GB2156724A - Press and method of operating same - Google Patents

Abstract

A coining or other press has a drive for a tool carrier (14) including a continuously rotated crankshaft (24) and a connecting rod (31) which transmits drive from a crank (30) on the crankshaft to an eccentric element connected by a further connecting element (32) with a toggle linkage (17) which imparts reciprocation to the tool holder. The tool carrier (14) comes to rest for a part of each operating cycle whilst feeding of workpieces takes place. The carrier (14) is moved a longer distance whilst the feed disc (16) is at rest and a shorter distance whilst the disc is feeding workpieces. <IMAGE>

Description

SPECIFICATION Press and method of operating same This invention relates to a press having, in use, a pair of tools which are subjected to relative movement between open and closed postions. In the open position, the tools are spaced apart to permit removal of a formed workpiece from the tools and insertion of a blank workpiece between them. In the closed position, the tools both engage the workpiece and cause same to assume a form determined by the tools. The invention is especially concerned with the kind of press commonly referred to as a coining press.

In a coining press, one of the tools is, during the coining operation, stationary and the other of the tools is carried on a reciprocating slide. The slide is normally driven from a flywheel through a toggle linkage. The toggle linkage is suitable for applying the required force to the reciprocating tool at a rapid cycle rate and moves into a straight configuration when the tools are closed.

During operation of a coining press, a feed step, that is removal of the formed workpiece from the tools and placing of a blank workpiece between the tools, must be completed whilst the tools are open. It is inherent in a machine in which the reciprocating tool moves with one end of a toggle linkage that the velocity of that tool is much higher when it is spaced substantially from the stationary tool than when the reciprocating tool is close to the stationary tool. The acceleration to which the reciprocating tool is subjected on reversal of the direction of movement when the tools are open is very high, considerably higher than the acceleration on reversal of the direction of movement when the tools are closed.Furthermore, in known coining presses, the stroke must be long, relative to the travel of the reciprocating tool which is required to just clear a feed device, in order that the reciprocating tool will be clear of the feed device for a period which is sufficiently long for all movement of the feed device to take place within that period. The vibration which results from a long stroke and rapid acceleration of the reciprocating tool deters operation of a coining press with short cycle times.

It is an object of the present invention to enable a shorter cycle time than is common at the present time to be used.

According to a first aspect of the invention, a reciprocating tool of a press is moved a shorter distance whilst a formed workpiece is being moved from a position between the tools and a blank workpiece is being moved into the position between the tools by a feed device and the reciprocating tool is moved a longer distance whilst the feed device is at rest.

In a method in accordance with the first aspect of the invention, a relatively short stroke can be used, since the major part of that stroke is executed between successive feed steps to provide sufficient clearance between a feeding device and the tools throughout the feed strip. Since the movement, if any, of the tool during a feed step is relatively small, the acceleration of the tool when the tools are open can be moderate, even when the cycle time is short.

The reciprocating tool preferably moves, at least between successive feed steps, with a slide and the acceleration of the slide at completion of an opening stroke may be not substantially greater than the acceleration of the slide at completion of a closing stroke.

During the feed step, the reciprocating tool may rest on a stationary abutment whilst a relatively small movement of the slide occurs.

According to a second aspect of the invention, there is provided a press comprising a first tool carrier which is stationary in use, a second tool carrier which is moved towards and away from the first tool carrier and a feed device for feeding workpieces intermittently into and from a position between the first and second tool carriers and driving means for reciprocating the second tool carrier and for driving the feed device, wherein the driving means is arranged to move the second tool carrier a longer distance whilst the feed device is at rest, and a shorter distance, or not at all, whilst the feed device is feeding workpieces into and from the position between the tools.

The driving means preferably includes a slide which reciprocates towards and away from the first tool carrier to carry the second tool carrier towards the first tool carrier.

The maximum acceleration of the slide or reciprocating tool at one end of the stroke may be within the range 75% to 125% of the maximum acceleration reached at the other end of the stroke.

The driving means may include a toggle linkage, one pivot of which moves with the slide, a rotary member which is rotated and has an eccentric element, a connecting member connected with the eccentric element to be moved to and fro substantially with simple harmonic motion, and a transmitting member which transmits a part of said simple harmonic motion from the connecting member to the toggle linkage.

An example of a press in accordance with the invention which is used in a method in accordance with the invention will now be described, with reference to the accompanying drawings, wherein: Figure 1 shows certain parts of the press diagrammatically; Figure 2 is a diagram illustrating the positional relation of certain parts of the press; and Figure 3 is a timing diagram illustrating operation of the press.

