Drawing press with dynamically optimized blank holding

Abstract

The drawing press (10) according to the invention has for driving its ram (15) a directionally reversing gear mechanism (22, 54), for example a coupling gear mechanism, and at least one servomotor (23). The servomotor (23) passes through the reversal point (Ut) of the ram movement, which is predetermined by the kinematics of the coupling gear mechanism, for example the extended position of an eccentric drive. During the closing of the die (18), that is to say during a press stroke, the servomotor (23) is activated in such a way that it first passes through this reversal point (Ut), then stops, reverses and then passes through it once again, in order to open the die (18) again. Consequently, the braking to a standstill and re-acceleration of the servomotor for the upper ram (15) takes place while the actual drawing operation is still or already being performed, i.e. during the forming of the metal blank, which significantly reduces the cycle time.

Claims

1. Drawing press (10) comprising: a press frame, a ram (15) provided for accommodating a matrix tool (18) for deforming a blank (20), said ram (15) being supported in a manner so as to be adjustable in an adjustment direction (16), the matrix tool (18) comprising a rim (19) for contacting a rim of the blank (20) and a lower contour into which the blank (20) is to be deformed, a blank holder (35) opposite the ram (15), said bank holder abutting against an abutment (47) and configured to cooperate with the rim (19) of the matrix tool (18) to clamp the rim of the blank; a ram drive (22) comprising at least one servomotor (23) connected to the ram via a coupling gear mechanism (25) or a cam mechanism (54), said coupling gear mechanism or cam mechanism having a reversal point (U.sub.t) corresponding to a lower dead center position of said ram (15) resulting in the rim (19) of the matrix tool (18) clamping the rim of the blank against the blank holder, a table (31) for accommodating a punch tool (34) with an upper contour for cooperating with the lower contour of the matrix tool (18) for deforming the blank (20), said table being associated with a table drive (36) in order to move said table back and forth in the adjustment direction (16), wherein the ram (15) in accordance with the ram drive (22) is configured to: (1) in a single press stroke with the at least one servomotor (23) running and the matrix tool (18) closed to clamp the rim of the blank (20) against the blank holder (35), passes the reversal point (U.sub.t) at least in two chronologically spaced apart points in time TA and TB; (2) in a single press stroke a directional reversal of the ram (15) is performed between the points in time TA and TB via the at least one servomotor (23); and, (3) in a single press stroke the ram (15) is lifted from the reversal point (U.sub.t) by a small amount with the matrix tool (18) still closed until the at least one servomotor (23) is reversed at a point of time TC located between the points in time TA and TB and then moves downward again in order to pass the reversal point (U.sub.t) of the second point of time TB; wherein the ram drive (22) is configured to in a single press stroke to not stop the at least one servomotor (23) at the points of time TA and TB, but the at least one servomotor (23) continues to rotate and decelerates after the ram (15) has passed through the reversal point (U.sub.t) at time TA and accelerates at the point of time TC before the ram (15) passes the reversal point (U.sub.t) at time TB; and wherein the table drive (36) assigned to the punch tool (34) is configured to start when the reversal point (U.sub.t) of the ram (15) and the matrix tool (18) is reached for the first time, the punch tool (34) in accordance with the table drive (36) is configured in a single press stroke to perform a drawing operation of the blank (20) between the points in time TC and TB and not between the points of time TA and TB.

2. Drawing press as in claim 1, characterized in that the coupling gear mechanism is an eccentric gear mechanism.

3. Drawing press as in claim 1, characterized in that the abutment (47) is stationarily arranged on the press frame.

4. Drawing press as in claim 1, characterized in that the abutment (47) and the rain (15) are arranged so as to be resilient relative to each other.

5. Drawing press as in claim 1, characterized in that the abutment (47) is associated with an adjustment drive (48) in order to regulate the blanking holding force.

6. Drawing press as in claim 1, characterized in that the table drive (36) comprises a gear mechanism (25, 38) with at least one rest position in which the gear mechanism does not transfer movement to the table.

7. Drawing press as in claim 6, characterized in that the gear mechanism (25, 38) for the table drive (36) is a coupling gear mechanism.

