EP3174650B1 - Punching device and method for punching a workpiece - Google Patents

Description

The present invention relates to a punching apparatus comprising: a punch which is movable during a punching stroke along a stroke axis on a workpiece to be punched and during a return stroke of the punched workpiece, the punching tool having a first component and a second component, the for the common movement along the lifting axis are hydraulically coupled, and a punch drive for moving the first component along the lifting axis, wherein the punching device is formed during the punching stroke to move the second component with a first gear ratio relative to the first component and, if in the punching stroke a threshold value of a counterforce is exerted, which exerts the workpiece to be punched on the punching tool to move the second component with a second, different from the first gear ratio relative to the first component. The invention also relates to an associated method for punching a workpiece.

From the EP 1 593 444 A1 For example, a punching device has become known which has a punching tool which is movable along a longitudinal axis. The punching device includes drive means for moving the punching tool in a linear, pendulum-shaped motion which includes a downstroke and a return stroke. When punching a metal plate during the downward stroke, the metal plate exerts a force directed counter to the direction of movement of the punching tool on the punching tool. The punching tool has a first component which is moved by the drive device during the downward stroke and the return stroke with a predetermined first movement law. The punching tool also has a second component which cooperates in operation with a plunger for punching the metal plate. The second component is connected to the first component in a sliding manner. If the counterforce is below a predetermined value, the second component is moved axially in the downward stroke substantially with the same law of motion as the first component. The punching device also has pressure means to move the second component with a second, different from the first law of motion, when the counterforce corresponds to at least the predetermined value.

The first component of the punching tool is moved by a drive device which comprises an electric motor acting on a threaded spindle. If the predetermined value of the counterforce is exceeded, the force of the electric motor is not sufficient to punch through the workpiece. In this case, the pressure means are activated in order to strengthen the force exerted on the workpiece and to punch through the workpiece. The first component is moved in this case to the second component, which rests against the workpiece and therefore initially prevented from further downward movement. Due to the relative movement between the first component and the second component, the hydraulic force is amplified to the second component. When the first component is moved upward again after the punching of the workpiece, the first component initially moves away from the second component along the stroke axis until the first component abuts against a stop of the second component, so that the second component rebounds after the second component can take upstairs.

From the EP 0 575 343 B1 a device for carrying out a two-stage linear movement has become known, in which a movable assembly has a hydraulic piston with a cavity into which a plunger protrudes. The hydraulic piston carries a rotatable spindle of an electric motor and the plunger is axially displaceable by means of the spindle in the hydraulic piston and a hydraulic cylinder to build up a pressure in this. The device may comprise an auxiliary cylinder communicating with the cylinder space of the hydraulic cylinder. In the auxiliary cylinder is a piston which is coupled to the hydraulic piston via a support plate and moves uniformly with this.

From the US 2009/0084277 A1 For example, a device has been disclosed which has a connection mechanism for connecting an output shaft to an input shaft such that they are not movable relative to one another. In order to apply high pressure to the output shaft, a fluid pressure mechanism is provided which is adapted to establish a hydraulic connection between the output shaft and the input shaft to move them relative to each other. The linkage mechanism detects the contact of the output shaft with the workpiece and releases the connection between the output shaft and the input shaft. If the input shaft is returned to a position prior to the high pressure application after punching the workpiece, the connection can be automatically restored by the connection mechanism. A similar device, in which a through hole extending from a second liquid chamber in the axial direction, which is formed between the output shaft and a fixing part, is made of EP 1 652 660 A1 known.

A punching machine, which is to allow for a motor with constant power both a movement with low compressive force and high speed before punching editing and a movement with high pressure force and low speed when punching a workpiece, is from the JP 2000-141092 A known. For this purpose, an oil chamber is formed in a housing and a first piston is provided which is fixed at its front end to the rear end of a second piston. Of the first piston has a pressure generating surface and the second piston has at its rear end a pressure receiving surface whose surface is larger than the surface of the pressure generating surface.

From the WO 2011/079333 A2 a drive device for a bending press has become known which comprises a stationary press bar and a press bar adjustable by means of a hydraulic linear actuator having bar adjusting means. The linear actuator has a first piston arrangement with a first piston which divides a cylinder space into a first pressure space and a second pressure space. The linear actuator also has, in another cylinder chamber, a further piston arrangement with a further piston and at least one further pressure chamber. The first piston assembly and the second piston assembly are coupled together.

Object of the invention

The invention has for its object to improve a punching device of the type mentioned and a method for punching a workpiece, in particular with regard to the achievable stroke rate.

Subject of the invention

This object is achieved by a punching device of the type mentioned, which is designed to maintain at least along a part of the return stroke of the punch along the stroke axis a right after the punching of the workpiece occupied relative position of the two components to each other. For the purposes of this application, components are not necessarily understood to mean one-part components, but instead a respective component may be composed of a plurality of components that are rigidly connected to one another.

In the punching device according to the invention, a punching drive, in particular an electric punching drive, is used to move the first component along the lifting axis. To get the largest possible area on the workpiece To cover applied punching force, the punching device realized two power levels, of which the first by the punch drive (possibly in combination with a fluid translation) is realized, while the second power stage is realized with greater punching force by a larger gear ratio between the first and the second component. The hydraulic coupling between the two components, which are typically realized as piston components is realized in the punching device by a closed hydraulic circuit, ie there are no hydraulic units (pumps, etc.) for increasing the punching force or the transmission ratio required.

In order to achieve the largest possible number of strokes in such an energy-efficient punching device, it is proposed according to the invention to freeze the relative position or position which the two components assume each other immediately after the punching of the workpiece along the stroke axis along at least part of the return stroke. In other words, after the punching, the two components are moved away from the workpiece, without resulting in a relative movement of the two components to each other. This applies both to the operation of the punching device with the first gear ratio and for the operation of the punching device with the second gear ratio.

The return stroke begins at bottom dead center of the two components after punching through the workpiece. The portion of the return stroke in which the relative position of the two components is frozen, is typically chosen so large that the punch or the punching tool is completely withdrawn from the workpiece before the freezing of the relative position of the two components is released. By freezing the relative position of the two components, the punching tool can be moved very quickly away from the workpiece along this section. As a result, the workpiece can already be displaced laterally relative to the punching tool shortly after the punching and can be suitably positioned for a subsequent punching stroke. The freezing of the relative position is typically canceled when the second component has taken a defined position (reference position) along the stroke axis. If the reference position is reached, the second component is typically clamped hydraulically (possibly with the aid of a spring force), ie in its reference position along the Stroke axis held. The first component is then further displaced by means of the punching drive relative to the second component along the lifting axis, until it has reached the top dead center of the pendulum movement of the punching tool. Alternatively, it is also possible to perform a so-called flying reset or a flying reset. In this case, during the reset, the second component is moved along the stroke axis, ie it is not necessary to reset to a reset position of the second component.
The punching device can be designed in particular to move the first and the second component with a first transmission ratio of 1: 1, if the threshold value of the counterforce is not exceeded. The second gear ratio between the first and second components, ie the ratio between the distance the first component traverses along the stroke axis and the distance which simultaneously covers the second component along the stroke axis, is typically greater to achieve increased power transmission as the first gear ratio and may for example be more than 5: 1, 8: 1, etc.
If the first gear ratio is 1: 1 and the threshold value of the counterforce is not exceeded in the punching stroke, no change in the relative position of the two components, so that they are moved back to the top dead center in the return stroke with the same relative position, without a reset is required. In this case, a new punching stroke can be performed immediately after the return stroke of the punching tool. If a relative movement between the two components has taken place during the punching stroke, ie if the threshold value of the counterforce has been exceeded, then it is necessary to carry out a further punching stroke such that the two components once again assume the relative position which they assumed before switching to the second transmission ratio have, as described in more detail above.

