Punching machine

Abstract

A punching machine is provided for punching a workpiece with a metallic surface coating, wherein the punching machine comprises a first punching element for punching the workpiece, a first drive element associated with the first punching element which drives the first punching element for punching the workpiece along at least one punching axis which is oriented perpendicular to a longitudinal axis of the workpiece to be punched, at least one hold-down device for fixing the workpiece during the punching process and at least one die.The punching machine further comprises a control device configured to control the first drive element such that, during the punching process, the first punching element is driven in a pulsating manner with a feed movement towards the workpiece and a return movement away from the workpiece in the opposite direction to the feed movement. A cutting gap provided between the first punching element and the die along the longitudinal axis of the workpiece to be punched is 0.5% of the workpiece material thickness along the punching axis.

Description

[0001] The present invention relates to a punching machine for punching a workpiece provided with a metallic surface coating.

[0002] Workpiece surfaces produced by machining processes, such as the cut surfaces of stamped parts, are increasingly being used as functional surfaces without the need for post-processing. However, during the machining of workpieces, particularly during cutting or forming, microcracks can develop in the workpiece surfaces, which can lead to a notch effect when the components manufactured from the workpieces are subjected to dynamic stress. This, in turn, can negatively impact the service life of the respective components. For this reason, very high demands are already placed on the surfaces produced by machining processes.

[0003] In the course of efforts to achieve an improved surface quality of workpiece machining surfaces, various devices and methods have been proposed in recent times.

[0004] In this context, for example, processes have been developed to improve the cut surface quality of precision parts manufactured by shearing. The cut surface quality is defined, for example, by the parameters edge indentation, smooth cut surface, smooth cut surface proportion, roughness of the smooth cut surface, fracture surface angle, roughness of the fracture surface, width and height of the fracture surface, cutting burr, shell-shaped tear, tear, influenceable edge zone, material hardness before / after cutting, etc. The focus here, however, is on the smooth cut surface proportion, the roughness of the smooth cut surface, punch indentation, and punch burr. The ideal here is a smooth cut surface proportion of 100% of the material thickness, without punch indentation and punch burr. Since this ideal cannot currently be achieved with any progressive die, such parts require complex remachining.

[0005] A well-known method for achieving high-quality cut surfaces is the so-called fine blanking process. In this process, the workpiece is held along the cutting contour using a V-shaped ring during machining, and the workpiece is worked with a reduced cutting gap. In contrast to conventional shear cutting, this process produces cut surfaces that are free of cracks and tears across the entire material thickness, and it is also possible to achieve the tightest dimensional and flatness tolerances. However, the use of the V-shaped ring is dependent on a certain material thickness of more than 1 mm, since with thinner workpieces the transverse forces occurring in the cutting area can lead to unevenness due to the smaller material volume.In addition, the materials for which the fine blanking process can be used are limited in terms of hardness and brittleness, and in addition, a triple-action press is required, which has a particularly high guidance accuracy of the punch and a rigid press frame.

[0006] Another well-known method for achieving improved cut surface quality is so-called counter cutting, which is classified as shear cutting and in which a distinction is made between three-stage counter cutting and two-stage counter cutting. In these processes, the workpiece is machined in two or three stages, with a reversal of the cutting direction of the cutting punches used between the individual stages. Thus, in three-stage counter cutting, the workpiece is initially cut in the first stage; in the second stage, after a reversal of the cutting direction, counter cutting occurs; and in the third stage, after another reversal of the cutting direction, the workpiece is finally cut through.The cutting surface in three-stage counter cutting is characterized in particular by its complete absence of burrs, two smooth cutting surfaces, and the fracture zone between these smooth cutting surfaces. However, given the approximately 50% smooth cutting rate achievable with this process, and especially the remaining fracture zone between the two smooth cutting surfaces, there is room for improvement in this process as well.

