EP0353479A1 - Method and apparatus for reducing the press load of a cutting press with positive stops - Google Patents

Abstract

The stroke of the ram (2) is limited by at least one positive stop (5, 6). At least one positive stop (5, 6) has at least one sensor (15) which determines the resilient deformation of the respective stop (5, 6) resulting from the impact force. The output signals of the respective sensor (15) are fed to the control device for the ram height adjustment. This ram height adjustment is carried out by a servomotor (9) and adjoining gear train (10). By means of the positive stops (5, 6), the bottom dead centre of the ram (2) relative to the lower tool part can be set according to the requirements. In this way, it is also possible to define exactly the plunging depth of the upper tool part (3) with the stampers (8) into the lower tool part (4), and it can also be zero or less. The ram height, which can be corrected depending on the impact force on the positive stops (5, 6), reduces the press load, which would otherwise increase greatly in line with the increasing number of strokes. …<IMAGE>…

Description

The present invention relates to a method for reducing the press load on a cutting press, in which a relative position between the upper and lower tool is limited by at least one fixed stop. It further relates to a device for carrying out the method according to claim 1, wherein the cutting press has at least one fixed stop used in the upper and / or lower tool part and is equipped with a control device containing an actuator for changing the ram height during operation.

Especially with high-speed cutting presses, the height of the ram must be given special attention. For example, a very precise bottom dead center position of the ram is required in the entire operating stroke range if very precise bends, embossing, cutting open tear-open covers, etc. is required. If the dead center is inaccurate, scrap is produced. There is also an endeavor to keep the plunging of the punch of the upper tool part in the lower tool part to a minimum value, so that as little as possible of the punch and the cutting plate has to be ground away when the tool is resharpened. With a big immersion depth, more material has to be removed from the punch and die during each re-sharpening than with a small immersion depth. The corresponding tool can therefore be re-sharpened less often until it needs to be replaced.

This means that the total number of parts fixed with a particular tool is consequently lower and the corresponding production costs are correspondingly higher.

To avoid these undesirable phenomena, fixed stops are generally provided on the lower and upper tool parts. These fixed stops keep the relative end position of the upper and lower parts of the tool constant over the entire stroke rate range of a given cutting press. however, the minimum collision forces required with a small number of strokes increase sharply with an increasing number of strokes and therefore put additional strain on the cutting press.

The invention seeks to remedy this. The invention, as characterized in the claims, achieves the object of providing a method and a device for carrying out the same, in which the force exerted on the mechanical impact is measured and the height position of the ram is changed as a function of the measured impact force, that it stays within a specified range.

The advantages achieved by the invention can be seen essentially in the fact that the impact force is measured where it actually arises, so that an exact correction of the ram height position can be carried out. This means an increased quality of a produced product and less wear of a particular tool.

In the following, the invention will be described with reference to only one drawing, which represents an embodiment explained in more detail.

• Fig. 1 schematisch eine Ansicht einer Schnitt­presse, zur Erklärung einer Ausführung der Erfindung,
• Fig. 2 teilweise einen Schaltkreis zur Höhen­verstellung des Stössels,
• Fig. 3 und 4 Diagramme, in denen der Verlauf der pressenbelastung mit steigender Hubzahl dargestellt ist, und
• Fig. 5 bis 7 Diagramme, in denen der Verlauf des Stösselweges im unteren Totpunktbereich dargestellt ist.

It shows:

• 1 schematically shows a view of a cutting press for explaining an embodiment of the invention,
• 2 partially a circuit for height adjustment of the ram,
• 3 and 4 are diagrams showing the course of the press load with increasing number of strokes, and
• 5 to 7 diagrams in which the course of the ram path is shown in the bottom dead center area.

In the schematic representation of FIG. 1, the cutting press is generally designated by the reference number 1. The plunger 2 is also shown, which is articulated via pivot pins 14 to crank arms 16, which in turn are drive-connected to a crankshaft, eccentric shaft or other type of drive, not shown. Obviously, these components are only to be regarded as an example of the drive of the plunger 2.

An upper tool part 3 is connected to the plunger 2, which upper tool part 3 interacts with a lower tool part 4, for example with cutting plates.

