperated with it. This
was particularly true with tools for deep-drawn parts, since with
prior tools of the character described the length of the press
stroke had to be equal to about twice the depth of the finished
workpiece to accommodate both the working portion of the stroke and
an additional amount of stroke that opened the press for workpiece
unloading.
For best economy in press operation the press should have as fast a
motion as possible during formation of deep-drawn parts. The power
required by a press depends not only upon the force that it must
exert during the forming operation but also upon the speed at which
drawing is effected, hence a press must have a certain size for
formation of any particular part, or else its production rate must
be reduced to an uneconomically slow speed.
With the foregoing considerations in mind it is a general object of
this invention to provide a forming tool of the character described
which can be either an integral part of a press or an accessory for
a press and which requires substantially less press jaw travel and
jaw gap for a given draw depth than prior forming tools of this
general kind, and which therefore enables the forming of deeply
drawn workpieces with the use of a substantially smaller press then
was heretofore needed for that purpose.
It is also an object of this invention to provide a hydraulic
forming tool of the character described that utilizes press power
very efficiently, so as to make possible the production of
relatively deeply drawn workpieces at an economically high rate
with the use of a press having a relatively small stroke.
It is also an object of this invention to provide a hydraulic
forming tool of the character described which effectively increases
the jaw stroke of a forming press, is capable of being used for
both punch forming and die forming, and also provides for powered
automatic withdrawal of the punch from the workpiece or the
workpiece from the die.
With these observations and objectives in mind, the manner in which
the invention achieves its purpose will be appreciated from the
following description and the accompanying drawings, which
exemplify the invention, it being understood that such changes in
the precise method of practicing the invention and in the specific
apparatus disclosed herein may be made as come within the scope of
the appended claims.
The accompanying drawings illustrate several complete examples of
embodiments of the invention constructed according to the best
modes so far devised for the practical application of the
principles thereof, and in which:
FIG. 1 is a vertical sectional view of a hydraulic forming tool
embodying the principles of this invention, shown in the left-hand
half of the figure in its condition at the beginning of a forming
stroke and in the right-hand half of the figure in its condition at
the end of a forming stroke;
FIG. 2 is a view generally similar to FIG. 1 but illustrating a
modified embodiment of the invention;
FIG. 3 is another view generally similar to FIG. 1 but illustrating
a further modified embodiment of the invention;
FIG. 4 is a horizontal sectional view of a still further modified
embodiment of the invention;
FIG. 5 is a sectional view taken on the plane of the line 5--5 in
FIG. 4; and
FIG. 6 is a detailed horizontal sectional view on an enlarged scale
of the area embraced by the line 6 in FIG. 4.
Referring now to the accompanying drawings, the numerals 5 and 6
respectively designate the upper and lower jaws of a press that is
equipped with a forming tool embodying the principles of this
invention, which forming tool is designated generally by 7 and is
shown for purposes of illustration as an accessory attachment for
the press. The forming tool 7 comprises, in general, an upper
element 8 that defines a pressure chamber which is enclosed by a
resilient diaphragm 9 at its bottom, and a lower element 10
comprising a rigid central punch 11 and a rigid annular work holder
12 which concentrically surrounds the punch.
The upper element 8 comprises an outer cylindrical body member 18
having a bore 19 therethrough and which is carried by the press
head for limited motion up and down relative to it, a plunger or
piston 20 which is sealingly slidable in the upper portion of the
bore 19 and which is rigidly but removably secured to the press
head, and the resilient diaphragm 9, which extends across the bore
19 in the body member 18 near the bottom thereof.
The piston or plunger 20 is secured to a mounting plate 18 on the
underside of the upper press jaw or press head 5. The mounting
plate also has long studs 14 extending downwardly from it to mount
the cylindrical body member 18 for up-and-down motion relative to
the press head 5 and the plunger 20. These studs extend through
guide holes in brackets 15 that project laterally from the upper
portion of the cylindrical outer body member, and the latter is
biased upwardly by means of compression springs 16, one surrounding
each stud and reacting between the bracket 15 and a head 17 on the
bottom of the stud.
