EP0839594A1

EP0839594A1 - A machine for punching sheet metal

Info

Publication number: EP0839594A1
Application number: EP97203315A
Authority: EP
Inventors: Guido Salvagnini
Original assignee: Bruni Vincenzo
Current assignee: Bruni Vincenzo
Priority date: 1996-10-31
Filing date: 1997-10-24
Publication date: 1998-05-06
Also published as: IT1287112B1; ITMI962256A1

Abstract

A machine for punching sheet metal comprises means (3, 4, 5, 7) for feeding a sheet metal strip (1) to means (8, 9) for punching the strip (1) of sheet metal. Said means for punching the strip (1) comprise a plurality of punching presses each comprising a plurality of elementary individual punching tools (20, 21) that can be operated individually. Each of said punching presses has a supporting structure (16) shaped like a swan's neck with an intermediate channel (100) through which there passes the sheet metal strip (1); the punching presses (8, 9) are arranged in sequence along the longitudinal direction of the strip (1) so as to extend in part on one side and in part on the other side of the strip (1), and they are independently mobile along a transversal direction of the strip (1), so as to allow the complete extraction of the strip (1) from the respective channels (100) and the complete extraction of each swan's neck structure from the space extending between two adjacent swan's necks, and along the longitudinal direction of the strip (1) so as to allow the interchangeability of the individual punching presses (8, 9) within said sequence, so as to be able to position the respective elementary punching tools (20, 21) according to an arrangement pre-established in the plan of operations.

Description

The present invention relates to a machine for punching sheet metal.
Punching sheet metal consists in removing a certain number of parts of a given shape from a sheet or from a strip of metal laminate. The punching operation of each individual part to be removed is executed by placing the sheet metal between a tool called punch and a countertool called matrix, the outline of which has the profile of the part to be removed, and by pushing the punch to enter the matrix passing through the sheet metal, which at the end has a hole with a profile that is the same as that of the punch and of the matrix. The removed part is called scrap.
If on the same sheet metal there act in sequence or simultaneously several tools, each consisting of a punch and of a matrix, the resulting variously pierced piece is the product of a multiple punching operation.
The punching tool also includes in addition to the punch and to the matrix already mentioned an extractor or blank holder, that has the function of extracting the punch from the sheet metal, while keeping this pressed up against the matrix. The sheet metal actually has a tendency to contract round the punch after punching and to oppose by friction the exit of this from the hole that has just been made. The energy required for extraction is accumulated during punching as elastic energy in a compressible organ like a spring, which acts on the extractor or blank holder.
The pieces of sheet metal used normally in manufacturing industry are rarely the result of a simple punching operation, but almost always of a multiple punching operation.
In the current art, in order to execute a multiple punching operation two different methods are followed to which correspond specific tools and specific machine tools.
The first method, that can be called simultaneous multiple punching and that is the older, uses a composite tool, including all the punches, all the extractors and all the corresponding matrices, all the punches being integral one with the other in an upper part of the tool, all the extractors integral one with the other in the same upper part of the tool and all the matrices integral one with the other in the lower part of the tool. The upper part of said composite tool is made integral with the mobile carriage of a press, while the lower part of the same composite tool is made integral with the fixed table of the same press.
After a sheet of metal as been interposed between the lower part and the upper part of said tool, the mobile carriage moves with the necessary force toward the table, forcing the elastic means of the extractors to be compressed, accumulating energy, and the punches to penetrate into the matrices, perforating the sheet metal and causing the scrap to fall down below the matrices. When the carriage moves back up, the extractors keep the punched sheet metal up against the lower part of the tool and so the punches are freed thereof.
The second method, that can be called sequential multiple punching and that has been developed more recently, as it depends on the availability of numerical control machines and on the technique of information technology, uses a multiplicity of elementary tools, each consisting of a punch, of an extractor and of a matrix. The machine tool used by this second method is again a press, not as heavy as that used in simultaneous multiple punching, because it operates only one tool at a time, but it is a more complicated press, including a tool magazine and a handler for the sheet being processed. The tool magazine is arranged so that it brings the tool required for a given individual punching operation to a precise position under the carriage of the press and the handler is arranged so that under the punch of the tool there is taken exactly the point of the sheet wherein that tool is to perform its punching operation.
The fundamental differences between the two methods described are obvious.
The productivity of simultaneous punching is much higher than that of sequential punching, because with the first a finished piece is obtained for each stroke of the press and with the second only one hole is obtained for each stroke of the press. The larger the number of individual punching operations required by a piece, the greater is the productive advantage of simultaneous punching.
The time required for starting-up a production is much shorter for sequential multiple punching, because for this standard tools are often sufficient and the specific tools are simple, while the composite tools require more complex design and manufacturing processes. Small changes to the drawing of the punched piece are far more economical with sequential multiple punching, because they consist in corrections to a program for the numerical control unit, while in the other case they consist in substantial mechanical changes. The advantages of sequential multiple punching are expressed by the expression: greater flexibility.
Enumerating the reciprocal advantages of the two methods, the reciprocal disadvantages have been highlighted at the same time, and these can also be seen in the absolute sense.
The excessive rigidity of simultaneous multiple punching and the excessive slowness of sequential multiple punching are absolute disadvantages and constitute the limits of the current punching art, because in any case either one or the other is present.
In view of the state of the art described, the object of the present invention is to provide a machine that has a productivity comparable to that of a simultaneous multiple punching machine, and at the same exhibits the flexibility of a sequential multiple punching machine.
According to the present invention, such object is attained by means of a machine for punching sheet metal, comprising means for feeding a sheet metal strip and means for punching the strip of sheet metal, characterized in that said means for punching the strip comprise a plurality of punching presses each comprising a plurality of elementary individual punching tools that can be operated individually, said punching presses each having a supporting structure shaped like a swan's neck with an intermediate channel through which there passes the sheet metal strip and being arranged in sequence along the longitudinal direction of the strip so as to extend in part on one side and in part on the other side of the strip, said punching presses being independently mobile along a transversal direction of the strip, so as to allow the complete extraction of the strip from the respective channels and the complete extraction of the swan's neck structure from the space extending between two adjacent swan's necks, and along the longitudinal direction of the strip so as to allow the interchangeability of the individual punching presses within said sequence, so as to be able to position the respective elementary punching tools according to an arrangement pre-established in the plan of operations.
The machine forming the object of the present invention shares without any limitations with the machines dedicated to sequential multiple punching the advantage of the great speed of setting-up production of a given piece. The more numerous are the elementary tools that in this machine can be combined into composite tools, the more its productivity approaches that of machines dedicated to simultaneous multiple punching.
The choice of the individual punching operations, that for a given piece can be executed by a composite tool, follows a logic inherent in the architecture of the machine, that can be transferred to the numerical control unit that controls the machine itself and thus the design of the most productive arrangement is automatic.
The particular conformation of the individual presses, having a supporting structure like a swan's neck with an intermediate channel through which the strip of sheet metal moves, and the possibility of moving the individual presses transversally so as to determine the complete extraction of the strip from the respective channels and the complete extraction of the swan's neck structure from the space included between two adjacent swan's necks, and longitudinally to the strip, allows changes to be made in whatsoever manner to the sequence of presses along the direction of advance of the strip, so that the arrangement of the individual elementary punching tools can be varied in a simple manner in the plan of operations.
The features of the present invention will be made more evident by the following detailed description of an embodiment thereof, illustrated as a non-limiting example in the enclosed drawings, wherein:

