HOLD-DOWN DEVICE FOR A PROCESS DURING STAMPING AND/OR RIVETING

Abstract

The invention relates to a hold-down device for a joining drive and joining drive with a hold-down device. The hold-down device includes a hold-down cylinder, wherein the hold-down cylinder provides a hold-down force by means of a pressurized chamber. The pressure chamber consists of the hold-down cylinder and a punch of the joining drive. The pressurization required for the provision of the hold-down force is provided by a hydraulic circuit of the joining drive. In the joining mode, the pressure chamber of the hold-down device is connected to a pressure accumulator of the hold-down device, so that a change in volume in the pressure chamber of the hold-down device has no noticeable influence on the pressure in the pressure chamber.

Claims

1. A hold-down device for a joining drive, the hold-down device comprising: a hold-down cylinder; a pressure chamber to provide a hold-down force and/or a position of the hold-down device; and a pressure accumulator, wherein the pressure chamber is continuously hydraulically connected to the pressure accumulator during a joining process, the joining drive having a hydraulic unit that includes a pump with reversible delivery direction, the pump being a 4-quadrant pump, the pump being hydraulically connectable to the hold-down cylinder, the pressure chamber and the pressure accumulator.

2. The hold-down device according to claim 1, wherein the pressure accumulator has a supply line with at least one valve for connection with the hydraulic unit of the joining drive.

3. The hold-down device according to claim 2, further comprising at least one position sensor for detecting the relative position of the hold-down cylinder in relation to a punch, and/or a pressure sensor for detecting the pressure in the pressure accumulator or the pressure chamber of the hold-down device, and/or a temperature sensor for detection of the temperature of hydraulic medium used in the hold-down device.

4. The hold-down device according to claim 1, further comprising a punch, the pressure chamber is formed by the hold-down cylinder and the punch, wherein the pressure chamber is arranged radially between the hold-down cylinder and the punch.

5. The hold-down device according to claim 4, wherein the hold-down cylinder is mounted axially movable on the punch and the pressure chamber is permanently connected with the pressure accumulator of the hold-down device.

6. The hold-down device according to claim 4, wherein the punch has at least one radially protruding flange for provision of a stop.

7. The hold-down device according to claim 4, wherein the hold-down device has at least one cover that is detachably connected to the hold-down cylinder.

8. A joining device to produce a punch/riveting connection, the joining device comprising: a joining drive, the joining drive including: a hydraulic unit; an axially movable piston rod; and a hold-down device, the hold-down device including: a hold-down cylinder; a pressure chamber to provide a hold-down force and/or a position of the hold-down device; and a pressure accumulator, wherein the pressure chamber is continuously hydraulically connected to the pressure accumulator during a joining operation; and a differential cylinder with a piston chamber and an annular chamber to drive the axially movable piston rod, wherein the hydraulic unit includes a pump with reversible delivery direction, the pump being a 4-quadrant pump.

9. The joining device according to claim 8, wherein the piston chamber is connected to the hydraulic unit by way of a valve.

10. The joining device according to claim 8, wherein the pressure accumulator of the hold-down device is hydraulically connectable in a switchable manner by way of at least one valve with the hydraulic unit of the joining drive for the adjustment of a predetermined pressure in the pressure accumulator of the hold-down device.

11. The joining device of claim 8, wherein the hold-down cylinder is mounted to the axially movable piston rod, wherein the axially moveable piston rod and the hold-down cylinder limit the pressure chamber to provide the holding force.

12. The joining device according to claim 11, wherein the axially moveable piston rod has a radially protruding flange for providing a stop to limit an axial displacement of the hold-down cylinder.

13. The joining device according to claim 12, wherein the hold-down device has at least one cover that is detachably connected to the hold-down cylinder.

14. A method for operating the joining device of claim 8, the method comprising the steps of: detecting a pressure in the pressure accumulator or the pressure chamber; interrupting the joining operation dependent upon the detected pressure being a predetermined pressure; using the hydraulic unit of the joining drive for pressurization or pressure relief of the pressure chamber or the pressure accumulator for adjusting the predetermined pressure; and resuming the joining operation after adjusting the predetermined pressure.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein:

[0032] FIG. 1 illustrates an embodiment of a joining drive with controllable and/or adjustable hold-down device of the present invention;

[0033] FIG. 2 illustrates the hold-down cylinder with a pressure chamber; and

[0034] FIG. 3 illustrates the hold-down device with a hold-down cylinder.