[0007] Furthermore, DE 42 07 165 A1 describes a method for punching a metal foil using a pair of punching tools and a pair of cutting punches, which are respectively arranged above and below the metal foil to be processed and are driven by piezoelectric actuators. In this method, the cutting punches are set into vibration such that a half-punching process and a back-punching process are carried out repeatedly, with the cutting punches butting against both sides of the workpiece clamped between the cutting punches. In this known punching method, however, the two cutting punches are driven relative to one another with a certain time delay during the punching process, so that the workpiece section is deformed or broken between the cutting punches.is pressed together, which can lead to undesirable work hardening in the machining area of ​​the workpiece and thus to cracks in this area. Conventional punching machines operate with a cutting gap between the punch(s) and the die(s), which amounts to 4 to 5% of the material thickness of the workpiece to be punched. Furthermore, the arithmetic mean roughness values ​​of the punching element surfaces on conventional punching machines are in the range of 0.065–0.2 µm.

[0008] It can generally be stated that the material structure of a workpiece can be significantly influenced or damaged by a workpiece machining process, such as a punching process, in the machining area as a result of local deformation, and thus the remaining formability of the material can be significantly reduced. In previously known machining processes, such as known shearing cutting processes, single-stage, continuous linear movements of the machining elements are generated during the respective machining strokes of the workpiece. However, these single-stage movement strokes of the machining elements have a negative effect on the remaining formability of the workpiece in the machining area via the lattice defects present or arising in the workpiece material, which in turn can lead to undesirable cracks in this area.The same applies to a metallic surface coating of a workpiece that is subjected to punching.

[0009] In this context, the applicant of the present application has recognized that the surface quality of the cut surfaces of stamped parts produced from a workpiece provided with a metallic surface coating can play a major role even in cases where the cut surfaces are not intended to serve as functional surfaces.

[0010] When punching workpieces with a metallic surface coating, such as pre-tinned strips of steel or non-ferrous metal, a partial transfer of the metal forming the surface coating from the strip surface to the cutting surface occurs through the cutting punch. Upon impact with the strip surface, the cutting punch entrains a certain amount of metal particles from the metallic surface coating, guides them to the cutting surface during the punching process, and presses them into the cutting surface. In other words, the cutting punch pulls the metallic surface coating present on the surface of the workpiece across the resulting cutting surface during the punching process.In this way, when using known punching machines, between 30 and 50% of the cut surface of a workpiece provided with a metallic surface coating can be coated with the particles of the metallic surface coating during a punching process.

[0011] The proportion of the cut surface coated by the above process relative to the total cut surface is determined in particular by the surface quality of the cut surface, such as the presence and location of punch burrs, fracture zones, etc. The tin coating of the cut surface formed in this way when punching a pre-tinned copper strip with a conventional punching machine usually extends to the fracture zone.

[0012] However, if workpieces machined in this way have high corrosion resistance requirements, including at the cut surfaces, they must be recoated (e.g., retinned) as bulk material after the punching process. If the machined workpieces are subsequently to be returned to a manufacturing process, they must first be disentangled, sorted, and inspected for possible damage.

[0013] An object of the present invention is therefore to provide a punching machine which can provide an improved surface quality of workpiece punching or cutting surfaces and at the same time can improve the transfer of a material forming a metallic surface coating of the workpiece to the cutting surface during the punching process.

[0014] The object is achieved according to the invention by a punching machine according to claim 1.

[0015] The punching machine according to the invention according to one aspect of the invention is a punching machine for punching a workpiece provided with a metallic surface coating, wherein the punching machine comprises a first punching element for punching the workpiece, a first drive element assigned to the first punching element, which drives the first punching element for punching the workpiece along at least one punching axis that is aligned perpendicular to a longitudinal axis of the workpiece to be punched, at least one hold-down device for fixing the workpiece during the punching process and at least one die.The punching machine further comprises a control device configured to control the first drive element such that the first punching element is driven during the punching process in a pulsating manner, with a feed movement of the first punching element toward the workpiece and a return movement of the first punching element away from the workpiece, directed opposite to the feed movement. A cutting gap provided between the first punching element and the die along the longitudinal axis of the workpiece to be punched amounts to 0.5% of the material thickness of the workpiece along the punching axis.

