SHEET HOLDER FOR PERFORATING PRESS AND METHOD OF MOVING SHEET HOLDER

[0001] The invention relates to a perforating press for perforating sheet material, more particularly a perforating press comprising a sheet holder and a method for moving the sheet holder. The invention also relates to the use of the perforating press or the method.

[0002] Perforating presses for perforating sheet material are known from the state of the art. In known perforating presses, sheet material is fed into a perforating press according to a first direction, after which perforations are made in the sheet material by means of a punch holder with punches. This punch holder is moved up and down by a transmission shaft, causing the punches to periodically perforate the sheet material. By moving the sheet material according to the first direction during a period when the punches are not in contact with the sheet material, it is possible to apply a perforation pattern in the sheet material.

[0003] For particular applications, many small perforations are made at very short intervals in sometimes very thin sheet material. As a result, it is possible that the sheet material already deforms at the first contact with the punches of the punch holder or during the perforation of the sheet material. It also happens that during removal of the punches from the sheet material due to friction between punches and sheet material, edges of perforations partially move with the punches, creating raised edges around the perforations. The sheet material does not remain flat, which is not desirable.

[0004] To prevent this, a sheet holder is traditionally used to hold back the sheet material as much as possible during the perforation process, preventing the sheet material from deforming and keeping it flat. The sheet holder is fixed to the punch press or the die or is attached to the punch holder by springs. The disadvantage with fixed sheet holders is that they do not take tolerances on the sheet material into account. This is especially problematic with very thin sheet material, because as soon as the sheet holder does not hold the sheet material sufficiently, deformations can occur again. By default, the sheet holder cannot be pressed very strongly against the sheet material either, because in that case there is too much friction between the sheet material and the sheet holder, so that moving the sheet material in the first direction requires too much energy and possibly damages the sheet material. A sheet holder attached to the punch holder by means of springs cannot develop sufficient compressive force to prevent in particular in the case of very thin sheet material with a high density of perforations from nevertheless not deforming because the sheet holder is not pressed sufficiently long or hard against the sheet material.

[0005] JP H06 210366 A describes a perforating press in which the punch holder and the sheet holder are attached to each other by springs. U.S. Pat. No. 3,160,046 A also discloses a perforating press having a punch holder and a sheet holder. DE 196 22 844 A1 relates to a perforating press in which the movement of the punch holder and the sheet holder may be shifted in phase. DE 10 2009 034542 A1 is related to a perforating press driven by a hydraulic cylinder. In each of these perforating presses, the punch holder and the sheet holder have a fixed cycle of movement relative to each other.

[0006] The present invention seeks to solve at least some of the above-mentioned problems or drawbacks.

[0007] In a first aspect, the present invention relates to a perforating press for perforating sheet material comprising a feeding means for feeding sheet material in a first direction; a punch holder, wherein the punch holder extends in a second direction transverse to the first direction, and wherein the punch holder comprises at least one punch; a die, wherein the die comprises openings for receiving punches of the punch holder; a transmission shaft for converting a rotary movement of the transmission shaft into a linear movement of the punch holder in a stroke direction transverse to the first direction and transverse to the second direction and a discharge means for discharging perforated sheet material; characterized in that the perforating press comprises a sheet holder, wherein the sheet holder is positioned between the punch holder and the die according to the stroke direction, wherein the sheet holder is movable according to the stroke direction by the transmission shaft, and wherein the sheet holder comprises cut-outs for passage of punches of the punch holder.

[0008] The advantage of this perforating press is that it comprises a sheet holder which is positioned between the punch holder and the die according to the stroke direction and is movable according to the stroke direction by the transmission shaft. As a result, the sheet holder has no fixed position in relation to the sheet material, so that during a period when the punches are not in contact with the sheet material, the sheet holder can likewise not be in contact with the sheet material, so that the sheet material can be moved easily and without friction according to the first direction. Particularly advantageous is that because the sheet holder is movable by the transmission shaft, a time at which the sheet holder is pressed against the sheet material is adjustable, for example, by a phase shift between the movement of the punch holder and the sheet holder, so that an optimum operation of the sheet holder can be obtained according to a perforation pattern and a thickness of the sheet material. This is not possible with a fixed attachment of the sheet holder to the punch holder using springs.

[0009] In preferred embodiments, the perforating press is characterized in that: a distance over which the sheet holder is movable by the transmission shaft according to the stroke direction is at most% of a distance over which the punch holder is movable by the transmission shaft according to the stroke direction; the sheet holder and the punch holder have a fixed position relative to each other according to the first direction and the second direction; the punch holder is movable by the transmission shaft according to the stroke direction according to a linear path between a first extreme point and a second extreme point, and that the sheet holder is movable by the transmission shaft according to the stroke direction according to a linear path between a third extreme point and a fourth extreme point, the first extreme point and the third extreme point being farthest from the die, and wherein a distance according to the stroke direction between the first extreme point and the third extreme point is adjustable; there is a rotation of at least 20° and at most 40° of the transmission shaft between the first extreme point and the third extreme point; and/or the perforating press comprises a ram element, wherein the ram element is positioned between the transmission shaft and the sheet holder, wherein the ram element is movable by the transmission shaft according to the stroke direction, wherein the perforating press further comprises guide elements for guiding the sheet holder and the ram element according to the stroke direction, and wherein between the sheet holder and the ram element at least one hydraulic cylinder is positioned for preloading the sheet holder in the direction of the die, optionally wherein a first port of the at least one hydraulic cylinder is connected to a first side of an accumulator; a back pressure on a second side of the accumulator is adjustable; and/or the pressure at the first port of the at least one hydraulic cylinder is adjustable.

[0010] A specific preferred embodiment involves a perforating press comprising a ram element, wherein the ram element is positioned between the transmission shaft and the sheet holder, wherein the ram element is movable by the transmission shaft according to the stroke direction, wherein the perforating press further comprises guide elements for guiding the sheet holder and the ram element according to the stroke direction, and wherein between the sheet holder and the ram element at least one hydraulic cylinder is positioned for preloading the sheet holder in the direction of the die.

