CYLINDER ASSEMBLY, ESPECIALLY FOR PUNCHING OR NIBBLING MACHINES

Abstract: A cylinder assembly (1), especially for use in a punching or nibbling machine, has a cylinder (2) and a working piston (3) provided in the cylinder. The piston rod (4) of the working piston (3) extends out through one end wall (5) of the cylinder (2), especially for carrying a punch or nibbling tool. The working piston (3) is movable back and forth between a front end position in which the piston rod (4) is in an extended position, and a rear end position in which the piston rod is in a retracted position. A second piston (6) is provided in the cylinder (2) between the working piston (3) and the opposite end wall (7) of the cylinder. The second piston (6) is movable back and forth between two end positions in order there to define two alternative rear end positions for the working piston (3).

Description: CYLINDER ASSEMBLY, ESPECIALLY FOR PUNCHING OR NIBBLING MACHINES The present invention relates to a cylinder assembly especially for use in a punching or nibbling machine, having a cylinder and a working piston which is arranged in said cylinder and whose piston rod extends out through one end wall of the cylinder, especially for carrying a punch or nibbling tool, the working piston being movable back and forth between a front end position in which the piston rod is in an extended position, and a rear end position in which the piston rod is in a retracted po- sition. Prior art cylinder assemblies of this type are used e.g. in punching or nibbling machines in order, for punch ing a piece of sheet metal, to move a punch or nibbling tool back and forth towards and away from a stationary punch or nibbling tool forming the matrix of the machine. • For changing tools in such a machine, it is necessary to raise the movable punch or nibbling tool through a con¬ siderable distance above the stationary punch or nibbling tool. The stroke length required for tool changing is about 150 mm while the stroke length required for the punching operation is about 5-15 mm. One and the same cylinder brings about the movement of the tool, both for tool changing and for punching. In order to ensure a preset working position, the working piston of the cylinder must be moved, also in connec¬ tion with punching, a distance corresponding to the total stroke length of the cylinder. In punching, the travel of the working piston therefore becomes much longer than would have been the case if the working piston were instead moved a distance corresponding to the stroke length required for the punching operation. This means that the time for completing a work cycle also becomes unnecessarily extended. The object of the present invention is to provide a cylinder assembly which is especially well suited for use in a punching or nibbling machine and in which the above-mentioned drawback is overcome. According to the invention, this object is achieved by means of a cylinder assembly of the type stated in the introduction to this specification, which is charac¬ terized in " that a second piston is arranged in the cy¬ linder between the working piston and the opposite end wall of the cylinder, said second piston being movable back and forth between two end positions in order there to define two alternative rear end positions for the working piston. In a preferred embodiment, the second piston, when in its end positions, engages abutments inside the cylin¬ der, one of said abutments consisting of said opposite end wall of the cylinder. * The interior of the cylinder "is divided into a front chamber for the working piston and a rear chamber for the _ second piston, said front chamber having a smaller cross- sectional area than said rear chamber. The invention will be described in more detail here¬ inafter with reference to the accompanying drawings in which: Fig. 1 is a longitudinal section of a cylinder as¬ sembly according to the present invention. Pigs. 2 and 3 show the cylinder assembly of Fig. 1 in different positions. The cylinder assembly 1 shown in Fig. 1 is intended for use in a punching or nibbling machine (not shown) and has a cylinder 2 with a working piston 3 disposed therein. The working piston 3 has two piston rods 4 and 8. The piston rod 4 extends out through one end wall 5 of the cylinder 2 and is intended to carry a punch or nibbling tool (not shown). The piston rod 8 extends out through the opposite end wall 7 of the cylinder and is intended to indicate the position of the working piston 3 in the cylinder 2. The cylinder assembly 1 further has a second piston 6 which has a through bore and is disposed in the cylin- der 2 between the working piston 3 and the opposite end wall 7 of the cylinder in such a manner that the piston rod 8 passes through its bore. The second piston 6 further has two sealing rings 9 and 10 by means of which the second piston 6 sealingly engages the internal sur- face of the cylinder 2. The working piston 3 also has two sealing rings 11 and 12 by means of which it sealing¬ ly engages the internal surface of the cylinder 2. It further appears from Fig. 1 that the interior of the cylinder 2 is divided into a front chamber 13 for the working piston 3 and a rear chamber 14 for the second piston 6, the front chamber 13 having a smaller cross- sectional area than the rear chamber 14. The second pis¬ ton 6 has a front portion 6a of the same cross-sectional area as the front chamber 13, and a rear portion 6b of the same cross-sectional area as the rear chamber 14. This means that the second piston 6, when in its front end position (Fig. 1), engages the circumferential abut¬ ment 15 formed at the transition from the front to the rear chamber. The pistons 3 and 6 of the cylinder assembly 1 are movable back and forth in the cylinder 2 under the ac¬ tion of a pressure medium being supplied and discharged through lines 16, 17 and 18 which are connected, respec¬ tively, at the second or opposite end wall 7 of the cylinder, at the rear portion of the front chamber 13 of the cylinder, and at the end wall 5 of the cylinder. The direction of flow of the pressure medium in the different lines is determined by valve arrangements 19 and 20, these valve arrangements as well as the equipment required for controlling them being of a conventional type. Since these componentes are no part of the invention proper, they will not be described in more detail here. As appears from Fig. 1, the line 18 is provided with a bypass line 21 with a nonreturn valve 22 for bypassing the pressure medium with respect to a throttle orifice 23 provided in the line 18. The function of the cylinder assembly will now be described with reference to Figs. 1-3. When the punching or nibbling machine is in operation, the punch or nibbling tool carried on the piston rod 4 of the working piston 3 should be moved back and forth towards and away from a stationary punch or nibbling tool (not shown) for punch¬ ing a workpiece (not shown). Figs. 1 and 2 show the positions of the working, pis¬ ton 3 and of the second piston 6 in the cylinder assembly 1 during the punching operation. In Fig. 1, the working piston 3 is shown in its rear end position in which the piston rod 4 is in a retracted position and. the p ; Iston rod 8 is in an extended position, the second piston 6 - being in its front end position. In Fig. 2, the working piston 3 is shown in its front end position in which the piston rod 4 is in an extended position "and the piston rod 8 is in a retracted position, the second piston still being in its front end position. For moving the working piston 3 from its rear end position to its front end position, a pressure medium is supplied under full system pressure through the line 17 to the front chamber 13 in the boundary area between the working piston 3 and the second piston 6. The rear chamber 14 and the part of the front chamber 13 located in front of the working piston 3 are also subjected to full system pressure. Since the second piston 6 has a rear effective piston area which is larger than its front effective piston area, its position will not be altered. The working piston 3, on the other hand, will be displaced towards its front end position since its rear effective piston area is larger than its front effective piston area. In this manner, the pressure medium in the part of the front chamber 13 located in front of the working piston will be discharged through the orifice 23. The reason why also the part of the front chamber 13 in front of the working piston 3 is pressurized during the outward movement of the piston rod 4 from the cylinder 2 is that it is desirable to damp the impact of the movable punch or nibbling tool on the stationary punch or nibbling tool at the end of the punching stroke. When the working piston 3 should then be moved from its front end position to its rear end position, the pressure medium in the part of the front chamber 13 located between the working piston and the second piston is first discharged through the line 17, whereupon pres- sure medium is supplied under full system pressure through the bypass line 21 and the line 18 to the part of the front chamber 13 located in front of the working piston 3. In this manner, the working piston 3 is im¬ parted such a movement that its piston rod 4 is retracted into the cylinder 2. In order to exchange e.g. a worn punch or nibbling tool carried by the piston rod 4 of the working piston 3, it is necessary to raise the tool a considerable distance as compared with the stroke length required for the punching operation, which means that when chang¬ ing tools, the rear end position of the working piston 3 must be located further backwards in the cylinder 2 than during the punching operation. Thus, in connection with tool changing, no pressure medium is supplied by the line 17 to the boundary area between the working piston 3 and the second piston 6 when the working piston is in the rear end position shown in Fig. 1. Instead, the pressure medium in the rear cham¬ ber 14 is discharged by the line 16 concurrently as pressure medium is supplied by the line 18 to the part of the front chamber 13 located in front of the working piston 3. This entails that both the second piston * * _•_ 6 6 and the working piston 3 are moved rearwards in the cylinder 2 until the rear portion 6b of the second pis¬ ton 6 enters into engagement with the opposite end wall 7 of the cylinder (Fig. 3). The tool can then be changed, whereupon pressure medium is supplied by the line 16 to the rear cham¬ ber 14 while full system pressure is still prevailing in the front chamber 13. Since the rear effective piston area of the piston 6 Is larger than the front effective piston area of the working piston 3, both pistons will be moved forwards in the cylinder 2. This displacement proceeds until the rear portion 6b of the second piston 6 engages the abutment 15 of the cylinder 2. During the final phase of this displacement, it is necessary to discharge the pressure medium which may collect immediately above the abutment 15 of the cylin¬ der 2 since such an entrapped pressure medium volume . would be subjected to a very high pressure when the • lower sealing ring 10 of the second piston 6 has passed the abutment. This pressure medium may be discharged e.g. to a'storage tank (not shown) by a line (not shown).

