U.S. patent application number 09/843713 was filed with the patent office on 2002-10-31 for end-forming toggle-press.
Invention is credited to Petersen, Horst Udo.
Application Number | 20020157442 09/843713 |
Document ID | / |
Family ID | 25290809 |
Filed Date | 2002-10-31 |
United States Patent
Application |
20020157442 |
Kind Code |
A1 |
Petersen, Horst Udo |
October 31, 2002 |
End-forming toggle-press
Abstract
The press has a punch that slides in a punch-guide, and a ram
that slides in a ram-guide, ther respective lines of action forming
a T-configuration, whereby one unidirectional stroke of the
ram-head provides a complete in/out stroke of the punch. The ram is
driven by a prime-mover, which may be a hydraulic ram coupled
directly to the ram-head, or preferably is a ball-screw-jack
operated by an electric servo motor, under computer control. The
ratio between the prime-mover and the ram-head remains constant
throughout the stroke of the ram-head.
Inventors: |
Petersen, Horst Udo;
(Kitchener, CA) |
Correspondence
Address: |
ANTHONY ASQUITH
173 WESTVALE DRIVE
WATERLOO
ON
N2T1B7
CA
|
Family ID: |
25290809 |
Appl. No.: |
09/843713 |
Filed: |
April 30, 2001 |
Current U.S.
Class: |
72/316 |
Current CPC
Class: |
B21J 9/18 20130101; B30B
1/008 20130101; B21J 9/022 20130101; B21J 9/06 20130101; B21D 41/02
20130101 |
Class at
Publication: |
72/316 |
International
Class: |
B21D 041/02 |
Claims
1. Punch press, wherein: the press includes a die, for holding a
workpiece; the press includes a punch-head, and a punch mounted
therein; the press is arranged such that, in operation, the punch
moves towards and away from the workpiece in the die, as the
punch-head moves along a line termed the punch-line; the press
includes a punch-head-guide, for guiding the punch-head along the
punch-line; the press includes a ram-head, and includes a
ram-head-guide, for guiding the ram-head along a ram-line; the
arrangement of the press is such that the punch-line and the
ram-line intersect, at a point-of-intersection, to form a T; the
configuration of the T is such that the ram-line comprises the
cross-bar of the T, and the punch-line comprises the stem of the T;
the press includes a toggle-lever, having a punch-end and a
ram-end; a punch-end-connection connects the punch-end of the
toggle-lever to the punch-head; a ram-end-connection connects the
ram-end of the toggle-lever to the ram-head; the arrangement of the
press is such that, during operation, the punch-head undergoes a
punch-cycle of movement, being movement of the punch-head along the
punch-line from a punch-withdrawn start-position, to a
punch-extended position, and back to a punch-withdrawn
finish-position; the arrangement of the press is such that, during
operation, the ram-head undergoes a ram-cycle of movement, being
movement of the ram-head along the ram-line from a start-point,
through the point-of-intersection, to a finish-point; the
arrangement of the press is such that, during operation, the
punch-cycle corresponds to the ram-cycle; the point-of-intersection
lies on the ram-line, intermediate between the start-point and the
finish-point; the punch-extended position of the punch-head occurs
when the ram-end-connection is at the point-of-intersection; the
arrangement of the press is such that when the punch-head lies at
its fully extended position, the ram-head lies at the
point-of-intersection, and the toggle-lever is aligned dead-centre
with the punch-line, in that a line joining the
punch-end-connection to the ram-end-connection lies along the
punch-line; whereby the finish-point of the ram-head lies on the
opposite side of the point-of-intersection from the start-point of
the ram-head; the press includes an operable ram-actuator; the
ram-actuator is effective, when operated, to drive the ram-head
forcefully along the ram-line, from its start-point, through the
point-of-intersection, to its finish-point, all in a first
ram-sense along the ram-line; the ram-actuator includes a
prime-mover, having a fixed-element fixed to the frame of the
press, and having a movable-element, the prime-mover being an
apparatus that converts prime energy from an energy source into
powered mechanical motion of the movable-element along a
prime-line; the ram-actuator includes a
force-transmission-assembly, for converting forceful movement of
the movable-element of the prime-mover along the prime-line into
forceful movement of the ram-head along the ram-line; the
force-transmission-assembly is so arranged as to introduce and
define a mechanical-ratio between the movement of the
movable-element of the prime-mover along the prime-line and the
movement of the ram-head along the ram-line; and the structural
arrangement of the ram-actuator is such that the mechanical-ratio
when the ram-head is at the point on the ram-line where the
mechanical-ratio is largest, is no more than double the
mechanical-ratio when the ram-head is at the point on the ram-line
where the mechanical ratio is smallest.
2. Apparatus of claim 1, wherein the structural arrangement of the
ram-actuator is such that, in operation: the mechanical-ratio
between the movable-element of the prime-mover and the ram-head, as
introduced by the force-transmission-assembly, varies with the
position of the ram-head along the ram-line; and the
mechanical-ratio is largest when the ram-head is at the
point-of-intersection.
