DD283085A5 - DOUBLE-ACTING PRESS FOR THE PULLING OF SHEETS - Google Patents

Abstract

The invention relates to a double-acting press for drawing sheet metal parts, with a hubreibreibbaren Blechhalterstoeszel and with a separate, also hubaufreibbaren Ziehstoeszel. In order to be able to set the blank holder force reproducibly and in a low-level manner individually and to keep it at the preset value, a servohydraulic blank holder force control is separately provided for each connecting rod of the blank holder. Each Blechhalterpleuel is associated with a piston / cylinder unit which determines the blank holder force. Via a pressure transmitter connected thereto or via a force plate integrated force transmitter, the force attributable to the associated area of the plate holder can be measured. The controlled pressure chamber of the piston / cylinder unit can be adjusted individually to the required pressure via a controlled system formed from a regulator and an electrohydraulically controllable proportional valve. This controlled system works low-inertia and largely hysteresis-free, so that even during a pressing cycle the setpoint for the blank holder force can be changed after a repetitive sequence of operations. For example, the regulated blank holder force can be raised or lowered individually during the drawing process. Fig. 8 {double acting press; Pull; Sheet metal parts; hub-drivable metal holder holder; lift-drive pull-toe; Blank holder force; connecting rods; servohydraulic plate holding force control; Piston / cylinder unit; Thrusters; Preszzyklus}

Description

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Double-acting press for drawing sheet metal parts Field of application of the invention

The invention relates to a double-acting press for drawing sheet metal parts "as used in industrial manufacturing practice"

Characteristic of the known state of the art

The joints between the blank holder and the drawing plunger on the one hand and the respective associated connecting rods are adjustable in height relative to the corresponding plungers and thus movably guided against the plungers) also at least in the sheet metal tappets between the connecting rod bearing and the plunger acted upon by hydraulic fluid piston / cylinder The force-determining pressure chamber of this piston / cylinder unit is set at a presettable constant pressure. Namely, a relatively low, controllable pneumatic pressure is proportionally proportional via a stepped piston having a very large area ratio between the small and large piston surfaces, acting as a pressure booster Thus, the force-determining pressure chamber of the piston / cylinder unit is also pneumatically controlled. The hydraulics are only used passively as pressure transmission medium; pressure adjustment is pneumatic at the low pressure level · The purpose of the interposed short-stroke piston / cylinder unit is to limit the transferable force to a presettable value) when the preset pressure or «force value is exceeded

Dodge the stepped piston on the low pressure side, causing the machine to switch off «

It is known that different sheet metal parts are produced with the generic presses in a temporal change · When converting the press from a first Blechpreßteil to another workpiece not only the pressing tool must be replaced «but it must also the adjustment data on the press on the new tool or the changing the workpieces «This changeover of the production data of the press is considerably more time consuming and costly. The actual changing of the tool" A lot of test dimensions have to be made before the press presses off the new workpiece in high quality with constant accuracy " Adjustment data for a specific workpiece or, * Tool accurately noted from an earlier production phase and adjusted accordingly for the new production process »are numerous, time-consuming and costly Trial

To this end, measurements may inevitably "contribute different influences _B, but not yet clearly understood and

could be isolated in its scope

Object of the invention

The aim of the invention is to increase the _r value in use properties of double-action presses of the generic type in a cost effective manner "

Explanation of the essence of the invention The object of the invention is »a double-acting press for

To design sheet metal parts in such a way that after being converted to a modified sheet metal part or to a corresponding tool, it can be adjusted to the changed production conditions in a more targeted and faster reproducible manner. In particular, such a conversion should be possible with far fewer sample samples than before «

This object is achieved in that * to the Bbchhalterkraf t determining pressure chamber each piston / cylinder unit, a pressure transducer or each belonging to a connecting rod area dee plate holder a attributable to this area of Blechhaltere proportion of Blechhalterkraft each detecting force transmitter is assigned. each generating a pressure or force value corresponding electrical signal «that for each pressure transducer or · force transmitter is assigned a similar signal donating setpoint generator is that farner each pressure transducer or« force encoder incoming the respective instantaneous actual signal and the associated target signal comparative controller assigned * is the each via a proportional valve and by means of a pressure source in accordance with the target / actual deviation, the pressure in the piston / cylinder unit in the sense of an immediate return to the setpoint increases, decreases or "keeps constant" Thanks to the immediate eervohydraulisch Regulation of the force-determining working chamber pressure in the interposed piston / cylinder unit of each blank holder can be precisely adjusted with high reproducing accuracy "Hyetereeefrei and inertia-free each required blank holder force" The servohydraulieche Etechhalterkraftregelung is eo exact, eo exactly reproducible and so low in inertia »that even within a pressing cycle the setpoint

can be changed depending on the stroke or crank angle depending on a presettable program «The blank holder force can