8. Drawing press as in claim 7, characterized in that the coupling gear mechanism is an eccentric gear mechanism.

9. Drawing press as in claim 8, characterized in that the table drive (36) comprises at least one servomotor (40, 41) that is configured to go in reverse.

10. Drawing press as in claim 9, characterized in that the table drive (36) comprises an eccentric gear mechanism whose eccentric (42) is configured to move through an angle of rotation smaller than 90 degrees during one press stroke.

11. Drawing press as in claim 1, characterized in that the press frame comprises a head (13), a table (31) and interposed stands (11, 12).

12. A method for deep-drawing a sheet metal part, in particular a vehicle body part, with the use of a drawing press (10) comprising a ram (15) for the accommodation of a matrix tool (18), said matrix tool (18) comprising a rim (19) for contacting a rim of the sheet metal part (20) and a lower contour into which the sheet metal part (20) is to be deformed, a blank holder (35) opposite the ram (15), said bank holder abutting against an abutment (47) and configured to cooperate with the rim (19) of the matrix tool (18) to clamp the rim of the sheet metal part (20); said ram being movable between an open position and a closed position using a ram drive (22) comprising at least one servomotor (23) connected to the ram via a coupling gear mechanism (25) or a cam mechanism (54), said coupling gear mechanism or cam mechanism having a reversal point U.sub.t corresponding to a lower dead center position of the ram (15) resulting in the rim (19) of the matrix tool (18) clamping the rim of the sheet metal part (20) against the blank holder (35), wherein the ram (15) reaches and passes through its lower dead center position defining the closed position, wherein a servomotor driving said ram is decelerated and reversed after passing through the reversal point U.sub.t in order to move the ram (15) after its renewed passage through the dead center position, again into its open position through the reversal point U.sub.t; wherein the servomotor (23) performs a directional reversal of the ram (15) between points in time TA and TB defining two chronologically spaced apart points in time when the ram (15) passes through the reversal point U.sub.t during a single press stroke of the ram (15) with the servomotor (23) running and the matrix tool (18) closed to clamp the rim of the sheet metal part (20) against the blank holder (35), wherein the ram (15) is lifted from the reversal point U.sub.t by a small amount with the matrix tool (18) still closed until the servomotor is reversed at a point in time TC located between the points in time TA and TB and then moves downward again in order to pass the reversal point of time TB; wherein the servomotor then accelerates the ram through the reversal point Ut of time TB; and wherein the servomotor (23) is not stopped at the points of time TA and TB, but continues to rotate and decelerates after the ram (15) has passed through the reversal point at TA and accelerates at the point of time TC before the ram has passed the reversal point at TB; and wherein a table drive assigned to a punch tool is started when the reversal point Ut of the ram and the matrix tool is reached for the first time, the punch tool in a single press stroke performing a drawing operation of the sheet metal part between the points in time TC and TB and not between the points in time TA and TB.

Description

IN THE DRAWINGS

(1) FIG. 1a schematized representation of the drawing press, with the tool open;

(2) FIG. 2the press as in FIG. 1, at the start of a drawing operation;

(3) FIG. 3the press as in FIG. 1, at the completion of a drawing operation;

(4) FIG. 4a schematized representation of a modified embodiment of the drawing press in accordance with the invention;

(5) FIG. 5a modified drive that can act as the ram drive or, alternatively, also as the table drive, in the drawing press in accordance with the invention;

(6) FIG. 6another modified drive that can act as the ram drive in the drawing press in accordance with the invention;

(7) FIG. 7distance vs. time curves of the ram drive.

DETAILED DESCRIPTION OF THE INVENTION

(8) FIG. 1 shows a drawing press 10 that can be used for the manufacture of large sheet metal components, for example, vehicle body parts. The drawing press 10 comprises a press frame that is supported by at least one, preferably several, vertically oriented stands 11, 12, a head 13, said head being supported by the stands 11, 12, and by a pedestal 14 that is located under or between the stands 11, 12. The head 13, the stands 11, 12 and the pedestal 14 form a closed frame. In said frame, a ram 15 is supported so as to be linearly movable, e.g., in vertical moving direction 16. Linear guides 17 provided on the stands 11, 12, for example, are disposed for bearing the ram 15.