3. Apparatus of claim 1, wherein the structural arrangement of the
ram-actuator is such that, in operation, as the ram-head moves from
its start-point through the point-of-intersection to its
finish-point, the said mechanical-ratio remains substantially the
same.
4. Apparatus of claim 3, wherein the structural arrangement of the
ram-actuator is such that, in operation, after the ram-head reaches
the said finish-point, the ram-head reverses its direction of
travel and travels back along the ram-line, all in the opposite
ram-sense to the said first ram-sense along the ram-line, from the
said finish-point, through the point-of-intersection, back to the
said start-point of the ram-head.
5. Apparatus of claim 4, wherein the structural arrangement of the
ram-actuator is such that, in operation: the ram-head undergoes
movement along the ram-line, in correspondence to the movement the
movable-element of the prime-mover undergoes relative to the
fixed-element along the prime-line; and the ram-head undergoes a
reversal of movement only when the movable-element undergoes a
reversal of movement, and in correspondence thereto; whereby, when
the movement of the ram-head along the ram-line is all in the said
first ram-sense, the movement of the movable-element is all in a
corresponding first prime-sense along the prime-line.
6. Apparatus of claim 5, wherein the structural arrangement of the
ram-actuator is such that, in operation: the movable-element of the
prime-mover undergoes movement relative to the fixed-element, along
the prime-line, in correspondence to the movement the ram-head
undergoes along the ram-line; when the movement of the ram-head
along the ram-line is all in the said first ram-sense, the
corresponding movement of the movable-element is all in a
corresponding first prime-sense along the prime-line; and when the
movement of the ram-head along the ram-line is all in the said
opposite ram-sense along the ram-line, the corresponding movement
of the movable-element along the prime-line is all in the opposite
prime-sense to the said first prime-sense along the prime-line.
7. Apparatus of claim 1, wherein the force-transmission-assembly
comprises a direct mechanical connection between the
movable-element of the prime-mover and the ram-head, having no
capacity for relative movement.
8. Apparatus of claim 7, wherein the prime-line is co-linear with
the ram-line.
9. Apparatus of claim 8, wherein the prime-mover is a hydraulic
ram.
10. Apparatus of claim 1, wherein the prime-line is a circle, being
the line of movement of a point on the armature of an electric
motor, about the axis of the motor.
11. Apparatus of claim 10, wherein the force-transmission-assembly
includes a re-circulating-ball screw-jack, driven by the electric
motor.
12. Apparatus of claim 1, wherein the force-transmission-assembly
includes the said mechanical-ratio as a gear-ratio, and the
gear-ratio remains constant during operation.
13. Apparatus of claim 1, wherein the structural arrangement of the
ram-actuator is such that, in operation: when the ram-head lies at
its start-point on the ram-line, the toggle-lever lies inclined at
no more than about sixty degrees to the punch-line, in a first
sense; and when the ram-head lies at its finish-point on the
ram-line, the toggle-lever lies inclined at no more than about
sixty degrees to the punch-line, in the opposite sense.
14. Apparatus of claim 13, wherein the structural arrangement of
the ram-actuator is such that, in operation: when the ram-head lies
at its start-point on the ram-line, the toggle-lever lies inclined
at about forty-five degrees to the punch-line, in a first sense;
and when the ram-head lies at its finish-point on the ram-line, the
toggle-lever lies inclined at about forty-five degrees to the
punch-line, in the opposite sense.
15. Apparatus of claim 13, wherein the structural arrangement of
the ram-actuator is such that, in operation: when the ram-head lies
at its start-point on the ram-line, the toggle-lever lies inclined
at more than about thirty degrees to the punch-line, in a first
sense; and when the ram-head lies at its finish-point on the
ram-line, the toggle-lever lies inclined at more than about thirty
degrees to the punch-line, in the opposite sense.
16. Apparatus of claim 1, wherein: the ram-actuator includes a
start-point-adjuster, which is effective to adjust the start-point
of the ram-head on the ram-line; the ram-actuator includes a
finish-point-adjuster, which is effective to adjust the
finish-point of the ram-head on the ram-line.
17. Apparatus of claim 16, wherein the start-point-adjuster and the
finish-point-adjuster comprise: a means for measuring the distance
of travel of the movable-element along the prime-line; a means for
reversing the directional sense of the movement of the
movable-element along the prime-line when the movable-element
reaches a set-point; and a means for moving the set-point along the
prime-line.
18. Apparatus of claim 17, wherein: the force-transmission-assembly
includes a re-circulating-ball screw-jack, driven by an electric
motor, the motion of which is under the control of a computer, as
to the extent of the travel of the movable-element along the
prime-line; and the means for moving the said set-point along the
prime-line comprises a means for controlling the computer.
19. Apparatus of claim 1, wherein the structural arrangement of the
ram-actuator is such that, in operation, the punch-line is a
straight line, and the ram-line is a straight line at right angles
to the punch-line.