The press comprises a body 10, a part only of which is represented in Fig. 1, and which is stationary during use of the press. There is releasably mounted on the body, by means of an upper tool carrier, an upper tool 11 which, during a coining operation, is stationary and has a downwardly presented working face for co-operation with a workpiece to be formed in the press. A lower tool 1 2 is mounted for reciprocation towards and away from the upper tool along a vertical path and has an upwardly presented face for co-operation with the workpiece. The lower tool is mounted on a movable tool carrier 14 which can be moved towards the stationary tool carrier by a slide 1 3 guided by the body 10 for vertical sliding motion. The tool carrier 14 is urged downwardly relative to the body by springs 37.

The body 10 includes a horizontal plate 1 5 which lies above the tool carrier 1 4 and slide 1 3 and which defines an opening through which the lower tool 1 2 extends towards the upper tool. Adjacent to the upper surface of the plate 15, there is provided a dial plate 1 6 for feeding workpieces in succession to a position between the tools 11 and 1 2. The dial plate may be a part of a known feed system. The dial plate is formed with apertures to receive respective workpieces and when a workpiece occupies one of these apertures, it rests on the upper surface of the plate 15, when moving towards and when moving away from the position between the tools.

The press further comprises drive means for reciprocating the slide 1 3 relative to the body 10. The drive means comprises a toggle linkage 1 7 having upper and lower limbs connected for relative pivoting about a middle axis 1 8. The upper limbs are connected with the slide 1 3 for relative pivoting about an upper axis 1 9 and the lower limbs are connected with a bearing 20 for relative pivoting about a lower axis 21.The bearing 20 is connected with the body 10 through the intermediary of a screw and nut mechanism 22 having a handle 23, by means of which the lower axis 21 can be adjusted upwardly and downwardly relative to the body, thereby adjusting the position of-the lower tool 1 2 relative to the upper tool 11, for a given configuration of the toggle linkage.

The drive means comprises a crankshaft 24 supported for rotation about a horizontal axis relative to the body 1 0, carrying a flywheel and clutch unit 25 and carrying a brake 26, by means of which rotation of the crankshaft relative to the body 10 can be braked. The crankshaft 24 is connected with an electric motor 27 by a belt and pulley drive 28.

A shaft 29 is mounted for rotation relative to the body 10 about an axis parallel to the axis of the crankshaft 24 and parallel to the axes 18, 19 and 21. The crankshaft 24 has a crank 30 connected by a connecting rod 31 with a first crank on the shaft 29. The respective throws of these cranks are such that a complete revolution of the crankshaft 24 causes the shaft 29 to oscillate through an angle of somewhat less than 90 . Further cranks on the shaft 29 are connected with the toggle linkage 1 7 at the middle axis 1 8 by respective parallel connecting rods 32 and 33.

As shown in Fig. 2, the axis 34 about which the connecting rod 31 can pivot relative to the crank on the shaft 29 is spaced angularly about the axis 35 of the shaft 29 from the axis 36 about which the connecting rods 32 and 33 can pivot relative to their cranks on the shaft 29. The angle subtended at the axis 35 by a line joining the axes 34 and 36 is preferably within the range 80 to 45 and is more preferably within the range 60 to 70o. The arrangement is such that, during rotation of the crankshaft 24, the axis 34 makes equal excursions in opposite directions from a plane which contains the axis 34 and the axis 35 when the distance between the axis 35 and a longitudinal centreline of the connecting rod 31 has a maximum value.

As the axis 34 approaches one end of its arcuate path, the longitudinal centreline of the connecting rod 32 passes through the axis 35. Accordingly, when the axis 34 moves through this end portion of its arcuate path, substantially no longitudinal motion is applied to the connecting rod 32 and the toggle linkage is held in the retracted configuration illustrated in Fig. 1. As the taxis 34 approaches the other end of its arcuate path, the angle between the longitudinal centreline of the connecting rod 32 and the plane containing the axis 35 and 36 increases to a maximum value, which is in the range 55 to 75 .

Accordingly, as the axis 34 moves through the second end portion of its arcuate path, substantial longitiudinal movement is imparted to the connecting rod 32 and the toggle linkage is moved into a straight configuration.

During use of the press, the crankshaft 24 is rotated continuously and at substantially uniform speed by the motor 27. The press is caused to execute a number of cycles of operation, typically many thousands of cycles, without the crankshaft 24 coming to rest.