[0016] The invention thus provides for the first time a punching machine in which a workpiece positioned between the punching elements is punched by driving the first punching element in a pulsating manner with a feed movement of the first punching element in the direction towards the workpiece and with a return movement of the first punching element directed opposite to the feed movement away from the workpiece, and the cutting gap provided between the first punching element and the die along the longitudinal axis of the workpiece to be punched amounts to 0.5% of the material thickness of the workpiece along the punching axis.

[0017] The inventive return movement of the first punching element as part of its pulsating drive allows the material of the workpiece to relax, allowing the crystals or atoms in the material to realign. This in turn leads to less work hardening due to machining and thus to improved deformation behavior during a subsequent feed movement of the first punching element towards the workpiece, which ultimately results in an improved surface quality of the machined workpieces with fewer cracks. The same applies to the material of the metallic surface coating, which can thus be transferred to a larger area of ​​the cutting surface during the punching process. In addition, the gentle machining avoids an increasing material deposit on the first punching element with increasing batch numbers due to the deposition of microparticles of the workpiece.This increases service life while maintaining the same quality.

[0018] By means of the cutting gap according to the invention, which amounts to 0.5% of the material thickness of the workpiece along the punching axis, the flow of the material forming the metallic surface coating of the workpiece during the punching process can be optimized compared to previously customary cutting gaps in the range of 4-5% of the material thickness of the workpiece, and thus the transfer of the particles forming the metallic surface coating of the workpiece to the cutting surface can be increased to up to 95% of the cutting surface.

[0019] Advantageous developments of the punching machine according to the invention are the subject of the dependent claims.

[0020] In a preferred embodiment, the arithmetic mean roughness Ra of at least the surface of the first punching element which comes into contact with the workpiece during the punching process can be 0.025 µm.

[0021] According to this preferred embodiment, a lower roughness of the first punching element can be achieved by a special microfinishing process compared to the prior art, whereby adhesion of the material forming the metallic surface coating of the workpiece to the punching element is suppressed.

[0022] In a further preferred embodiment, the first punching element can be formed from an ultra-fine grain hard metal with a Rockwell hardness HRA > 93.

[0023] According to this preferred embodiment, deformation of the punching element during machining of the workpiece and the associated formation of depressions in the punching element can be prevented, thereby suppressing adhesion of the material forming the metallic surface coating of the workpiece to the first punching element.

[0024] In a further preferred embodiment, the punching machine may further comprise a lubricant / lubricant supply device configured to supply a lubricant / lubricant to a punching area of ​​the workpiece during the punching process, wherein the lubricant / lubricant is suitably selected according to the material of the first punching element and the material of the surface coating of the workpiece.

[0025] Also according to this preferred embodiment, by forming a sliding / lubricating film between the punching element and the workpiece, adhesion of the material forming the metallic surface coating of the workpiece to the first punching element can be suppressed.

[0026] In a further preferred embodiment, the punching machine can further comprise a second punching element and a second drive element associated with the second punching element, which drives the second punching element to punch the workpiece along the at least one punching axis. The first and second punching elements can have the same geometry and structure and can be arranged opposite one another along the at least one punching axis. Furthermore, the workpiece to be punched can be positioned between the first and second punching elements.

[0027] According to this preferred embodiment, the particles forming the metallic surface coating of the workpiece can be transferred to the cutting surface both from the side of the first punching element and from the side of the second punching element, and the cutting surface coating formed thereby can thus reach 100% of the entire cutting surface.

[0028] In a further preferred embodiment, the first punching element may correspond to a cutting punch which is driven by a servomechanical drive as the first drive element, and the second punching element may correspond to a spring base which is mechanically or hydraulically prestressed towards the workpiece and which follows the movement of the first cutting punch over the workpiece.

[0029] According to this preferred embodiment, the above-mentioned coating of 100% of the cut surface can be achieved during the punching process with a simple configuration.

[0030] In a further preferred embodiment, the first punching element may correspond to a first cutting punch which is driven by a first servomechanical drive as the first drive element, and the second punching element may correspond to a second cutting punch which is driven by a second servomechanical drive as the second drive element.

[0031] According to this preferred embodiment, the controllability of the punching elements during the punching process can be improved and the above-mentioned coating of 100% of the cut surface can be achieved more reliably.