[0011] In this preferred embodiment, the perforating press comprises a ram element. The ram element is movable by the transmission shaft according to the stroke direction. The ram element is arranged between the sheet holder and the transmission shaft, and at least one hydraulic cylinder is arranged between the sheet holder and the ram element for preloading the sheet holder in the direction of the die. A hydraulic cylinder is advantageous because it allows a suitable preload to be set depending on a pressing force of the perforating press, so that the sheet holder remains in contact with the sheet material during perforation, which is not possible with a sheet holder attached to the ram element by means of springs.

[0012] In a second aspect, the present invention relates to a method for moving a sheet holder from a perforating press including: feed sheet material according to a first direction; perforating the sheet material by moving a punch holder in a stroke direction by a transmission shaft, wherein the punch holder extends in a second direction transverse to the first direction, wherein the punch holder comprises at least one punch, wherein the transmission shaft converts a rotary movement of the transmission shaft into a linear displacement of the punch holder in the stroke direction, transverse to the first direction and transverse to the second direction, and wherein the at least one punch is moved through the sheet material into a die, wherein the die comprises openings for receiving punches of the punch holder; repeat previous steps until a predetermined pattern of perforations is established in the sheet material; characterized in that a sheet holder is moved according to the stroke direction by the transmission shaft, wherein the sheet holder is positioned according to the stroke direction between the punch holder and the die, and wherein the at least one punch of the punch holder is moved through a cut-out in the sheet holder into the die. This method has, among other things, the advantage, in that during the perforation of the sheet material, a sheet holder is moved according to the stroke direction by the transmission shaft, as a result of which the sheet holder does not have a fixed position in relation to the sheet material and as a result of which, during a period in which the punches are not in contact with the sheet material, the sheet holder also does not have to be in contact with the sheet material, that the sheet material can be moved easily and without friction according to the first direction. Particularly advantageous is that the method allows, in function of a perforation pattern and a thickness of the sheet material, to set an optimal period during which the sheet holder presses against the sheet material.

[0013] Preferred embodiments of the method are characterized in that the punch holder is moved by the transmission shaft according to the stroke direction according to a linear path between a first extreme point and a second extreme point, and that the sheet holder is moved by the transmission shaft according to the stroke direction according to a linear path between a third extreme point and a fourth extreme point, the first extreme point and the third extreme point being farthest from the die, and a distance according to the stroke direction between the first extreme point and the third extreme point being set before feeding the sheet material; optionally wherein the fourth extreme point is set so that the sheet holder does not touch the sheet material, the fourth extreme point is set such that the sheet holder presses against the sheet material after the at least one punch of the punch holder perforates the sheet material and the sheet holder continues to press at least against the sheet material until the at least one punch of the punch holder is removed from the sheet material, or the fourth extreme point is set such that the sheet holder presses against the sheet material before the at least one punch of the punch holder perforates the sheet material and the sheet holder continues to press at least against the sheet material until the at least one punch of the punch holder is removed from the sheet material.

[0014] In a third aspect, the present invention relates to a use of a perforating press or a method described herein for the manufacturing of grilles for household appliances.

[0023] Unless otherwise defined, all terms used in the description of the invention, including technical and scientific terms, have the meaning as generally understood by those skilled in the technical field of the invention. For better assessment of the description of the invention, the following terms are explicitly explained.

[0024] “A,” “the,” and “the” refer to both singular and plural in this document unless the context clearly assumes otherwise. For example, “a segment” means one or more than one segment.

[0025] The terms “comprise”, “encompass”, “consist of”, “provide with”, “contain” are synonyms and are inclusive or open-ended terms that indicate the presence of what follows, and do not exclude or preclude the presence of other components, features, elements, members, steps, known from or described in the prior art.

[0026] Citing numeric intervals by the endpoints includes all integers, fractions and/or real numbers between the endpoints, these endpoints included.

[0027] In a first aspect, the invention relates to a perforating press for perforating sheet material.

[0028] According to a preferred embodiment, the perforating press comprises a feeding means for feeding sheet material in a first direction, a punch holder, a die, a sheet holder, a transmission shaft for converting a rotary movement of the transmission shaft into a linear displacement of the punch holder in a stroke direction, and a discharge means for discharging perforated sheet material.

[0029] The first direction is preferably a horizontal direction. The sheet material is preferably supplied to the perforating press in a horizontal plane.

[0030] The feeding means may be a table equipped with conveyor belts, transport belts, transport wheels, transport rollers or any other suitable means for moving sheet material in the first direction. A table is advantageous in case the sheet material consists of individual sheets.

[0031] The feeding means may be a powered uncoiler suitable for uncoiling sheet material from a coil, for example a steel coil. The sheet material is fed directly from the roll. Optionally, the perforating press comprises a cutting device for cutting unrolled sheet material into individual sheets and the sheet material is supplied as individual sheets. In this case, as previously described, the perforating press may also include a table as a feeding device. Optionally, the perforating press comprises means for flattening the unrolled sheet material prior to perforating, such as, for example, straightening rollers.

[0032] The feeding means is preferably suitable for feeding sheet material with a width, measured transverse to the first direction of at least 100 mm and at most 2000 mm, preferably at most 1900 mm, more preferably at most 1800 mm and even more preferably at most 1700 mm.

[0033] The perforated sheet material was preferably discharged according to the first direction.

[0034] The discharge means may be a table equipped with conveyor belts, transport belts, transport wheels, transport rollers or any other suitable means for moving sheet material.

[0035] In the case where the sheet material is supplied directly from a roll, the discharge means may be a powered reeling reel suitable for reeling the perforated sheet material into a roll. Alternatively, the perforating press comprises a cutting device for cutting the perforated sheet material into individual sheets. In this case, as previously described, the perforating press may also include a table as a discharging device.