Fig. 1 is a diagrammatic plan view of the entire machine;
Fig. 2 is a front view of swan's necks including presses for individual punching tools, the corresponding tools, sliding guides for the swan's necks and an automatic loader of tool holders;
Fig. 3 is a horizontal cross-section of the swan's necks of Fig. 2;
Fig. 4 is a vertical cross-section of an individual tool and of the corresponding operating cylinder.

With reference to the drawings, there is indicated in Fig. 1 with the reference 1 a strip of sheet metal, coming from a roll 2 supported and made to rotate by an unwinding reel 3. The strip 1 enters a flattener 4, that has the task of eliminating the residual imperfections of the strip due to the lamination and the winding up into a roll.
At the output from the flattener 4 the strip 1 is trimmed along the edges by two circular shearing machines 5, that reduce its width from the original one to that required for the piece that is about to be produced. The trimming scrap is wound up or crumbled.
Downstream from the trimmer shearing machines 5 the strip 1 forms a loop 6 and then enters a strip feeder unit with rollers 7, that has the task of making the strip advance in programmed steps, reducing and allowing the depth of the loop 6 fed by the flattener 4 alternately to increase or decrease. A sensor not shown in the drawing detects the depth of the loop 6 and consequently adjusts the speed of the flattener 4.
All that is described up to this point falls within the prior art.
Immediately downstream from the strip feeder unit 7 there is a first punching press 8 having a supporting structure shaped into a swan's neck, having an intermediate channel 100 through which the strip 1 passes with a depth that is about twice the width of the strip (as shown in detail in Fig. 2). Continuing along the path of the strip 1, there is a succession of further punching presses 9, that also have a swan's neck supporting structure like the press of Fig. 2 and all alike, but arranged alternately symmetrically with respect to the longitudinal center line of the strip 1, that is so that the respective channels 100 extend alternately from one side and from the other of the strip 1.
All the swan's necks 8 and 9 are mobile transversally and longitudinally with respect to the strip 1, on guides 10 and 11, respectively, and their positions are controlled numerically.
Thanks to such freedoms of movement, the swan's necks 8 and 9 can be distributed in any sequence in the direction parallel to the strip 1. It is in fact sufficient that they be arranged at a reciprocal distance in a transversal direction to the strip 1 such as not to interfere one with the other when they will be displaced in a direction parallel to the strip, so that they can be shuffled like a pack of playing cards. It is thus possible to vary in whatsoever manner the sequence of the presses 8 and 9 in the direction parallel to that of the movement of the strip 1.
Continuing along the path of the strip 1 there is a strip tightener 12, consisting of two pairs of rollers 12' and 12'' symmetrical with respect to the center line of the strip 1. This tightener 12 co-operates with the feeder unit 7, with which it is synchronized, for moving the strip 1 forward in programmed steps and, by keeping the strip tight, it prevents the latter from curling up due to the effect of some tools getting stuck. The tightener 12 cannot grasp the strip like the feeder unit 7, that is with rollers as long as the strip is wide, because these would compress any protrusions generated by the tools on the sheet metal and would in any case interfere with the burrs generated by the tools along the outlines of the holes. The rollers 12' and 12'' of the tightener 12 thus have very short generating lines and they are distributed between two heads 12''' and 12^IV mobile independently and asymmetrically under numerical control in a direction transversal to the strip 1. The position of said heads 12''' and 12^IV are programmed automatically so that the rollers 12' and 12'' touch the strip where it cannot be damaged.
Downstream from the tightener 12 there is a shearing and blanking press 13, wherein there is housed a tool 14 that has at least the function of shearing the strip 1 transversally in order to separate from it the piece 15 completely punched. The tool 14 can also have the function of simultaneously grasping (head-tail) the two ends of the punched piece 15. Said function of the tool 14 further reduces the number of individual punching operations, contributing to the productivity of the machine being the object of the present invention.