20. Apparatus of claim 19, wherein the ram-head-guide includes a
fixed ram-head-abutting-surface, which faces towards the punch, and
against which the ram-head slides as the ram-head moves along the
ram-line.
21. Apparatus of claim 20, wherein: the ram-head-abutting-surface
is a flat, straight surface; the ram-head includes an
abutment-surface, which is correspondingly flat and straight, and
which slides and rubs directly against the
ram-head-abutting-surface as the ram-head moves along the ram-line;
the ram-head-abutting-surface is aligned at right angles to the
punch-line; and the structural arrangement of the apparatus is such
that, at dead-centre, all the force acting along the punch-line on
the punch is reacted to the frame of the apparatus through the
direct engagement of the said surfaces.
22. Apparatus of claim 1, wherein: the press includes a plurality
of punches, and includes a magazine in which the punches are
mounted; and the press includes an operable indexing-means, which
is effective, when operated, to index the magazine, and thereby to
move one of the punches into a position in which the said one of
the punches is co-linear with the punch-line.
23. Apparatus of claim 22, wherein the structural arrangement of
the indexing-means is such that, when the press is operated, and
the punch-head moves towards and away from the punch-extended
position, along the punch-line, the whole magazine, with the
punches carried therein, moves, as a whole unit, in unison with the
punch-head.
24. Apparatus of claim 1, wherein the workpiece comprises a length
of hollow tubing.
25. Apparatus of claim 1, wherein: the press includes first and
second jaws, for clamping the workpiece, and includes an operable
clamping-means, which is effective, when operated, to hold the
workpiece securely, as the press is operated; the clamping-means
includes respective operable first and second jaw-movers; the
clamping-means includes a jaw-datum, located on the fixed frame of
the press; the first jaw-mover is effective, when operated, to move
the first jaw into abutment against the jaw-datum; the second
jaw-mover is effective, when operated, to move the second jaw into
abutment against the first jaw; the clamping-means includes a
locking-means, which is effective to hold the first jaw in abutment
against the jaw-datum when the second jaw moves into abutment
against the first jaw.
Description
[0001] This invention relates to punch presses, of the kind used
for forming metal components. The invention especially relates to
presses of the kind in which a tube is gripped in a die, and an
end-form is produced on the end of the tube by punching the end of
the tube in an axial direction.
BACKGROUND TO THE INVENTION
[0002] Traditionally, such presses have a capacity of a few tons
(e.g five tons), and have used, as the means for generating the
forces needed to create an end-form on a pipe, a hydraulic ram.
Conventionally, the ram has been mounted in the press in such a
manner that the ram applies force directly to the punch in a
simple, in-line sense; that is to say, the line of action of the
ram has been co-axial with the axis of the pipe.
[0003] This direct, in-line, manner of operation of the (hydraulic)
ram has some disadvantages. The piston of the ram must be of a
large enough area (several square inches) for the ram to deliver
the several tons to the punch, and a hydraulic pressure supply unit
is required, to supply pressurised fluid to the ram. Usually, the
full high pressure is only needed right at the end of the stroke,
as the punch fully engages the workpiece. This is especially so, if
the workpiece is to be coined--coining being characterised by the
application, right at the end of the stroke, of a large force. Most
of the rest of the travel of the punch is occupied with slack
take-up, which involves very little force resistance from the
engagement of the punch with the workpiece.
[0004] When the hydraulic ram is in-line with the punch, the
hydraulic supply unit has to be capable of delivering full
pressure, i.e enough pressure to coin the workpiece--not just at
the end of the travel-stroke of the piston, but over the whole
travel-stroke. That is to say, although nearly all of the operation
of the hydraulic supply unit takes place at very low pressure, the
supply unit is capable of supplying full working pressure over the
whole stroke.
[0005] The power required of the hydraulic supply unit may be
measured in terms of the volume of hydraulic fluid delivered,
multiplied by the pressure of the fluid. This product may be termed
the P-V requirement of the system. Slack take-up involves moving a
large volume at a low pressure, whereas punching and coining
involve moving a small volume at a high or very high fluid
pressure. The total or aggregate P-V, integrated over the
travel-stroke of the ram, may be quite modest, in terms of the P-V
required actually to operate the press; however, when the ram is
in-line with the punch, the supply unit is capable of supplying
full high pressure over the whole stroke, whereby the supply unit
is capable of delivering a P-V many times in excess of the P-V that
is actually needed to operate the press.
[0006] Thus, when the ram was in-line with the punch, even a small
press needed a massive supply unit. One of the aims of the
invention is to enable the press to be operated using a hydraulic
supply unit that supplies only the needed P-V, not an order of
magnitude more. In fact, when the supply system can be designed for
overall P-V, rather than for maximum flow rate at maximum pressure,
now pneumatic operation of the press becomes feasible.