[0036] The punch holder extends in a second direction. The second direction is transverse to the first direction. The second direction is preferably horizontal. The punch holder comprises at least one punch. A punch is a tool suitable for perforating sheet material by moving the punch holder in the stroke direction whereby the at least one punch is pressed through the sheet material. The striking direction is transverse to the first direction and transverse to the second direction. The striking direction is preferably a vertical direction. The at least one punch comprised in the punch holder is preferably interchangeable. In this case, a punch holder comprises holes for positioning punches. A punch comprises a circular, hexagonal or other suitable cross-section, depending on a desired perforation. Punches comprised in a punch holder can have either equal or different dimensions, depending on a desired perforation pattern. Punches included in a punch holder are preferably arranged on one or more lines according to the second direction. The at least one punch holder preferably extends across the full width of the fed sheet material. This is advantageous to be able to punch the fed sheet material over the full width. It is apparent to one skilled in the art that the number of punches comprised in a punch holder depends on the desired perforation pattern and a desired width over which the fed sheet material is to be perforated. It is also apparent to a person skilled in the art that in the case of interchangeable punches, it is not necessary to have a punch placed in every hole for positioning punches in a punch holder. It is clear to a person skilled in the art that a punch press may include multiple rows of punches. According to the second direction, the punch holder extends over at least 1000 mm, preferably at least 1250 mm, more preferably at least 1500 mm, and even more preferably at least 1600 mm.

[0037] The punch press comprises a passage for the sheet material between the punch holder and the die. The die comprises at least one opening for receiving punches of the punch holder. The die comprises at least as many openings for receiving punches as comprised in the punch holder. The punch holder comprising at least one punch is movable from a first extreme position to a second extreme position and back by the transmission shaft according to the stroke direction. In the first extreme position, the punch holder is positioned at a distance from the die so that the passage for the sheet material is free and the sheet material is freely movable between the punch holder and the die. When perforating the sheet material, at least one punch comprised in the punch holder is in the second extreme position of the punch holder pressed through the sheet material and at least partially received in an opening of the die. It is obvious to a person skilled in the art that if a perforating press comprises multiple rows of punches, the die comprises openings for receiving punches from all rows of punches.

[0038] As previously described, the stroke direction is preferably a vertical direction where the punch holder is positioned above the die according to the vertical direction. This positioning is advantageous for automatic removal of material removed by the perforating press from the sheet material by gravity.

[0039] The plate holder is positioned between the punch holder and the die according to the stroke direction. The plate holder is movable by the transmission shaft according to the stroke direction. According to the stroke direction, the sheet holder is movable from a third extreme position to a fourth extreme position and back. In the third extreme position, the sheet holder is positioned at a distance from the die so that the passage for the sheet material between the sheet holder and the die is free and the sheet material is freely movable between the sheet holder, the dies comprises in the die holder and the die. The sheet holder comprises at least one cut-out for passage of punches of the punch holder. The sheet holder comprises at least as many cut-outs for passage of punches as comprised in the punch holder. In perforation of the sheet material, at least one punch included in the punch holder is pushed through the sheet material in the second extreme position of the punch holder and through a cut-out for passage of punches included in the sheet holder and at least partially received in an opening of the die. In the fourth extreme position of the sheet holder, the sheet holder is positioned near or against the sheet material. Near means in this context that the sheet holder is positioned at a distance, measured according to the stroke direction, of at most 2 mm, preferably at most 1 mm and more preferably at most 0.75 mm from the sheet material. It is obvious to a person skilled in the art that if a perforating press comprises several rows of punches, the sheet holder has cut-outs for passage of punches of all rows of punches.

[0040] The advantage of a perforating press according to the present invention is that the sheet holder does not have a fixed position in relation to the sheet material, so that during a period when punches are not in contact with the sheet material, the sheet holder can likewise not be in contact with the sheet material by moving the sheet holder to the third extreme position by means of the transmission shaft, thus allowing the sheet material to be moved easily and without friction according to the first direction. Particularly advantageous is that because the sheet holder is movable by the transmission shaft, a time at which the sheet holder is positioned near the sheet material or pressed against the sheet material is adjustable, for example, by a phase shift between the movement of the punch holder and the sheet holder, as a result of which an optimum operation of the sheet holder according to a perforation pattern and a thickness of the sheet material can be obtained. This is not possible with a fixed attachment of the sheet holder to the punch holder using springs.

[0041] For example, for sheet material that is sufficiently thick so that the sheet material does not deform during perforation, but where punches take the sheet material with them after perforation due to friction between the punches and the sheet material, the sheet holder can be positioned near the sheet material so that the sheet material is pushed off the punches.

[0042] For example, in the case of thin sheet material, which bends due to perforation and when the punches are removed from the sheet material, the sheet holder for perforation can be pressed against the sheet material until after the punches are removed from the sheet material, so that the sheet material remains flat.

[0043] For example, with sheet material, where edges of perforations are carried by the punches during the removal of the punches from the sheet material and causing the edges to deform as a result, after the punches enter the sheet material and before the punches are removed from the sheet material, the sheet holder may be pressed against the sheet material and only after the punches are removed from the sheet material can the sheet material be released.

[0044] According to an embodiment, the transmission shaft is a camshaft. A camshaft is known to a skilled person in the art. The camshaft translates a rotational movement of the camshaft into a translational displacement in the stroke direction of the punch holder and sheet holder. A camshaft is advantageous for accurately timed displacement of the punch holder and sheet holder. In addition, a camshaft is advantageous for transmitting a large impact force to the punches. A large impact force can be transferred faster with a camshaft compared to a punch holder moved with a hydraulic piston.