As shown in Figs. 2 and 3, the swan's necks of individual punching 8 and 9 consist of a channel-like structure 16. At the end of the upper branch of the channel-like structure 16 there is a block 17 containing a series of hydraulic cylinders 18 aligned transversally to the strip 1, each of which operates independently by means of a piston 19 (shown in Fig. 4) a respective punch 20, guided by a punch guide 21. At the end of the lower branch of the channel-like structure 16 there is a block 22 containing a corresponding of matrix holders 23, wherein there are inserted matrices 24 (Fig. 4). The punch guides 21 and the matrix holders 23 are made integral with the block 17 and with the block 22, respectively, by the interposition of dovetail-shaped guides, housed in similar dovetail slots, obtained in the blocks 17 and 22 (Fig. 4). This method of fastening the punch guides and the matrix holders to the blocks 17 and 22, thanks also to the fact that the upper ends of the punches 20 are shaped like a hammer head and that the lower ends of the pistons 19 have a slot corresponding to said head, allows their quick removal and subsequent clamping by friction on the inclined planes of the dovetails, for a new machine set-up. The distance between the axes of the end punches of the series is slightly greater than the maximum width of the strip 1. Thanks to the abovementioned dimensions, the swan's necks 8 and 9, moving transversally to the strip 1, can take each punch 20 to any position of the strip 1.
There is also shown in Figs. 2 and 3 a device for the automatic change of the tool holder blocks. For the material execution of the change of tool holders in the proper seats of the swan's necks, aligned with each swan's neck, on the opposite part of the strip, there is a magazine 25 containing series of tool holders loaded with tools. Each series of tool holders consists of as many punch guides 21 and of as many matrix holders 23, as there are contained in each swan's neck, so that the change can be made for the entire series with just one simple operation, of rectilinear movement on the part of pusher devices incorporated in the magazine 25 and not shown in the figure, because they are known in themselves, avoiding leapfrogging.
Said magazine consists of a series of horizontal guides 26 integral with one another, on which there slide the tool holders 21 and 23, moved by said horizontal pusher devices. The entire pack of said guides 26 is raised and lowered and translated horizontally with its content by a device that can be made with the prior art, until the axes of the two series of tool holders to be changed coincide.
The change takes place with a first expulsion of the series of tool holders already present in the swan's neck on the part of a pusher device incorporated in the channel-like structure 16 and with the subsequent insertion of the new series of tool holders coming from the magazine 25. Once the change has been made, the dovetail clamps come into action.
The devices for the displacement and the control of the displacement of the swan's necks 8 and 9, consisting of electric motors, ball-type guides and screws, encoder, control cards, etc., belong to the prior art and are therefore not shown in Fig. 2.
The fundamental feature of the machine being the object of the present invention is that the positions of both the strip being processed and of each tool can be programmed freely in the punching plan. This allows a certain number of tools to be arranged previously in the positions prescribed by the drawing of the piece to be produced and then to operate these tools simultaneously, as soon as the strip of sheet metal has executed its step.
Nothing prevents the displacements of the tools and of the strip from taking place simultaneously, saving additional time. The operation of the machine thus consists of a sequence of changes of the distribution of the tools in the punching plan, of steps of the strip, often simultaneous with the displacements of the tools, of individual punching operations and of simultaneous punching operations, the more numerous the higher the number of tools positioned according to the drawing.
The program for the control unit of the punching machine according to the present invention uses the time prior to start-up of a lot of a given piece to be processed analysing the drawing of that piece in search of all the possible cycles of simultaneous punching, that is the combinations of tools to be operated simultaneously, each consisting of some small displacement of a tool (small because the swan's neck has a large inertia) and some (larger) displacements of the strip, and calculating the times required for the execution of those cycles, in all the possible sequences of the different steps, selecting at the end to actually execute the quickest cycle and printing out the benefit in financial terms obtained by giving up the usual sequential punching operations.
The probability of reaching with this method a total simultaneousness, that is to succeed in making up with elementary tools the multiple tool capable of punching the entire piece with just one stroke of the press, is not to be excluded due to the fact that in principle the present invention does not place any limits on the number of swan's necks, or on the number or the dimensions of the tools.