In a preferred embodiment, a cavity is formed in the second component into which a portion of the first component forming a piston protrudes. The cavity forms a hydraulic cylinder, in which the piston forming portion of the first component is guided linearly displaceable. Under a piston forming Section is understood in the context of this application also an end of a piston rod whose end face forms an effective piston surface. In this case, the diameter of the piston rod is slightly smaller than the diameter of the cavity. In the cavity may be formed a shoulder on which the piston rests during operation with the first gear ratio. If you switch to the second gear ratio, the piston is lifted from the paragraph. If the cavity in this case is in fluid communication with a hydraulic cylinder in which the second component is guided, the second transmission ratio can be realized in this way. Also, the heel can be used in a return stroke to the plant of the piston to take the second component in the return stroke movement, unless the hydraulic coupling due to a fault does not allow.

In a further, preferred embodiment, the first component has a first piston which is displaceably guided in the stroke direction in a first hydraulic cylinder. Due to the movement of the first component and thus of the piston in the first hydraulic cylinder, a force transmission to the second component can take place due to a hydraulic coupling with a second hydraulic cylinder, so that this is moved together with the first component along the lifting axis, without that for this purpose a separate drive is required. As will be described below, however, it is not absolutely necessary for the first component to have a piston guided in a hydraulic cylinder.

In a further, preferred embodiment, the second component has a second piston, which is displaceably guided in the stroke direction in a second hydraulic cylinder. By a suitable hydraulic coupling of the second hydraulic cylinder with the first component, more precisely with the first hydraulic cylinder, in which the piston of the first component is displaceably guided, can be realized in a simple manner, a hydraulic power transmission between the two components.
In an advantageous embodiment, during operation of the punching device with the first gear ratio, an effective piston surface of the first component coincides with an effective piston surface of the second component. In the hydraulic coupling of the first and second hydraulic cylinder can during Present equal effective piston surfaces of the first and second pistons, a first transmission ratio of 1: 1 can be realized. Optionally, in addition to the effective piston surfaces formed on the first and second pistons, the first and / or the second component also have further effective piston surfaces, for example on further pistons, which are displaceably guided in further hydraulic cylinders. The piston surfaces of these other pistons contribute to the effective piston area of the two components.

In a further preferred embodiment, the first hydraulic cylinder and the second hydraulic cylinder are formed both as the synchronizing cylinder during operation of the punching device with the first gear ratio as well as in operation with the second gear ratio. In a synchronizing cylinder, the two opposite sides of the effective piston surfaces are equal in size so that the piston is moved toward and away from the workpiece at the same speed. It has proved to be particularly advantageous when both hydraulic cylinders are designed as a synchronous cylinder, since in this case can be completely dispensed with the provision of a reservoir for hydraulic fluid (tank) as a balance memory and on Nachsaugventile. It may only be necessary during the punching process to connect the unpressurized side to a compensation reservoir of very small volume, which serves to compensate the compression and the temperature compensation volume. To form the two hydraulic cylinders in both gear ratios as a synchronous cylinder, it is necessary to suitably coordinate the effective piston surfaces of the two components or the two hydraulic cylinders. It is understood that in such a vote, any other effective piston surfaces, e.g. in an auxiliary cylinder (s.u.), must be considered.

In a further preferred embodiment, the first component has a cavity into which a stationary piston of the first hydraulic cylinder protrudes. By the piston, the stroke length of the first hydraulic cylinder can be reduced. This is particularly advantageous in the embodiment described above, in which synchronizing cylinders are used, since synchronizing cylinders usually require an increased space requirement for structural reasons.

In a preferred embodiment, the second hydraulic cylinder comprises an auxiliary cylinder into which a further piston of the second component protrudes. The further piston rigidly fastened, for example, to the second component via a common carrier plate moves uniformly with the second piston of the second component along the stroke axis. The auxiliary cylinder is mounted adjacent to or parallel to the master cylinder of the second hydraulic cylinder, so that by this the stroke length of the second hydraulic cylinder can be reduced, which is particularly favorable in the case that the second hydraulic cylinder is designed as a synchronizing cylinder.

In a further preferred embodiment, the second component carries a punch of the punching device or the second component itself acts as a plunger. In this case, the second component, more precisely its punch, contacts the workpiece in order to punch it through during the punching stroke. The punching device can have a measuring device, for example in the form of an optical or mechanical sensor, in order to detect and, if necessary, regulate the position of the punch or the second component along the stroke axis or, for example, to detect a return position at which the return should take place.
In an alternative embodiment, the first component has a cavity in which a piston of a plunger of the punching device is guided displaceably in the stroke direction. In this case, the second component is not used as a plunger, but rather a cavity is formed in the second component, through which the plunger is guided in the axial direction, to punch through the workpiece with its end facing away from the first component. The plunger in this case typically has a second piston, which is guided linearly displaceably in the cavity of the second component serving as a hydraulic cylinder. A punching device with such a design has proven to be advantageous, in particular in the realization of the above described flying reset, since in this case the reset can be done directly by a hydraulic coupling between two pressure chambers surrounding the piston of the plunger of the first component.

In a further preferred embodiment, the punching device comprises at least one hydraulic switching valve for switching between a movement of the two components with the first transmission ratio and a movement of the two Components with the second transmission ratio when the threshold value of the counterforce of the workpiece is exceeded on the punching tool. The switching valve typically switches between two switching states in which different fluid paths for the hydraulic fluid (typically a hydraulic oil) are blocked and / or released. The switching from the first to the second switching state (and vice versa) can take place with the aid of a control device of the punching device, which is coupled to a sensor device which measures the counterforce exerted by the workpiece on the punching tool. The switching from the second to the first switching state of the switching valve is typically carried out when the counterforce drops below the threshold again. If necessary, the changeover valve can be selectively activated by a control device, ie switched over from the first to the second switching state, even if the counterforce is less than the threshold value. This may be necessary in order to effect a return during the return stroke, ie to allow a relative movement between the two components, for example by fixing the second component in its position along the lifting axis.