During each cycle of operation, the connecting rod 31 is reciprocated towards and away from the shaft 29 with simple harmonic motion. During a part of each cycle of this simple harmonic motion, there is substantially no longitudinal movement of the connecting rod 32. During the remainder of each cycle of the motion of connecting rod 31, the connecting rod 32 moves longitudinally and transmits motion to the toggle linkage 1 7. During that part of the cycle in which there is no substantial longitudinal movement of the connecting rod 32, the lower tool 1 2 occupies a lowered position in which it is withdrawn from the dial plate 1 6. Whilst the tool is in this position, the dial plate is indexed to moved a formed workpiece from the position between the tools and to move a succeeding workpiece into a position between the tools. The dial plate is driven in a known manner from the crankshaft 24.

A complete cycle of operation is represented in Fig. 3. At the origin of Fig. 3. the dial plate 1 6 is half-way through a feed step and is moving relatively quickly. The dial plate comes to rest at time t, and remains at rest until time t2, when the next feed step commences. The curve 38 in Fig. 3 represents the relation between displacement of the slide 1 3 and time.

It can be seen that, from time to to time t1, there is only slight displacement of the slide.

Almost the whole of the displacement of the slide occurs between time t, and time t2.

The curve 39 in Fig. 3 represents the relation between displacement and time for the slide of a conventional coining press having a toggle linkage, the centre joint of which is reciprocated with simple harmonic motion.

In this case, the speed of the slide is low only in the middle of the cycle, that is when the toggle linkage is extended and the tools are acting together on the workpiece. The curve 38 shows that, in the press illustrated in the drawings, the speed of the slide is low in the middle of the cycle, when the toggle linkage is extended, and is also low at the end of the cycle, when the toggle linkage is retracted.

In order to eliminate movement of the lower tool 1 2 during the feed step, downward movement of the tool 1 2 is arrested by engagement between an abutment fixed with respect to the boy and the carrier 1 4 interposed between the tool and the slide. There is freedom for limited vertical movement of the carrier relative to the slide. Whilst the slide undergoes the slight displacement which occurs from time to to time t, and from time t2 to time to, the carrier is held in engagement with the abutment by springs 37 which urge the carrier downwardly relative to the body 10.

Around time to, the slide is substantially at rest and therefore has no substantial acceleration. Throughout the time from t to t2, slide platen is accelerating, eitherupwardly or downwardly. The maximum acceleration at completion of the opening (i.e. downward) stroke is within 75% to 120% of the maximum acceleration at the completion of the closing (i.e. upward) stroke.

During the closing stroke of the lower tool, an upper end of that tool rises into the aperture in the dial plate 1 6 to engage the underside of a blank workpiece and carries that workpiece into engagement with the upper tool 11. Whilst being formed between the tools, the workpiece is confined at its periphery by a collar (not shown) fixed with respect to the upper tool. When the lower tool descends, the formed workpiece is held in the collar by friction. To eject the workpiece from the collar, the upper tool is moved downwardly by an ejector, which may be arranged in a known manner. The ejector is reciprocated relative to the body 10 by a lever (not shown) driven by a further eccentric (not shown) on the crankshaft 24.

The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the dislosed function, may, separately or any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims (5)

1. A press comprising a first tool carrier which is stationary in use, a second tool carrier which is moved towards and away from the first tool carrier, a feed device for feeding workpieces intermittently into and from a position between the first and second tool carriers and driving means for reciprocating the second tool carrier and for driving the feed device, wherein the driving means is arranged to move the second tool carrier a longer distance whilst the feed device is at rest and a shorter distance whilst the feed device is feeding workpieces.

2. A press according to Claim 1 wherein the driving means includes a slide which reciprocates towards and away from the first tool carrier to carry the second tool carrier towards the first tool carrier, a toggle linkage, one pivot of which moves with the slide, a rotary member which is rotated and has an eccentric element, a connecting member connected with the eccentric element to be moved to and fro substantially with simple harmonic motion and a transmitting member which transmits a part of said simple harmonic motion from the connecting member to the toggle linkage.

3. A method of forming a workpiece wherein a first drive element is moved to and fro with simple harmonic motion, a selected part of each cycle of said simple harmonic motion is transmitted by connecting means from the said first drive element to a tool to cause the tool to reciprocate towards and away from a second tool during execution of said part of said cycle, during the remainder of said cycle a workpiece is fed into a position between the tools and during the remainder of the next cycle the workpiece is fed away from the tools, the tools remaining substantially stationary during feeding of the workpiece.

4. A press having driving means arranged substantially as hereinbefore described with reference to the accompanying drawings.

5. Any novel feature or novel combination of features disclosed herein and/or shown in the acccompanying drawings.