Punch assembly

Abstract

 Sheet metal or similar is punched by means of a ram (6), which is moved in a straight reciprocating movement defined by a down stroke to punch at least one metal sheet, and by a return stroke, and has a first member (9) moved with a given law of motion during the down stroke and the return stroke, and a second member (19) which is connected in sliding manner to the first member (9), is brought into contact with a punch to punch the metal sheet, and is moved, during the down stroke, with substantially the same law of motion as the first member (9) when the metal sheet produces a resisting force below a given value, and with a law of motion different from that of the first member (9) when the metal sheet produces a resisting force at least equal to the given value.

Description

[0001] The present invention relates to a punch assembly.

[0002] In the working of sheet metal or similar, a punch assembly is known comprising a ram movable along a given longitudinal axis; and an actuating device for moving the ram axially in a straight reciprocating movement comprising a down stroke to punch at least one sheet, and a return stroke.

[0003] The actuating devices of known punch assemblies of the above type are normally of two types.

[0004] In a first type, the actuating device comprises a hydraulic pump, and a hydraulic circuit for supplying the ram with pressurized fluid, and has various drawbacks due to losses mainly caused by the efficiency of the hydraulic pump and leakage in the hydraulic supply circuit.

[0005] In a second type, the actuating device comprises an electric motor having an output shaft normally connected to the ram by a screw-nut screw coupling, and has various drawbacks, mainly due to the fact that, for the thrust exerted on the ram to be greater than the resisting force of the sheet, the electric motor and the screw-nut screw coupling must be designed as a function of relatively high resisting force values, and as such are relatively expensive and bulky.

[0006] It is an object of the present invention to provide a punch assembly designed to eliminate the aforementioned drawbacks, and which is cheap and easy to produce.

[0007] According to the present invention, there is provided a punch assembly as claimed in Claim 1.

[0008] A non-limiting embodiment of the present invention will be described by way of example with reference to the accompanying drawings, in which:

Figure 1 shows a schematic longitudinal section, with parts removed for clarity, of a preferred embodiment of the punch assembly according to the present invention;

Figures 2 to 5 show, schematically, the Figure 1 punch assembly in four different operating positions.

[0009] Number 1 in Figure 1 indicates as a whole a punch assembly for punching sheet metal or similar, and comprising a tubular supporting frame 2 having a substantially vertical longitudinal axis 3 and in turn comprising a wide top portion 4 and a narrow bottom portion 5.

[0010] Assembly 1 also comprises a ram 6 movable along frame 2 in a vertical direction 7 parallel to axis 3; and an actuating device 8 for imparting to ram 6 a straight reciprocating movement comprising a down stroke, in which ram 6 moves from a raised position to a lowered position to punch at least one metal sheet (not shown), and a return stroke, in which ram 6 moves back into the raised position.

[0011] Ram 6 comprises a top member 9 mounted coaxially with axis 3 and in turn comprising a substantially cup-shaped top portion 10 extending along portion 4, and a pin-like bottom portion 11 extending along portion 5 of frame 2.

[0012] Portion 10 is connected by a screw-nut screw coupling to a screw 12 forming part of device 8, and which is rotated about axis 3 by an electric motor 13 having an output shaft 14, which is mounted to rotate about a longitudinal axis 15 substantially parallel to axis 3, and is connected to screw 12 by a belt drive 16 comprising two pulleys 17 fitted to shaft 14 and screw 12 respectively, and a belt 18 looped about pulleys 17. As screw 12 rotates about axis 3, member 9 is moved in direction 7 between the raised and lowered positions with a given law of motion.

[0013] Ram 6 also comprises a bottom member 19 in turn comprising a tubular top body 20, which is fitted in sliding manner to both portion 5 of frame 2 and portion 11 of member 9, defines a variable-volume, annular first chamber 21 together with frame 2 and portion 11 of member 9, and is closed at a free end by a pin 22. In actual use, pin 22 activates a punch (not shown) for working the metal sheet (not shown), and defines, together with body 20 and with a piston 23 fixed to the end of portion 11 and perpendicular to axis 3, a variable-volume, cylindrical second chamber 24 with a smaller cross section than chamber 21.