[0045] The camshaft comprises at least one pointed cam for moving the punch holder and one pointed cam for moving the sheet holder. Preferably, the camshaft comprises two pointed cams for moving the punch holder and one pointed cam for moving the sheet holder, wherein the pointed cam for moving the sheet holder according to the second direction is centrally located between the two pointed cams for moving the punch holder, and wherein preferably the two pointed cams for moving the punch holder according to the second direction are equidistant from a central point of the punch holder. Two pointed cams at an equal distance according to the second direction from the central point of the punch holder for moving the punch holder is advantageous to obtain equal displacement with minimal torque effect of the punch holder. This is additionally advantageous because a greater compressive force is required on the punches for punching the sheet material, than the compressive force required for the sheet holder. This larger compression force can therefore be distributed over two pointed lugs.

[0046] According to an embodiment, the transmission shaft is a crankshaft. A crankshaft is known to a person skilled in the art. The crankshaft translates a rotational motion of the crankshaft to a translational displacement in the stroke direction of the punch holder and the sheet holder. A crankshaft is advantageous for transferring a large impact force to the punches. A large impact force can be transferred faster with a crankshaft compared to a punch holder moved with a hydraulic piston.

[0047] The crankshaft comprises a first crank and a first connecting rod for moving the punch holder and a second crank and a second connecting rod for moving the sheet holder. The first connecting rod connects the first crank to the punch holder. The second connecting rod connects the second crank to the sheet holder. Preferably, the crankshaft comprises two first cranks for moving the punch holder and a second crank for moving the sheet holder, wherein the second crank for moving the sheet holder according to the second direction is centrally located between the two first cranks for moving the punch holder, and wherein preferably the two first cranks for moving the punch holder according to the second direction are equidistant from a central point of the punch holder. Two first cranks at an equal distance according to the second direction from the central point of the punch holder for moving the punch holder is advantageous to obtain an equal displacement with minimal torque effect of the punches. This is additionally advantageous because a greater compressive force is required on the punches for punching the sheet material, than the compressive force required for the sheet holder. This larger compressive force can therefore be distributed over two first cranks.

[0048] According to a preferred embodiment, a distance over which the sheet holder is movable by the transmission shaft according to the stroke direction is at most 60% of a distance over which the punch holder is movable by the transmission shaft according to the stroke direction. Preferably, the sheet holder is displaceable by the transmission shaft over a distance according to the stroke direction of at most 55% of the distance over which the punch holder is displaceable by the transmission shaft according to the stroke direction, more preferably at most 52.5%. This is advantageous because the sheet holder must be able to be moved only as far as against the sheet material in order to prevent deformation of the sheet material during punching, while at the same time punches comprised in the punch holder must be able to be moved further in order to move completely through the sheet material.

[0049] Preferably, the sheet holder is displaceable by the transmission shaft over a distance according to the stroke direction of at least 40% of the distance over which the punch holder is displaceable by the transmission shaft according to the stroke direction, more preferably at least 45%, and even more preferably at least 47.5%. By using a transmission shaft for converting a rotational motion of the transmission shaft into a linear motion according to the stroke direction of the placeholder, the amplitude of the linear motion according to the stroke direction of the placeholder has a sinusoidal shape. The displacement of the sheet holder over a distance of at least 40% of the distance over which the punch holder is displaceable by the transmission shaft according to the stroke direction is advantageous in order to have a sufficiently long period of time during which the distance between the sheet holder and the sheet material is sufficiently large to allow the sheet material to be displaced without friction in the first direction.

[0050] The movability of the sheet holder and the punch holder according to the stroke direction over a different distance can be obtained, for example, by determining dimensions for the pointed cam or the second crank for moving the sheet holder that are, in a direction transverse to the camshaft or crankshaft, respectively, at most 60% of the dimensions of the pointed cam or the first crank for moving the punch holder.

[0051] The movability of the sheet holder and the punch holder over a different distance according to the stroke direction can be obtained, for example, by determining dimensions for the pointed cam or the second crank for moving the sheet holder that are at least 40% of the dimensions of the pointed cam or the first crank for moving the punch holder in a direction transverse to the camshaft or crankshaft, respectively.

[0052] According to a further embodiment, the sheet holder is movable according to the stroke direction over a distance of at least 10 mm and at most 18 mm. This is sufficient to be able to press the sheet holder against sheet material with a thickness up to 5 mm, measured according to the stroke direction, for a sufficiently long time and also to be able to remove it from the sheet material for a sufficiently long time so that the sheet material can be moved without friction according to the first direction.

[0053] According to a preferred embodiment, the sheet holder and the punch holder have a fixed position relative to each other according to the first direction and the second direction. This means that the sheet holder and the punch holder can only move relative to each other according to the stroke direction. This is advantageous to ensure that punches of the punch holder can be passed through cut-outs for punch passage in the sheet holder without damaging the punches. This is particularly advantageous in the case where very small perforations with a very high density are to be made in the sheet material.

[0054] According to a preferred embodiment, the punch holder is movable by the transmission shaft according to the stroke direction according to a linear path between a first extreme point and a second extreme point. The sheet holder is movable by the transmission shaft according to the stroke direction according to a linear path between a third extreme point and a fourth extreme point. The first extreme point and the third extreme point are farthest from the die. A distance according to the stroke direction between the first extreme point and the third extreme point is adjustable.

[0055] The distance according to the stroke direction between the first extreme point and the third extreme point is adjustable, for example, by using a ram element, included in the perforating press. The ram element is arranged between the transmission shaft and the sheet holder. The ram element is movable by the transmission shaft according to the stroke direction. The sheet holder is attached to the ram element. The pointed cam of a previously described camshaft displaces the ram element and thereby the sheet holder according to the stroke direction. The second connecting rod of a previously described crankshaft is attached to the sheet holder via the ram element and thus the sheet holder is displaceable by the transmission shaft according to the stroke direction using the ram element. The distance between the ram element and the sheet holder is adjustable, for example by adjustment screws or by a hydraulic cylinder between the ram element and the sheet holder. The ram element will be moved by the transmission shaft according to the stroke direction according to a linear path between an extreme fifth point and an extreme sixth point. The extreme fifth point and the extreme sixth point remain unchanged from the extreme first point and the extreme second point of the punch holder. Changing the distance between the ram element and the sheet holder does change the distance according to the stroke direction between the extreme first point of the punch holder and the extreme third point of the sheet holder.

