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(11) | EP 1 445 042 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Multipress operating head for sheet metal punching machine with numerical control |
| (57) A multipress operating head for sheet metal punching machine with numerical control
is described comprising a plurality of hydraulic presses (1), close to each other
and each one made up of a hydraulic cylinder (2) in which a respective piston (3)
slides, and a plurality of punches (6) set into action by respective pistons (3).
The pistons (3) are grouped into sets of pistons associated with a respective single
position transducer (20) with unidirectional mechanical connection so that the transducer
(20) follows the punching movement of any one of said pistons (3) while the other
pistons (3) remain at rest. At least one of said pistons (3) is coupled to several
punches (6) through a selector (22) so as to control each time the punching movement
of a selected one of said punches (6). Said pistons (3) are operatingly connected
with said punches (6) so that said punches (6) rigidly follow the movement of said
punching pistons (3) and have instead back strokes elastically controlled in a way
independent from the position of said pistons (3). |
[0001] The present invention concerns a multipress operating head for sheet metal punching machine with numerical control.
[0002] Punching machines with multipress head are known, which are made up of a plurality of hydraulic presses, close to each other, each one of which controls the vertical motion of a single punch.
[0003] The main advantage of this constructive system resides in the fact that all the different punches that must be used in sequence in order to accompish the punching working of a piece are available and ready to operate, without need to carry out any tool change operation during the productive cycle; an improved productivity and precision of the machine is thus obtained, because the operations of tool substitution are avoided during the cycle and the total length of the distance that the piece, displaced by a manipulator along two directions perpendicular to each other, must cover in order to allow the execution of all the workings required on its surface is reduced.
[0004] The main disadvantage of the current embodiment of this constructive system resides in the fact that the presses cover a same vertical stroke, independent from the type of working and from the thickness of the material that must be worked, reason for which the vertical stroke of descent and the relative time of execution of the single punchings are as a result often excessive as compared with what would be strictly necessary, and this is to the prejudice of the productivity of the machine. In particular, the maximum frequency of repetition of the punching movements is limited and inversely proportional to the working stroke of the punch (that is pre-established during the designing of the machine).
[0005] In modem punching machines of this type, operating with numerical control, it is also important to carry out the detection of the position of the punch being each time operated. In the case of multipunch machines however this would mean to use a position transducer for each punch. Such solution would involve great complexity and high cost for the machine.
[0006] There are also tower-type punching machines, whose commonly adopted constructive system provides for the presence of two discs with vertical axis, one above and one under the sheet, which bear on their periphery, housed in appropriate housings, one the punches and the other one the dies. The press that controls the descent of the punch is a single one, located in a fixed position on the edge of the structure. Appropriate controls make the two discs rotate in synchronous way, by taking under the ram of the piston of the single hydraulic press, each time, the punch and the relative die that are necessary to the execution of the working; simultaneously the manipulator brings the sheet in the correct position as regards the punch, in order to allow the execution of the holes and of the other workings. Usually the control of the piston is servo-hydraulic, with continuous measurement of the vertical position of the piston along its own stroke.
[0007] The resulting advantage is that punching frequencies higher than the ones obtained with the operating head of the punching press with multipress head can be obtained. Such advantage is achieved only by using punches for which the action of extraction of the cutter from the sheet is done due to the effect of a spring (or of a group of springs) inserted in opportune way in the cartridge that holds the same tool in guide and in position in the tool holder disc.
[0008] In case one wishes to use punches in which the extraction is mechanically controlled by the piston, in order to limit the strokes to the strictly necessary and thus to obtain favourable production rates, it is necessary in any case to predispose the operating head at a reduced height, variable as a function of the thickness and of the conditions of working, by vertically moving the entire upper punch holder disc, which creates a not negligible complication; in practice, no manufacturer adopts this latter solution.
[0009] The main disadvantage of this type of operating head consists in that each time that the shape of the punch must be changed, it is necessary to make the tower rotate, operation whose duration is not negligible, and that in practice adds up to the time for the execution of the punchings.
[0010] There are finally single-punch punching machines with tool change. One of these provides for the presence of a single servo hydraulic press with numerical control vertical movement, on which an appropriate mechanism of punch change installs, each time, the punch and the relative motor necessary for the working of the piece, between a sequence of punchings and the other one.
[0011] In this case too the advantage is given by the high frequency of punching that is obtainable.
[0012] The disadvantage is the time for the tool change that adds up to the one for the execution of the punchings and to the ones for the movement of the sheet between one punching and the other one.