[0035] Further advantageous forms of the invention are explained on the basis of design examples, with reference to the drawings. The features mentioned cannot only be advantageously implemented in the combination shown, but can also be combined individually with each other.

[0036] Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate embodiments of the invention and such exemplifications are not to be construed as limiting the scope of the invention in any manner.

DETAILED DESCRIPTION OF THE INVENTION

[0037] Referring now to the drawings, and more particularly to FIG. 1 which illustrates a joining device 1 with a joining drive 2 with a hold-down device 10. Joining drive 2 has a differential piston with a piston chamber 4 and an annular chamber 5. Piston chamber 4 is connected with a hydraulic unit 3 via a supply line 7. A valve 6 is provided in supply line 7. In the embodiment shown, a directional valve V.sub.3 is provided as valve 6, through which a connection of hydraulic unit 3 and piston chamber 4 can be established and separated.

[0038] Annular chamber 5 is connected to the hydraulic unit via a supply line 8. No valve is provided in this supply line 8. A position sensor 55 is provided for detecting the position of the piston. Pressure P.sub.A provided by the hydraulic circuit is detected by pressure sensor 52. Temperature T.sub.A of the hydraulic medium is recorded by a temperature sensor 51. Pressure sensor 53 is intended for detection of pressure P.sub.B in supply line 8 to annular chamber 5. Between valve 6 and the hydraulic unit, a hydraulic branch is provided to an accumulator 13 of hold-down device 10. In this supply line another valve, here directional valve 15, is arranged. Through this valve 15, the supply line can be switched from hydraulic unit 3 to accumulator 13 or pressure chamber 12 of hold-down device 10. Pressure P.sub.X in pressure chamber 12 of hold-down device 10 is detected by a pressure sensor 54. Temperature T.sub.X of the hydraulic medium can be detected by a provided temperature sensor 57. The position of the hold-down device or respectively hold-down cylinder 11 relative to punch 22 can be detected by looking at a position sensor 56. Accumulator 13 is connected to pressure chamber 12. By means of accumulator 13, it can be achieved that an almost constant pressure is applied in the pressure chamber regardless of the position of hold-down cylinder 11.

[0039] Hold-down force F.sub.X is generated by the hydraulic cylinder, also known as hold-down cylinder 11. The pressure for hold-down force P.sub.X is maintained in a pressure accumulator 13. The adjustability of the force is achieved by changing accumulator pressure P.sub.X. To adjust accumulator pressure P.sub.X, operating pressure P.sub.A, P.sub.B present on hydraulic actuator 20 is used for the joining process. The adjustment of the accumulator pressure occurs outside the joining processes. A differential cylinder is provided here as an actuator 20.

[0040] The hydraulic joining drive represents the linear movement on piston rod 21. As an alternative to the herein illustrated hydraulic actuator, an electromechanical drive with lifting spindle or a combination of both may also be provided.

[0041] A punch 22, shown in FIG. 2, also known as a joining punch 22, is attached to piston rod 21. Hold-down cylinder 11 is designed as a ring cylinder 11. The active movement (“downwards”) is limited by a flange 26 on joining punch 22. Likewise, the back movement of the hold-down device in the passive position is constraint by cylinder bottom 27 and flange 25. The hold-down force is generated by the pressure in pressure chamber 12, which is supplied via pressure connection 24.

[0042] A hold-down device 30 is attached on hold-down cylinder 11. In a downward movement of joining die 22, it initially impinges on a first metal sheet 32 as the first component 32, under which a second metal sheet 33 is arranged as the second component 33 to be joined. If joining punch 22 moves further toward the metal sheets 32 and 33 the pressure in pressure chamber 12 applies a force in the direction of metal sheets 32 and 33 onto hold-down cylinder 11 and hold-down device 30 attached thereto.