In a preferred development, the changeover valve has a hydraulic control line, which is connected to a pressure-side pressure chamber of the punching tool to switch over when the threshold value of the counterforce between the movement of the two components with the first transmission ratio and the movement of the two components with the second transmission ratio , A pressure-side pressure chamber of the punching tool is understood to mean a pressure chamber which is delimited by a piston surface of one of the two components, which is arranged on the side of the component facing away from the workpiece. In such a pressure space, the pressure increases as the counterforce of the workpiece on the punch increases. The switching valve or the control line are formed so that the switching valve automatically switches when a pressure threshold is exceeded in the pressure-side pressure chamber, which corresponds to the desired threshold value of the back pressure of the workpiece. If the pressure threshold is undershot, the change-over valve automatically switches back to the first switching state. Optionally, the switching valve in the event that the pressure threshold is exceeded, by means of an additional control line be switched from the first to the second switching state.
In a particularly preferred embodiment, the punching device comprises a return device with at least one hydraulic return valve for changing the relative position of the two components during or after the return stroke along the lifting axis. The return valve is typically activated independently of the counterpressure of the workpiece by means of a control device. The control device can in principle activate the return valve at any position of the punching tool during the return stroke along the lifting axis in order to change the relative position of the two components or to restore the original relative position of the two components at the beginning of the punching stroke. As a rule, before activating the return valve, the movement of the second component along the stroke axis should be stopped, ie, the second component should be in a reset position and not move when the reset valve is activated.
In order to effect the return, the return valve acts on the hydraulic circuit of the punching device suitably, with a plurality of possibilities for such action, as will be described below. As previously stated, it may be necessary to activate another hydraulic valve to effect recovery. The further valve may in particular be the change-over valve, which is activated by the control device simultaneously with the return valve and thus itself serves as a return valve.

In a preferred embodiment, the return valve is designed as a control valve. If the return is not made in a stationary reset position of the second component, but during the movement of the second component along the lifting axis, a difference occurs between the speeds at which the first and the second component are moved in the provision. In this case, it is therefore advantageous, if necessary even necessary, to design the return valve as a control valve. A control valve can be switched not only between two switching positions, but at least in one of the switching positions, the flow through the control valve can be controlled or regulated by means of a control device. The Regulation of the flow can be made such that the return is completed when the two components occupy a predetermined relative position to each other, which typically corresponds to the relative position before switching from the first to the second gear ratio. The use of a control valve has proven particularly favorable in the embodiment described above in which the first component has a cavity in which a plunger of the punching device is guided displaceably.
In a further development of this embodiment, the return valve is designed to hydraulically isolate the positioning of the two components relative to one another, ie in the active switching position, hydraulically isolating at least one pressure chamber of the second hydraulic cylinder, ie to block a fluid connection to the pressure chamber of the second hydraulic cylinder. In a further pressure chamber of the second hydraulic cylinder springs may be attached, which press the second component against the isolated pressure chamber of the second hydraulic cylinder. In this way, the second component in the second hydraulic cylinder is fixed in its position along the lifting axis, while the first component is displaced in the reset relative to the second component. As an alternative to fixing the second component in the second hydraulic cylinder by means of compression springs, it is also possible to clamp or fix the second component in the second hydraulic cylinder by also hydraulically isolating the other pressure chamber of the second hydraulic cylinder.

In a further preferred embodiment, the changeover valve is designed to produce a hydraulic connection between a pressure chamber of the first hydraulic cylinder and a reservoir for a hydraulic fluid when the threshold value of the counterforce is exceeded. In this case, in the switching position of the switching valve in which the second gear ratio is present, a portion of the hydraulic fluid from the pressure chamber of the first hydraulic cylinder in the reservoir (typically a high-pressure tank) is promoted. In a first switching position, the switching valve can serve to establish a fluid connection between a pressure chamber of the first hydraulic cylinder and a pressure chamber of the second hydraulic cylinder, which is disconnected when switching. In the not active switching position of the return valve can connect this another pressure chamber of the first hydraulic cylinder with a pressure chamber of the second hydraulic cylinder. If the return valve is activated and this connection interrupted, the pressure chamber of the second hydraulic cylinder is completed or hydraulically isolated.
In an alternative embodiment, the changeover valve is designed to produce a hydraulic connection between a first and a second pressure chamber of the first hydraulic cylinder when the threshold value of the counterforce is exceeded. In this case, in the switching position of the switching valve, in which the second gear ratio is present, a portion of the hydraulic fluid from a first pressure chamber of the first hydraulic cylinder is not conveyed into a reservoir but into a second pressure chamber of the first hydraulic cylinder. In this way it can be dispensed with the provision of a pressure tank or a pressure reservoir. This embodiment can be realized in particular if both hydraulic cylinders are designed as synchronizing cylinders in both gear ratios.
In a further alternative embodiment, the switching valve is designed to disconnect a hydraulic connection between a first and a second pressure chamber of the second hydraulic cylinder when exceeding the threshold value of the counterforce, more precisely, to hydraulically isolate the two pressure chambers of the second hydraulic cylinder. In this way, the guided in the second hydraulic cylinder second component is clamped or fixed in the movement in the stroke direction. In this embodiment, a ram guided in the second component typically serves to punch through the workpiece. In the first switching state of the switching valve typically the first and the second pressure chamber of the second hydraulic cylinder are hydraulically connected to each other.

In a preferred development of this embodiment, the return valve is designed to produce a hydraulic connection between a first pressure chamber and a second pressure chamber of the cavity formed in the first component for varying the positioning of the two components relative to each other. The return valve is preferably formed in this embodiment as a control valve and makes it possible to change the relative position between a guided in the cavity of the first member ram and the first component along the stroke axis. In the first switching state of the return valve this typically separates the connection between the first pressure chamber and the second pressure chamber of the cavity in the first component or hydraulically isolates the two pressure chambers, so that the plunger is clamped or fixed in the first component and together with the first Component can be moved without a change in the relative position to the first component along the Hubachse.

In a further preferred embodiment, the punching device additionally comprises a control device for controlling the punching drive and for controlling at least one return valve of the return device. As described above, the activation of the at least one return valve of the return device for changing the relative position of the two components to each other either in a reset position in which the first component (and thus the second component) is not moved, or the provision can carried out flying, ie while the two components are moved along the stroke axis. In both cases, a coordination between the punch drive and the activation or deactivation of the at least one return valve is required, which takes over the control device. It is understood that the control device can possibly also serve to control the punching stroke or the movement of the punching tool. In this case, the control device is connected to one or more sensors, which measure the position of the first component, the second component and / or the plunger along the stroke axis and possibly the force exerted by the workpiece on the punching counterforce. The above object is achieved according to the invention by a method according to claim 16. As described above, a gear ratio of 1: 1 can be selected as the first gear ratio, in particular. The method may in particular comprise the embodiments described above in connection with the punching device as advantageous variants.

As described above, for performing a new punching stroke, it is desirable to move the two components to a relative position along the stroke axis which they have assumed relative to each other prior to switching from the first to the second gear ratios.
The invention also relates to a computer program product, which is designed to carry out all the steps of the method described above, when the computer program runs on a data processing system.

