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.

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×travel, not pressure×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. 5 a, 5 b 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-assembly 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-assembly 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.

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.