[0056] The adjustability of the distance between the first extreme point and the third extreme point is advantageous to change a time at which a sheet holder is pressed against the sheet material, for example, relative to the time at which a punch contacts the sheet material. For example, by positioning the extreme third point closer to the sheet material, the sheet holder will be pressed against the sheet material earlier, and by positioning the extreme third point further from the sheet material, the sheet holder will be pressed against the sheet material later or even positioned only near the sheet material. A similar effect can be obtained by providing, for a camshaft described previously, an adjustable phase shift between pointed cams for moving the punch holder according to the stroke direction and the pointed cam for moving the sheet holder according to the stroke direction. A similar effect can be obtained by providing an adjustable phase shift between the first crank and the second crank in a previously described crankshaft. However, these are complex and expensive mechanical devices that are unnecessary in the present embodiment. Being adjustable is additionally advantageous to adjust the displacement of the sheet holder according to the stroke direction as a function of the thickness of the sheet material.

[0057] According to a further embodiment, in an active state there is a rotation of at least 20° and at most 40° of the transmission shaft between the first extreme point and the third extreme point. The rotation is a rotation over a fixed angle. The movement according to the stroke direction of the punch holder thus precedes the movement according to the stroke direction of the sheet holder. This embodiment corresponds to a fixed phase shift.

[0058] The rotation of the transmission shaft between the first extreme point and the third extreme point is preferably at least 22°, more preferably at least 24°, even more preferably at least 26° and even more preferably at least 28°.

[0059] The rotation of the transmission shaft between the first extreme point and the third extreme point is preferably at most 38°, more preferably at most 36°, even more preferably at most 34°and even more preferably at most 32°.

[0060] This embodiment is advantageous for modifying a time at which a sheet holder is pressed against the sheet material, for example, relative to the time at which a punch of the punch holder comes into contact with the sheet material, but is particularly advantageous, due to the phase shift, for having a different period of time between the sheet holder being pressed against the sheet material and punches coming into contact, and between the sheet holder being released from the sheet material and the punches being removed from the sheet material. The latter, as previously described, is particularly advantageous with sheet material, where edges of perforations are carried away by the punches during removal of the punches from the sheet material and the edges are thereby deformed. A rotation of at least 20° and at most 40° is sufficient, if the distance according to the stroke direction between the first extreme point and the third extreme point is set correctly, to press the sheet holder against the sheet material after the punches enter the sheet and before the punches are removed from the sheet material and to release the sheet holder from the sheet material only after the punches are removed from the sheet material.

[0061] According to a preferred embodiment, the perforating press comprises a ram element. The ram element is arranged between the transmission shaft and the sheet holder. The ram element is movable by the transmission shaft according to the stroke direction. The ram element may be as in a previously described embodiment, wherein the distance according to the stroke direction between the first extreme point and the third extreme point is adjustable. The perforating press further comprises guide elements for guiding the sheet holder and ram element according to the stroke direction. This is advantageous to ensure that a mutual position between the sheet holder and the ram element according to the first direction and the second direction cannot change. At least one hydraulic cylinder is placed between the sheet holder and the ram element for preloading the sheet holder in the direction of the die.

[0062] The at least one hydraulic cylinder is advantageous for pressing the sheet holder against the sheet material for a period of time, while the ram element is still moved by the transmission shaft in the direction of the sheet material, without creating excessive pressures on the sheet holder, the sheet material or other parts of the perforating press. These pressures are absorbed by pressing the at least one hydraulic piston.

[0063] The at least one hydraulic cylinder is particularly advantageous because it allows a suitable preload to be set depending on a pressing force of the punch press, so that the sheet holder remains in contact with the sheet material during punching, which is not possible with a sheet holder attached to the punch holder by means of springs. With too little preload, the first contact of punches with the sheet material could cause the sheet holder to detach from the sheet material due to recoil. With too high preload, indentations by the sheet holder in the sheet material could occur and unnecessary stresses could be created in the perforating press, which could lead to premature wear.

[0064] According to a further embodiment, a first port of the at least one hydraulic cylinder is connected to a first side of an accumulator. A hydraulic cylinder comprises a piston placed in the hydraulic cylinder. A hydraulic cylinder comprises a first port for moving the piston in a first direction and a second port for moving the piston in the second direction. An accumulator is a pressure vessel separated by a piston, diaphragm or bellows into a first and a second volume. The first side of the accumulator has access to the first volume. The second side has access to the second volume. Preferably, the access to the second volume is lockable. An accumulator is advantageous for capturing pressure pulses in the at least one hydraulic cylinder. When pressing the sheet holder against the sheet material, the piston of the at least one hydraulic cylinder is displaced in the first direction, which would cause a pressure increase in the hydraulic cylinder. This can be partially or wholly absorbed as the initial volume in the accumulator increases, either by displacement of the piston or deformation of the diaphragm or bellows. As a result, the pressure at which the sheet holder is preloaded against the sheet material remains more or less constant.

[0065] According to a further embodiment, a back pressure on the second side of the accumulator is adjustable. The second side of the accumulator is preferably connected with a pressure vessel for this purpose. The pressure vessel contains a gas, preferably nitrogen gas under pressure. A line between the pressure vessel and the second side of the accumulator preferably comprises a first pressure valve that closes when a maximum gas pressure on the second side of the accumulator is reached. Preferably, the maximum gas pressure is 115 bar. Preferably, the first pressure valve is adjustable. This embodiment is advantageous to set damping of the at least one hydraulic cylinder.