[0032] In a further preferred embodiment, the control device can be configured such that it controls the first and the second servomechanical drive in such a way that the first and the second cutting punch are driven during the punching process at least temporarily synchronously equidistant from one another in a pulsating manner with a feed movement of the first and the second cutting punch in the direction towards the workpiece and with a return movement of the first and the second cutting punch away from the workpiece in the opposite direction to the feed movement.

[0033] The synchronous, equidistant movement sequence of the first and second punches minimizes the plastic deformation of the workpiece in the punching area. The equidistant spacing of the punches during machining prevents the workpiece section between the punches from being compressed or deformed, which in turn leads to a lower number of lattice defects and a lower dislocation density in the punching area of ​​the workpiece. Due to the lower number of lattice defects in the workpiece material, undesirable work hardening of the material and thus the generation of cracks in the workpiece machining area are also suppressed.

[0034] Further features, aspects and advantages of the invention will become more apparent from the following detailed description of preferred embodiments with reference to the accompanying drawings.

[0035] Showing: Fig. 1 is a partial cross-sectional view of a punching machine according to the invention in accordance with a first embodiment; Fig. 2 is a diagram schematically illustrating the movement of the punching element of the punching machine according to the invention in accordance with the first embodiment during a punching operation; Fig. 3 is a partial cross-sectional view of a punching machine according to the invention in accordance with a second embodiment; Fig. 4A is a front view of a punching machine according to the invention in accordance with a third embodiment; Fig. 4B is a side view of the punching machine according to the invention in Fig. 4A punching machine according to the invention shown; Fig. 4C a cross-sectional view of the Fig. 4A punching machine according to the invention shown along the Fig. 4A shown line AA; Fig. 4A enlarged partial cross-sectional view of the Fig. 4A punching machine according to the invention shown along the Fig. 4A shown line AA during the execution of a punching operation; Fig. 4E a detailed view showing the Fig. 4D shown area A enlarged; and Fig. 5 is a schematic representation of a cam gear used in the punching machine according to the third embodiment.

[0036] Embodiments of the punching machine according to the invention are described in detail below with reference to the figures.

[0037] The following is with reference to Fig. 1 a punching machine 1 according to the invention according to a first embodiment is described. As in Fig. 1 As shown, the punching machine 1 comprises a punching element designed as a cutting punch 2 for punching a workpiece W along a punching axis B. The punching machine 1 further comprises a spring-loaded hold-down device and a die M, wherein the hold-down device is in Fig. 1 is not shown. The workpiece W to be punched, which is provided with a metallic surface coating C, can be, for example, a pre-tinned copper strip, which is guided on the punching machine 1 and fixed by the hold-down device during processing. However, the present invention is also applicable to a workpiece and a surface coating made of other metals. For example, the invention can be applied to a punching machine which is used for punching a strip coated with gold, silver or the like from steel or non-ferrous metal, such as brass, copper, bronze, etc. The punching machine 1 according to the first embodiment is further provided with a corresponding punch guide for the cutting punch 2, which is shown and described in connection with the third embodiment.

[0038] In the punching machine 1 according to the invention according to the first embodiment, a cutting gap SP provided between the cutting punch 2 and the die M along the longitudinal axis WL of the workpiece W to be punched amounts to 0.5% of the material thickness of the workpiece W along the punching axis B. The cutting gap results in a very uniform and fine-pored surface structure of the cut surface. This results in uniform and good adhesion while simultaneously applying a thin layer of the transferred coating.

[0039] Fig. 2 shows the movement profile of the cutting punch 2 during a punching process with the punching machine 1 according to the first embodiment over time. As in Fig. 2 As shown, the cutting punch 2 performs a feed movement towards the workpiece W and a return movement opposite to the feed movement away from the workpiece W. The feed amount during the feed movement of the cutting punch 2 is greater than the return amount during the return movement of the cutting punch 2, so that the workpiece W is punched in several stages and in a pulsating manner starting from the top of the workpiece. Fig. 2 The position s0 shown corresponds to a position of the cutting punch 2 on the workpiece W immediately before the start of the punching process.