[0007] Indeed, when the prime-mover can be designed for overall
P-V, the designer now has the option of operating the press with a
prime-mover comprising an electric ram. When the ram was in-line,
and the force required at the ram was several tons, an electric ram
(e.g a ball-screw actuator) for supplying maximum punch force over
the whole travel-stroke would have been prohibitive. (In an
electric ram, the power requirement is measured as
force.times.travel, not pressure.times.volume, but both products
measure work.)
THE INVENTION IN RELATION TO THE PRIOR ART
[0008] A press that is in some respects similar to the presses as
depicted herein is shown in patent publication U.S. Pat. No.
5,916,345. This press operates the punch using a pivoting lever 18.
The ram-end of the lever 18 moves along a ram-line from a
start-point, through a dead-centre point, to a finish-point, all in
the same directional sense; correspondingly, the punch-end of the
lever 18 undergoes and completes its whole cycle from the
punch-retracted position, out to the punch-extended position, and
then back to the punch-retracted position.
[0009] The invention makes use of a toggle-lever, which undergoes
much the same modes of movement as the pivoting-lever 18 in
'345.
[0010] In '345, the ram-end of the lever 18 is driven by a crank
arm 36. It is a feature of any crank mechanism that one end (the
drive-end) of the crank-arm goes round in a circle, generally
always in the same rotational sense, while the far-end of the
crank-arm moves back and forth along a line. With a crank
mechanism, there is a good deal of variation in the mechanical
ratio between the movement of the drive-end of the crank-arm, as
driven by the prime-mover, and the movement of the far-end. The
ratio is a maximum when the crank-arm makes a tangent to the
crank-arm radius, and decreases to zero when the crank-arm is at
dead centre.
[0011] It is recognised that driving the ram-end of the
toggle-lever by means of a rotary crank mechanism, as depicted in
'345, gives quite the wrong characteristics to the motion. In the
invention, although the punch is driven forwards via a
toggle-lever, the forces on the punch, and the movements of the
components of the press, are much more favourable to the
requirements of a punch press.
[0012] In the invention, as mentioned, the press includes a
toggle-lever. The punch-end of the toggle-lever is connected to the
punch-head, and the ram-end of the toggle-lever is connected to the
ram-head. The punch-end travels along a punch-line, and the ram-end
travels along a ram-line, as determined by the punch-head-guide and
the ram-head-guide. The ram-end of the toggle-lever is driven by a
prime-mover, and the ram-end is connected to the prime-mover by a
force-transmission-assembly. This force-transmission-assembly has a
mechanical-ratio.
[0013] It is preferred, in the invention, that the mechanical ratio
of the force-transmission-assembly not vary at all, during
operation. This is the case when the prime-mover is a hydraulic
ram, and the force-transmission-assembly comprises a simple direct
connection between the piston thereof and the ram-head. (In that
case, the mechanical-ratio is one-to-one, the
force-transmission-assembly being a direct mechanical connection,
with no interposed gears or levers.)
[0014] It is also the case that the mechanical ratio of the
force-transmission-assembly does not vary at all, during operation,
when the prime-mover is a recirculating-ball screw-jack, and the
force-transmission-assembly includes a constant-ratio drive between
the nut of the screw-jack and the armature of the electric motor
driving the screw-jack.
[0015] Preferably, the punch-line and the ram-line are straight
lines, at right angles to each other, disposed in a
T-configuration.
[0016] Other drive arrangements are contemplated within the
invention. For example, the arrangement of the press may be such
that the ram-line is arcuate and/or the punch-line is arcuate, in
which case, of course, the force-transmission-ratio would change as
the position on the arc changed. However, it would be outside the
invention if the mechanical ratio of the
force-transmission-assembly were to change or vary so much that the
maximum ratio were more than about double the minimum ratio.
[0017] Preferably, the maximum ratio occurs when the toggle-lever
is at its dead-centre position.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0018] By way of further explanation of the invention, exemplary
embodiments of the invention will now be described with reference
to the accompanying drawings, in which:
[0019] FIG. 1 is a diagrammatic side-elevation showing some of the
components in a press that embodies the invention.
[0020] FIG. 2 is a side-elevation of another press that embodies
the invention.
[0021] FIG. 3 is a pictorial view of a workpiece clamp of the press
of FIG. 2.
[0022] FIG. 4 is a pictorial view of a bolster of the fixed frame
of the press of FIG. 2.
[0023] FIGS. 5a, 5b are pictorial views of a punch magazine of the
press of FIG. 2.
[0024] FIG. 6 is a pictorial view of a ram actuator of the press of
FIG. 2.
[0025] The apparatuses shown in the accompanying drawings and
described below are examples which embody the invention. It should
be noted that the scope of the invention is defined by the
accompanying claims, and not necessarily by specific features of
exemplary embodiments.
[0026] FIG. 1 is a diagram showing a basic manner in which a press
can be arranged, in the new invention. The workpiece 20 is gripped
in a clamp 23. For high speed production, the workpieces must be
fed in and out of the press, i.e in and out of the clamp 23, by
automated feed and handling mechanisms; but these can be
conventional. The clamp 23 is in two halves, which open in a
lateral sense relative to the workpiece, to allow the workpiece to
be fed into the press. The clamp is opened and closed by means of a
clamp-ram.