[0066] According to a preferred embodiment, the pressure at the first port of the at least one hydraulic cylinder is adjustable. The pressure is preferably adjustable between 0 bar and 180 bar, more preferably between 0 bar and 170 bar, and even more preferably between 0 bar and 160 bar. For this purpose, the first port is connected via a pressure line to an output of a pump. The pump comprises a suction line for drawing oil from a tank. Preferably, the pressure line comprises a pressure relief valve that opens when the pressure at the first port exceeds a predetermined maximum pressure. The predetermined maximum pressure is preferably 200 bar, more preferably maximum 190 bar, and even more preferably maximum 180 bar. The pressure relief valve preferably comprises a return line to the tank. Preferably, the pump is connected to the first port of the at least one hydraulic cylinder by means of a two-position four-way valve. The four-way valve is operable by means of a solenoid valve. In a first position of the four-way valve, the first port of the at least one hydraulic cylinder is connected to the tank through the return line. This is advantageous if the pressure at the first port of the at least one hydraulic cylinder needs to be reduced. In a second position of the four-way valve, the first port of the at least one hydraulic cylinder is connected to the pump. This is advantageous if the pressure at the first port of the at least one hydraulic cylinder is to be increased.

[0067] Preferably, an adjustable pressure valve is positioned between the pump and the four-way valve. The adjustable pressure valve is advantageous for setting a maximum pressure at the first port of the at least one hydraulic cylinder. When the maximum pressure is reached, the adjustable pressure valve closes, preventing the pressure at the first port from increasing further.

[0068] This embodiment is advantageous in order to accurately control the preload of the sheet holder as a function of a pressing pressure of the perforating press. The applicant found that a preload that is 10%±5 percentage points of the pressing pressure of the perforating press produces optimum results. Thus, at a press pressure of 5000 kN, a preload through the sheet holder of 500 kN is already required. This cannot be reliably achieved with springs.

[0069] This embodiment is preferably combined with previously described embodiments in which the first port of the at least one hydraulic cylinder is connected to an accumulator. According to a further embodiment, the line between the pressure vessel and the second side of the accumulator comprises a second pressure valve, positioned viewed from the pressure vessel after the first pressure valve. The second pressure valve closes when a gas pressure is reached that is up to 80% of the pressure at the first port of the at least one hydraulic cylinder, preferably up to 75% and more preferably up to 70%. A higher value would result in insufficient damping by the at least one hydraulic cylinder.

[0070] In a Second Aspect, the Invention Relates to a Method for Moving a Sheet Holder of a perforating press.

[0071] According to a preferred embodiment, the method comprises the steps of:

• • [0072] feed sheet material according to a first direction;
  • [0073] perforating the sheet material by moving a punch holder in a stroke direction by a transmission shaft;
  • [0074] repeat previous steps until a predetermined pattern of perforations is established in the sheet material.

[0075] The first direction is preferably a horizontal direction.

[0076] The sheet material is supplied as individual sheets according to the first direction. Alternatively, the sheet material is unrolled from a roll, for example a steel roll, and fed according to the first direction. Optionally, in this case the sheet material is cut into individual sheets during feeding. Optionally, in this case the sheet material is flattened after unrolling and before perforation, for example by means of straightening rollers.

[0077] The punch holder extends in a second direction. The second direction is transverse to the first direction. The second direction is preferably horizontal. The punch holder comprises at least one punch. A punch is a tool suitable for perforating sheet material by moving the punch holder in the stroke direction whereby the at least one punch is pressed through the sheet material. The striking direction is transverse to the first direction and transverse to the second direction. The stroke direction is preferably a vertical direction. The transmission shaft converts a rotational movement of the transmission shaft into a linear displacement of the punch holder in the stroke direction. The at least one punch is moved through the sheet material into a die. The die comprises openings for receiving punches of the punch holder. Between the punch holder and the die is a passage for the sheet material. The die comprises at least as many openings for receiving punches as comprised in the punch holder. When perforating the sheet material, the at least one punch is comprised in the punch holder and at least partially received in an opening of the die.

[0078] A sheet holder is moved by the transmission shaft according to the stroke direction. The sheet holder is positioned between the punch holder and the die according to the stroke direction. The sheet holder comprises cut-outs for passage of punches of the punch holder. The sheet holder comprises at least as many cut-outs for passage of punches as are included in the punch holder. The at least one punch of the punch holder is moved through a cut-out in the sheet holder into the die.

[0079] One of the advantages of this working method is that the sheet holder does not have a fixed position in relation to the sheet material, so that during a period when the punches are not in contact with the sheet material, the sheet holder also does not have to be in contact with the sheet material, so that the sheet material can be moved easily and without friction according to the first direction. Particularly advantageous is that the method allows, in function of a perforation pattern and a thickness of the sheet material, to set an optimal period during which the sheet holder presses against the sheet material.

[0080] According to a preferred embodiment, the punch holder is moved by the transmission shaft according to the stroke direction according to a linear path between a first extreme point and a second extreme point. The sheet holder is moved by the transmission shaft according to the stroke direction according to a linear path between a third extreme point and a fourth extreme point. The first extreme point and the third extreme point are farthest from the die. A distance according to the stroke direction between the first extreme point and the third extreme point are set before feeding the sheet material.

[0081] In the first extreme position, the punch holder is positioned at a distance from the die so that the passage for the sheet material is clear and the sheet material is freely movable between the punch holder and the die. When perforating the sheet material, at least one punch comprised in the punch holder is pushed in the second extreme position of the punch holder through the sheet material and at least partially received in an opening of the die.

[0082] In the third extreme position, the sheet holder is positioned at a distance from the die so that the passage for the sheet material between the punch holder and the die is free and the sheet material is freely movable between the sheet holder, the punches comprised in the punch holder and the die. In the fourth extreme position of the sheet holder, the sheet holder is positioned near or against the sheet material. Near means in this context that the sheet holder is positioned at a distance, measured according to the stroke direction, of at most 2 mm, preferably at most 1 mm and more preferably at most 0.75 mm from the sheet material.