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optionally during the Preßvorgangee targeted targeted and reproducibly increased or lowered. In individual cases, this depends on the workpiece to be pressed and must be tried on a case-by-case basis *

It is advantageous * when the setpoint value for each individual controller during each press cycle can be varied depending on the stroke or crank angle depending on a repetitive pattern. Furthermore, it is advantageous if the force transmitter is designed in the form of strain gauges applied to supporting wall sections of the sheet metal holder. It is likewise advantageous if the wall at the point of the rotary measuring strip is locally deliberately weakened with low notch effect in the load bearing capacity Wall a pair of horizontally adjacent holes is mounted, which include between them a vertically standing, biconcave web; In addition, it is advantageous if at least on one side a cup-shaped depression is incorporated in the wall "on the smooth? flat "bottom" or the strain gauges is attached or "are"

embodiment

The solution according to the invention will be described below in several Ausfühn.ingsbeiepielen with reference to the accompanying drawings are explained in more detail.

It is a schematic sectional view of a double-acting press for drawing sheet metal parts ι

Fig. 2: an enlarged detail view of a section

through the piston-cylinder unit of the height-adjustable connecting rod bearing on the blank holder ram of the press according to Fig. 1;

Fig. 3: a horizontal section through the upper tool along the section line III - III;

4, cross-section (FIG. 4) and view (FIG. 5) through one and 5: bearing walls of the sheet-metal holder in the area of a force transmitter;

Fig. 6: the outside view of a load-bearing wall section

the sheet holder in the field of a modified design of a force transmitter;

Fig. 7: the hydraulic scheme for a servohydraulic blank holder force control using plate holder integrated force transmitters and

8: a modified hydraulic scheme using pressure sensors «

The double-acting press shown schematically in vertical section in FIG. 1 has a press stand 2 and a press table IO on which the lower tool 9 is fastened for the sheet metal part 1 to be pressed. In the press stand 2, a sheet metal support push rod 4 is guided vertically via the symmetrically arranged connecting rod The actual drawing ram 3 is arranged within the sheet metal holder, which is guided so as to be movable in a stroke relative to it and is separated by a plurality of likewise symmetrically arranged connecting rods 5

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Hubc.itreibbar is · At the blank holder ram 4, the blank holder 7 dee upper tool * and on the drawing ram 3 of the drawing punch 8 of the upper tool is attached «When going down

of the top tools sets first of the blank holder on the still unpressed on the lower die 9 resting board with a defined force; only when the edge of the board is clamped with a defined force «the drawing punch 8 comes into contact with the sheet metal part 1 and presses this under defined ^ slipping out of the sheet edge from the edge restraint in the die" Here, the extent of the blank holder force is of particular importance; For each individual workpiece, the blank holder force must be optimized on a case-by-case basis and kept as accurate as possible over all the pressing cycles. "With this aspect, the present invention deals in a special way" which will be discussed in more detail below. "

When passing the Blechhalterstößelo 4 and the pull-ram 3 through the bottom dead center, this must match the overall height of the lower tool 9 and upper tool. After this total height can turn out differently, a height adjustment is provided individually for the blank holder ram 4 and for the pull ram 3. In the illustrated embodiment, this simplifies shown in the form of a connecting rod bearing ", in the respective ram vertically movable Pleuellageretiefeis 12; Usually, this connecting rod bearing boot is not in the ram, but

In each case, an adjusting spindle 13 is arranged within the connecting rod bearing boot 12, which is in engagement with a nut thread attached to the lower end of the connecting rod bearing boot. The adjusting spindle in turn can be rotated by means of an adjusting spindle 13

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The worm wheel 28 in turn can be rotated defined by means of a worm gear, not shown, and a corresponding motor drive defined «At the lower end of the adjusting spindle 13 is the already mentioned above piston / Cylinder unit 11 attached "the between the corresponding piston and the surrounding cylinder includes a pressure chamber 14 which is provided with a corresponding fluid port. According to the spatial extension of the sheet holder 7 and the sheet holder ram 4 are a total of four connecting rods - there are only two, connecting rods 6 and 6 - 6 '- and four connecting rod bearings for the blank holder ram 4 provided »the different Umfangebereichen» the areas 17; 17 ";17"; Accordingly, each of these peripheries is a different piston / cylinder unit llj II ¹ , 11 "; II ^"1 assigned · It makes sense not to hold the edge clamping of the material to be pressed sheet metal around the entire circumference constant" but regionally also adjust lower blank holder force; this depends individually by the respective workpiece or "to this designed tool from · Also these things must individually Once this has been determined, however, thanks to the invention, the corresponding production parameters can be quickly adjusted again to exact reproducibility for lot sizes to be produced later.