(9) The ram 15 is disposed for the accommodation of an upper tool component that is configured as the matrix tool 18. Said ram is shown in a sectional view in FIG. 1 and has a rim 19 that is disposed for clamping and holding in place the rim of a workpiece during the drawing operation. The workpiece is a blank 20, i.e., an initially plane metal sheet. The rim 19 circumscribes the hollow space 21 of the tool into which the workpiece is to be formed.

(10) A ram drive 22 is disposed for driving the ram 15, said ram drive comprising one or also more servomotors 23, 24 that are connected with the ram 15 via one or more gear mechanisms 25, 26. The two gear mechanisms 25, 26 are coupling gear mechanisms of a suitable design. In the present exemplary embodiment, eccentric gear mechanisms designed so as to be mirror-symmetrical with respect to each other are used as an example. Each of said eccentric gear mechanisms comprises an eccentric 27, 28 that is coupled with the ram 15 via an eccentric rod 29, 30.

(11) Furthermore, the drawing press 10 comprises a press table 31 on which may be arranged a mobile table 32. In a manner known per se, the mobile table 32 is disposed for the change of tools. The mobile table 32 carries the lower tool part that comprises a tool support 33 with a punch tool 34 arranged thereon, and a blank holder 35. The punch tool 34 is a male mold whose upper contour matches the hollow space 31. In most cases, this male mold is enclosed by the rectangular blank holder 35, in which case the blank holder 35 and the punch tool 34 can be moved relative to each with respect to the moving direction 16.

(12) The unit comprising the punch tool 34, the tool support 33, the mobile table 32 and the press table 31 is seated on a table drive 36 that can be moved in moving direction 16 (see the appropriate arrow) in the direction toward the ram 15 and away from said ram. The press table 31 and its table drive 36, respectively, can be linearly moved in moving direction in the press frame on the stands 11, 12 and/or on the pedestal 14 by means of guide arrangements. The table drive 36 comprises one or more gear mechanisms 38, 39 that are configuredlike the gear mechanisms 25, 26as coupling gear mechanisms. They comprise a blocking position. For example, they are configured as eccentric gear mechanisms that bring the press table 31 into driving connection with one or more servomotors 40, 41. Each of the gear mechanisms 38, 39 comprises an eccentric 42, 43 that is connected with the press table 31 via an eccentric rod 44, 45.

(13) Via suitable abutment elements, for example in the form of setbolts 46, the blank holder 35 abuts against an abutment 47. In the simplest case, the abutment 47 may be arranged stationarily relative to the pedestal 14. Alternatively, said abutment may be in connection with an adjustment device 48 that is able to adjust the position of the abutment 47 relative to the moving direction 16, for example. Usually, this is accomplished in load-free state. However, the adjustment device 48 can also be configured in such a manner that it can adjust the abutment 47 under load, for example in order to affect or regulate the force acting on the blank holder 35 and thus on the drawing edge of the workpiece, in a targeted manner. The adjustment device 48 may be hydraulic cylinders, toggle mechanisms, spindle-type lifting gears or the like. Linear guides 49 may be provided between the abutment 47 and the table drive 36, said linear guides being oriented in moving direction 16.

(14) The in so far described drawing press 10 operates as follows:

(15) First, the drawing press 10 is in open position. To do so, the ram 15 is moved into an upper position by an appropriate rotation of the eccentrics 27, 28. The press table 31 is moved into a lower position by an appropriate rotation of the eccentrics 42, 43. Consequently, the punch tool 34 projects slightly or not slightly beyond the blank holder 35. An essentially flat blank 20 can be placed on the blank holder 35.