[0083] The adjustability of the distance between the first extreme point and the third extreme point is advantageous to change a time at which a sheet holder is pressed against the sheet material, for example, relative to the time at which a punch contacts the sheet material. For example, by positioning the extreme third point closer to the sheet material, the sheet holder will be pressed against the sheet material earlier and by positioning the extreme third point further from the sheet material, the sheet holder will be pressed against the sheet material later or even positioned only near the sheet material. Being adjustable is additionally advantageous for adjusting the displacement of the sheet holder according to the stroke direction according to the thickness of the sheet material.

[0084] According to a preferred embodiment, the fourth extreme point is set so that the sheet holder does not touch the sheet material.

[0085] This embodiment is advantageous, for example, in the case of sheet material that is sufficiently thick so that the sheet material does not deform during perforation, but in which punches of the punch holder, due to friction between the punches and the sheet material after perforation, take the sheet material with them, so that the sheet material is pressed by the sheet holder of the punches.

[0086] According to a preferred embodiment, the fourth extreme point is set such that the sheet holder presses against the sheet material after the at least one punch of the punch holder perforates the sheet material and the sheet holder continues to press against the sheet material until the at least one punch of the punch holder is removed from the sheet material.

[0087] This embodiment is advantageous, for example, with sheet material, where edges of perforations are carried away by the punches during the removal of the punches from the sheet material, causing the edges to deform as a result, in that the sheet holder is pressed against the sheet material after the punches enter the sheet material and before the punches are removed from the sheet material, and only after the punches are removed from the sheet material is the sheet material released by the sheet holder, preventing the edges of the perforations from being carried away by the punches and deforming.

[0088] According to a preferred embodiment, the fourth extreme point is set such that the sheet holder presses against the sheet material before the at least one punch of the punch holder perforates the sheet material, and the sheet holder continues to press at least against the sheet material until the at least one punch of the punch holder is removed from the sheet material.

[0089] This embodiment is advantageous, for example, for thin sheet material, which is bent by perforating and when removing the punches from the sheet material, because, by pressing the sheet holder against the sheet material before perforating until after removing the punches from the sheet material, the sheet material remains flat.

[0090] A person skilled in the art will appreciate that a method according to the second aspect is preferably performed using a perforating press according to the first aspect and that a perforating press according to the first aspect is preferably configured to perform a method according to the second aspect. Accordingly, each feature described herein, above as well as below, may relate to any of the three aspects of the present invention.

[0091] In a third aspect, the invention relates to a use of a perforating press according to the first aspect and/or a method according to the second aspect for manufacturing grilles for household appliances.

[0092] This use results in the inexpensive manufacture of grilles for household appliances, such as, for example, grilles in microwave oven doors, grilles over a drain in dishwashers, or cooling grilles in computer casings, for example. These grilles are very frequently made of very thin sheet material, sometimes with a thickness less than dimensions of the perforations, and include a perforation pattern with a high density of perforations. Such grilles are prone to deformation by perforation of the sheet material, which is avoided by using a perforating press according to the first aspect and/or a method according to the second aspect.

[0093] In what follows, the invention is described using non-limiting figures illustrating the invention, which are not intended or to be interpreted to limit the scope of the invention.

[0094] FIG. 1 shows a steering of a punch comprised in a punch holder and of a sheet holder according to an embodiment of the present invention.

[0095] The chart shows on the horizontal axis (1) a position of a transmission shaft in degrees. A complete rotation corresponds to 360°. The vertical axis (2) corresponds to a displacement of a punch comprised in a punch holder (5) in mm according to the stroke direction and a displacement of a sheet holder (6) in mm according to the

[0096] stroke direction. The sheet material is about 3 mm thick. A bottom side (4) of the sheet material is taken as a reference at 0 mm. A top side (3) of the sheet material is logically located at about 3 mm.

[0097] The punch of the punch holder and the sheet holder move according to a sinusoid. The movement of the sheet holder trails the movement of the punch by 30°. The punch is at a first extreme point according to the stroke direction at 0° and 360°. This is at about 23 mm from the bottom side (4) of the sheet material. The sheet holder is located in a third extreme point according to the stroke direction at 30°. This is at about 16.25 mm from the bottom side (4) of the sheet material. The punch is located in a second extreme point according to the stroke direction at 180°. In this position, the punch has fully perforated the sheet material and is at least partially received in a die located below the sheet material. The second extreme point is at about −2 mm from the bottom side (4) of the sheet material. The sheet holder is at a fourth extreme point according to the stroke direction at 210°. This is at about 4.38 mm from the bottom side (4) of the sheet material or about 1.38 mm from the top side (3) of the sheet material. Thus, with this steering, the sheet holder is positioned at the fourth extreme point near the sheet material. The sheet holder does not press on the sheet.

[0098] FIG. 2 shows an alternative steering of a punch comprised in a punch holder and of a sheet holder according to an embodiment of the present invention.

[0099] The steering is completely similar to the steering from FIG. 1, with the difference that the third extreme point is now about 13.13 mm from the bottom side (4) of the sheet material. The distance between the sheet holder in the third extreme position and the punch holder in the first extreme position has increased by about 3.12 mm from FIG. 1. As a result, the sheet holder touches the top side (3) of the sheet material after the punch of the punch holder makes contact with the top side (3) of the sheet material and the sheet holder remains in contact with the top side (3) of the sheet material after the punch of the punch holder is completely removed from the sheet material.

[0100] FIG. 3 shows yet another alternative steering of a punch comprised in a punch holder and of a sheet holder according to an embodiment of the present invention.