[0027] The two halves of the clamp 23 are shaped to serve also as
the two halves of a die, into which the axial end 26 of the
workpiece will be punched.
[0028] The end 26 of the workpiece is acted-upon by one or more
punches. In this case, three punches 28 are provided. The punches
are mounted in a punch-rack 29. A punch-rack-positioning-ram can be
operated to move the punch-rack, whereby a desired one of the
punches 28 can be brought into line with the end 26 of the
workpiece. The punch 28 itself is carried on a punch-holder 32,
which is mounted in the punch-rack 29 for sliding towards and away
from the workpiece 20 (i.e left/right in FIG. 1). The punch-rack 29
moves only up/down, and its up/down movement is used to bring a
selected one of the punches 28 to bear; then the punch-rack remains
stationary while the selected punch moves left/right, into and out
of contact with the end 26 of the workpiece.
[0029] The frame of the press is provided with a horizontal
punch-head-guide 34, in which a punch-head 35 can slide in the
left/right sense. The punch-head 35, upon moving to the left, makes
contact with the end of the appropriate one of the punch-holders
32.
[0030] A connecting-rod or toggle-lever 37 is in operative
engagement with the right end of the punch-head 35. As shown, the
toggle-lever 37 is pivoted to the punch-head, at punch-end-pivot
38, but other coupling structures may be used.
[0031] The frame of the press is provided with a vertical
ram-head-guide 39, in which runs a ram-head 40. The toggle-lever 37
is also pivoted to the ram-head, at ram-end-pivot 42. The ram-head
40 is driven into up/down movement by means of a hydraulic ram
43.
[0032] Instead of the punches being housed in the linearly-movable
punch-rack 29, the punches may be housed in a rotary turret. Where
the number of punches is more than two or three, accurate alignment
of the several punches is easier with a rotary turret, where the
turret can be rotary-indexed by means of a suitable
stepper-motor.
[0033] The design as depicted provides a sliding ram-head 40,
connected by a toggle-lever 37 to a sliding punch-head 35. The
design provides two complete in/out punch-strokes per one complete
in/out cycle of the ram 43. The motion is such that a single stroke
of the ram 43 accomplishes both the forceful leftwards movement of
the punch, plus the rightwards return movement of the punch, all in
one smooth movement of the ram-head 40. The punch moves in/out, but
the movement of the ram is one-directional. That is to say, the
comparatively heavy ram and ram-head 40 reverses direction at only
half the rate of the (lighter) punch-head 35. This is very useful
for speeding up presswork operations that involve many punches 28,
applied in sequence one after the other to the end 26 of the
workpiece.
[0034] The punch-cycle starts with the punch components in the
punch-withdrawn-start position as shown in FIG. 1. As the
toggle-lever moves downwards, the punch moves to the left, and
reaches its punch-fully-extended position as the toggle-lever
passes through dead-centre. As the toggle-lever moves downwards
further, the punch starts to move back to the right, eventually
reaching a punch-withdrawn-finish position. During the course of
these movements, the axis of the pivot at the punch-end of the
toggle-lever follows a punch-line PL, which in this case is a
straight horizontal line.
[0035] The ram-head undergoes just one single downwards movement as
the punch-head moves through its in/out cycle. The axis of the
pivot at the ram-end of the toggle-lever follows a ram-line RM,
which in this case is a straight vertical line.
[0036] The punch-line intersects with the ram-line at a
point-of-intersection. Together, the punch-line and the ram-line
define a T, the ram-line forming the cross-bar of the T and the
punch-line forming the stem of the T. The punch lies at the
fully-extended limit of its travel (leftwards in FIG. 1) when the
ram is at the mid-point of its travel, i.e when the ram-pivot is at
the point-of-intersection.
[0037] The designer may arrange for the punch-head and the ram-head
to be guided in a different manner from the linear slideways as
shown, in which case the punch-line and the ram-line might not be
straight. The components may be guided by pivoting arms, for
example, in which case the ram-line and the punch-line would be
arcuate. However, in the invention, the punch-line and the ram-line
should still define a basic T, even if the lines are not quite
straight.
[0038] FIG. 2 is a similar diagram to FIG. 1, and shows a practical
version of the press apparatus. FIGS. 3-6 show some of the
structural details thereof. In FIG. 2, the ram-slide is driven by
an electric-ram 45.
[0039] FIG. 3 shows details of the workpiece clamp. The clamp
comprises upper and lower clamp-jaws 46,47, which are carried on
upper and lower jaw-slides 48,49. The jaws are forced together by
the action of a pneumatic clamp-ram 50. The upper clamp-jaw 46
moves up/down in unison with the piston of the clamp-ram 50.
[0040] In order to enable the movements of the workpieces into and
out of the press to be smoothly automated, it is preferred to move
both jaws well out of contact with the workpieces before and after
the jaws are actually clamping onto the workpiece. Sometimes, it is
convenient for the designer to have one of the jaws fixed, e.g the
lower jaw; the designer then provides a means for lifting the
workpiece upwards, i.e upwards out of the fixed lower jaw, after
the jaws have separated.