Claims: AMENDED CLAIMS [received by the International Bureau on 7 March. 1988 (07.03.88), original claims 1-4 replaced by new claim 1 (1 page)] A cylinder assembly for use in a punching or nibbling machine, having a cylinder (2) and a working piston (3) which is arranged in the cylinder and whose piston rod (4) extends out through one end wall (5) of the cylinder for carrying a punch or nibbling tool, the working piston being movable back and forth between a front end posi¬ tion in which the piston rod is In an extended position, and a rear end position in which the piston rod is in a retracted position, a second piston (6) being arranged In the cylinder (2) between the working piston (3) and the opposite end wall (7) of the cylinder, c h a r c ¬ t e r i z e d in that the interior of the cylinder (2) is divided into a front chamber (13) for the working piston (3) and a rear chamber (14) for the second piston (6), said front chamber having a smaller cross sectional area than said rear chamber, that the second piston (6) is adapted, during punching or nibbling, to permanently engage an abutment (15) formed at the transition from the front to the rear chamber, and that the rear piston (6) is adapted, for tool changing, to be moved backwards by means of the working piston (3) into engagement against said opposite end wall (7) of the cylinder (2).

Inventors: PETTERSSON OLOF, PETTERSSON, OLOF
Applicants: NIBBLER FABRIKS AB
Application year: 1987
Main classification: B26D5
IPC codes: B21D28, B23D15, B23D27, B30B15