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Claims  |
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The invention is defined by the following claims:
1. A fluid forming apparatus having a forming tool comprising a pair of
rigid tool parts that are movable in opposite directions, a piston element
for each tool part, a cylinder for each piston element, and means defining
a constant-volume pressure cavity in which there is confined a quantity of
fluid by which force can be exerted over one face of a sheet metal blank
to shape the blank to a configuration determined by the forming tool, and
wherein each of the tool parts is constrained to move with its piston
element and each piston element cooperates with its cylinder to define a
pressure chamber at the side of the piston remote from the pressure cavity
means, said apparatus being characterized by:
A. pressure control valve means connected with a source of fluid under
pressure and having a connection with the pressure chamber of each of said
cylinders, said valve means being responsive to demand value signals
1. to direct fluid from said source to one of said pressure chambers, and
thus cause one of said tool parts to be moved in a direction inward of the
pressure cavity means with resultant displacement of fluid therein, and
2.
2. to maintain pressure in the other pressure chamber at a value signified
by a prevailing demand value signal applied to the valve means, while
permitting outflow of fluid from said other pressure chamber, so that
movement of the other tool part in the opposite direction, due to
displacement of fluid in the pressure cavity means, is yieldingly
restrained and fluid in the pressure cavity remains under a pressure
determined by the demand value signal; and
B. signal generating means for producing pressure demand value signals to
which said valve means can respond and which correspond to the pressures
desired in the pressure cavity means from instant to instant during a
forming operation as related to the instantaneous relative positions of
the forming tool parts and in accordance with a predetermined program of
pressure variation, said signal generating means comprising
1. cooperating camming elements, one of which is confined to motion in
opposite directions and is connected with at least one of the rigid tool
parts to move in correspondence with motions of that rigid tool part, and
the other of which is movable transversely to said opposite directions,
a. one of said camming elements comprising a cam having a profile denoting
said program,
b. the other of said camming elements comprising a cam follower engaged
with said profile, and
2. output means connected with said transversely movable camming element
for producing an output having a magnitude which corresponds to the
instantaneous position of said transversely movable camming element and
which constitutes said demand value signal; and
C. means connecting said output means in controlling relation to said valve
means. 2. A press actuatable by fluid pressure medium and having a rigid
forming tool by which sheet metal blanks can be formed, wherein the
forming tool comprises a pair of tool parts which engage one face of a
blank during forming and which are movable in a pair of opposite
directions, one of said tool parts substantially surrounding the other and
providing a first blank engaging surface that faces in one of said
directions, said tool parts being cooperable with means defining a
constant volume cavity filled with fluid, for maintaining a reaction force
upon the opposite face of a blank during forming, said means defining said
cavity comprising a cylinder member having a plunger relatively movable in
one end portion thereof and having means at its other end defining a
second blank engaging surface which is cooperable with the first blank
engaging surface to flatwise clampingly confine edge portions of a blank,
said press being characterized by:
A. a rigid frame having a pair of opposite portions that are spaced apart
in said directions, said plunger being fixed to one of said portions, and
said cylinder member being axially movable toward and from the other
portion;
B. a stationary cylinder fixed to the other of said portions of the frame;
C. a first piston element movable in said directions and
1. having one end portion received in said stationary cylinder and
cooperating with the same to define a first pressure chamber at the side
of the first piston element remote from said cavity means,
2. said first piston element having said one rigid tool part at its other
end, and
3. said first piston element having a portion which is hollow and which
comprises a movable cylinder;
D. a second piston element movable in said directions, both with the
movable cylinder and relative to the same, said second piston element
1. having one end portion received in the movable cylinder and cooperating
therewith to define a second pressure chamber at the side of said second
piston element that is remote from said cavity means, and
2. having said other rigid tool part at its other end;
E. cooperating stop means constrained to move with said tool parts and
engageable to define a limit of motion of one of said tool parts relative
to the other at which said rigid tool parts are disposed substantially at
a common level, said one tool part being movable relative to the other
from said limit to a forming position in which the tool parts cooperate to
define a shape to which a blank is to be formed;
F. means for introducing pressure fluid from a source thereof into the
pressure chamber associated with the other tool part to move said rigid
tool parts, with the stop means engaged, in unison from a press-open
position in which both tool parts are spaced a substantial distance from
said cavity and towards a press-closed position in which said blank
engaging surfaces are juxtaposed; and
G. means for forcing pressure fluid simultaneously into both of said
pressure chambers and for venting fluid from said source as necessary to
maintain a desired pressure in one of said pressure chambers, to effect
forming of a blank confined between said surfaces.