[0014] With reference to Figures 2 to 5, chambers 21 and 24 form part of a hydraulic oil circuit 25 comprising a first portion 26, which extends between chambers 21 and 24, and has a valve device 27 for selectively controlling pressurized-oil flow between chambers 21 and 24.

[0015] Device 27 comprises a known first valve 28 having a slide 29, which is normally maintained by a spring 30 in a closed position closing portion 26 (Figures 2, 4, 5), and is moved, in opposition to spring 30 and by the pressurized oil, from the closed position to an open position (Figure 3) permitting oil flow from chamber 24 to chamber 21. Device 27 also comprises a known second valve 31, which is mounted parallel to valve 28, is normally set to a closed position closing portion 26, and is movable by the pressurized oil from the closed position to an open position permitting oil flow from chamber 21 to chamber 24.

[0016] Chamber 21 communicates hydraulically with an oil tank 32 via a second portion 33 of circuit 25 having three valve devices 34, 35, 36 for selectively controlling pressurized-oil flow between tank 32 and chamber 21.

[0017] Device 34 comprises a known first valve 37 having a slide 38, which is normally maintained by a spring 39 in a closed position closing portion 33 (Figures 2, 3, 4), and is moved, in opposition to spring 39 and by the pressurized oil, from the closed position to an open position (Figure 5) permitting oil flow from chamber 21 to tank 32. Device 34 also comprises a known second valve 40, which is mounted parallel to valve 37, is normally set to a closed position closing portion 33, and is movable by the pressurized oil from the closed position to an open position permitting oil flow from tank 32 to chamber 21.

[0018] Device 35 is mounted between chamber 21 and device 34, and comprises a slide 41, which is normally maintained by a spring 42 in a first operating position (Figures 2, 3) permitting pressurized-oil flow from tank 32 to chamber 21, and is moved, in opposition to spring 42 and by an actuating device (not shown) controlled by an electronic central control unit (not shown), from the first operating position to a second operating position (Figures 4, 5) permitting oil flow from chamber 21 to tank 32.

[0019] Device 36 comprises a known valve 43, which is mounted parallel to devices 34 and 35, is normally set to a closed position closing portion 33, and is movable by the pressurized oil from the closed position to an open position permitting oil flow from tank 32 to chamber 21.

[0020] Operation of punch assembly 1 will now be described with reference to Figures 2 to 5, and as of the instant (Figure 2) in which:

ram 6 is in the raised position, and chamber 24 is therefore at maximum volume and substantially full of oil at a higher pressure than the oil in tank 32;

valves 28 and 31 of portion 26 are in the closed position;

valves 37, 40, 43 of portion 33 are in the closed position; and

slide 41 is in the first operating position.

[0021] Electric motor 13 is operated to rotate output shaft 14 and, therefore, screw 12 to move top member 9 of ram 6 in direction 7 with said given law of motion.

[0022] As top member 9 moves in direction 7, bottom member 19 is moved downwards in direction 7 by top member 9 via the interposition of the oil in chamber 24 and into contact with said punch (not shown), and the volume of chamber 21 increases to open valves 40 and 43 and so feed the oil in tank 32 to chamber 21.

[0023] When the metal sheet (not shown) being punched exerts a resisting force below a given value on the punch (not shown), and therefore on bottom member 19, members 9 and 19 move downwards with the same law of motion, i.e. the law of motion imposed on members 9 and 19 by rotation of screw 12, thus enabling the punch (not shown) to punch the metal sheet (Figure 2).

[0024] As shown in Figure 5, at the end of the down stroke to punch the metal sheet (not shown), the electronic central control unit (not shown) moves slide 41 into the second operating position, the rotation direction of screw 12 is inverted, and members 9 and 19 are moved in direction 7 from the lowered position to the raised position with the same law of motion, i.e. the law of motion imposed on members 9 and 19 by rotation of screw 12.