The height of the ram can be adjusted during operation of the high-speed cutting press, for which purpose there is a schematically represented servomotor 9, which acts on the ram 2 via a gear train 10. The position indicator of the ram height adjustment is indicated by reference number 11. Cutting punches 8 are inserted in the upper part 3 of the tool.

According to the schematic representation of FIG. 1, two fixed stops 5 are arranged in the upper part 3 of the tool. In the lower part 4 there are also two Fixed stops 6 shown. It should be noted here that this representation is purely for example. Basically, only a fixed stop in one of the two tool parts, in particular in the lower tool part 4, is necessary. There can be more than two fixed stops per tool part or, in the case of follow-up cutting tools, only one work station can be provided with at least one fixed stop.

These fixed stops can be, for example, a steel block, a steel cylinder, etc. Due to the fact that the lifting movement of the upper tool part 3 in the lower dead center area relative to the lower tool part 4 is limited by at least one fixed stop, there is certainly no or only the minimally required immersion of the upper tool part 3 in the lower tool part 4 with associated wear, so that the immersion depth 0 or the desired size. This immersion depth, e.g. when embossing, also accept negative values, i.e. the cutting punch then does not reach the die. Obviously, a certain immersion depth can be made possible by appropriate selection of the height of the fixed stops, depending on the prevailing conditions with regard to the tools.

If the height of the ram is too low or becomes too low due to the high speeds of the high-speed cutting press, this would result in a significantly higher impact force on a respective fixed stop. Correspondingly, at least one fixed stop with one or more sensors, in the embodiment shown it is the two fixed stops 6 in the lower tool part 4, equipped with a sensor.

Obviously, the impact of the upper part 3 of the tool on a respective fixed stop 6 causes the latter to move in the direction of the ram hubs deformed elastically, since a collision force is exerted on them. Of course, this elastic deformation is extremely small, but can still be detected with a suitable component. For example, a strain gauge, which is connected in a known manner via a Wheatstone bridge, can be arranged on the respective fixed stop, or a piezo element could be present.

Reference is now made to FIG. 2. The plunger 2, a fixed stop 5 in the upper tool part 3 and a fixed stop 6 in the lower tool part 4 are shown in this. A number of cutting punches 8 are also shown.

The fixed stop 6 is now equipped with a component 15 as described above, which, depending on the respective collision force, emits an electrical signal by registering the elastic deformation of the fixed stop 6.

This signal is fed to a signal amplifier 12 and the output of this signal amplifier 12 is fed to a control part 13 for adjusting the ram height. The control part 13 is connected to the servomotor 9 for adjusting the ram height and to the position transmitter 11 for adjusting the ram height. The servomotor 9 drives the gear train 10 for the ram height adjustment. The units 9-11 and 13 are of a known type, as is also the case with the signal amplifier 12, and a detailed description of these devices is therefore unnecessary.

The operation of the embodiment described above is as follows. It is assumed that during the operation of the cutting press there is an impact on a fixed stop with each stroke. As already mentioned, the resulting small elastic deformation of the fixed stop is converted into an electrical signal. Obviously, a precisely determinable impact force and thus electrical signal now corresponds to perfect operation with a set height position of the ram. A single value does not necessarily have to be defined, but a value range or a value with tolerance limits.

If the height of the ram is too high, so that there is no or too little impact on the fixed stop, scrap could be produced, since a corresponding tool part, e.g. a stamp that does not penetrate deep enough into a workpiece during embossing or does not penetrate completely through the workpiece during cutting.

The corresponding signal lies below a predetermined limit, which state is determined in the control part 13, and which, in accordance with the servomotor 9 for the ram height adjustment, transmits a signal which causes the height of the ram to be changed until the collision force specified for the correct operation occurs.

If a collision force that is too large compared to the specified value or value range is determined, this is a sign of an excessively low ram end position, which results in an undesirable additional press load. Correspondingly, the servomotor 9 is controlled in such a way that the height of the plunger is increased until a predetermined drive-up force prevails and the press is thus relieved.

This control of the height of the ram is used in particular at different speeds or strokes in high-speed cutting presses, e.g. when starting up or changing the number of strokes in normal operation.