3. A press for forming sheet metal blanks, comprising a cylinder member
having a surface at one of its ends that is engageable with one face of a
blank to be formed, a plunger movable in the other end portion of the
cylinder member and cooperating with it to define a constant volume
pressure cavity which is filled with fluid, and a hydraulically operated
forming tool comprising a pair of tool parts for engaging the other face
of a blank and each of which is movable in directions axially of the
cylinder member, one of said forming tool parts substantially surrounding
the other and being cooperable with said surface on the cylinder member,
during forming of a blank, to flatwise clamp edge portions of the blank,
said forming tool further comprising a pair of piston elements, one for
each of said tool parts and each connected with its tool part, and means
cooperating with each piston element to define a pressure chamber for it
that is at its end remote from the pressure cavity means, said press being
characterized by:
A. an upright rigid frame having a pair of vertically spaced portions that
are fixed in relation to one another,
1. one of said frame portions having the plunger fixed thereon, with the
cylinder member axially movable on the plunger toward and from the other
of said frame portions, and
2. the forming tool being supported on the other of said frame portions
with at least one of its pressure chamber means fixed thereto;
B. cooperating stop means connected with the respective rigid tool parts to
move therewith and engageable to define a limit of motion of one of said
tool parts relative to the other in which the blank engaging portions of
said tool parts are at substantially a common level, said stops being so
arranged that said one tool part is movable relative to the other from
said limit to a forming position in which the tool parts cooperate to
define a shape to which a blank is to be formed;
C. hydraulic source means providing a supply of hydraulic fluid under
pressure;
D. control means connected with said hydraulic source means and with at
least one of said pressure chambers for effecting movement in unison of
said tool parts, with said stop means engaged, from a press-open position
of the tool parts in which they are both spaced a substantial distance
from the pressure cavity to a press-closed position in which said one tool
part is clampingly juxtaposed to said surface on the cylinder member;
E. pressure control valve means connected with said source means and having
a connection with each of said pressure chambers;
F. program means for said pressure control valve means, responsive to the
relative positions of said parts and cooperating with said control valve
means to cause said parts to move from said press-closed position to
forming positions in which the tool parts define the shape to which a
blank is to be formed and said one tool part is clampingly juxtaposed to
said surface on the cylinder member, said program means being arranged
1. to direct flow of pressure fluid from said source means into the
pressure chamber associated with the tool part that moves inwardly of the
pressure cavity means during forming; and
2. to control the pressure in the other pressure chamber by throttling of
fluid flowing therefrom as the other tool part moves outwardly of the
pressure cavity means during forming so that motion of said other tool
part, due to displacement of fluid in the pressure cavity means, is
yieldingly and controlledly resisted to determine the forming pressure in
the pressure cavity means.
4. A fluid forming apparatus comprising a frame, a forming tool carried by
said frame and having a pair of rigid tool parts that are movable relative
to one another and said frame, and means on said frame defining a pressure
cavity in which forming fluid is contained and which cooperates with the
forming tool to effect a forming operation during which said fluid is
under pressure and applies force over one face of a sheet metal blank
while the forming tool engages the other face of the blank and relative
movement of one of said tool parts in a direction towards the interior of
the cavity brings it to a forming relationship with the other tool part at
which the forming tool defines a shape that the blank is compelled to
take, said forming apparatus being characterized by:
A said pressure cavity means being arranged to confine a volume of forming
fluid which remains constant all during a forming operation;
B. a piston element for each of said tool parts, each piston element being
connected with its tool part to be constrained to move therewith in said
direction and in the opposite direction;
C. a cylinder on the frame for each piston element, each cylinder
cooperating with its piston element to define a pressure chamber at the
side of its piston element that is remote from the pressure cavity means
and in which the piston element is movable in said directions;
D. means defining a limit of motion in said opposite direction of said one
tool part relative to the other tool part, to establish a starting
relationship of the tool parts, the last mentioned means being arranged to
permit motion of said other tool part in said directions relative to its
cylinder;
E. means operative when the tool parts are in their starting relationship
for effecting relative movement in said one direction between the forming
tool and the pressure cavity means from a press-open relationship in which
the forming tool is substantially spaced from the pressure cavity means to
a press-closed relationship in which the forming tool is adjacent to the
pressure cavity means;
F. source means providing a supply of fluid under pressure;
G. means operative when the pressure cavity means and the forming tool are
in their press-closed relationship for directing pressurized fluid from
said source means to the pressure chamber for said one tool part, to force
said one tool part in the first mentioned direction and thereby cause it,
acting through a blank, to displace forming fluid in the cavity; and
H. control valve means for metering flow of fluid out of the pressure
chamber for the other tool part at a rate to maintain a fluid pressure
therein which controls the pressure of forming fluid in said pressure
cavity but which can be substantially lower than pressure in said cavity.