[0025] During the return stroke of members 9 and 19, the volume of chamber 21 decreases, and the oil in chamber 21 is fed along portion 33 of hydraulic circuit 25 and through slide 41 to close valves 40 and 43, open valve 37, and so feed the oil back to tank 32.

[0026] When the metal sheet (not shown) being punched exerts a resisting force greater than a given value on the punch (not shown), and therefore on bottom member 19, member 9 is moved in direction 7 from the raised position to the lowered position with the law of motion imposed by rotation of screw 12, whereas member 19 is initially prevented from moving in direction 7 by the resisting force of the metal sheet (not shown).

[0027] As member 9 moves with respect to member 19, the oil in chamber 24 is first compressed by piston 23 to open valve 28 (Figure 3), and is then fed from chamber 24 to chamber 21. Since chamber 21 has a larger cross section than chamber 24, the pressure of the oil in chamber 21 generates on member 19, and therefore on the punch (not shown), a thrust which is greater than the thrust generated by the pressure of the oil in chamber 24, is greater than the resisting force of the metal sheet (not shown), thus enabling the punch (not shown) to punch the metal sheet (not shown), and moves member 19 downwards in direction 7 with a different law of motion from that of member 9, i.e. from the law of motion imposed by rotation of screw 12.

[0028] In connection with the above, it should be pointed out that, during punching of the metal sheet (not shown), valve device 35 prevents the oil fed along portion 26 and through valve 28 from opening valve 37 and so being fed to tank 32.

[0029] Once the down stroke is completed and the metal sheet (not shown) is punched:

chamber 24 is at minimum volume (Figure 3), so that valve 28 is again closed by spring 30 (Figure 4);

the electronic central control unit (not shown) opens slide 41 (Figure 4);

the punch (not shown) is disengaged from the metal sheet (not shown) by a known elastic thrust device (not shown) associated with the punch (not shown) itself; and

the rotation direction of screw 12 is inverted to move member 9 back from the lowered position to the raised position (Figure 4).

[0030] As slide 41 opens and the volume of chamber 24 increases, the oil in chamber 21 is fed along portion 26 and through valve 31 to chamber 24, as well as along portion 33 to open valve 37 (Figure 5) and flow back into tank 32.

[0031] Finally, when member 9 is in the raised position, slide 41 is deactivated and moved by spring 42 back into the first operating position, and valve 37 is again closed by spring 39 (Figure 2).

[0032] Punch assembly 1 therefore has various advantages, mainly due to the fact that, when the resisting force of the metal sheet (not shown) is below said given value, the metal sheet (not shown) is punched by means of the thrust imparted to members 9 and 19 by electric motor 13, i.e. by a relatively small electric motor, whereas, when the resisting force of the metal sheet (not shown) is greater than said given value, the metal sheet (not shown) is punched by means of the thrust imparted to member 19 by the pressurized oil in hydraulic circuit 25, i.e. in a hydraulic circuit with no hydraulic pumps.

Claims

1. A punch assembly comprising a ram (6) movable along a given longitudinal axis (3); and actuating means (8) for imparting to the ram (6) a straight reciprocating movement comprising a down stroke to punch at least one metal sheet or similar, which produces a resisting force in opposition to the ram (6), and a return stroke; the ram (6) comprising a first portion (9) moved with a given first law of motion by said actuating means (8) during the down stroke and the return stroke, and a second portion (19) which, in use, engages a punch to punch the sheet metal; the punch assembly being characterized in that the second portion (19) is connected in sliding manner to the first portion (9); thrust means (25) moving the second portion (19) axially, during said down stroke, substantially with said first law of motion when the resisting force is below a given value, and with a second law of motion, different from the first law of motion, when the resisting force at least equals said given value.

2. A punch assembly as claimed in Claim 1, wherein the thrust means (25) selectively generate on said second portion (19), during said down stroke, a first and a second thrust to move the second portion (19) axially with said first and said second law of motion respectively; said first and said second thrust being less than and greater than said given value respectively.