Fig. 1

eine schematische Darstellung eines Ausführungsbeispiels einer Stanzvorrichtung mit einem Stanzwerkzeug mit zwei relativ zueinander entlang einer Hubachse beweglichen Bauteilen beim Beginn eines Stanzhubs,

Fig. 2

eine Darstellung analog Fig. 1 mit dem Stanzwerkzeug in einem unteren Totpunkt eines Stanzhubs, in dem die beiden Bauteile eine veränderte relativen Position zueinander einnehmen,

Fig. 3

eine Darstellung analog Fig. 1 und Fig. 2 mit dem Stanzwerkzeug in einer Rückstellposition, in welche die beiden Bauteile während eines Rückhubs unter Beibehaltung ihrer relativen Position entlang der Hubachse verschoben wurden,

Fig. 4

eine Darstellung eines weiteren Ausführungsbeispiels einer Stanzvorrichtung, in welcher die beiden Bauteile in zwei Gleichlaufzylindern in Hubrichtung verschiebbar geführt sind,

Fig. 5

eine Darstellung eines weiteren Ausführungsbeispiels einer Stanzvorrichtung mit zwei Bauteilen, in deren Hohlräumen eine Kolbenstange eines Stößels verschiebbar geführt ist, im Betrieb mit einem ersten Übersetzungsverhältnis, und

Fig. 6

eine Darstellung der Stanzvorrichtung von Fig. 5 im Betrieb mit einem zweiten, vom ersten verschiedenen Übersetzungsverhältnis.

The embodiments shown and described are not to be understood as exhaustive enumeration, but rather have exemplary character for the description of the invention.
Show it:

Fig. 1

a schematic representation of an embodiment of a punching device with a punching tool with two relative to each other along a lifting axis movable components at the beginning of a punching stroke,

Fig. 2

a representation analog Fig. 1 with the punching tool in a bottom dead center of a punching stroke, in which the two components assume an altered relative position to one another,

Fig. 3

a representation analog Fig. 1 and Fig. 2 with the punching tool in a return position, in which the two components have been displaced during a return stroke while maintaining their relative position along the stroke axis,

Fig. 4

a representation of another embodiment of a punching device, in which the two components are guided displaceably in two synchronous cylinders in the stroke direction,

Fig. 5

a representation of another embodiment of a punching device with two components, in whose cavities a piston rod of a plunger is guided displaceably, in operation with a first gear ratio, and

Fig. 6

an illustration of the punching device of Fig. 5 in operation with a second, different from the first gear ratio.

In the following description, the same reference numerals are used for identical or functionally identical components.

Fig. 1 shows an exemplary structure of a punching device 1 for punching a plate-shaped workpiece 2, which is arranged in a support plane (XY plane) on a die 3, which is arranged at a predetermined distance L from a housing 4 of the upper part of the punching device 1. Both the die 3 and the housing 4 are stationary in the example shown here, that move this not along a stroke axis (Z-direction) perpendicular to the support plane. This does not apply to a Fig. 1 also shown punching tool 5, which is shown as all along the lifting axis Z movable parts of the punching device 1 to distinguish them from the stationary components without hatching.

The punching tool 5 which is movable or displaceable along the lifting axis Z comprises a first component 6 and a second component 7 whose relative position ΔP can be varied along the lifting axis Z, as will be described in more detail below. The first component 6 is coupled to a punch drive 8, which serves as an electrical drive, e.g. is formed in the form of a torque motor, which acts on a threaded nut 8a, which sets a formed on the first component 6 ball screw 9 in a rotational movement to move the first component 6 along the lifting axis Z.

The first component 6 of the punching device 1 has a piston rod 10, on which a first, upper piston 11 is formed, which is guided in a first, upper hydraulic cylinder 12 in the stroke direction Z slidably. Accordingly, the second component 7 also has a piston 13, which is displaceably guided in a second, lower hydraulic cylinder 14 formed in the housing 4. In the second component 7, a cavity 15 is introduced into which a further, lower piston 16 forming end-side portion of the piston rod 10 of the first component 6 protrudes into it. As in Fig. 1 can also be seen, at the bottom, the workpiece 2 facing the end of the second component 7, a punch 17 is mounted, which is brought into the punching operation with the workpiece 2 in Appendix.

Fig. 1 shows the punching tool 5 at the beginning of the punching operation, ie at a top dead center of a pendulum movement, the punching tool 5 travels in a punching stroke on the workpiece 2 and in a return stroke after punching away from the workpiece 2 away. At the in Fig. 1 shown initial position, the two components 6, 7 take a relative position .DELTA.P along the lifting axis Z to each other, in which the upper side of the lower piston 16 of the first component 6 abuts an axial shoulder 18 of the cavity 15 of the second component 7. This relative position ΔP is (arbitrarily) defined as zero position, ie it applies to the in Fig. 1 shown starting position Δ P = 0.

The punching tool 5 is based on the in Fig. 1 shown starting position on the workpiece 2 moves by the punch drive 8, the first component 6 along the lifting Z moves down. A first, upper pressure chamber D1 of the first hydraulic cylinder 12 is hydraulically coupled to a second, lower pressure chamber D2 'of the second hydraulic cylinder 14 via a second switching valve UV2, which is located in a first switching position and serves as a return valve. Correspondingly, a second, lower pressure chamber D2 of the first hydraulic cylinder 12 is hydraulically coupled via a first switching valve UV1 located in a first switching position to a first, upper pressure chamber D1 'of the second hydraulic cylinder 14. The first pressure chamber D1 'of the second hydraulic cylinder 14 is in permanent hydraulic communication with a third pressure chamber D3' of the second hydraulic cylinder 14 situated in the cavity 15 of the second component 7.

The piston surface B3 at the top of the first piston 11 of the first component 6 is the same size as the piston surface A3 on the underside of the piston 13 of the second component 7. Accordingly, the piston surface B2 on the underside of the first piston 11 of the first component 6 is also as large as the piston surface A2 at the top of the piston 13 of the second component 7. In the in Fig. 1 shown initial position in which the lower piston 16 of the first component 6 abuts against the shoulder 18 of the second component 7, the piston surface A3 on the underside of the lower piston 16 of the second component 7 plays no role. The effective piston surface B3 - B2 of the upper piston 11 of the first component 6 and the effective piston surface A3 - A2 of the piston 13 of the second component 7 are thus equal in size. As a result, the two components 6, 7 are displaced along the stroke axis Z with a transmission ratio of 1: 1, ie the two components 6, 7 are moved towards the workpiece 2 during the punching stroke without their relative position ΔP along the stroke axis Z changed.

If a counterforce F, which exerts the workpiece 2 on the punching tool 5, does not rise above a predetermined threshold value, the driving force of the electric punching drive 8 is sufficient to punch through the workpiece 2. In this case, both the punching stroke and the return stroke of the punching tool 5, without that the relative position of the two components 6, 7 changes, ie it remains during the entire pendulum movement ΔP = 0.

Increases the counterforce F of the workpiece 2 during the punching operation and thus the pressure in the upper pressure chamber D1 'of the second hydraulic cylinder 14 so strong that one with the upper pressure chamber D1' in hydraulic communication, pressurized control line 19, the first switching valve UV1 of the first, in Fig. 1 shown switching state in a second, in Fig. 2 switched switching state is switched between the first operating state with the first gear ratio (1: 1) between the first component 6 and the second component 7 in a second operating state with a second, larger transmission ratio (eg, about 5: 1 or more) as follows from Fig. 2 is explained.