5. The fluid forming apparatus of claim 4, further characterized by:
said control valve means being connected with
said source means and with the pressure chamber for said one tool part.
6. The fluid forming apparatus of claim 5, wherein said means on the frame
defining a pressure cavity comprises a plunger which remains in a fixed
position relative to the frame during a forming operation, and a further
cylinder, slidably embracing the plunger, further characterized by:
I. sensing means for constantly detecting the position of at least said one
of the tool parts relative to said plunger;
J. program means defining a predetermined variation of pressure of forming
fluid in the pressure cavity in relation to the changing position of said
one tool part relative to said plunger;
K. signal generating means connected with said sensing means and with said
program means for producing an output which at every instant has a
magnitude that corresponds to the forming fluid pressure signified by the
program means for the sensed position of said one tool part relative to
said plunger; and
L. actuator means for the control valve means, connected with said signal
generating means and operative to cause the control valve means to
maintain the pressure in said one pressure chamber at a value that
corresponds to the magnitude of said output.
7. The forming apparatus of claim 4 wherein said means defining said limit
of motion in said opposite direction of said one tool part relative to the
other comprises:
cooperating abutment means constrained to motion in said directions with
the respective tool parts and engageable when said tool parts are in their
starting relationship.
8. The forming apparatus of claim 4 wherein said means on the frame
defining a pressure cavity comprises a plunger which is fixed in relation
to the frame and said cylinders, and a further cylinder slidably embracing
said plunger, further characterized by:
said means for effecting relative movement in said one direction between
the forming tool and the pressure cavity means comprising means for
introducing pressure fluid into the pressure chamber for said other tool
part in a volume sufficient to carry the forming tool, with the tool parts
in their starting relationship, from its press-open relationship to the
pressure cavity means to its press-closed relationship thereto. |
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Claims |
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Description |
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This invention relates to apparatus for the forming of sheet metal blanks,
of the type wherein fluid pressure is applied to one face of a blank to
force the blank to assume a shape that is determined by a rigid forming
tool at its other face; and the invention is more particularly concerned
with fluid forming apparatus wherein forming pressure is applied to the
blank by means of fluid confined in a constant-volume pressure cavity.
Forming apparatus of the general type to which the present invention
relates is disclosed in U.S. Pat. No. 3,635,061. Such apparatus comprises
means defining a constant-volume pressure cavity, cooperating with a rigid
forming tool. The forming tool comprises a pair of tool parts that are
movable relative to one another in directions toward and from the cavity.
One of the rigid tool parts can be a more or less annular blank holder or
draw ring unit that provides a blank-engaging surface which faces towards
the pressure cavity. The other rigid tool part, which is more or less
surrounded by the blank holder, may be either a punch or a die.
The pressure cavity is defined by a cylinder member in which a quantity of
fluid is contained, a plunger received in one end portion of the cylinder
member with a slideable sealing fit, and a resilient diaphragm that closes
the other end of the cylinder member and cooperates with the plunger to
confine the fluid in the cylinder member. The exterior surface of the
diaphragm opposes the blank engaging surface on the annular rigid tool
part and cooperates with it to flat-wise clampingly confine edge portions
of a blank being formed.
During a forming operation, relative movement between the forming tool and
the cavity means carries one of the tool parts in the direction inwardly
of the pressure cavity. That tool part tends to reduce the volume of the
cavity, but since the quantity of fluid confined in the cavity remains
constant, the fluid is merely displaced. If, for example, that tool part
is an upwardly moving punch, it deflects the central portion of the
diaphragm upwardly into the pressure cavity, and as a result the cylinder
member of the cavity means is displaced downwardly relative to its
plunger. The cylinder member forces the draw ring unit to move downwardly
with it, but such downward movement of the draw ring unit is yieldingly
resisted. The fluid in the cavity is thus subjected to a pressure which
depends upon the resistance to downward movement of the draw ring unit,
and such pressure, imposed through the diaphragm upon the entire upper
surface of a blank to be formed, forces the blank into a shape determined
by the rigid forming tool.