3. A punch assembly as claimed in Claim 1 or 2, wherein the thrust means (25) are hydraulic thrust means comprising a first and a second variable-volume chamber (24, 21) interposed between said first and said second portion (9, 19); and a hydraulic circuit (25) for selectively feeding a pressurized fluid to the first and second chamber (24, 21); the second chamber (21) having a larger cross section than the first chamber (24).

4. A punch assembly as claimed in Claim 3, wherein the hydraulic circuit (25) comprises a first circuit portion (26) hydraulically connecting said first and said second chamber (24, 21); and first valve means (27) located along the first circuit portion (26) to selectively control flow of the pressurized fluid between said first and said second chamber (24, 21).

5. A punch assembly as claimed in Claim 4, wherein the first valve means (27) comprise a first valve (28), which is normally set to a first closed position to prevent flow of the pressurized fluid from the first (24) to the second (21) chamber, and is movable, in the presence of a resisting force value at least equal to said given value, from the first closed position to a first open position to permit flow of the pressurized fluid from the first (24) to the second (21) chamber during said down stroke.

6. A punch assembly as claimed in Claim 5, wherein said first valve means (27) also comprise a second valve (31) mounted parallel with said first valve (28) to permit flow of the pressurized fluid from the second (21) to the first (24) chamber during said return stroke, when the resisting force is at least equal to said given value.

7. A punch assembly as claimed in any one of Claims 3 to 6, wherein said hydraulic circuit (25) comprises a tank (32) for the pressurized fluid; a second circuit portion (33) hydraulically connecting the second chamber (21) and the tank (32); and second valve means (34, 35, 36) located along the second circuit portion (33) to selectively control flow of the pressurized fluid between the second chamber (21) and the tank (32).

8. A punch assembly as claimed in Claim 7, wherein the second valve means (34, 35, 36) comprise a third valve (37), which is normally set to a second closed position to prevent flow of the pressurized fluid from the second chamber (21) to the tank (32), and is movable, during said return stroke, from the second closed position to a second open position to permit flow of the pressurized fluid from the second chamber (21) to the tank (32).

9. A punch assembly as claimed in Claim 8, wherein the second valve means (34, 35, 36) also comprise a fourth valve (40) mounted parallel with the third valve (37) to permit flow of the pressurized fluid from the tank (32) to the second chamber (21) during said down stroke.

10. A punch assembly as claimed in Claim 8 or 9, wherein the second valve means (34, 35, 36) also comprise a fifth valve (41) for selectively controlling movement of the third valve (37) from the second closed position to the second open position.

11. A punch assembly as claimed in Claim 10, wherein the fifth valve (41) is mounted between the second chamber (21) and said third and fourth valve (37, 40).

12. A punch assembly as claimed in Claim 10 or 11, and also comprising further actuating means for moving the fifth valve (41) between a third closed position, in which the fifth valve (41) prevents flow of the pressurized fluid to the third valve (37), and a third open position, in which the fifth valve (41) permits flow of the pressurized fluid to the third valve (37).

13. A punch assembly as claimed in any one of the foregoing Claims, wherein said actuating means (8) comprise an electric motor (13) having an output shaft (14), and a drive (16) from the output shaft (14) to said first portion (9); the drive (16) comprising a screw-nut screw coupling.

14. A method of punching at least one metal sheet by means of a ram (6), which is moved along a longitudinal axis (3) in a straight reciprocating movement comprising a down stroke to punch the metal sheet, and a return stroke, and comprises a first portion (9), which is moved axially with a given first law of motion during the down stroke and the return stroke, and a second portion (19) which, in use, engages a punch to punch the metal sheet; the method being characterized in that, during said down stroke, the second portion is moved axially substantially with said first law of motion, when the metal sheet produces a resisting force below a given value, and with a second law of motion, different from the first law of motion, when the metal sheet produces a resisting force at least equal to said given value.

Drawing