The diaphragm 9 is substantially cup shaped, having a cylindrical
sidewall and a flat bottom wall, and it is securely held in the
bore 19 in the body member 18 by means of a radially outwardly
projecting circumferential rib or land 22 on its sidewall that is
received in a closely fitting groove in the body member that opens
inwardly to its bore. As is conventional, a clamping ring (not
shown) engages the inner surface of the diaphragm sidewall to
maintain the land 22 engaged in the groove.
The pressure chamber 21 that is conjointly defined by the body
member 18, the plunger 20 and the diaphragm 9 can be filled with
hydraulic fluid through a normally closed filler passage 23. A
normally closed vent passage 24 permits air to bleed out of the
chamber as it is filled.
It will be observed that the outer cylindrical body member 18, in
being able to move axially relative to the plunger 20, can
accommodate changes in volume of the pressure chamber 21 due to
upward flexing displacement of the central portion of the diaphragm
into it. It will also be noted that the force which the pressure
fluid in the chamber 21 exerts upon the diaphragm in reaction to
such flexing displacement is to some extent determined by the
biasing force exerted by the springs 16. The plunger 20 can be
formed, as shown, with a cavity in its underside that provides
adequate space for such diaphragm flexing.
The press table or lower jaw 6 of the press supports the lower
element 10 of the forming tool, which comprises a bottom wall
member 25, concentric inner and outer annular upright wall members
26 and 27, respectively, and a top wall member 28. The several wall
members just mentioned cooperate to define an inner cylinder 29, in
which a plungerlike inner piston 30 is slidable, and an annular
outer cylinder 31, concentrically surrounding the inner cylinder
and in which an annular outer piston 32 is slidable.
The inner piston 30 has a reduced diameter coaxial stem portion 33
which can be integral with its body portion 33 which can be
integral with its body portion and which projects with a slidable
sealing fit through a hole in the top wall member 28. The punch 11
is rigidly secured to the top of this stem. Compression rods or
struts 34 project upwardly from the annular outer piston 32 at
circumferentially spaced intervals around it and extend with a
slidable sealing fit through holes in the top wall member 28. To
the upper ends of these struts is rigidly attached an annular tool
holder 35 on which the work holder 12 is readily removably carried.
Since the actual forming of a workpiece is performed by the work
holder 12 and the punch 11 in cooperation with the diaphragm 9, it
is intended that work holders 12 of different shapes will be
interchangeably mounted on the tool holder 35, and the connection
between the punch 11 and the piston stem 33 can also be such as to
permit punches to be readily interchanged.
To provide for motion of the punch and work holder in opposite
directions during a forming operation, the inner cylinder 29 is
communicated with the outer annular cylinder 31 by means of
passages 38 in the bottom wall member 25 through which hydraulic
fluid can flow relatively freely.
When the press is open, with the press head or upper press jaw 5
fully raised, there is a substantial spacing between the work
holder 12 and the bottom of the upper element 8, through which a
finished formed workpiece can be removed from the press and a new
sheet metal blank 36 can be set in place. With the press open, the
top of the punch 11 is at the level of the top surface of the work
holder 12, and the bottom of the punch can rest on the top surface
of the top wall member 28; but the bottom surface of the tool
holder 35 is spaced above the upper surface of the top wall
member.
With a blank 36 in place, the press head is lowered. At the left
side of FIG. 1 there is illustrated what can be regarded as a
press-closed condition, in which the diaphragm 9 has just flatwise
engaged the blank, and the punch 11 and work holder 12 still remain
in their initial conditions. With continued descent of the press
head, the work holder now moves downwardly, but with sufficient
resistance to downward motion so that it cooperates with the
diaphragm in clampingly confining the marginal edge portions of the
blank. At the same time, the punch moves upwardly, cooperating with
the central portion of the diaphragm in forming the blank.