In the press attachment of U.S. Pat. No. 3,635,061, the plunger of the
constant volume pressure cavity was secured to the movable upper jaw of a
press, and each of the rigid tool parts comprised a piston that was
movable up and down in a cylinder which rested on the press table. Each of
the cylinders thus defined a pressure chamber beneath its piston, and
these pressure chambers were interconnected. Hence as one of the pistons
was forced down into its cylinder by downward motion of the movable press
jaw, the fluid displaced from its pressure chamber was transferred into
the lower chamber for the other piston, causing the latter to move
upwardly in its cylinder. Such upward motion was yieldingly opposed by a
body of fluid in the upper portion of the cylinder of the upwardly moving
piston, which fluid was controlledly bled out of that cylinder. Forming
pressure in the constant-volume pressure cavity thus depended upon the
rate of downward motion of the movable press jaw as well as upon the
restriction to flow of fluid out of the pressure chamber above the
upwardly moving rigid tool part.
In any hydraulic forming apparatus wherein fluid in a pressure cavity
exerts the forming force upon the blank, it is necessary to control the
pressure of that fluid during the forming operation. In the forming of a
deeply drawn part, such control of forming pressure is especially
important, inasmuch as the forming pressure should usually be increased at
a more or less steady rate as forming progresses. In the forming apparatus
of U.S. Pat. No. 3,635,061, there were sensing and control devices for
automatically regulating fluid outflow from the pressure chamber beneath
the downwardly moving rigid tool part, such regulation being effected
partially in response to the pressure prevailing in that chamber and
partially in response to the rate of motion of the upwardly moving rigid
tool part.
U.S. Pat. No. 2,783,727 discloses forming apparatus in the nature of a
press attachment wherein the rigid tool parts are movable in opposite
directions, without any substantial restraint being imposed upon the
movements of either of them, and wherein forming pressure is controlled
during the forming operation by varying the volume of fluid in the
pressure cavity. That expedient for control of forming pressure is
undesirable for several reasons. For one, it is difficult to effect
accurate throttling of flowing fluid that is subjected to the extremely
high pressures that obtain in the pressure cavity during a forming
operation, which pressures can attain values as high as 2,000
Kg./cm.sup.2. It is also difficult to meter just the right amount of fluid
back into or back out of the pressure cavity at the completion of a
forming operation, to establish the diaphragm in the right condition for
initiation of the next succeeding forming operation.
With these considerations in mind, it is an object of the present invention
to provide fluid forming apparatus having a pressure cavity of constant
volume and wherein the forming pressure in the pressure cavity is exerted
solely by the forming tool, so that control of such pressure can be
effected in a relatively simple manner, even when the forming pressure
must vary during the course of a forming operation.
Another object of this invention is to provide, in a hydraulic forming
press having a constant volume pressure cavity, simple and effective
control means whereby the forming pressure can be closely and continuously
regulated all during the forming operation, in accordance with a
predetermined program, so that the pressure can be increased at a suitable
rate as the forming progresses. Still another object of this invention is
to provide a press wherein the means for generating forming pressure in
the cavity and the means for regulating such pressure both operate at
fluid pressures that are relatively low and hence easily controlled and
contained.
A further object of this invention is related to the fact that the
apparatus in which the invention is embodied can comprise a self-contained
press, rather than merely a press attachment. In fluid forming apparatus
of the type here under consideration, wherein the rigid tool parts move in
opposite directions during actual forming, the punch should be at the same
level as the blank-holding unit -- or slightly below that level -- at the
point in the stroke at which the blank begins to be subjected to clamping
force.
At the conclusion of the forming operation, and after the formed blank is
disengaged from the pressure cavity diaphragm, the rigid tool parts should
be brought back to that same starting relationship to one another, to
disengage the punch from the formed workpiece. When the press is open, the
space between the forming tool and the pressure cavity should be about
equal to the depth of a workpiece to be formed, to leave room for
withdrawal of formed workpieces from the apparatus; and therefore the tool
parts should also be in the starting relationship to one another at that
time, to afford maximum spacing with a minimum press stroke. The two tool
parts should of course move in unison from their press-open positions to
their positions at which clamping force begins to be imposed upon the
blank.