In the second operating state (translator mode), the first switching valve UV1 connects the second, lower pressure chamber D2 of the first hydraulic cylinder 12 with a reservoir 20 for the hydraulic fluid in the form of a high-pressure tank, which is subjected to a pressure of, for example, about 10 bar. The reservoir 20 is connected via three check valves RV1 to RV3 to the upper pressure chamber D1 of the first hydraulic cylinder 12 and to the upper and lower pressure chambers D1 ', D2' of the second hydraulic cylinder 14, respectively. During the movement of the first component 6 toward the workpiece 2, the hydraulic fluid from the second pressure chamber D2 of the first hydraulic cylinder 12 is conveyed into the reservoir 20 in the translator mode. At the same time hydraulic fluid from the second pressure chamber D2 'of the second hydraulic cylinder 14 is conveyed into the upper pressure chamber D1 of the first hydraulic cylinder 12, since both are in hydraulic communication in the second switching position of the first switching valve UV1. The lower piston 16 of the first member 6 is lifted in the translator operation of the paragraph 18 of the second component 7, so that there is a transmission ratio, which is the sum of the piston area A2 of the piston 13 of the second component 7 and the piston surface A1 in the with upper pressure chamber D1 'in further hydraulic pressure related space D3' to the piston surface A1 of the piston 16 in the further pressure chamber D3 'is formed, ie it applies to the transmission ratio: A2 / A1.

In a circular piston surface A1 with a diameter of 35 cm and a circular piston surface A2 with a diameter of 100 cm results in a ratio ratio of about 8: 1 in the translator mode Thus, the first component 6 sets eight times the distance of the second component 7 along the Hubachse Z back, whereby the pressure exerted by the second component 7 on the workpiece increases accordingly. The missing due to the different speeds of the two components 6, 7 in the translator operation in the upper pressure chamber D1 of the first hydraulic cylinder 12 hydraulic fluid is sucked in via the first check valve RV1 from the reservoir or from the tank 20.

Fig. 2 shows the punching tool 5 in the translator mode in a bottom dead center of the movement along the stroke axis, on which the workpiece 2 has been completely punched through. Due to the 1: 1 different ratio of 8: 1 in the translator mode have the two components 6, 7 immediately after the punching of the workpiece 2 a non-zero relative position Δ P ', of the distance traveled with the second transmission ratio along the Hubachse Z depends. It is understood that unlike in Fig. 2 shown the punching tool 5 can be moved further down after punching the workpiece 2 down until the bottom dead center of the movement is reached. Since, after the punching of the workpiece, the further downward movement takes place with the gear ratio of 1: 1, the relative position Δ P 'of the two components 6, 7 does not change in this case.

As will be described below, the relative position .DELTA.P ', which the two components 6, 7 occupy at the end of the downward movement relative to each other, at least along a part of the return stroke of the punch 5 in the in Fig. 1 Retained shown starting position, ie, the relative position Δ P 'is virtually "frozen" until a designated as the reset position position along the lifting axis Z is reached, at which the relative position Δ P' of the two components 6, 7 in the original relative position P = 0 is transferred.

Since after the complete punching of the workpiece 2, the counterforce F of the workpiece 2 and thus the pressure in the upper pressure chamber D1 'of the second hydraulic piston 14 abruptly decreases, the first switching valve UV1 is switched over the control line 19 from the second switching state to the first switching state. Since the gear ratio in the first switching position of the first switching valve UV1 is 1: 1, the second component 7 is moved with the movement of the first component 6 by means of the punch drive 8 away from the workpiece 2 without the relative position Δ P 'changing , Thus, it is not necessary in the punching device 1 to perform a relative movement between the first component 6 and the second component 7 in the translator mode at the beginning of the return stroke. Such a movement would lead to a comparatively large stroke movement of the first component 6 and thus a comparatively large time duration being required for moving the second component 7 out of the workpiece 2 upwards on account of the transmission ratio of 8: 1. By the movement of the punching tool 5, at least at the beginning of the return stroke in normal operation, the punching tool 5 or the second component 7 can be quickly withdrawn from the workpiece 2, so that in the area of the support level can quickly repositioning of the workpiece 2 for a subsequent punching stroke done. Since the return to the original relative position .DELTA.P is not done in the translator mode, also the time required for the total return stroke is significantly reduced.

In order to restore the original relative position .DELTA.P of the two components 6, 7 to each other, the punching tool 5 is in a in Fig. 3 shown reset position, which between the in Fig. 1 shown position at top dead center and the in Fig. 2 shown position at the bottom dead center of movement along the lifting axis Z is located. The reset position should be selected so that at least the portion of the return stroke, which is required to pull out the punch 17 from the workpiece 2, has already been covered in the upward movement. If the return is achieved, as in the example shown, by preventing the second component 7 from moving along the lifting axis Z, it is typically favorable if the return position is at least offset by the amount of the relative position .DELTA.P 'from the top dead center of the movement Punching tool 5 is removed.

To effect the provision, an electronic control device 21 of the punching device 1 acts on the punch drive 8 in order to move the first component 6 and thus the punching tool 5 into the desired return position along the lifting axis Z. If the desired reset position is reached, the control device 21 acts on the second switching valve UV2 to switch it from the first to a second switching state in which the second switching valve UV2 serves as a return valve. The control device 21 and the return valve UV2 together form a return device 23 of the punching device 1. The activation of the return valve UV2 by the control device 21 can be effected for example by a pneumatic control line shown in dashed lines. In the in Fig. 3 shown second switching position of the return valve UV2, the lower pressure chamber D2 'of the second hydraulic cylinder 14 is hydraulically isolated. With the help of provided in the upper pressure chamber D1 'of the second hydraulic cylinder 14 compression springs 22, the second component 7 is fixed or clamped in the second hydraulic cylinder 14, so that it can no longer be moved along the lifting axis Z in the second switching state of the return valve UV2.

While the second component 7 is clamped in the stroke direction Z, the second component 7 is further displaced upward until the two components 6, 7 assume their original relative position .DELTA.P = 0 to one another, in which the first and the second component 6, 7 abut each other at the shoulder 18. During this return movement, the return valve UV2 establishes a hydraulic connection between the upper pressure chamber D1 of the first hydraulic cylinder 12 and the reservoir 20 in order to return the hydraulic fluid conducted into the reservoir 20 in the ratio mode back into the upper pressure chamber D1. After the reset, the return valve UV2 can be deactivated and the two components 6, 7 can again without changing the relative position Δ P = 0 along the lifting axis Z to the top dead center (see. Fig. 1 ) are moved. It is understood that the return position along the lifting axis Z can also be selected so that after moving the first component 6 to reach the original relative position Δ P = 0, the in Fig. 1 shown starting position of the punching tool 5 along the lifting axis Z is taken.