The reason the punch moves upwardly as the work holder descends is
that downward motion of the annular outer piston 32 displaces
hydraulic fluid out of the chamber 39 beneath it, and through the
passages 38 in the bottom wall member into the chamber 40 that
comprises the bottom portion of the inner cylinder 29, raising the
inner piston 30. Such displacement of fluid from the outer cylinder
to the inner one can take place because the area of the work holder
12 that is engaged by the diaphragm, and against which the
pressurized fluid in the upper pressure chamber 21 effectively
reacts, is substantially greater than the corresponding area of the
punch 11. Since the area of the annular outer piston 32 that acts
upon fluid in the bottom chamber 39 is substantially greater than
the corresponding area of the inner piston 30, the punch moves up
faster and farther than the work holder moves down. Thus in the
example illustrated in FIG. 1, the effective area of the outer
annular piston is twice that of the inner piston, and therefore the
punch moves upwardly relative to the press table 6 through twice
the distance that the work holder 12 moves downwardly. This is to
say that the working stroke of the forming tool is triple the
working stroke of the press.
It has already been mentioned that reaction force which fluid in
the upper pressure chamber 21 exerts upon the diaphragm 9 is
influenced by the biasing force of the springs 16. However, the
pressure in that chamber is also materially influenced by the rate
of upward motion of the punch (or, what is really the same thing,
of downward motion of the work holder) since this determines the
extent to which the springs 16 will be compressed at any instant
during the working stroke. Hence the pressure in the chamber 21 is
controlled by regulating the rate at which the punch is permitted
to move upwardly, and this, in turn, is accomplished by metering
the displacement of hydraulic fluid out of a pressure chamber 41 in
the top of the inner cylinder 29, above the punch-actuating piston
30. Such metering also serves to regulate the clamping force that
the diaphragm and the blank holder exert upon the marginal edge
portion of the blank, inasmuch as it determines the resistance of
the work holder to downward motion.
Fluid outflow from the chamber 41 is controlled automatically,
partially in response to the rate of upward motion of the punch, as
detected by a rate-responsive motion transducer or sensor 43, and
partially in response to the fluid pressure prevailing in the
chamber 41, as detected by a pressure transducer 44 that is mounted
in said chamber, on a wall thereof. The motion sensor 43 can be
actuated by a rod 42 or the like that is attached to the punch 11
or its piston 30 to be moved lengthwise in unison with the
punch.
The respective electrical outputs of the motion and pressure
sensors are fed, by way of conductors 45 and 46, to an
electroresponsive pilot valve 47 which in turn governs a pressure
control valve 48. The pressure control valve is connected in a
metered flow duct 49 that is communicated, through a four-port
two-position valve 50, with a passage 51 in the top wall member 28,
which passage in turn communicates with the chamber 41. Hence the
rate at which fluid is permitted to flow out of the chamber 41
during upward movement of the inner piston 30 is determined by the
pressure control valve 48 in accordance with rate and pressure
values detected by the sensors 43 and 44.
From the pressure control valve 48 the expelled fluid flows by way
of a return fluid duct 52 to a fluid reservoir 53.
At the conclusion of the forming operation, after the press head
has returned to its fully raised position, hydraulic fluid is fed
back into the pressure chamber 41 to force the punch-actuating
piston 30 back down to its initial position, and the work holder 12
is concomitantly moved back up to its initial position as a result
of displacement of fluid out of the chamber 40 and into the chamber
39 through the passages 38.
For such refilling of the chamber 41 there is a pump 54 or other
fluid pressure source that has its inlet communicated with the
reservoir 53 and its outlet connected with an electrically actuated
two-position valve 55. Except during the time that the tool is
actually in its return stroke, the two-position valve 55 is in a
normal unenergized condition in which it communicates the pump
outlet with a bypass duct 56 that leads into the return fluid duct
52, for return of the pump output to the reservoir 53. When the
press head reaches the top of its stroke at the end of its
operating cycle, it closes a switch 58 that is connected with the
actuator of the two-position valve 55 by means of a conductor 59 in
which there is a then-closed switch 60. Such closure of the switch
58 energizes the actuator of the two-position valve 55, and said
valve shifts to a position in which the pump outlet is communicated
with the duct 49 by way of a duct 61 and a check valve 62, and
thence, by way of the four-port two-position valve 50 and the
passage 51, with the chamber 41.