In the press attachment of U.S. Pat. No. 3,635,061, coordinating the
sequence of movements of the forming tool parts was a relatively simple
matter, inasmuch as the press-opening and press-closing motion was
effected by movement of the movable press jaw, by which the pressure
cavity means was carried, and consequently the rigid tool parts were only
required to move in opposite directions relative to one another. The press
table could therefore serve as a reference level so that they could be
readily brought to their starting relationship to one another.
But where fluid forming apparatus of the general type disclosed in that
patent is to be embodied in a self-contained press, the apparatus must
accommodate not only relative motion between the rigid tool parts during
the forming portion of the press stroke but also relative press-opening
and press-closing motions as between the pressure cavity means and the
forming tool as a whole. Control of forming pressure by control of the
forming tool implies that it is to the rigid tool parts, rather than the
pressure cavity means, which should make the press-opening and
press-closing movements. This is to say that the pressure cavity means
should remain stationary and that the movements of the tool parts, both
with one another and relative to one another, must be properly coordinated
so that they will have the proper positions, in relation to one another
and in relation to the cavity means, in every part of the cycle.
With the foregoing in mind, it is another object of this invention to
provide simple means in fluid forming apparatus of the character described
for achieving the above described sequence of movements of the rigid tool
parts, while also maintaining such control over the tool parts as will
assure desired forming pressures during every part of the forming
operation.
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 changes may be made in the specific apparatus
disclosed herein without departing from the essentials of the invention
set forth in the appended claims.
The accompanying drawings illustrate two 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 longitudinal sectional view of a forming press embodying the
principles of this invention, shown in the left hand half of the drawing
in its condition just before a forming operation begins and in the right
hand half of the figure in its condition at the completion of a forming
stroke;
FIG. 2 is a view generally similar to FIG. 1 but illustrating a modified
embodiment of the invention; and
FIG. 3 is a diagram of the pressure regulating system of the presses shown
in FIGS. 1 and 2.
Referring now to the accompanying drawings, the numeral 1 designates an
upright, rigid frame having vertically spaced top and bottom portions to
which are secured the cooperating force applying members which comprise
the forming press of this invention. To the upper portion of the frame
there is secured means defining a constant volume pressure cavity,
designated generally by 2. To the lower portion 18 of the frame there is
secured a hydraulic unit 19 that provides for actuation of a rigid forming
tool comprising a pair of tool parts 35 and 38 which are movable relative
to one another and to the pressure cavity means 2. As shown, the rigid
tool part 38 comprises an annular draw ring unit or blank holding unit,
and the tool part 35 comprises a punch that is surrounded by the draw ring
unit.
The hydraulic unit 19 comprises a stationary cylinder 20, an outer piston
element 26 that is movable up and down in the stationary cylinder and
comprises a movable cylinder 27, and an inner piston element 31 that is
movable up and down in the movable cylinder.
The outer piston element 26 carries at its upper end the blank holding unit
or draw ring unit 38, while the other rigid tool part 35 is fixed to the
top of the inner piston element 31.
During a forming operation, a sheet metal blank 3 is compelled to take a
shape determined by the rigid tool, under the influence of force exerted
over its entire upper surface by the constant volume cavity means 2. The
cavity means comprises a plunger 6 that is fixed to the upper portion of
the frame 1, a cylinder member 4 that has the plunger received in its
upper end portion with a slideable sealing fit, and a more or less
cup-shaped resilient diaphragm 13 that extends across the bottom of the
cylinder member 4 to close the same and cooperate with it and the plunger
6 in confining a quantity of fluid 15. It will be understood that the bore
5 in the cylinder member is machined to have an accurate fit on the
plunger 6, and that the plunger is encircled by at least one sealing ring.