Force=ring surface*pressure in pressure chamber

Ring surface=(D.sub.I.sup.2*.sub.TT/4)−(D.sub.A.sup.2*.sub.TT/4) [0043] D.sub.I=inside diameter of the hold-down cylinder [0044] D.sub.A=outside diameter of the joining die

[0045] With hold-down device 30 mounted on the sheet metal, hollow rivet 31 is driven into sheet metals 32, 33 and establishes the joining connection. On the return stroke, joining punch 22 moves hold-down cylinder 11 again upward with flange 26.

[0046] Piston rod 21 of the rivet drive as joining drive 1 is driven by pressures P.sub.A and P.sub.B in pressure chambers 4, 5. The pressures are generated in hydraulic unit H with reference sign 3. Hydraulic unit 3 can be a throttle control with pressure generation and throttle valves, or a displacement control, in which a pump arrangement acts directly upon pressure chambers 4 and 5.

[0047] Sensor 55 measures position S.sub.A of piston rod 21 of rivet drive 2. Sensors 52 and 53 measure pressures P.sub.A and P.sub.B in pressure chambers 4, 5 of rivet drive 2. Sensor 51 measures temperature T.sub.A of the fluid in piston chamber 4. Additional pressure sensors and temperature sensors can detect additional conditions in the system. A CNC/PLC control unit that is not illustrated here collects the sensor signals and uses them for condition monitoring and to control the riveting process.

[0048] Hold-down cylinder 11 is arranged coaxially to joining punch 22 and moves with joining punch 22. The joining punch is attached to the active end of piston rod 21 and moves with piston rod 21. Thus, hold-down cylinder 11 also moves with piston rod 21. Pressure chamber 12 is supplied by pressure accumulator 13 with pressure C.sub.X. Hold-down cylinder 11 will be located at the lower stop, retained by flange 26. Pressure P.sub.X and temperature T.sub.X in pressure chamber 12 are measured with sensors 54, 57. Position S.sub.X of hold-down cylinder 11 relative to joining punch 22 can be measured with sensor 56.

[0049] In one embodiment, pressure chamber 12 can be connected via valve V.sub.1, reference sign 15, with line 7 to hydraulic unit 3. This first embodiment can be supplemented with a valve V.sub.3, reference sign 6, which can separate pressure chamber/piston chamber 4 from hydraulic unit 3.

[0050] In another embodiment, pressure chamber 12 can be connected via valve V.sub.2, reference sign 16 with line 8 to hydraulic unit 3. This second embodiment can correspondingly be supplemented with a valve V.sub.4 (not shown in the sketch), wherein pressure chamber/annular chamber 5 can be separated from hydraulic unit 3 by means of the valve.

[0051] In a further embodiment, as shown in FIG. 1, both valves 15 and 16 may also be provided.

[0052] By means of measuring position S.sub.X of hold-down cylinder 11, it can be detected at which position of piston rod 21 the system meets metal sheets 32, 33. With the known geometry/position of metal sheets 32, 33 and piston rod 21, process monitoring can take place. Incorrect sheet metal thickness or wrong number of metal sheets can be detected as well as damage to hold-down down cylinder 11/hold-down device 10, die 34 or joining punch 22.

[0053] According to the invention, instead of position signal S.sub.X, impingement of hold-down cylinder 11 on metal sheet 32 can also occur through observing pressure signal P.sub.X. The impingement of hold-down cylinder 11 will result in a small but detectable pressure increase in pressure chamber 12 of the hold-down device.

[0054] Observation of pressure P.sub.X is advantageous compared to observation of pressure P.sub.A, because the range of force of hold-down device 10 amounts to only 5 to 20% of the range of force of rivet drive/joining drive 2. Thus, sensor 54 has a higher resolution in the range of smaller forces compared to pressure sensor 52 of the piston chamber, which benefits the accuracy of the detection. For example, when measuring the sheet metal thickness indirectly using this method, it is desirable to be able to reliably detect possible small impact forces.

[0055] The method for adjusting pressure P.sub.X and for operating the hold-down device is briefly described below.