(16) As soon as the workpiece transport means such as, for example, feeders, suction spiders or other grippers, these not being specifically shown here, have been moved out of the tool space it is possible for the tool to close. To do so, the drawing press 10 is moved into the position depicted by FIG. 2. The servomotors 23, 24 that are not specifically shown here have moved the eccentrics 27, 28 far enough that the ram 15 reaches its lower reversal point U.sub.t for the first time. Just before reaching the lower reversal point Ut, the rim 19 of the matrix tool 18 is seated on the rim of the blank 20 and starts to press said blank against the blank holder 35. Via the abutment elements 46, the blank holder 35 rests in an unyielding manner on the abutment 47, so that now the press frame is tensioned in moving direction 16. Interacting with the adjusted position of the blank holder 35, the spring constant of said press frame determines the clamping force acting on the rim of the blank in a highly precise manner.

(17) Once the lower reversal point U.sub.t of the ram 15 and thus the tensioned position of the matrix tool 18 has been reached at a point in time TA (FIG. 7, curve I), the servomotors 23, 24 are completely, or at least partially, load-free. The blank holding force is supported by the head 13 via the eccentric rod arrangement of the gear mechanism 25 and 26 that is in extended position. No energy is used for maintaining the holding force acting on the rim of the blank 20. In addition, there is no energy exchange between the ram drive and any drawing cushion.

(18) As they approach the reversal point U.sub.t the servomotors 23, 24 begin to decelerate, move through the reversal point U.sub.t and then stop, as can be inferred from the diagram of FIG. 7, curve I. Thus, the ram 15 performs a barely noticeable movement away from the reversal point U.sub.t after having moved through the point in time TA. The servomotors 23, 24 then stop at the point in time TC and immediately, or shortly thereafter, reverse their direction of rotation in order to again move through the reversal point U.sub.t. This takes place at the point in time TB. Preferably, the gear mechanisms 38, 39 reach their extended positions exactly at this point, thus marking the completion of the drawing operation. From hereon in, the opening movement of the matrix tool 18 begins in that said matrix tool moves away from the reversal point U.sub.t with the servomotors 23, 24 already rotating, said servomotors having already been pre-accelerated in the section of time between TC to TB. Therefore, the opening of the tool occurs very rapidly, i.e., at least more rapidly that would be the case if the servomotors were still at a standstill at the point in time TB.

(19) The same also applies already to the closing of the tool. The deceleration of the servomotors when the ram position is approaching the reversal point U.sub.t may occur delayed, relatively speaking, so thatdespite the potentially full deceleration power at point TAa stand-still of the motor is still not reached at point TA but only at point TC.

(20) Starting with the state at the point in time TA, the actual drawing operation is initiated via TC toward TB, the end of said operation being illustrated in FIG. 3. In order to perform the drawing operation, the servomotors 40, 41 are activated so that the eccentrics 42, 43 with their eccentric rods 44, 45 move into extended position and thus reach the top dead center of the table drive 36. In it, the punch tool 34 has been moved fully upward into the matrix tool 18. When the extended position is being approached, the gear reduction between the servomotors 41, 42 and the press table 31 moves toward infinite, so that the punch tool 34 is able to apply very high pressures to the workpiece.

(21) In continuation, the tool comprising the matrix tool 18 and the punch tool 34 is opened again after the point TB in thatwhile the blank holder 35 continues to be at restthe ram 15 is being moved upward and the press table 31 is being moved downward.

(22) FIG. 4 shows a schematized representation of a modified embodiment of the drawing press in accordance with the invention. The so far described drawing press 10 offers a concept that is suitable for the continued use of drawing tools that, until now, have been used in presses comprising drawing cushions located at the bottom. To do so, the press table 31 comprises a group of openings 61, 62, 63 which the abutment elements 46 can be optionally inserted. In so far, it is possible to use differently sized tools, said tools comprising blank holders 35 spanning different distances. This results in a geometrically variable force introduction for the blank holder 35. In addition, this offers increased latitude or convenience in tool design. The presented concept of operation comprising at least two passes of the reversal point U.sub.t, in one press cycle reduces the cycle time and increases the stroke rate and the output. Considering the presented press concept, numerous modifications are possible while maintaining the basic principle. For example, the ram 15 may be moved by the gear mechanisms 25, 26 in a drawing manner when the servomotors 23, 24 are arranged on the pedestal 14.