The plunger 6 is secured to the underside of a mounting plate 7 that is
fixed on the top portion of the frame. Also extending down from that
mounting plate, at spaced locations around the cylinder member 4, are a
number of rigid vertical struts 8 which can be threaded into the mounting
plate and secured with locking nuts 10. Brackets 9 that project radially
from the cylinder member 4 near the top thereof are slideably guided on
these struts, and each strut is surrounded by a coiled expansion spring 12
that reacts between the bracket 9 and a nut 11 that is threaded onto the
bottom of the strut. The springs thus bias the cylinder member upwardly,
to maintain some pressure upon the fluid 15 in the cavity and, of course,
to bias the cylinder member 4 towards a neutral position in which it is
illustrated in the left-hand half of FIG. 1 and to which it returns after
each forming operation. To enable the cavity to contain an ample quantity
of fluid, the underside of the plunger is preferably concavely dished, as
shown. The pressure cavity can be charged with fluid through a sealable
filling passage 16 that leads down through the plunger from its upper
portion, and air displaced during filling can pass out of the cavity by
way of a sealable vent passage 17 through the plunger. It will be
understood that no fluid enters or leaves the pressure cavity during a
forming operation.
The diaphragm 13 has a cylindrical side wall, around the exterior of which
there is a circumferential bead 14 that is received in a closely-fitting
groove in the bore surface of the cylinder member 4. As is conventional, a
clamping ring (not shown), encircling the inner surface of the diaphragm
side wall, confines the bead 14 In its groove to secure the diaphragm in
place. The bottom wall of the diaphragm has a substantially flat
underside, and the diaphragm thus provides a downwardly facing blank
engaging surface which opposes the upwardly facing surface of the blank
holding unit 38 and which cooperates with the latter to flatwise
clampingly confine the edge portion of a sheet metal blank being formed.
The diaphragm also serves as a medium whereby reaction forces produced in
the body of fluid 15 within the cavity are imposed upon and distributed
over the top surface of the blank, to compel the blank to assume the shape
determined for it by the rigid tool.
The hydraulic unit 19 that comprises the actuating means for the rigid tool
parts is, in general, a telescoping arrangement of coaxial cylinder means
and pistons. Its largest diameter component is the stationary cylinder 20,
which is fixed to the bottom portion 18 of the rigid frame and which is
generally cup-shaped and opens upwardly. The stationary cylinder has a
uniform inside diameter through most of its height, but a ring 22 that is
coaxially affixed to its rim defines a reduced diameter bore at its upper
end portion.
The outer piston element 26 has a uniform outside diameter along most of
its length, such as to have a slideable sealing fit inside the ring 22,
but at its bottom it has a coaxial larger diameter portion 28 which has a
slideable sealing fit in the larger-diameter bore portion of the
stationary cylinder. Beneath this larger diameter portion of the outer
piston element, and in part defined by it, the stationary cylinder has a
lower pressure chamber 30. The larger diameter portion 28 of the outer
piston element also cooperates with the fixed ring 22 to define, in the
interior of the stationary cylinder, an annular pressure chamber 41, so
that the piston element 26 and the stationary cylinder 20 comprise a
double-acting cylinder mechanism.
Affixed to the top of the outer piston element 26 is a rigid carrier 36
that has an axially elongated annular body 37. Attached to that carrier,
or made integral therewith, is the draw ring unit or blank holding unit
38, said unit being here illustrated as a separate ring that is removably
received in a closely fitting well in the top of the carrier.
The smaller diameter upper portion of the outer piston element 26 is hollow
and defines the coaxial movable cylinder 27 in which the inner piston
element 31 is sealingly slideable up and down. The movable cylinder is
thus generally cupshaped, and its interior opens upwardly. The carrier 36
has a lower annular portion 39 that projects radially inwardly from the
rim of the outer piston element to define a coaxial reduced diameter upper
bore portion for the movable cylinder.
The lower portion 32 of the inner piston element 31 has an outside diameter
such as to have a slideable sealing fit in the larger inside diameter
portion of the movable cylinder, and it has a smaller diameter upper
portion that is received with a similar fit in the smaller bore portion of
the movable cylinder that is defined by the carrier 36. Note that the
lower portion 39 of the carrier 36 cooperates with the enlarged outside
diameter portion 32 of the inner piston element to define a second upper
annular pressure chamber 40, in the movable cylinder. The inner piston
element also cooperates with the movable cylinder to define a second lower
pressure chamber 34, so that these cooperating parts constitute another
double-acting mechanism.