As is well known, the immersion depth of an upper tool takes on uncontrolled cutting presses an associated lower tool with increasing working speed, ie higher number of strokes. In the present training, the fixed stops ensure that the immersion depth is absolutely limited, or even 0 if necessary. The height of the ram can now be controlled in operation, depending on the prevailing conditions, the basis of the control not being based on a measurement, for example the speed, but on the actually occurring collision force. The collision force is determined directly on the part affected, namely the fixed stop, whereby an elastic deformation is sensed. No measurement is therefore carried out at a point distant from the point of impact with the fixed stop, which measurement becomes inaccurate due to deformations of machine parts and changes in bearings during operation. Thus, the load on the fixed stops, ie the collision force that occurs on them, can be kept constant with a changing number of strokes. In the control section 13, a selectable basic correction can be set with respect to the ram height, as a function of the number of strokes, when retracting a newly equipped machine, and after engagement, control can then be carried out, depending on the predetermined collision force, in accordance with that of the sensor or sensors , delivered values, can be switched. It is also possible to set the tappet height correction, which is dependent on the number of strokes, in the control part 13, the values supplied by the sensors then overriding the previously set values. The control of the height of the ram also comes into play when the temperature changes, for example when the cold press starts up and when the ambient temperature changes.

Reference is now made to FIGS. 3 and 4. The speed (number of strokes) of each cut press is marked with "n", and the press load generally with "F". A punch press is generally designed for a nominal pressing force F _N. This design therefore determines the size of the machine and thus crucially the purchase price for the user of a particular machine. The cutting force or embossing force is designated F _St. This is the force generated in the tool and to be applied by the cutting press for a particular work step, eg punching, embossing, bending, etc., in accordance with the product to be manufactured. The impact force on the fixed stop, or the fixed stops, which is also to be absorbed by the cutting press, is designated F _A. The sum F _St + F _A thus determines the force to be exerted by the cutting press (apart from the internal losses of the machine resulting from, for example, bearing friction), that is to say determines the design or size, and thus ultimately the costs thereof.

In Figure 3, a number of strokes n₁ is now assumed, purely for example 100 strokes per minute. The press load F is therefore composed of F _St + F _A. It is assumed that a tool with fixed stops is available. It should also be assumed that the ram height remains the same, i.e. there are no precautions to change the ram height (e.g. depending on the number of strokes or impact force), so that the force to be applied by the cutting press increases with an increasing number of strokes. The press force F increases with increasing n according to the solid curve line. The number of strokes n2, for example 1000 strokes per minute, is the maximum number of strokes of this cutting press. At n₂ there is now the nominal pressing force F _{N of} this cutting press, i.e. the design size and ultimately the cost of the same.

The dashed curve line now gives the pressing force F to be used in the case of the invention Cutting press equipped with height adjustment. It should be noted in particular that the collision force on the fixed stop, or the fixed stops, is kept constant in the entire stroke rate range due to the ram height correction that is now taking place. The dashed curve line runs below the solid line again up to the maximum number of strokes n₂. This results in a decisive reduction in the press force to be exerted by the press, which reduction is marked with F _R. If the cutting press is designed the same, the load on the cutting press is reduced by 20 to 30%! This means that in the case of fixed stops, combined with ram height adjustment, the cutting press to be purchased does not have to be designed for the same work output for F _N , but for F _N - F _R. The result is a "smaller" machine, which leads to decisive cost savings when purchasing the same.

Reference is now made to FIG. 4, in which all designations correspond to those in FIG. 3. The diagram is based on a cutting press which is identical to that of FIG. 3 with the nominal pressing force F _N , that is to say the press load without ram height correction increases with an increasing number of strokes along the solid curve line (FIG. 3).

In the press, on which the diagram in FIG. 4 is based, the ram height correction and the stroke limitation by means of fixed stops are present. The value F _A , that is the impact force on a respective fixed stop, is equal to that of FIG. 3 at the number of strokes n 1 and is kept constant as the number of strokes increases. However, since the press load may increase with increasing number of strokes up to n₂ again to the same value F _N according to the nominal pressing force, F _St can now be correspondingly and noticeably larger. It means that With a given cutting press, which is equipped with fixed stops and ram height control, the available manpower is significantly greater. The difference can be up to 40%. And this obviously results in significant savings when purchasing a punch press, because the punch press equipped accordingly has a much higher workforce available for machining workpieces.