[0040] During the punching process described above, the cutting punch 2, upon impacting the surface of the workpiece W, i.e., upon impacting the metallic surface coating C, and upon penetrating the latter, carries along a certain quantity of particles of the metallic surface coating, such as tin particles in the case of a pre-tinned copper strip, and guides these to the cutting surface. The quantity of particles of the metallic surface coating carried along depends in particular on the cutting gap, the surface quality of the cutting punch, the layer thickness of the surface coating, and other factors. The particles of the metallic surface coating carried along by the cutting punch 2 are pressed through the workpiece W into pores and other depressions in the cutting surface as the cutting punch 2 moves.This allows the metallic surface coating transferred to the cutting surface to be fixed to the cutting surface.

[0041] Due to the above-described movement profile of the cutting punch 2, the material of both the workpiece and the metallic surface coating C of the workpiece W can relax during machining, allowing the crystals or atoms in the material to realign. This, in turn, leads to less work hardening due to machining and thus to improved deformation behavior during a subsequent feed movement of the cutting punch 2 toward the workpiece W, which ultimately leads to an improved surface quality of the cut surface and a larger proportion of the coating of the cut surface obtained by the punching process with the metallic surface coating of the workpiece W.The movement profile of the cutting punch 2 described above makes it possible to achieve a cutting surface without punching burrs and fracture zones as well as a uniform surface finish of the cutting surface with an arithmetic mean roughness Ra of 0.15 µm for non-ferrous metals and <1.5 µm for stainless steel and conventional carbon steels.

[0042] This allows the material of the metallic surface coating C to be applied to an area of ​​up to 95% of the cutting surface during the punching process. Furthermore, the described movement profile of the cutting punch 2 can suppress the increasing material deposition on this punching element with increasing piece numbers by applying microparticles of the workpiece and the metallic surface coating. This increases the service life while maintaining consistent quality.

[0043] The following is with reference to Fig. 3 a punching machine 1A according to the invention according to a second embodiment is described. As in Fig. 3 As shown, the punching machine 1A comprises first and second opposing punching elements, between which the workpiece W to be punched is arranged. The punching machine 1A further comprises a spring-loaded blank holder and cutting dies M, wherein the blank holder in Fig. 3 is not shown. The workpiece W may, for example, be a workpiece having the same configuration as the workpiece described in the first embodiment.

[0044] In the second embodiment, the first punching element is designed as a cutting punch 2A, which is located in Fig. 3 above the workpiece W. The cutting punch 2A is driven by a Fig. 3 not shown servomechanical drive, which has the same configuration as the servomechanical drives, which are explained in the context of the third embodiment explained below and in the Figuren 4A bis 4C are shown.

[0045] The above-mentioned servomechanical drive is controlled by a control device of the punching machine 1A such that the cutting punch 2A is driven during the punching process in a pulsating manner with a feed movement of the cutting punch 2A in the direction towards the workpiece W and with a return movement of the cutting punch 2A away from the workpiece W in the opposite direction to the feed movement.

[0046] In the second embodiment, the second punching element is designed as a mechanically preloaded spring base 4A, which corresponds to a punching element preloaded by a spring F toward the workpiece W. The section of the spring base 4A facing the workpiece W, which comes into contact with the workpiece W during punching, is identical in geometry and structure to the corresponding section of the cutting punch 2A, which comes into contact with the workpiece W during punching. The spring force, characteristic curve, etc.The spring F is suitably selected, for example, depending on the workpiece material and its corresponding deformation behavior, so that the spring base 4A directly follows a movement of the cutting punch 2A over the workpiece W, without the punching slug located between the cutting punch 2A and the spring base 4A being plastically deformed or a free space being created between the punching elements and the punching slug. Therefore, the cutting punch 2A and the spring base 4A move synchronously and equidistant from one another during the machining of the workpiece W. Alternatively, the spring base 4A can be preloaded hydraulically or in another way in order to directly follow a movement of the cutting punch 2A and serve as a second punching element.