The second lower pressure chamber 34 is of substantially large volume
inasmuch as the inner piston element is of inverted cup shape, with an end
wall 33 across its top. The radially inner one of the two rigid forming
tools, here shown as the punch 35, is concentrically fixed to said end
wall 33 and projects upwardly therefrom. The tool part 35 can of course be
removable, so that it can be replaced with rigid tool parts of other
shapes and sizes, including die or matrix parts as well as other punch
parts.
Fluid can flow into and out of the first lower pressure chamber 30, in the
stationary cylinder, by way of eccentric passages 45 through its bottom
wall 21, which passages communicate with ducts 43. Fluid can flow into and
out of the first upper pressure chamber 41, in that cylinder, by way of a
duct 52 that connects with a passage through its side wall.
To conduct fluid to and from the second lower pressure chamber 34, in the
movable cylinder 27, there is a tubular member 25 that is fixed in a
closely fitting bore 23 in the bottom wall of the stationary cylinder and
projects upwardly to about the level of the ring 22. That tube has a
slideable sealing fit in a concentric bore 29 through the bottom wall of
the cup-shaped outer piston element 26, through which bore the tube
projects into the second lower pressure chamber 34. A duct 44 is connected
with the tubular member at its bottom end, and it will be evident that
fluid can flow between that duct and the second lower pressure chamber 34
by way of the bore 24 of the tubular member 25. The substantial axial
depth of the interior of the inverted cup-shaped inner piston element
provides for clearance between the top of the tubular member and the upper
end wall 33 of that piston element, even when the two piston elements are
bottomed in their respective cylinders.
Fluid can flow into and out of the second upper pressure chamber 40, in the
movable cylinder, by way of a passage in its side wall that is connected
with a flexible duct 51.
It will be understood that the several slideable seals mentioned above
comprise suitable sealing rings.
In the illustrated arrangement, wherein the inner rigid tool part 35 is
shown as a punch that moves upwardly relative to the other tool part 38
during the forming portion of the stroke, the two rigid tool parts are so
arranged that when the inner piston element 31 is bottomed in the movable
cylinder 27, the top of the punch 35 is at or slightly below the level of
the blank holder 38. It will be apparent that if the two rigid tool parts
are brought into this relationship to one another when they are in their
press-open positions, then they can be readily moved upward in unison to
their positions illustrated at the left-hand side of FIG. 1, in which the
blank 3 just begins to be subjected to clamping force. Such unison upward
movement of the tool parts is of course effected by filling fluid into the
first lower pressure chamber 30 and allowing the inner piston element to
be carried upwardly by the outer one. The bottom of the inner piston
element and the bottom of the movable cylinder thus serve as cooperating
abutments that define the starting positions of the tool parts relative to
one another.
During the portion of the stroke in which forming is effected, as will be
apparent from the right-hand side of FIG. 1, fluid is forced into the
second lower pressure chamber 34 to effect upward motion of the inner
piston element and the punch 35 that is carried by it. Such upward motion
of the punch of course effects an upward and inward resilient deformation
of the central portion of the diaphragm, displacing fluid to cause a
corresponding downward displacement of the circumferential portion of the
diaphragm along with the cylinder member 4 that carries it. As the punch
is being forced upwardly, fluid is restrainedly permitted to bleed out of
the first lower pressure chamber 30, and consequently the draw ring unit
38 can descend against yielding resistance and in response to the downward
reaction force imposed upon it by fluid in the pressure cavity. With
pressure thus imposed upon it, the fluid in the cavity, acting through the
diaphragm, applies force over the entire top surface of the blank whereby
the blank is compelled to assume a form determined by the rigid tool
parts.
At the conclusion of the forming operation, cooperating abutments on the
two tool parts can engage to define their forming relationship to one
another, towards which relationship they are shown moving in the
right-hand side of FIG. 1. As shown, these abutments comprise the
circumferential upwardly facing shoulder 67 on top of the larger diameter
portion 32 of the inner cylinder element 31 and the bottom of the
bore-defining portion 39 of the carrier 36. The tool parts can therefore
be moved downwardly in unison by allowing fluid to flow into the first
annular upper pressure chamber 41 and simultaneously permitting fluid to
flow out of the first and second lower pressure chambers 30 and 34.
Keeping the two tool parts in their forming relationship to one another
until the newly formed workpiece is clear of the diaphragm enables the
forming tool to support the workpiece against deformation by fluid
pressure acting through the diaphragm.