In order to suitably control or regulate the punching tool 5 or the punching drive 8 by means of the control device 21, the punching device 1 has an optical sensor 24, for example, for determining the position of the second component 7 along the lifting axis Z. It is understood that further sensors for determining the position of the first component 6 and / or for determining the counterforce F, which exerts the workpiece 2 on the punching tool 5, can be provided in the punching device 1.

A further embodiment of a punching device 1, which in Fig. 4 is shown based on the above related Fig. 1 to Fig. 3 described basic principle. At the in Fig. 4 Punching device 1 shown, the upper component 6 is moved via an electric punch drive 8 in the form of a linear drive along the stroke axis Z and it is realized by means of the further component 7, a hydraulic fluid transmission. The main difference of the punching device of Fig. 4 to the punching device 1 described above is that in the in Fig. 4 both the first hydraulic cylinder 12 and the second hydraulic cylinder 14 are designed as a synchronizing cylinder, that is, the opposing piston surfaces and the corresponding surfaces of the pressure chambers are the same size in each of the two hydraulic cylinders 12, 14, as will be described below:

The first, upper hydraulic cylinder 12 has a first, upper pressure chamber D1. In the first component 6 of the punching device 1 of Fig. 4 a cavity 25 is formed, in which a stationary plunger 26 of the housing 4 protrudes into and in which a second pressure chamber D2 is formed. The first hydraulic cylinder 12 also has a lower, third pressure chamber D3. The hydraulically effective surfaces of the pressure chambers D1 to D3 or the hydraulically active surfaces of the piston 11 of the first component 6 are coordinated so that the upper hydraulic cylinder 12 forms a synchronizing cylinder.

The second, lower hydraulic cylinder 14 also has a first, upper pressure chamber D1 'and a second, lower pressure chamber D2', between which a piston 13 of the second component 6 is guided displaceably. The second hydraulic cylinder 14 has an auxiliary cylinder 27, in which a further piston 28th of the second component 7 protrudes to reduce the height of the second hydraulic cylinder 14. The further piston 28 is rigidly connected to the parallel guided piston 13 of the second component 7 via a support plate 29. On the support plate 29, a punch of the punching device 1 may be attached to a in Fig. 4 punch through the workpiece 2, not illustrated. In addition, a third pressure chamber D3 'is formed in the auxiliary cylinder 27, which is in permanent hydraulic communication with the second, lower pressure chamber D2' of the second hydraulic cylinder 14. The hydraulically effective surfaces of the pressure chambers D1 ', D2', D3 'and the corresponding hydraulically active surfaces of the piston 16 and the other piston 28 are coordinated so that the lower hydraulic cylinder 14 also forms a synchronizing cylinder.

In normal operation, ie at the in Fig. 4 shown position of the two switching valves UV1, UV2, both the third pressure chamber D3 and the second pressure chamber D2 of the upper hydraulic cylinder 12 with the upper pressure chamber D1 'of the lower hydraulic cylinder 14 are hydraulically connected. The hydraulically effective surfaces of the two pressure chambers D2, D3 (or the associated piston surfaces) of the upper hydraulic cylinder 12 are equal to the hydraulically effective area of the upper pressure chamber D1 'of the lower hydraulic cylinder 14. The first, upper pressure chamber D1 of the first hydraulic cylinder 12 is permanently connected to the second, lower pressure chamber D2 '(and thus also to the third pressure chamber D3') of the second hydraulic cylinder 14. The hydraulically effective surface of the upper pressure chamber D1 of the upper hydraulic cylinder 12 corresponds to the hydraulically active surfaces of the second and third pressure chamber D2 ', D3' of the lower hydraulic cylinder 14. In this way, a transmission ratio of 1: 1 is realized in normal operation, ie the two components 6, 7 move in normal operation in the in Fig. 4 shown relative position .DELTA.P = 0, wherein the lower piston 16 of the first component 6 abuts a shoulder 18 of the second component 7, along the lifting axis Z.

In the translator mode, ie when a threshold value of the counterforce F, which exerts the workpiece 2 on the punching tool 5, the pressure in the upper pressure chamber D1 'of the lower hydraulic cylinder 14 increases and the first switching valve UV1 is in hydraulic communication with the latter Control line 19 is activated and switches from the first to the second switching state. In the second switching state, the first switching valve UV1 establishes a hydraulic connection between the first pressure chamber D1 and the third pressure chamber D3 of the upper hydraulic cylinder 12 and disconnects the hydraulic connection between the third pressure chamber D3 of the upper hydraulic cylinder 12 and the first pressure chamber D1 'of the lower hydraulic cylinder 14 The hydraulically acting surfaces of the first pressure chamber D1 and of the third pressure chamber D3 are in opposite directions, so that the resulting hydraulically effective surface of the first hydraulic cylinder 12 is the hydraulically effective surface of the second pressure chamber D2, which acts on the hydraulically effective surface of the first pressure chamber D1 '. of the second hydraulic cylinder 14 acts. Due to the different size of the hydraulically effective surfaces of the second pressure chamber D2 of the first hydraulic cylinder 12 and the first pressure chamber D1 'of the second hydraulic cylinder 14 results in the translator operation a transmission ratio of D1' / D2, which may for example be about 5: 1 or above ,

After the punching of the workpiece 2, the pressure in the upper pressure chamber D1 'of the second hydraulic cylinder 14 drops rapidly and the first switching valve UV1 switches back to the first switching state. The punching tool 5 is retracted in normal operation, ie with a transmission ratio of 1: 1, along the lifting axis Z until a return position is reached. In the reset position, as related to above Fig. 1 to Fig. 3 has been described, the second component 7 is clamped in the second hydraulic cylinder 14 to move the first component 6 by means of the punch drive 8 relative to the second component 7 and the original, in Fig. 4 shown relative position .DELTA.P = 0 of the two components 6, 7 restore.

To enable this return movement, both the first switching valve UV1 and serving as a return valve second switching valve UV2 are simultaneously switched from the first to the second switching state by the controller 21 acts on both switching valves UV1, UV2 by means of a respective pneumatic control line. By activating both switching valves UV1, UV2, the upper pressure chamber D1 'of the second hydraulic cylinder 14 is hydraulically isolated, so that the guided in this second Component 7 can not be moved further up. At the same time, a hydraulic connection between the first pressure chamber D1 and the third pressure chamber D3 of the upper hydraulic cylinder 12 is produced by means of the second changeover valve UV2, ie, the upper hydraulic cylinder is short-circuited.