[0041] Having one of the jaws fixed is beneficial from the
standpoint of setting the position to which the jaws clamp the
workpiece, and it is important that this position be accurately
repeatable over very many cycles of operation, and the fact that
the lower jaw remains fixed means that the datum setting to which
the jaws are clamped is determined by components that are bolted
tightly together, rather than by components that separate and come
together with each stroke of the press.
[0042] But, if the lower jaw does remain fixed, now the need arises
to lift the workpiece upwards out from the lower jaw, before the
workpiece can be moved out of the press, and, as mentioned, this
can impose difficulties in moving the workpieces smoothly. For ease
of automating the workpiece movements, the designer prefers the
handling and transfer movements of the workpieces to take place all
within the same (horizontal) plane, if possible.
[0043] Thus, to simplify automating the movements of the
workpieces, it is preferred that, as the jaws separate, both jaws
46,47 move, as shown in FIG. 3.
[0044] When the jaws are closed together, the workpieces must be
accurately located in the correct position. In practice it is very
important, to the performance of the press, that this accuracy be
still present after a long period of continuous operation. This
requirement for accurate positioning of the workpiece is no less
stringent, just because both jaws move.
[0045] The clamped-together position of the jaws is determined by
the clamp-ram 50 driving the upper jaw-slide 48 down onto the lower
jaw-slide 49, the lower jaw-slide abutting against a cam-block 52.
The cam-block 52 rests in the bolster 53 of the frame of the press.
To open the jaws, the clamp-ram 50 is withdrawn, which lifts the
upper jaw-slide 48. Then, the cam-block is moved to the right by
the action of a (pneumatic) cam-actuator 54. A peg-and-slot
engagement 56 of the jaw-slide 49 with the cam-block 52 draws the
lower jaw-slide 49 downwards. When a new workpiece has been loaded,
the cam-block 52 is moves to the left, which lifts the lower
jaw-slide 49. The heavy clamping forces are taken, not by the
peg-and-slot engagement 56, but by the abutment of the feet 57 of
the jaw-slide 49 onto the top face 58 of the cam-block 52. The top
face 58 has cut-outs, as shown, for accommodating the feet 57 when
the jaws 46,47 are apart.
[0046] The clamp jaws 46,47 serve to define a die, which defines
the shape or form into which the punches drive the workpiece. It
will be understood that the press as depicted herein is intended
for cases where several punches operate on the workpiece while the
workpiece is clamped in the jaws, i.e is clamped in the die. The
press as depicted would not be so suitable if the work was such
that the workpiece had to be taken out of one pair of jaws/dies and
put into another pair. Arranging for jaws/dies to be interchanged,
e.g on a turret, is considerably more difficult than arranging for
punches to be interchanged on a turret. If different pairs of
jaws/dies are required, generally, more than one of the presses
would be provided, and the workpieces moved from press to
press.
[0047] FIG. 4 shows the bolster 53 into which the jaws and
jaw-slides are assembled. The bolster also accommodates the punches
and rotary turret in which the punches are mounted, which will now
be described.
[0048] The turret-unit 59 as shown in FIGS. 5a,5b combines the
punch-turret with the sliding punch-head. As shown, the unit
includes a punch-pivot-block 60 for receiving the
punch-end-connection of the toggle-lever 63.
[0049] The turret-unit 59 slides, as a whole unit, in the
punch-head-guide slideway 64 in the bolster 53. It may be noted
that, in FIG. 1, each punch-holder 32 moved relative to the rack
29. A difficulty with the FIG. 1 arrangement was that the datum
which defines the depth at which the punch bottoms out was
determined by engagement between surfaces that move apart and
together with each stroke of the press. As mentioned, it is easier
to ensure repeatable accuracy if the datum is determined mainly by
components that remain tightly bolted together. When the whole unit
moves, with each stroke, as in FIGS. 5a,5b, the depth-datums, once
set, can be expected to be accurately repeatable over a long
period. Shims may be placed between the punches and their
respective punch-holders, to set the depth-determining datum for
each punch.
[0050] The punches are carried in punch-holders 65, six of which
are mounted in the turret 67. The turret 67 is rotated by means of
a turret stepper-motor, or in this case a servo-motor 68.
[0051] The bolster 53 also accommodates the sliding ram-head and
associated components. As shown in FIG. 6, a length of screwed rod
69 is fixed into the sliding ram-head 70. The ram-head includes a
pivot connection 72, for making a ram-end pivoting connection
between the ram-head 70 and the toggle-lever 63.
[0052] At the upper end of the screwed rod 69, the rod passes
through a ram-nut 73. The ram-nut is driven to rotate by means of a
ram-servo-motor 74. The ram-nut 73 includes ball bearings, and
channels for re-circulating the balls along the helical grooves in
the nut and on the screwed rod 69. Thus, when the ram-nut 73
rotates, the screwed rod 69, and with it the ram-head 70, is caused
to move up/down, guided by the ram-head-slideway 75 in the bolster
53.