Once the unison descent of the rigid tool parts has carried the workpiece
clear of the diaphragm, fluid can be pumped into both of the upper
pressure chambers 40 and 41 and exhausted from the two lower pressure
chambers 34 and 30 to bring the rigid tool parts to their press-open
positions, in which both piston elements are bottomed in their respective
cylinders and the punch is freed from the workpiece.
It will be obvious that a mere reversal of the illustrated relationships of
the abutments that define the relative positions of the tool parts would
allow the male punch member 35 to be replaced by a female die or matrix
that was intended to move downwardly relative to the draw ring unit 38
during the forming operation. Specifically, the circumferential shoulder
67 on the inner piston element would engage the underside of the carrier
36 to establish the rigid tool parts in their starting relationship, and
the inner piston element would bottom in the movable cylinder to establish
the forming relationship.
It will be apparent that the abutments which define the respective starting
and forming relationships could be on the tool parts themselves instead of
on the components of the hydraulic unit 19, so that a variety of
interchangeable forming tools could be accommodated.
The ducts 43 that communicate, through the passages 45, with the first
lower pressure chamber 30 are connected with valve means 47. Also
connected with the valve means 47 are a source of pressure fluid, here
shown as a pump 46, a tank or fluid reservoir 48, and the duct 44 that
communicates with the second lower pressure chamber 34 by way of the bore
24 in the tubular member 25. The valve means 47, as explained below,
serves to direct pressure fluid into one of the lower pressure chambers 30
or 34 during a forming operation and to control the pressure of fluid
issuing out of the other of those pressure chambers. The connection
between the valve means 47 and the reservoir 48 permits a portion of such
outflowing fluid to be exhausted to the reservoir. There is also a
connection between the reservoir and the pump 46 through which the latter
can draw fluid from the reservoir.
The ducts 51 and 52, which communicate with the annular upper pressure
chambers 40 and 41, respectively, are communicable with a low pressure
auxiliary pump 49 through another valve 50. The auxiliary pump also has an
inlet connection with the reservoir 48. Although not shown, it will be
understood that there is a return fluid connection between the valve 50
and the reservoir. The hydraulic system that comprises the auxiliary pump
49 and the valve 50 functions during movement of the rigid tool parts in
their return strokes, when the tool parts are brought back to their
press-open positions from the positions they occupy at the conclusion of a
forming stroke. During that time, of course, the valve 50 directs the
output of the pump 49 into the first upper pressure chamber 41 until the
outer piston element 26 has bottomed therein, and then directs the pump
output into the second upper pressure chamber 40.
The hydraulic system comprising the pump means 46 and the valve means 47,
which is essentially independent of the system comprising the pump 49 and
the valve means 50, produces and controls pressures applied during the
forming operation to the piston elements that carry the rigid tool parts.
In order to control the forming pressure in accordance with the relative
position of the tool parts, there is associated with the valve means 47 a
sensing and control system comprising a cam template 56 that is
constrained to move with at least the inner piston element 31, and a
sensor 58 that cooperates with the cam template and with a potentiometer
60 to produce signals for control of the valve means 47.
As shown, the cam template 56 is confined to up and down sliding movement,
and it is constrained to move with at least the inner piston element 31 by
means of a cord or cable 53 which is connected between it and that piston
element and which is trained over guide pulleys 54 and 55. It will be
understood that the cord 53 can pass through an opening in the carrier 36.
It will also be appreciated that the template is interchangeable with
others, to accommodate different forming tools, each template having its
camming surface so profiled as to represent a desired program of forming
pressure variation relative to position of the forming tool parts during a
forming operation with the tool for which it is intended.
FIG. 3 illustrates details of the pressure programming apparatus. The
camming surface of the template cooperates with a cam follower 62 that
adjusts the potentiometer 60. As illustrated, the cam follower comprises a
plunger-like element that is lengthwise slideable in fixed guide means 61
in directions transverse to the directions in which the template moves. A
roller 63 or the like on the cam follower, at its end adjacent to the
template, tracks on the template camming surface, being maintained in
engagement therewith by a lengthwise biasing force on the cam follower.
There is a constant potential difference, denoted by U, between the two
ends of the potentiometer 60, and there is a mechanical connection between
its slideable element and the cam follower plunger, so that the potential
at the potentiometer slider corresponds to the forming pressure desired
when the forming tool is in the position that it momentarily occupies. The
potential at the slider thus constitutes a p | | |