[0013] In this type of embodiment the punches can be both with extraction controlled by springs, and with extraction controlled mechanically; in this second case an adjustment of the head span is effectively provided, that is possible in a simple way because it consists in positioning in height the cartridge of the only punch that is mounted on the edge of the operating head.
[0014] In view of this state of the art, object of the present invention is to provide a multipress head for punching machine that allows to overcome the current disadvantages of the multipress head, while conserving at the same time the positive characteristics intrinsic to the peculiar architecture..
[0015] According to the invention such object is attained with a multipress head comprising a plurality of hydraulic presses, close to each other and each one made up of a hydraulic cylinder in which a respective piston slides, and a plurality of punches driven by respective pistons of said hydraulic presses, characterised in that:
a) said pistons are grouped into sets of pistons that are associated with a respective single position transducer with unidirectional mechanical connection in such a way that the transducer follows the punching movement of any one of said pistons while the other pistons remain at rest;
b) at least one of said pistons is coupled to several punches through a selector in order to control each time the punching movement of a selected one of said punches;
c) said pistons are operatively connected with said punches in such a way that said punches rigidly follow the punching movement of said pistons and have instead back stroke elastically controlled in a way independent from the position of said pistons.
[0016] In this way, by combining the hydraulic pre-selection of the piston with the possible mechanical pre-selection of the punch to be stricken, applied by using punches with spring extraction, which have the property of executing the extraction by using the lower portion of the working stroke to charge the spring, and do not require therefore the adjustment of the working span of the head, allows to provide the desired improvement of the working cycle, by combining the advantages of the multipress head with the ones of the numerical control of the vertical position of the punch and of the amplitude of its usable stroke.
[0017] The time for the hydraulic pre-selection of the piston that one wants to operate, and also the time for the possible simultaneous commutation necessary to take the section of the selector disc above the punch, is much smaller than the time for the tool change of the other cited systems, and they are almost always carried out simultaneously with the movement for the repositioning of the piece to be worked by the manipulator.
[0018] The object to have all the punches of a multipress operating head carry out only the vertical stroke strictly necessary to the execution of the working is thus attained, being such stroke numerically controlled through a system provided with pistons connected with position transducers, which are controlled in turn by a servovalve, the entire unit being controlled by an appropriate programmable electronic control unit.
[0019] These and other characteristics of the present invention will be made more evident by the following detailed description of an embodiment that is illustrated as a non limiting example in the enclosed drawings, in which:
Figure 1 schematically shows in perspective view a multipress head according to the present invention;
Figure 2 shows the hydraulic scheme of principle of the multipress head of Figure 1;
Figures 3-5 show the magnified detail of the operating and elastic return system of the punches in the steps of rest, cut and back to rest.
[0020] In Figure 1 a multipress head 4 comprising a plurality of hydraulic presses 1 is shown that is made up of a cylinder 2 within which a piston 3 slides that has, in its upper part, a stem 16 that proj ects out of a block 17 in which the housings of the cylinders 2 are obtained; the stem 16 has an arm 18 that rests on a mobile equipment 19 (biased in rest position by a spring 30 or a similar elastic mean) of a position transducer 20. Below the head 4 there are punching tools 6, hereinafter simply called punches, which are vertically guided and withheld in position in the horizontal plane by an appropriate tool holder plate 21 integral with the head 4, extractable for the operations of preparation of the tooling out of the working cycles of the machine. Under each press 1 one or more punches 6 are located, some of which are grouped in sets and selectable with a mechanical selector 22 made up of a disc 7 mounted onto the lower end of the piston 3, put in rotation and positioned by an appropriate motorization with gear train (not shown), which disc 7 has a sector 8 with increased thickness. The positioning of the punches 6 is provided as a function of their radial volume; in particular, usually the punches 6 having large dimensions are controlled each one by a piston 3, whereas the ones with small dimensions can be grouped in sets with two or more, controlled by a single piston 3 through a mechanical selector 22.
[0021] Below the punch holder plate 21 a die holder plate 31 is positioned which bears a plurality of dies 29 operatingly associated with respective punches 6.
[0022] In Figure 2 the principle of combination of the hydraulic pre-selection with the mechanical one and with the transducer 20 common for several pistons 3, that is suitable to provide in complete way the concept of multipress head with direct numerical control of the vertical motion of all the punches 6 is summarised in schematic way. The unidirectional motion of the pistons 3 is controlled by a control unit 10 through a hydraulic circuit that regulates the descent/ascent of a pistons 3 by means of a control servovalve 12 and of pre-selection valves 13.