When the tool holder 35 reaches its fully raised position, it
actuates the switch 60 to its open position, breaking the circuit
through the conductor 59 that energizes the actuator for the
two-position valve 55, and that valve then returns under bias to
its normal position in which it directs the pump output back to the
reservoir.
It will be seen that the valve 55 remains in its normal position
all through the subsequent forming stroke because at least one of
the switches 58 or 60 always remains open from the time the press
head begins to descend until it returns to its fully raised
position.
For filling hydraulic fluid into the chambers 39 and 40 at the
bottoms of the inner and outer cylinders 29 and 31, the four-port
two-position valve 50 is manually rotated through 90.degree. from
its illustrated position, so that it communicates the duct 49 with
a duct 64 that leads to a filler passage 65 in the outer annular
wall member 27. The actuator of the two-position valve 55 is then
energized (as by manual actuation of a separate switch, not shown)
to shift that valve to its position in which the output of the pump
54 is directed to flow successively through duct 61, check valve 62
the four-port valve 50, and duct 64 to the filler passage 65. A
closable vent for bleeding air out of the chambers 39 and 40 is of
course provided and can comprise a passage 66 extending up through
the stem portion 33 of the inner piston.
For draining the lower chambers 39 and 40 there is a duct 67 which
communicates the four-port two-position valve 50 with a manually
controllable normally closed shutoff valve 68. From the shutoff
valve a duct 69 leads to the return fluid duct 52. Hence the
chambers 39 and 40 can be drained by leaving the four-port valve 50
in its normal (illustrated) position and opening the shutoff valve
68. Similarly, the chamber 41 in the upper portion of the inner
cylinder can be drained by rotating the four-port valve 50 through
90.degree. from its illustrated position, to communicate the
passage 51 with the duct 67, then opening the shutoff valve 68 and
forcing the tool holder 35 down to raise the inner piston 30.
FIG. 2 illustrates essentially the same tool apparatus as FIG. 1,
but adapted for so-called die forming, with an appropriately
different punch 11' and work holder 12' installed thereon. In this
case the punch 11' does not participate actively in the formation
of the workpiece, but instead serves to define the bottom surface
of the cavity of a die, the remainder of which is defined by the
work holder 12'; and instead of being flexed upwardly into the
upper pressure chamber 21 by the rigid tool parts, the diaphragm 9
is forced downwardly into the die cavity thus defined, to serve, in
effect, as the male member of the forming tool.
For this type of work the tool holder 35 is in a lowered position
at the beginning of each forming cycle (see the left half of FIG.
2), and it can rest on the top wall member 28, while the punch,
which is axially short, again has its top surface flush with that
of the work holder 12' but has its bottom surface spaced a
substantial distance above the top of the top wall member 28.
Die forming is usually employed for the shaping of relatively wide,
shallow workpieces, and therefore the punch 11' has a top surface
area which is large relative to the top surface area of the work
holder 12'. For this reason the work holder can be forced to rise
in consequence of downward movement of the punch.
In this case, to adapt the tool for die forming as well as punch
forming, its hydraulic circuit is somewhat modified, inasmuch as
die forming requires that the chamber 70 above the annular outer
piston 32 contain hydraulic fluid, and the outflow of such fluid
out of said chamber must be metered as the annular piston is raised
during the forming stroke. There must also be a pressure sensor 44'
in the upper annular chamber 70, and means for selectively
connecting the pilot valve 47 with either that sensor or the
pressure sensor 44 in the upper portion of the inner cylinder,
depending upon the type of work to be done.