(23) Furthermore, the press table 31 in this as well as in all other embodiments can be driven by a single servomotor 40 if the toothed wheels of the eccentrics 42, 43 mesh with each other or if the eccentrics 42, 43 are connected to each other in another manner by suitable gear means. In addition, the eccentrics 42, 43 can optionally be configured as full circle wheels. This measure can also be used in the eccentrics 27, 28 and their toothed wheels, respectively.

(24) Furthermore, FIG. 5 shows a driving arrangement that can optionally be used as the ram drive 22, as well as the table drive 36. This drive also comprises a rest position when its connecting rods 52, 53 are in extended position. In this extended position, a rotation of the driving servomotor 23, 24 (or, correspondingly, 40, 41) does not effect anyor only an extremely minimallinear adjustment of the connected member, for example the ram 15. Forces acting thereon are supported in a straight line through the connecting rods 52, 53 on the machine frame, without loading the servomotors.

(25) FIG. 6 is a schematic representation of a gear mechanism 22 that is configured as a cam mechanism 54. Said mechanism also comprises a cam disk 55 driven by a servomotor 23 and comprises a cam follower 56, e.g., in the form of a roller following the cam circumference, and thus performs a linear back and forth movement that is prespecified by the different radii of the cam disk. To do so, the cam follower 56 is guided in a linear guide 57 and connected to the ram 15. The cam mechanism can produce the motion curve II of FIG. 7. For example, the cam disk 55 has one section 58 with a constant radius. This radius defines the reversal point U.sub.t.

(26) The above provided functional description applies, accordingly to the function of a press comprising this cam mechanism 54. In addition, the following applies: The servomotor 23 can be operated so as to be reversible and, alternatively, also so as to be continuously moving. Then the ram 15 moves into the reversal point U.sub.t and assumes this position at the point in time TA, the point in time TB and, optionally, the additional point in time, e.g., between TA and TB. In this phase, the blank holding force need not be provided by the rotating servomotor becausedue to the constant radius of the cam disk in section 58the forces acting on the ram 15 do not generate any torque. Depending on the design of the cam disk 55, the servomotor 23 can be operated at a constant rotational speed, at varying rotational speeds, with a constant direction of rotation or with changing directions of rotation. Also in this case no time is required for decelerating and accelerating the servomotor before and after the drawing operation. As has already been the case in the previous example using the eccentric gear mechanism, these acceleration phases can be moved into the time period of the drawing operation. Alternatively, at least in the embodiment of FIG. 6, it is possible to partially or completely dispense with the accelerating and decelerating operations.

(27) The drawing press (10) according to the invention has for driving its ram (15) a directionally reversing gear mechanism (22, 54), for example a coupling gear mechanism, and at least one servomotor (23). The servomotor (23) passes through the reversal point (U.sub.t) of the ram movement, which is predetermined by the kinematics of the coupling gear mechanism, for example the extended position of an eccentric drive. During the closing of the die (18), that is to say during a press stroke, the servomotor (23) is activated in such a way that it first passes through this reversal point (U.sub.t), then stops, reverses and then passes through it once again, in order to open the die (18) again. Consequently, the braking to a standstill and re-acceleration of the servomotor for the upper ram (15) takes place while the actual drawing operation is still or already being performed, i.e. during the forming of the metal blank, which significantly reduces the cycle time.

LIST OF REFERENCE SIGNS

(28) 10 Drawing press 11, 12 Stand 13 Head 14 Pedestal 15 Ram 16 Moving direction 17 Linear guide 18 Matrix tool; die 19 Rim 20 Blank 21 Chamber 22 Ram drive 23, 24 Servomotor 25, 26 Gear mechanism 27, 28 Eccentric 29, 30 Eccentric rod 31 Press table 32 Mobile table 33 Tool base plate 34 Punch tool 35 Blank holder 36 Table drive 37 Linear guide 38, 39 Gear mechanism 40, 41 Servomotor 42, 43 Eccentric 44, 45 Eccentric rod 46 Abutment elements 47 Abutment 48 Adjustment device 49 Linear guide 61, 62, 63 Openings 52, 53 Connecting Rod 54 Cam mechanism 55 Cam disk 56 Cam follower 57 Guide 58 Section