[0053] Re-circulating-ball screw-jacks, driven by an electric
motor, are available proprietarily, and these can be used, in the
invention, if required.
[0054] Preferably, both the ram-head and the punch-head are made as
flat-sided blocks, which run in slab-sided guides built into the
fixed frame of the press. In most cases, the designer requires the
depth at which the punch bottoms out to be set very accurately, but
does not require the position to which the punch retracts to be
particularly accurate. The depth the punch penetrates into the die
is critical to the performance of the press, as is accurate
repeatability of the depth, over a large number of cycles. It would
be hard to maintain quality if the punch depth were to vary. In the
press as described, the slab-like ram-head slides over the
slab-like ram-head-guide, and the inter-engagement therebetween is
very solid and robust.
[0055] The components of the press that lie on the punch-line,
between the toggle-arm and the punch, are similarly solid and
robust. In FIG. 1, the magazine holding the several punches does
not move forwards as the punches move forwards. That is to say, the
punches slide relative to the magazine. In FIGS. 5a,5b, on the
other hand, the several punches are bolted solidly into the
magazine, and the magazine moves as one solid whole unit, as the
punch moves forward. It would be detrimental to accuracy and
repeatability, in a press, if, at each cycle of the press, the
punch were to break contact with the component pushing the punch;
preferably, for accurate repeatability, the punch, and all the
components in the load line from the punch to the toggle-lever,
should be tightly bolted together, and should remain so throughout
the cycle. Once the punches have been set into the punch-holders,
the solidity of the components ensures that the setting of the
depth to which the punch bottoms out will not change.
[0056] It will also be understood that, as the punch reaches its
most extended position, the toggle-lever passes through the
dead-centre position. This motion is smooth, and, although the
punch reverses direction at this point, the reversal is
accomplished smoothly, without any tendency for the components to
jerk or bounce at this critical point. One of the difficulties with
the traditional type of end-forming press, which, as described,
uses an in-line ram, has been with setting the datum point at which
the punch bottoms out. Operation requires that full pressure is
applied in the punch-out direction, and then that pressure has to
be released, and pressure applied to the other side of the piston.
As a result, movement of the punch can be jerky and the sudden
reversals are not conducive to maintaining accuracy over many
cycles.
[0057] Some aspects relating to the prime-mover, as used in the
invention, will now be described.
[0058] A prime-mover includes a movable-element and a
fixed-element. The prime-mover is an apparatus for converting prime
energy from an energy source into powered mechanical motion of the
movable-element along a prime-line.
[0059] Thus, an electric motor converts electrical energy into
powered mechanical motion of the armature. The armature moves along
the prime-line, and in the case of a rotary motor the prime-line is
a circle centred on the axis of the armature.
[0060] An electrical solenoid is a prime-mover that converts
electrical energy into powered mechanical motion of the plunger.
The plunger moves along the prime-line, and in the case of a
solenoid the prime-line is the axis of the plunger.
[0061] A hydraulic ram is a prime-mover that converts the energy
stored in pressurised fluid into powered mechanical motion of the
piston. The piston moves along the prime-line, and in the case of a
hydraulic ram the prime-line is the axis of the piston.
[0062] Between the movable-element of the prime-mover and the
ram-head lies the force-transmission-assembly. The
force-transmission-assembly may include a gear ratio, or may be
direct (i.e the gear ratio is 1:1). When the prime-mover is a
hydraulic ram, the force-transmission-assembly may be direct,
comprising simply a strut between the piston and the ram-head. When
the prime-mover is an electric motor, the
force-transmission-assembl- y may include a worm-gearbox and rack,
for converting the motion of the motor armature (the armature being
the movable-element of the prime-mover) into movement of the
ram-head. Or the force-transmission-assembly of the ram-actuator
may comprise the ball-screw actuator as described.
[0063] It is a feature of the invention that the
force-transmission-assemb- ly should provide a constant, or nearly
constant, mechanical ratio between the movable-element and the
ram-head, and some further aspects of this feature will now be
described.
[0064] In a press of the type as depicted herein, the toggle-lever
starts off aligned at a considerable angle to the punch-line. For a
punch operation, the toggle-lever moves from this large angle of
inclination to the dead-centre position, in which it is aligned
along the punch-line, where the angle-of-inclination is zero. As
the punch is driven forwards, there is a change in the mechanical
ratio, i.e the ratio between the movement of the ram-end of the
toggle-lever and the movement of the punch-end. At first, the
mechanical advantage is small, i.e the movement of the ram-end of
the toggle-lever is almost the same as the movement of the
punch-end. This provides for a rapid take-up of slack, over the
first part of the travel, when the load on the punch is small.