[0047] With regard to the spring base 4A according to the second embodiment, it should be noted that, in a standby state of the punching machine 1A in which no workpiece is located in the punching machine 1A, it can be fixed by a locking device (not shown) in such a way that a workpiece to be subsequently machined can be inserted into the machine.

[0048] Furthermore, the following must be observed with regard to the movement of the cutting punch 2A and the spring base 4A during the punching process. The feed movement(s) of the cutting punch 2A towards the workpiece W can be smaller in a first stage of the punching process than the subsequent return movement(s) of the cutting punch 2A away from the workpiece. As a result, during the first stage of the punching process, the workpiece can initially be punched from the underside of the workpiece by the spring base 4A serving as the punching element. When the spring base 4A impacts the underside of the workpiece and penetrates the metallic surface coating, it entrains a certain amount of particles of the metallic surface coating and guides these during the first stage of the punching process to the resulting partial cut surface of the workpiece.

[0049] Subsequently, in a second stage of the punching process, the feed rate of the cutting punch 2A during its forward feed movement can be greater than the return rate of the cutting punch 2A during its subsequent return movement, whereby the workpiece is punched starting from the top side of the workpiece in the second stage of the punching process. As the cutting punch 2A penetrates the metallic surface coating, it entrains a certain amount of particles of the metallic surface coating and guides them to the resulting cut surface of the workpiece during the punching process.

[0050] By the above-mentioned processing in the first stage of the punching process with the punching machine 1A according to the second embodiment, the cut surface section formed by the processing on the underside of the workpiece is thus first coated with the particles of the metallic surface coating C of the workpiece W, wherein this cut surface section on the underside of the workpiece corresponds, for example, to an area of ​​at least 5% of the total cut surface of the finished workpiece.Through the subsequent processing in the second stage of the punching process, as explained above, the cut surface section formed on the workpiece's upper side by this processing is then coated with the particles of the metallic surface coating of the workpiece W. This cut surface section on the workpiece's upper side corresponds, for example, to an area of ​​up to 95% of the total cut surface of the finished workpiece. Thus, 100% of the cut surface can be provided with the metallic surface coating of the workpiece through this processing.

[0051] Fig. 4A shows a front view of a punching machine 1B for punching a workpiece W provided with a metallic surface coating according to a third embodiment, wherein the Fig. 4A The arrow shown in the immediate vicinity of the workpiece W indicates a feed direction of the workpiece W, which is present, for example, as strip material, along the longitudinal axis WL of the workpiece W. Fig. 4B is a side view of the Fig. 4A illustrated punching machine 1B according to the invention and Fig. 4C is a cross-sectional view of the Fig. 4A punching machine 1B shown along the Fig. 4A shown line AA, wherein the section AA corresponds to a stepped cut which does not pass through servo actuators 14 of the punching machine 1B, which are in Fig. 4B and Fig. 4C are shown. In the Fig. 4C In the figure shown, the longitudinal axis WL of the workpiece W to be machined extends along a Y direction and a punching axis B extends along a Z direction.

[0052] The punching machine 1B comprises first and second cutting punches 2B, 4B, which are Fig. 4C shown illustration are arranged opposite each other along the punching axis B. The first and second cutting punches 2B, 4B are in the Fig. 4C The punching machine 1B shown is surrounded by first and second punch guides 3, 5, which enable precise linear guidance of the cutting punches 2B, 4B along the punching axis B. The punching machine 1B further comprises a spring-loaded hold-down device 7, two cutting dies M, and first and second servomechanical drives for driving the first and second cutting punches 2B, 4B, which are respectively assigned to and connected to the cutting punches 2B, 4B. The first and second servomechanical drives each comprise a servo actuator 14 and a cam mechanism 15 with a cam member 6, an engagement member 8, a pendulum lever 24, and two take-off rollers 12' and 12", wherein the engagement member 8 is coupled to a corresponding cutting punch 2B, 4B via a punch holder in order to transmit a movement of the engagement member 8 to a corresponding cutting punch 2B, 4B.It should be noted that the movement of the cutting punches 2B, 4B is determined by the design of the cam element 6 provided in the cam mechanism 15. Thus, the movement sequence of the individual cutting punches 2B, 4B can be changed as desired by varying the design of the cam element 6.