Claims

A machine for punching sheet metal, comprising means (3, 4, 5, 7) for feeding a sheet metal strip (1) to means (8, 9) for punching the strip (1) of sheet metal, characterized in that said means for punching the strip (1) comprise a plurality of punching presses each comprising a plurality of elementary individual punching tools (20, 21) that can be operated individually, said punching presses each having a supporting structure (16) shaped like a swan's neck with an intermediate channel (100) through which there passes the sheet metal strip (1) and being arranged in sequence along the longitudinal direction of the strip (1) so as to extend in part on one side and in part on the other side of the strip (1), said punching presses (8, 9) being independently mobile along a transversal direction of the strip (1), so as to allow the complete extraction of the strip (1) from the respective channels (100) and the complete extraction of each swan's neck structure from the space extending between two adjacent swan's necks, and along the longitudinal direction of the strip (1) so as to allow the interchangeability of the individual punching presses (8, 9) within said sequence, so as to be able to position the respective elementary punching tools (20, 21) according to an arrangement pre-established in the plan of operations.
A machine according to claim 1, characterized in that said plurality of elementary tools of each punching press (8, 9) is arranged in succession transversally to said sheet metal strip (1).
A machine according to claim 2, characterized in that said presses (8, 9) are mobile transversally to the strip (1) along first sliding guides (10) transversal to the strip (1), and in a direction parallel to said strip (1) along second sliding guides (11) parallel to the strip (1).
A machine according to claim 3, characterized in that in each of said punching presses (8, 9) the individual elementary tools (20, 21) of said respective said plurality of elementary tools can be operated, in addition to individually, also simultaneously so that each press (8, 9) can participate in a multiple punching operation of the sheet metal strip (1).
A machine according to claim 4, characterized in that each of said punching presses (8, 9) comprises a first block (17), mounted on an upper branch of the supporting structure (16), containing punch portions (20, 21) of the plurality of elementary tools and respective operating means (18, 19) for operating the elementary tools, and a second block (22), mounted on a lower branch of the supporting structure (16), containing matrix portions (23) for the plurality of elementary tools (20, 21).
A machine according to claim 5, characterized in that said operating means (18, 19) comprise a plurality of piston-hydraulic cylinder means (18, 19), each associated with a respective elementary tool (20, 21).
A machine according to claim 6, characterized in that said means for feeding the sheet metal strip (1) comprise an unwinding reel (3) of a roll (2) of sheet metal strip, a flattener (4) for flattening the sheet metal strip unwound from the roll (2), trimming means (5) for trimming the strip (1) laterally and a feeder unit with rollers (7) for feeding the strip (1) to said punching presses (8, 9).
A machine according to claim 7, characterized in that it comprises, downstream from said punching presses (8, 9), shearing and blanking means (13) for shearing transversally the punched strip (1) so as to obtain punched pieces of sheet metal.
A machine according to claim 8, characterized in that said punch portions (20, 21) and said matrix portions (23) of each elementary tool of said plurality are slidable on said first block (17) and second block (22), respectively, so that they can be changed with rectilinear movements.
A machine according to claim 1, characterized in that it comprises tool holder magazines (25) arranged to the sides of said punching presses (8, 9) and mobile with respect to them to allow the change of the tools (20, 21).