If the changeover of the two changeover valves UV1, UV2 is not exactly synchronous, this has no negative effects on the punching device 1, ie this does not lead to tension. In the Fig. 4 shown punching device 1 also has the advantage that no pressure tank or the like for receiving hydraulic fluid is needed, since the two hydraulic cylinders 12, 14 are formed as a synchronous cylinder and the hydraulically effective surfaces of the two hydraulic cylinders 12, 14 are coordinated so that in the Translator operation, ie at the second gear ratio, the synchronization is guaranteed. The coordination of the hydraulically effective surfaces is in Fig. 4 realized by the fact that for the pressure chambers D1, D2, D3 of the upper hydraulic cylinder 12 and for the first pressure chamber D1 'of the lower hydraulic cylinder 14 applies: D1' = D2 + D3. In addition, in the example shown, D2 '= D3'. As in Fig. 4 can be seen, only a reservoir 20 'is required with a very small capacity, which via two check valves RV1, RV2 with the third pressure chamber D3 of the upper hydraulic cylinder 12 and with the second pressure chamber D2' of the lower hydraulic cylinder 14 (ie with the unpressurized Page) is connected. The reservoir 20 'serves as a compensation volume, more precisely as a temperature compensation volume and as a compression compensation volume. Overall, the comes in Fig. 4 shown punching device 1 with a small number of components and can therefore be realized in a compact design. In addition, in the area switching, ie when switching between the first gear ratio and the second gear ratio, no force jump but a steady transition, so that the (closed) hydraulic circuit and in particular the switching valves UV1, UV2 are not stressed too much. At the in Fig. 4 shown embodiment, no power transmission over the stop 18 is also necessary during the return stroke, ie the stop 18 is only for safety and is not mandatory for the implementation of the punching stroke.

A further embodiment of the punching device 1 is described below with reference to FIG Fig. 5 and Fig. 6 described. A major difference in Fig. 5 and Fig. 6 described punching device 1 and the punching devices 1 described above is that in addition a plunger 30 is provided which serves for punching the workpiece 2 and which can be moved relative to the first component 6 and the second component 7 along the lifting axis Z. The plunger 30 has a piston rod 33 on which a first piston 31 and a second piston 32 are formed. The first piston 31 of the plunger 30 is slidably guided in a cavity 25 of the first component 6 in the stroke direction Z. Also, the second component 7 has a cavity 15 in which the second piston 32 of the plunger 30 is slidably guided in the stroke direction Z. The second component 7 also has, on its outer side, a piston 13, which is displaceably guided in a second or single hydraulic cylinder 14 in the housing 4 of the punching device 1. The first component 6, however, is not slidably guided in a hydraulic cylinder, but is driven directly by means of an electric punch drive 8, which may be formed for example as a linear drive, so that the first component 6 acts as a linear actuator.

At the in Fig. 5 shown position of the two components 6, 7 relative to each other is the piston 16 of the first component 6 with its upper side against an axial stop 18 of the second component 7, ie, the two components 6, 7 assume a relative position .DELTA.P = 0 to each other. In normal operation, in which a first switching valve UV1 is in a first switching state, a hydraulic connection is established between an upper pressure chamber D1 'and a lower pressure chamber D2' of the hydraulic cylinder 14. The piston 13 of the second component 7 or the hydraulic cylinder 14 is designed as a synchronizing cylinder, ie the upper and lower piston surface C1, C2 of the piston 13 are the same size. In normal operation, a first, upper pressure chamber D3 of the cavity 15 in the second component 7 is hydraulically separated by the second switching valve UV2 located in a first switching state, ie, the upper piston 31 of the plunger 30 is clamped, so that the plunger 30 in a corotating motion is displaced along the lifting axis Z together with the first component 6 and with the second component 7.

Fig. 6 shows the punching device 1 in the translation mode in which the threshold value of the counterforce F of the workpiece 2 has been exceeded, so that the pressure in an upper pressure chamber D3 'of the cavity 13 in the lower component 7 has risen so far that the first switching valve UV1 on the Control line 19 has switched to the second switching position. In the second switching position, the upper pressure chamber D1 'and the lower pressure chamber D2' of the hydraulic cylinder 14 are hydraulically separated, so that the second component 7 is clamped in the hydraulic cylinder 14. The first, acting as a linear actuator component 6 is moved in the translator operation by means of the punch drive 8 further down until the workpiece was completely punched through and the two components 6, 7, the in Fig. 6 shown position .DELTA.P 'along the lifting axis Z to each other. Due to the smaller effective piston area A1 of the piston 16 of the first component 6 relative to the effective piston surface B1 at the top of the lower piston 32 of the plunger 30, a gear ratio of B1 / A1 is generated in the translator mode. In this case, use is made of the fact that the lower pressure space D4 'of the cavity 15 of the second component 15 is permanently hydraulically connected to an upper pressure space D3 of the cavity 25 of the upper component 6.

In order to move the first component 6 relative to the second component 7 during a return stroke and in this case the in Fig. 5 shown relative position .DELTA.P = 0 of the two components 6, 7, during the return stroke, that is, during the movement of the first component 6 along the lifting axis, the second, serving as a return valve switching valve UV2 switched to the second switching state. In the second switching state, the second switching valve UV 2 connects the upper pressure chamber D 3 with the lower pressure chamber D 4 of the cavity 25 of the first component 6.

The second changeover valve UV2 is a control valve in which the flow rate in the second switching state can be adjusted or regulated by means of the control device 21 as a function of the reset speed. In this way, during the movement of the first component 6 along the lifting axis Z, the relative movement between the plunger 30 and the first component 6 can be directly influenced. Depending on the valve opening or the flow through the serving as a return valve second switching valve UV2 of the return stroke or the relative movement between the plunger 30 and the first component 6 or between the first component 6 and the second component 7 are regulated, whereby the dynamics during the return stroke can be substantially increased. The regulation is typically carried out in such a way that the provision is completed when the deceleration movement is completed. The volume difference of the hydraulic fluid, which occurs due to the different speeds of the plunger 30 and the first component 6 and the second component 7 in the respective pressure chambers D1 ', D2', D3, D4, D3 ', D4', by two reservoirs ( Pressure tanks) 20, 20a are compensated, in which the corresponding volume of liquid is conveyed or from which the required liquid volume of the hydraulic fluid can be removed. For this purpose and to compensate for leakage losses of the hydraulic fluid three check valves RV1 to RV3 are arranged in the punching device 1. To return the plunger 30 in the in Fig. 5 shown relative position .DELTA.P = 0 is in the upper pressure chamber D3 of the cavity 25 of the first member 6, a first compression spring 34, which defines the zero position of the first component 6 relative to the first piston 31, and in the second, lower pressure chamber D4 'of second component 7, a second compression spring 35 is arranged, which serves to reset and which exerts on the upper pressure chamber D3 'of the cavity 13 a force which increases the pressure in the upper pressure chamber D3'. The second compression spring 35 thus influences the threshold value of the counterforce F at which switching is effected between the first transmission ratio and the second transmission ratio.

It is understood that the embodiments of the punching device 1 described above can also be modified. For example, it may be dispensed with the provision of a paragraph 18 on the second component 7 or it is not mandatory a piston at the lower end of the first component 6 is required, which cooperates with such a shoulder 18. In this case, for example, the lower end face of the piston rod designed as the portion of the first component 6 serve as a hydraulically effective surface. Also, at the in Fig. 1 to Fig. 3 described embodiment, the clamping of the second component 6 to the in Fig. 5 and Fig. 6 described way, ie by the two pressure chambers D1 ', D2' of the second hydraulic cylinder 14 are hydraulically isolated, so that the piston 13 of the second component 7 is hydraulically clamped.