[0053] The Fig. 4C The punching machine 1B shown is configured such that the cutting punches 2B, 4B move synchronously equidistant from one another in a multi-stage manner during the punching of the workpiece W by the drive by means of the first and second servomechanical drives. This movement during the machining process results from the superposition of a mechanical curve and an electronic curve. For this purpose, the Figuren 4A bis 4E The punching machine 1B shown further comprises a control device not shown in the figures, which is designed such that it controls the synchronous operation of the two servo actuators 14.

[0054] In the Figuren 4D und 4E a part of the punching machine 1B according to the invention is shown during the execution of a punching process. Figuren 4D und 4E show a processing state between two consecutive processing stages within the framework of the multi-stage drive of the first and second cutting punches 2B, 4B before completion of the punching process. As is particularly evident in Fig. 4E As shown, the workpiece W is not deformed between the first and second cutting punches 2B, 4B during the processing shown here, and the first and second cutting punches 2B, 4B have a constant distance from one another during the punching processing of the workpiece in each of the several processing stages, that is to say the cutting punches 2B, 4B are arranged equidistant from one another in each processing stage.

[0055] During operation of the punching machine 1B, a rotation of the servo actuator 14 is transmitted via an output shaft thereof to the cam member 6 of the cam gear 15 and the rotation of the cam member 6 is converted, as will be described in detail later, into a linear movement of the engagement member 8 via a coupling with the pendulum lever 24 mounted in the engagement member 8.

[0056] The hold-down device 7 in Fig. 4C The punching machine 1B shown is spring-loaded relative to the punch guide 3 and is designed to be advanced relative to the cutting punch 2B, that is to say, the hold-down device 7 is in an initial position before the workpiece W is fixed with the help of the hold-down device 7 along the punching axis B in Fig. 4C opposite the cutting punch 2B and, when the cutting punch 2B moves along the punching axis B in the direction of the workpiece, comes into contact with the workpiece W in front of the cutting punch 2B in order to fix it. In addition to this configuration of the hold-down device, it can also be provided in any other suitable design in order to fix the workpiece during machining. The hold-down device 7 can, in a suitable form, also have a contour provided on the workpiece so that it is held securely and as free of play as possible. By fixing the workpiece W with the hold-down device 7, it is thus ensured that the workpiece W does not move during machining, and thus the machining can be carried out with the required precision.

[0057] The following is with reference to Fig. 5 the cam gear 15 is described in detail, which is used in the servomechanical drives described above.

[0058] As in Fig. 5As shown, the cam member 6 of the cam gear 15, in the form shown here, is designed as a counterclockwise rotating cam disk 6, which is coupled to an output shaft of the servo actuator 14, and the engagement member 8 of the cam gear 15, in the form shown here, is designed as a linear slide 8. The linear slide 8 is guided so as to be longitudinally displaceable in a guide which is designed as a housing structure and which resembles a web 22. The cam gear 15 used here has at least two take-off rollers 12' and 12". The two take-off rollers 12' and 12" are carried by the pendulum lever 24, on which they are rotatably mounted, wherein the pendulum lever 24, in turn, is rotatably mounted with an end section 26 facing the linear slide 8 in the end section of the linear slide 8 facing the cam disk 6.

[0059] Via the two take-off rollers 12' and 12" respectively, the drive force applied by the cam disc 6 can be broken down into two drive force components 28, 34, which act respectively on the take-off roller 12' and on the take-off roller 12". The first drive force component 28 (arrow F') can be broken down by the take-off roller 12' into a first transverse force component 30 (arrow F transverse ') and a first effective force component 32 (arrow F effective '). By means of the take-off roller 12", the second drive force component 34 can be broken down into a second transverse force component 36 (arrow F transverse ") and a second effective force component 38 (arrow F effective "). The two effective force components 32 and 38 add up to the final total effective force acting on the linear slide 8. The two transverse force components 30 and 36 compensate each other and lead to the transverse forces being reduced to zero in the ideal case.