A passage 71 leads through the top wall member 28 from the upper
annular chamber 70, and a four-port two-position valve 72 provides
for selectively communicating either said passage 71, or the
passage 51 that leads to the chamber 41, with the metered outflow
duct 49 that leads to the pressure control valve 48. Whichever of
the two upper chambers 41 or 70 is not thus communicated with the
pressure control valve 48 is connected through the four-port
two-position valve 72 with a duct 67' that leads to a normally
closed manually positionable shutoff valve 68'. The shutoff valve
68' is in turn connected with a duct 69' that leads to the return
fluid line 52; hence opening of said shutoff valve provides for
draining either of the chambers 41 or 70, depending upon the
position of the four-port valve 72.
The passage 65 in the annular sidewall member 27, through which the
communicated bottom chambers 39 and 40 can be filled and drained,
is controlled by a three-position valve 73 that is normally closed.
In one of its open positions the three-position valve communicates
the passage 65 with a duct 74 that leads to the return fluid duct
52, for draining the bottom chambers; and in its other open
position it communicates the passage 65 with a duct 75 through
which pressure fluid from the pump outlet can be filled into the
bottom chambers by way of the electroresponsive two-position valve
55, a duct 61, the check valve 62, and a portion of the duct 49
that communicates the check valve with the duct 75.
The modified embodiment of the invention that is shown in FIG. 3,
which is illustrated in its adaptation for die forming, is
especially desirable where it is important to have compactness in
directions transverse to press head travel but where there is a
reasonably large gap between the press jaws, or where the press
table can have a substantially deep well. In this case the inner
cylinder 29' is located below the annular outer cylinder 31'. If
there is a recess or well in the press table 6, the portion of the
lower element 10' that defines the inner cylinder 29' can have a
reduced diameter to be receivable in the well.
The stem portion 33' of the inner piston 30, upon which the punch
11' is secured, is necessarily rather long, extending with a
slidable sealing fit up through a tubular upright wall 26' that
defines the inner circumferential surface of the annular cylinder
31'. The tool holder 35 is again secured on upright struts 34 that
project up from the annular piston 32' at circumferentially spaced
intervals, through the top wall member 28. The passage 38' that
communicates the lower portions of cylinders 29' and 31' with one
another is naturally a vertical one along most of its length, and
is mainly formed in the sidewall of the inner cylinder 29'. In all
other respects the embodiment of the invention illustrated in FIG.
3 is like that shown in FIG. 2.
FIGS. 4-6 illustrate an embodiment of the invention having a
plurality of conventional cylinders 31" instead of a single annular
outer cylinder, the cylinders 31" being located in a ring around
the inner cylinder 29, as best seen in FIG. 4. Each of said
cylinders 31" is provided with a piston 32" that has an upwardly
projecting stem portion 34' which can be regarded as the
counterpart of one of the struts 34 in the previously described
embodiments of the invention. By reason of the fact that the
several stem portions 34' are rigidly secured to the tool holder
35, the several pistons 32" are constrained to move up and down in
unison.
Individual passages 38" in the bottom wall member 25", one for each
of the outer cylinders 31", communicate with the latter at their
bottoms with the bottom of the inner cylinder 29. At least certain
of these passages, as may be seen from FIGS. 4 and 6, are
controlled by shutoff valves 78 having manual actuators 80, such as
handwheels, that are accessible at the exterior of the tool. By
opening or closing various of the valves 78, the stroke of the tool
holder can be varied in relation to that of the punch, to adjust
the apparatus in accordance with the type of work to be performed
and the depth intended for the finished workpiece.
From the foregoing description taken with the accompanying drawings
it will be apparent that this invention provides a forming tool for
hydraulic presses that is both very efficient and very versatile,
and whereby the effective stroke of a forming press can be very
substantially increased.
Those skilled in the art will appreciate that the invention can be
embodied in forms other than as herein disclosed for purposes of
illustration.
* * * * *