In summary, high dynamics can be achieved in the punching devices 1 described above during the return stroke, in particular since the beginning of the return stroke, i. the beginning of the movement from the bottom dead center, not with the second, larger transmission ratio is performed, but while maintaining the relative position of the two components 6, 7 and with the first transmission ratio. In this way, a highly dynamic punching movement with two (or possibly more) force levels can be realized with a closed, energy-efficient hydraulic circuit.

Claims (17)

1. A punching apparatus (1) comprising:

   a punching tool (5) which, during a punching stroke, is movable along a stroke axis (Z) toward a workpiece (2) to be punched and, during a return stroke, is movable away from the punched workpiece (2), wherein the punching tool (5) has a first component (6) and a second component (7) which are able to be coupled hydraulically for joint movement along the stroke axis (Z), and

   a punching drive (8) for moving the first component (6) along the stroke axis (Z),

   wherein the punching apparatus (1) is configured to move the second component (7) at a first transmission ratio relative to the first component (6) during the punching stroke and, provided that a threshold value of an opposing force (F), which the workpiece (2) to be punched exerts on the punching tool (5), is exceeded during the punching stroke, to move the second component (7) at a second transmission ratio, different from the first, relative to the first component (6),

   characterized

   in that the punching apparatus (1) is configured to maintain a relative position (ΔP'), taken up immediately after the workpiece (2) has been punched through, of the two components (6, 7) with respect to one another at least along a section of the return stroke of the punching tool (5) along the stroke axis (Z).
2. The punching apparatus as claimed in claim 1, in which a cavity (15) is formed in the second component (7), an end portion, forming a piston (16), of the first component (6) projecting into said cavity (15), wherein the first component (6) preferably has a cavity (25) into which a positionally fixed plunger piston (26) of the first hydraulic cylinder (12) projects.
3. The punching apparatus as claimed in claim 1 or 2, in which the first component (6) has a first piston (11) which is guided in a first hydraulic cylinder (12) so as to be displaceable in the stroke direction (Z), wherein the second component (7) preferably has a second piston (13) which is guided in a second hydraulic cylinder (14) so as to be displaceable in the stroke direction (Z).
4. The punching apparatus as claimed in claim 3, in which, during operation of the punching apparatus (1) at the first transmission ratio, an effective piston surface (B3-B2) of the first component (6) matches an effective piston surface (A3-A2) of the second component (7).
5. The punching apparatus as claimed in one of claims 3 or 4, in which the first hydraulic cylinder (12) and the second hydraulic cylinder (14) act as synchronized cylinders both during operation at the first transmission ratio and during operation at the second transmission ratio.
6. The punching apparatus as claimed in one of claims 3 to 5, in which the second hydraulic cylinder (14) has an auxiliary cylinder (27) into which a further piston (28) of the second component (7) projects.
7. The punching apparatus as claimed in one of the preceding claims, in which the second component (7) bears a punching die (17) of the punching apparatus (1).
8. The punching apparatus as claimed in one of claims 1 to 6, in which the first component (6) has a cavity (25) in which a piston (31) of a ram (30) of the punching apparatus (1) is guided so as to be displaceable in the stroke direction (Z), wherein the ram (30) preferably has a further piston (32) which is guided in the cavity (15) of the second component (7) so as to be displaceable in the stroke direction (Z).
9. The punching apparatus as claimed in one of the preceding claims, further comprising:
   at least one hydraulic switching valve (UV1) for switching between a movement of the two components (6, 7) at the first transmission ratio and a movement of the two components (6, 7) at the second transmission ratio, wherein the switching valve (UV1) preferably has a control line (19) which is connected to a pressure-side pressure chamber (D1', D3') of the punching tool (5) in order to switch between the movement of the two components (6, 7) at the first transmission ratio and the movement of the two components (6, 7) at the second transmission ratio in the event that the threshold value of the opposing force (F) is exceeded.
10. The punching apparatus as claimed in one of the preceding claims, further comprising:
    a resetting device (23) having at least one hydraulic reset valve (UV2; UV1, UV2) for changing the relative position (ΔP, ΔP') of the two components (6, 7) during the return stroke along the stroke axis (Z), wherein the reset valve (UV2) is preferably configured as a control valve.
11. The punching apparatus as claimed in claim 10, in which the reset valve (UV2) is configured to hydraulically isolate at least one pressure chamber (D2') of the second hydraulic cylinder (14) in order to change the positioning of the two components (6, 7) relative to one another.
12. The punching apparatus as claimed in one of claims 9 to 11, in which the switching valve (UV1) is configured to establish a hydraulic connection between a pressure chamber (D1) of the first hydraulic cylinder (12) and a reservoir (20) for a hydraulic fluid in the event that the threshold value of the opposing force (F) is exceeded.
13. The punching apparatus as claimed in one of claims 9 to 11, in which the switching valve (UV1) is configured to establish a hydraulic connection between a first and a second pressure chamber (D1, D3) of the first hydraulic cylinder (12) in the event that the threshold value of the opposing force (F) is exceeded.
14. The punching apparatus as claimed in one of claims 9 or 10, in which the switching valve (UV1) is configured to break a hydraulic connection between a first and a second pressure chamber (6, 7) of the second hydraulic cylinder (14) in the event that the threshold value of the opposing force (F) is exceeded, wherein the reset valve (UV2) is preferably configured to establish a hydraulic connection between a first pressure chamber (D3) and a second pressure chamber (D4) of the cavity (25) formed in the first component (6) to change the positioning of the two components (6, 7) relative to one another.
15. The punching apparatus as claimed in one of the preceding claims, further comprising:
    a control device (21) for controlling the punching drive (8) and for controlling at least one reset valve (UV2) of the resetting device (23).
16. A method for punching a workpiece (2), comprising:

    moving a punching tool (5), which has a first component (6) and a second component (7) that are able to be coupled hydraulically, in a punching stroke along a stroke axis (Z) toward a workpiece (2) to be punched, wherein the second component (7) is moved at a first transmission ratio relative to the first component (6) during the punching stroke, and, as soon as a threshold value of an opposing force (F), which the workpiece (2) to be punched exerts on the punching tool (5), is exceeded, the second component (7) is moved at a second transmission ratio, different from the first, relative to the first component (6),

    punching through the workpiece (2) by means of the punching tool (5), and

    moving the punching tool (5) away from the punched workpiece (2) during a return stroke along the stroke axis (Z),

    characterized

    in that a relative position (ΔP'), taken up immediately after the workpiece (2) has been punched through, of the two components (6, 7) with respect to one another along the stroke axis (Z) is maintained at least along a section of the return stroke of the punching tool (5), wherein the method preferably further comprises: changing the relative position (ΔP') of the two components (6, 7) with respect to one another during the return stroke along the stroke axis (Z) in order to re-establish a relative position (ΔP) which the two components (6, 7) took up with respect to one another before the threshold value of the opposing force (F) was exceeded.
17. A computer program product which is configured to execute all of the steps of the method as claimed in claim 16 when the computer program is running on a data processing system.

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