[0060] In order to further suppress the deposition or accumulation of the material of the metallic surface coating on the cutting punch(s) of the punching machines described above during the punching process described in this application, the respective cutting punch can also be made of an ultra-fine-grain hard metal with a Rockwell hardness HRA > 93. By selecting such a material for the cutting punch(s), deformation of the cutting punch due to the punching process and the associated formation of depressions in the cutting punch, which enable adhesion of the material forming the metallic surface coating to the cutting punch, can be suppressed. Furthermore, the arithmetic mean roughness Ra of at least the surface of the cutting punch(s) that comes into contact with the workpiece W during the punching process can be 0.025 µm.Such a surface quality of the cutting punch(s) can be achieved, for example, through a special microfinishing process. In this process, the wire-eroded and / or ground surfaces of the cutting punches are treated with a microblasting agent in a blasting cabinet in at least two steps (microblast). The cutting punches are then manually polished with a polishing device and examined microscopically (100-200x magnification).

[0061] As a further measure to prevent the material forming the metallic surface coating from being deposited on the cutting punch(s), a finely dosed addition of a liquid suitable for the respective material class being processed, such as a suitable lubricant (for example, a lubricant based on Castrol Honilo 988 for the starting material CuSn6), to a punching area of ​​the workpiece can be provided. For this purpose, a lubricant supply device can be provided that delivers the lubricant to the punching area of ​​the workpiece during the punching process. The lubricant is suitably selected according to the material of the cutting punch and the material of the surface coating of the workpiece.

Claims

1. Punching machine for punching a workpiece provided with a metallic surface coating, wherein the punching machine comprises a first punching element for punching the workpiece, a first drive element associated with the first punching element, which drives the first punching element for punching the workpiece along at least one punching axis that is oriented perpendicular to a longitudinal axis of the workpiece to be punched, at least one hold-down device for fixing the workpiece during the punching process and at least one die, wherein the punching machine further comprises a control device that is configured to control the first drive element in such a way thatthat the first punching element is driven during the punching process in a pulsating manner with a feed movement of the first punching element towards the workpiece and with a return movement of the first punching element away from the workpiece opposite to the feed movement, and a cutting gap provided between the first punching element and the die along the longitudinal axis of the workpiece to be punched amounts to 0.5% of the material thickness of the workpiece along the punching axis.

2. Punching machine according to claim 1, wherein the arithmetic mean roughness Ra of at least the surface of the first punching element which comes into contact with the workpiece during the punching process is 0.025 µm.

3. Punching machine according to claim 1 or 2, wherein the first punching element is formed from an ultra-fine grain cemented carbide with a Rockwell hardness HRA > 93.

4. Punching machine according to one of claims 1 to 3, wherein the punching machine further comprises a lubricant supply device configured to supply a lubricant to a punching area of the workpiece during the punching process, wherein the lubricant is suitably selected according to the material of the first punching element and the material of the surface coating of the workpiece.

5. Punching machine according to one of claims 1 to 4, wherein the punching machine further comprises a second punching element and a second drive element associated with the second punching element, which drive the second punching element for punching the workpiece along the at least one punching axis, wherein the first and the second punching element have the same geometry and the same structure and are arranged opposite one another along the at least one punching axis, and wherein the workpiece to be punched is positioned between the first and the second punching element.

6. Punching machine according to claim 5, wherein the first punching element corresponds to a cutting punch which is driven by a servomechanical drive as the first drive element, and the second punching element corresponds to a spring base which is mechanically or hydraulically prestressed towards the workpiece and which follows the movement of the first cutting punch over the workpiece.

7. Punching machine according to claim 5, wherein the first punching element corresponds to a first cutting punch which is driven by a first servomechanical drive as the first drive element, and the second punching element corresponds to a second cutting punch which is driven by a second servomechanical drive as the second drive element.

8. Punching machine according to claim 7, wherein the control device is configured such that it controls the first and the second servomechanical drive in such a way that the first and the second cutting punch are driven during the punching process at least temporarily synchronously equidistant from one another in a pulsating manner with a feed movement of the first and the second cutting punch in the direction towards the workpiece and with a return movement of the first and the second cutting punch away from the workpiece in the opposite direction to the feed movement.

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