[0101] The steering is completely similar to the steering from FIG. 1, with the difference that the third extreme point is now about 9.38 mm from the bottom side (4) of the sheet material. The distance between the sheet holder in the third extreme position and the punch holder in the first extreme position has increased by about 6.87 mm from FIG. 1. As a result, the sheet holder touches the top side (3) of the sheet material at about the same time as the punch of the punch holder and the sheet holder remains in contact with the top side (3) of the sheet material well after the punch of the punch holder is completely removed from the sheet material,

[0102] FIGS. 4, 5A and 5B show a general view from a number of perspectives, cross-sections and enlarged views, of a perforating press for perforating sheet material (16). The perforating press has a feeding means (18) in the form of top and bottom rollers for feeding sheet material (16) in a first direction towards the press itself, and more particular towards a sheet holder (15) which is designed to clamp the sheet material (16) down from above against a die (19), typically a monolithic block with a flat top surface against which the sheet material (16) is held by the sheet holder (15). The press further comprises a punch holder (14), with the punch holder (14) essentially extending laterally (in the width of FIG. 5A) along a second direction which is perpendicular with respect to the first direction and being movable downwards, in a stroke direction perpendicular to the first and second direction, to clamp the sheet material (16) against the die (19).

[0103] The punch holder (14) has one or more punches (9) fixed on its end facing the die (19), which are suitable to punch through the sheet material (16) positioned between the sheet holder and the die when the punch holder is brought down. The punch holder (14) and sheet holder (15) are both driven by a transmission shaft (10), forming part of a general frame, with the transmission shaft (10) being coupled to the punch holder and sheet holder and converting rotary movement of the transmission shaft (10) into a linear movement of the punch holder (14) and sheet holder (15) in a stroke direction transverse to the first direction and transverse to the second direction. The sheet holder (15) and punch holder (14) are moved separately from each other, in order to allow the punch holder (14) to move over a greater distance than and/or in a postponed movement from the sheet holder (15), as the sheet holder is moved to such a position as to when it is clamping the sheet material (16) between itself and the die (19) beneath it. The punch holder (14) is then configured to punch through the sheet material held in place at that time, with its punch (9), which can be accomplished by a later movement or a longer distance of movement, making sure that the punch doesn't contact the sheet material until the sheet holder is in place.

[0104] The die (19) comprises openings (7) which are dimensioned to receive the punch (9) of the punch holder (14) when the punch holder (14) moves down all the way, the punch (9) perforating the sheet material and moving into the openings (7).

[0105] The sheet holder (15) is positioned between the punch holder (14) and the die (19), with the sheet holder (15) being movable according to the stroke direction by the transmission shaft (10) in order to clamp the sheet material (16), and with the sheet holder (15) having cut-outs (20) for passage of punches (9) of the punch holder (14) during the perforation action through the sheet holder (15), and through the sheet material held there, and into the openings (7) of the die (19).

[0106] The press also comprises a discharge means (17) on the other side of the punch holder (14) with respect to the feeding means (18), again in the form of rollers, for discharging perforated sheet material (16) away from the sheet holder, after the punching operation has been performed.

[0107] As can be seen in FIG. 5B, and in particular in the bottom enlarged view, the sheet holder (15) is movable by the transmission shaft (10) according to the stroke direction over a lower distance than over which the punch holder (14) is movable by the transmission shaft (10) according to the stroke direction. This allows the sheet holder (15) to effectively hold the sheet material against the die (19), while the punch holder (14) and the punch (9) are moved further, in order to punch through the sheet material (16) after it is clamped by the sheet holder. The sheet holder (15) and the punch holder (14) have a fixed position relative to each other according to the first direction and the second direction, but are separately movable along the stroke direction.

[0108] The perforating press further comprises a ram element (8), with the ram element (8) being positioned between the transmission shaft (10) and the sheet holder (15). The ram element (8) is actuated by the transmission shaft (10) according to the stroke direction. Additionally, the perforating press further comprises guide elements (25) for guiding the sheet holder (15) and the ram element (8) according to the stroke direction. Between the sheet holder (15) and the ram element, a hydraulic cylinder (11) is positioned for preloading the sheet holder (15) in the direction of the die (19), with a first port (13) of the hydraulic cylinder connecting it to a first side of an accumulator (12), typically with a back pressure on a second side of the accumulator being adjustable, and/or the pressure at the first port of the at least one hydraulic cylinder being adjustable.

[0109] As visible in FIG. 5B and the bottom-most enlarged view, the punch holder (14) is integrated partly into the sheet holder (15), with the sheet holder (15) acting as a guide or sleeve for the movement of the punch holder (14), and having a cut-out (20) at its bottom face for allowing passage of the punch (9) in order to perforate captured sheet material (16).

[0110] As shown in FIG. 1-3, the punch holder (14) is movable by the transmission shaft 10 according to the stroke direction according to a linear path between a first extreme point (21) and a second extreme point (22). The sheet holder (15) is also movable by the transmission shaft (10) according to the stroke direction according to a linear path between a third extreme point (23) and a fourth extreme point (24), the first extreme point (21) and the third extreme point (23) being farthest from the die (19), and wherein a distance according to the stroke direction between the first extreme point (21) and the third extreme point (23) is adjustable. This shows that there is a rotation of at least 20° and at most 40° of the transmission shaft (10) between the first extreme point (21) and the third extreme point (23), as well as between the second extreme point (22) and fourth extreme point (24) for FIG. 1.

[0111] FIG. 6A shows a possible implementation in terms of how the transmission shaft (10) can separately drive the sheet holder (15) and punch holder (14) by acting as a camshaft, by using a pointed cams (31) for moving the punch holder (14) and another pointed cam (32) for moving the sheet holder (15). This allows the movements of the sheet and punch holder to start at a different time as well as be effected over a different distance.

[0112] FIG. 6B shows a possible implementation in terms of how the transmission shaft (10) can separately drive the sheet holder (15) and punch holder (14) by acting as a crankshaft, and using a first crank (33) and first connecting rod (35), and second crank (34) and second connecting rod (36) for moving the punch holder (14) and the sheet holder (15) respectively. The first connecting rod connects the first crank to the punch holder, while the second connecting rod connects the second crank to the sheet holder. This allows the movements of the sheet and punch holder to start at a different time as well as be effected over a different distance.