Then, as movement of the punch continues, the toggle-lever starts
to straighten up, i.e starts to come into alignment with the
punch-line. Now, the mechanical advantage becomes much larger,
whereby a large movement of the ram-end of the toggle-lever drives
the punch-end through only a very small distance, and the force
developed at the punch-end of the toggle-lever is a large multiple
of the force applied to the ram-end of the toggle-lever.
[0065] Some types of press-work require that the press force be
constant through the whole, or nearly the whole, stroke of the
punch. In that case, toggle presses are not of much use. But more
often, a press task requires rapid take-up of slack, at low force,
over a few centimeters, and then the application of the large
punching forces occurs over only the last millimeter or two of
punch travel. In that case, toggle presses are most favoured. The
toggle action is also favoured in cases where the workpiece is to
be coined, especially when coined as a final touch to a punching
operation, in that coining requires a very large force, but
operates over a very small distance.
[0066] In other words, some common types of press work require
exactly the kind of variation in mechanical ratio that arises from
the use of a toggle-lever between the ram and the punch. When the
push is direct, as by a hydraulic ram, the ram must be large,
together with a large power supply unit. But when the force is
applied to the punch through a toggle-lever, now the designer can
get away with using a ram that has a much smaller swept volume, and
a much smaller maximum force. Indeed, using the toggle system,
hydraulics are not really needed, and a ball-screw actuator can be
used to operate what is basically a five-ton press.
[0067] As mentioned, the toggle-lever of the press is disposed in
the manner of the invention when the ram-line and the punch-line
form a T. The lines need not be straight lines, and need not be
exactly at right angles, but the lines must basically form a
T-configuration.
[0068] As mentioned, the force-transmission-assembly, between the
prime-mover and the ram-head as the ram-head moves along the
ram-line, i.e along the cross-bar of the T, should be at a constant
ratio, or at least the ratio should not vary by more than about 2:1
over the whole stroke.
[0069] The beneficial effect of having a toggle action between the
ram-head and the punch-head (i.e a low mechanical advantage ratio
at first for rapid slack take-up, followed by a high ratio for
heavy punch force) would be spoilt if the ratio between the
prime-mover and the ram-head were to vary too much. It would be
quite inappropriate, for example, for the
force-transmission-assembly to include a crank mechanism between
the prime-mover and the ram-head, because that would largely negate
the said beneficial effects. That is to say, such a crank mechanism
would superimpose a second toggle action, having a high ratio for
slack take-up and a low ratio at the end of the stroke, which is
the opposite of what is required. There would be little point in
having a first toggle mechanism, and then cancelling the beneficial
effects of that by imposing a complementary toggle mechanism.
[0070] In the presses as depicted herein, the punch is fully
withdrawn when the toggle-lever has reached about forty-five
degrees. The toggle-lever should not be inclined much further,
because then it would be hard to control the movement of the punch
accurately by moving the ram-head, i.e further movement of the
ram-head would give too much movement of the punch. Sixty degrees
would be about the limit.
[0071] The punch stops being retracted when the toggle-lever
reaches this maximum angle of inclination. Then, the toggle stops,
and reverses. The ram-end of the toggle-lever does not go round in
a full circle, in which much of the movement would be wasted.
[0072] The maximum angle of inclination should not be too small,
i.e too close to dead-centre, because the rate at which the punch
withdraws, per unit travel of the ram-head, is very small when the
toggle-lever is near dead-centre. Again, setting the maximum angle
of inclination to about forty-five degrees is preferred, and the
practical minimum value of the maximum inclination of the
toggle-lever would be about thirty degrees.
[0073] The distance through which the punch retracts corresponds to
the maximum angle of inclination of the toggle-lever, which in turn
corresponds to the point at which the ram-head comes to a stop.
When the press is operated by a screw-jack, with electric motor,
the motor can be servo-controlled by a computer, and the point at
which the ram-head stops can be changed simply by the program data
in the computer. Thus, for example, between punch one and punch two
the punch-head should retract 25 mm, whereas between punch three
and punch four the punch-head should retract 19 mm; this difference
can be easily accommodated in the program software.
[0074] When the workpieces comprise lengths of pipe, it is
convenient, for automating the handling of the workpieces, if the
pipe lies generally horizontally. Thus, the end of the pipe, when
gripped in the die, faces horizontally, and the punch moves in a
horizontal sense, in line with the axis of the workpiece. In a
conventional press, the ram would be in direct line with the punch,
and thus the ram would be aligned horizontally, and in line with
the axis of the workpiece. The envelope on the factory floor
occupied by the press is determined by the plan-view dimensions of
the press, rather than its height: in the press as depicted herein,
the ram-line is aligned at right angles to the punch-line, so, if
the punch-line is horizontal, the ram-line may be vertical. This
vertical disposition of the ram takes up little space, whereby the
resulting press can be compact, in the plan-view of the press.
[0075] It will be noted that the design of press as depicted herein
enables a large number of punches to be provided, and to be
operated in rapid sequence. When there are many punches, each one
can be less disruptive. Consequently, the overall distortion of the
workpiece can be greater than can be tolerated when only one or two
punches are available.
* * * * *