[0056] The method is described for the first of the above embodiments having a joining device 1 with valve 15. Valve 15 is activated so that pressure chambers 4 and 12 are connected. Hydraulic unit 3 is now controlled in such a way that the desired pressure is set in P.sub.A and P.sub.X. For this setting, one of the pressure sensors 52, 54 can be used to measure pressure P.sub.A or P.sub.X. During this process, the piston rod of the joining drive can move out if the P.sub.X pressure to be set is correspondingly large. After the desired pressure is reached, valve 15 is deactivated and the pressure chambers of piston chamber 4 and pressure chamber 12 are separated again. Set pressure P.sub.X in pressure chamber 12 of hold-down device 10 is held by accumulator 13. Hydraulic unit 3 can now be used to control the joining drive, while hold-down device 10 provides the desired hold-down force. Changes in P.sub.X pressure due to temperature fluctuations T.sub.X or leaks are disadvantageous. These can be detected during operation of the rivet drive by sensor 54 or 57.

[0057] In particular, as soon as a tolerance limit for P.sub.X is exceeded, the continuous riveting process can be paused and with the described method, pressure P.sub.X in accumulator 13 can be tracked back to the required value.

[0058] In some cases, movement of piston rod 21 during pressure adjustment may be detrimental and should be avoided. In such cases, by providing valve 6 piston chamber 4 may be separated from hydraulic unit 3, by bringing valve 6 into the closed position. Only then is valve 15 opened. Subsequently, the pressure in pressure chamber 12 is set by hydraulic unit 3 or the adjustment of the pressure in the pressure chamber 12 is concluded. After hydraulic unit 3 has set the pressure in accumulator 13/pressure chamber 12 and valve 15 has been closed, valve 6 can be opened again, in order to control the desired movement of piston rod 21 with hydraulic unit 3. Valve 6 is deactivated in the open position, wherein valve 15 is deactivated in the closed position. Thus, no active switching of either of these valves is required during the riveting operation.

[0059] The method described can also be applied in a second arrangement in which pressure chamber P.sub.X is not connected via valve 6 to piston chamber 4 but is connected via a valve 16 with annular chamber 5. If a movement of piston rod 21 is to be avoided during the pressure adjustment, an additional valve V4 can separate annular chamber 5 from hydraulic unit 3 and pressure chamber 12 during the pressure adjustment.

[0060] Since the pressure chamber is limited by the punch together with the hold-down cylinder of the hold-down device, reference should have been correctly made to the hold-down unit. The hold-down unit consists of the hold-down device and punch 22. Depending on the axial longitudinal expansion of the punch, the hold-down device can also be arranged in the area of piston 21, deviating from the illustration shown, wherein then the axial length of hold-down device 30 is to be adjusted. See FIG. 3.

[0061] While this invention has been described with respect to at least one embodiment, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.

Component Identification Listing

[0062] 1 Joining device=joining drive+hold-down device [0063] 2 Joining drive [0064] 3 Hydraulic unit [0065] 4 Piston chamber [0066] 5 Annular chamber [0067] 6 Valve piston chamber [0068] 7 Supply line piston chamber [0069] 8 Supply line annular chamber [0070] 10 Hold-down device [0071] 11 Hold-down cylinder [0072] 12 Pressure chamber [0073] 13 Pressure accumulator [0074] 14 Hydraulic supply line [0075] 15 Valve pressure accumulator—supply line piston chamber [0076] 16 Valve pressure accumulator—supply line annular chamber [0077] 17 1. Cover; cover on the joining drive side [0078] 18 2. Cover; cover on workpiece side [0079] 20 Cylinder of rivet drive, hydraulic actuator [0080] 21 Piston rod of rivet drive [0081] 22 Joining punch [0082] 24 Pressure connection, supply line pressure chamber [0083] 25 Flange on the joining punch [0084] 26 Flange on the joining punch [0085] 27 Cylinder bottom of hold-down cylinder [0086] 30 Hold-down device [0087] 31 Hollow rivet [0088] 32 First component [0089] 33 Second component [0090] 34 Die [0091] 51 Temperature sensor (piston chamber) [0092] 52 Pressure sensor P.sub.A (piston chamber) [0093] 53 Pressure sensor P.sub.B (annular chamber) [0094] 54 Pressure sensor P.sub.X (hold-down device) [0095] 55 Position sensor S.sub.A (piston rod) [0096] 56 Position sensor S.sub.X (hold-down device) [0097] 57 Temperature sensor T.sub.X