[0023] The position transducer 20 detects the position of the piston 3 by means of the stem 16 and the arm 18 that moves the mobile equipment 19 of the transducer 20 thereby allowing the continuous measurement of the vertical position of the piston 3. For reasons of economy and availability of space a position transducer 20 is positioned every four-six cylinders 2, so that the position measurement is taken just of the lowest piston among the ones that refer to the transducer 20, that is the piston 3 that was preventively put in communication with the servovalve 12 through its own pre-selection valve 13. This solution (a single position transducer 20 serving several pistons 3) is described in detail in a copending patent application of the same Applicant and it is herein applied in repeated way to several sets of pistons 3.
[0024] The combination of the hydraulic pre-selection of the working piston 3 with the possible mechanical pre-selection of the punch 6 to be struck is applied using the punches 6 with extraction spring 14-15 (Figure 3-5), where the spring 14, more rigid, is interposed between a punch holder cup 28 and a terminal flange 24 of a stem 27 to which the punch 6 is fastened, whereas the spring 15, more tender, is interposed between the punch holder cup 28 and the tool holder plate 21. In the same figures the cutter of the punch 6 is indicated by 23, whereas 26 indicates the sheet to be punched.
[0025] The use of springs 14-15, associated with the fact that the flange 24 is only in contact with the piston 3, allows to carry out the extraction by using the lower portion of the working stroke of the piston and the consequent compression of the two springs. In particular, once the descent of the piston 3 is over and the lift back has started, the state of compression of the spring 14 thrusts upward the punch 6 connected with the stem 27 that transmits the motion to the piston 3 by means of the terminal flange 24, the state of compression of the spring 15 brings the cup 28 back to the rest position (Figure 4-5).
[0026] The advantage of said extraction system resides in that it does not need any adjustment of the working span of the head, it allows to provide the desired improvement of the working cycle, thus combining the advantages of the multipress head with the ones of the numerical control of the vertical position of the punch 6 and the amplitude of its usable stroke.
[0027] The time for the hydraulic pre-selection of the piston 3 that one wants to operate, as also the time for the possible simultaneous commutation necessary to take the sector 8 of the selector disc 7 above the desired punch, is much smaller than the times for the tool change of the other cited systems, and takes place almost always simultaneously with the movement for the repositioning of the piece 26 to be worked by the manipulator.
1. Multipress operating head with numerical control for sheet metal punching machine,
comprising a plurality of hydraulic presses (1), close to each other and each one
made up of a hydraulic cylinder (2) in which a respective piston (3) slides, and a
plurality of punches (6) driven by respective pistons (3) of said hydraulic presses
(1)1, characterised in that:
a) said pistons (3) are grouped into sets of pistons associated with a respective single position transducer (20) with unidirectional mechanical connection so that the transducer (20) follows the punching movement of any one of said pistons (3) while the other pistons (3) remain at rest;
b) at least one of said pistons (3) is coupled to several punches (6) through a selector (22) so as to control each time the punching movement of a selected one of said punches (6);
c) said pistons (3) are operatingly connected with said punches (6) so that said punches (6) rigidly follow the movement of said punching pistons (3) and have instead back strokes elastically controlled in a way independent from the position of said pistons (3).
2. Multipress operating head according to claim 1, characterised in that said pistons (3) are connected with said transducer (20) by means of a mobile equipment
(19), that is rigidly connected with said transducer (20), on which arms (18) rest
that are rigidly bound to respective pistons (3) and that is biased into rest position
by a spring (30).
3. Multipress operating head according to claim 1, characterised in that it comprises a control unit (10), connected with said transducer (20), that controls
a hydraulic circuit for the selection and the operation of said pistons (3) by means
of a control servovalve (12) and of pre-selection valves (13).
4. Multipress operating head according to claim 1, characterised in that it comprises that said mechanical selector (22) is made up of a disc (7) provided
with a part (8) with increased thickness.
5. Multipress operating head according to claim 4, characterised in that said mechanical selector (22) is put in the working position by a gear motorization
controlled by a control unit (10).
6. Multipress operating head according to claim 1, characterised in that said pistons (3) rest on said punches (6) and springs (14-15) are provided that control
said back stroke of said punches (6).
7. Multipress operating head according to claim 5, characterised in that a first spring (14) is operatingly interposed between the punch (6) and a punch holder
cup (28) in which said punch (6) slides and a second spring (15) is operatingly interposed
between said cup (28) and a tool holder plate (21) in which said cup (28) slides,
in such a way that, in the position of end of descent said pistons (3), said first
spring (14) controls said back stroke of said punches (6) and said second spring (15),
less rigid than said first spring (14), controls a back stroke of said cup (28).