Reference is now made to FIGS. 5-7. The course of the tappet path in the lower dead center area is shown schematically in these. Here, t means the passage of time and h the ram path.

5 shows the course of the ram path at a low number of strokes, for example when setting up the cutting press. If there are no fixed stops, the lowest ram position corresponds to point B, with the specific ram path being drawn without a fixed stop and without cutting or embossing as a dashed line. If there are fixed stops, the ram path (including cutting or embossing) follows the solid curve line, with the lowest ram position at A now. In particular, attention is drawn to the fact that the ram path at the lowest ram position is drawn as a straight line due to the fixed stop. There is no further downward movement. There is therefore a precisely defined lowest relative position with respect to the lower part of the tool through the fixed stops.

FIG. 6 shows the course of the ram path in the bottom dead center area during operation. Without fixed stops, without ram height control or correction and without cutting or embossing work, the ram path runs according to the dashed curve line, corresponding to the lowest ram position to reach the position of the letter B.

The ram path runs along the solid line with fixed stops and cutting or embossing work, with the lowest ram position at A. Note the relatively long horizontal distance, i.e. a relatively long period of time during which the contact force acts on the fixed stop. The large difference Δ h from A to B indicates a high impact pressure on the fixed stops.

Figure 7 shows the same operating state of the cutting press as Figure 6. The course of the ram path with fixed stops and with ram height control, which is regulated on the basis of the stop approach force, takes place along the solid line in Figure 7. The lowest ram position is again designated with A. The duration of this lowest tappet position according to the horizontal distance at A is now considerably shorter than the tappet travel according to Figure 6. The dashed line from which the bottom tappet position B can be seen represents the same without fixed stops, but with tappet height control.

The small difference Δ h 'from A to B confirms the low impact pressure on the fixed stops.

The sensor or sensors can also form a structural unit separate from the relevant fixed stop and can be installed next to or directly under the fixed stop. The fixed stop could also be designed in the form of a frame.

Claims (10)

1. A method for reducing the press load of a cutting press, in which a relative position between the upper and lower tool is limited by at least one mechanical fixed stop, characterized in that the impact force exerted on the mechanical stop (5; 6) is measured, and that The height of the ram (2) is changed depending on the measured impact force in such a way that the latter remains within a defined range. 2. The method according to claim 1, characterized in that the impact force is measured by the resulting deformation of the mechanical stop (5; 6) is sensed. 3. The method according to claim 2, characterized in that the sensed deformation is elastic and is converted into an electrical signal, which is amplified and then a control device (13) for controlling a drive (9, 10) for height adjustment of the ram (2) is fed. 4. The method according to claim 1, characterized in that the working stroke limitation, the measurement of the impact force and change in the height position of the ram (2) takes place during the working operation of the cutting press. 5. The device for carrying out the method according to claim 1, wherein the cutting press has at least one fixed stop (5; 6) used in the upper tool part (3) and / or lower tool part (4) and with a control device (9-11) containing a servomotor (9) ) is equipped to change the ram height during operation, characterized in that the fixed stop (5; 6) has one or more devices (15) for Scanning of the impact force exerted on it is or are assigned, the output signal of which is fed to the control device (9-11) for changing the ram height. 6. The device according to claim 5, characterized in that a plurality of fixed stops (5; 6) in the upper tool part (3) and / or lower tool part (4) are present, of which at least one has a device (15) for sensing the impact force. 7. The device according to claim 6, characterized in that the respective device (15) for sensing the impact force has a component by means of which a deformation of the fixed stop (5; 6) can be determined and this measured value can be converted into an electrical signal. 8. The device according to claim 7, characterized in that the component is designed to determine an elastic deformation of the respective fixed stop (5; 6) taking place in the ram stroke direction. 9. The device according to claim 8, characterized in that the component has a strain gauge attached to the respective fixed stop or a piezo element. 10. The device according to claim 5, characterized in that the device for sensing the impact force exerted on the fixed stop is formed separately from the fixed stop.

Images