To the blank holder force for each blank holder area »the areas 17; 17 '; 17 "and 17"'can be controlled exactly * without hysteresis and without inertia "is first of all in the embodiment illustrated in FIGS. 1 to 5 and 7, each hold-down area, the areas 17; 17 \\ 17 "; and 17"'each

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wells at least one separate, plate holder integrated force transmitter 15; 15 *; 15 "and 15" 'assigned. Namely, the force generators are formed by strain gauges 36, which are adhered to the surface of burdened by the blank holder force «wall sections of the sheet holder 7. As shown in FIGS. 5 and 7, integrated strain gauges with four strain resistors can be applied, in which the individual strain resistors are combined to form a Wheatstone bridge; Care must be taken here, however, that the individual bridge branches of the Wheatetone's bridge are either parallel or transverse to the power flow direction 37. In the embodiment shown in Fig. 4 and 5, each cup-shaped depressions 34 are incorporated on both sides of the supporting wall 35, the strain gauges 36 are attached to the smooth, flat "bottom". The depression 34 has the purpose of being able to push out the sensitive strain gauges from the area of the outer surface of the wall 35 and to be able to attach them in a protected and countersunk manner. On the other hand, the wall 35 is to be weakened locally targeted in the carrying capacity by the recess with low notch effect, so that the remaining disc-shaped central web is a kind of compression spring, which is deformed defined by the Blect age force. Another possibility of a locally targeted weakening of the wall 35, which shows only a slight notch effect, let shown in Fig. 6: there are horizontally juxtaposed two holes 32 which include between them a vertical ·, so in power flow direction 37 biconcave web 33 This web 33 also serves as a kind of compression spring which can be loaded by the blank holder force and whose deformation can be determined by the attached at the thinnest part of the web strain gauges 36 as a measure of the load · In itself, it would be conceivable «a separate force transmitter un-ter Press fit into a single box after

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On the other hand, however, have the worked out from the full of the wall 35 and equipped with strain gauges vulnerabilities, the advantage that there are no joints within the power flow, which would cause a hysteresis in the force measurement. The out of the full of the wall 35 force generator workers so completely hysteresis-free ¹ , which is important for the present application ·

The servohydraulic blank holder force control will be described below with reference to the hydraulic diagram according to FIG. 7. At the top in the illustration are the four piston / cylinder units 11 assigned to the different regions of the blank holder circumference; 11 '; 11 "and 11" · shown with the

different pressure chambers 14t 14 '; 14 "and 14" '. Also, the four different already mentioned force transmitter 15; 15 '; 15 "and 15" 'are shown there; they apply together from a single battery 38 fed and are in this respect parallel to each other. The Meßabgriffe the one Wheatstone bridge each representing expansion resistances of a force transmitter are led out separately for each force transmitter · Each individual piston / cylinder unit 11; 11 '; 11 "and 11". ' and each associated force transmitter 15; 15 '; 151 and 15 "'is in each case a controller 19; 19', 19" and 19 "'assigned * on whose input the Meßabgriff the force transducer 15 is connected Oedem said four controllers 19 is in each case a setpoint generator 18, 18', 18" and 18 "'assigned» whose output is also connected to the controller input · The force transmitter and the setpoint generator both emit a similar and comparable electrical signal «The controller 19 compares the reference signal with the actual signal and outputs at its output in accordance with the difference between the two a corresponding

Signal from, with which a control intervention can be made »which eliminates any detected target / actual deviation again · For this purpose, for each of the four control paths proportional valves 20; 20 '; 20 "and 20" "The proportional valves can initially be electrically pre-controlled by the controller via an electrohydraulic pilot valve. Hydraulically wdJtf the electro-hydraulic ^ pilot valve supplied from a control oil pump 21 »which sucks from a separate control oil sump 24; with regard to the sensitivity of the electro-hydraulic pilot valves this cycle is kept very clean, which is indicated by the filter 23. Oe the size of the control signal, the electro-hydraulic pilot valve is opened more or less strong and according to thee electrohydraulic amplification and the proportional valve 20 wehr or less strongly opened. With the proportional valves 20; · 20; 20 "and 20" · working oil in the force-determining pressure chambers 14; 14 '; 14 "or 14" 'pressed from a Oruckquelle or relieved to a Dlsumpf ** or it can be kept closed the relevant Oruckraum. The mentioned pressure source is formed by a Druckspetbher 25 and by a Arbeitsölpümpe * the work pump 22, the Jen corresponding pressure accumulator keeps constantly charged. It can therefore all four pressure chambers 14; 14 '; 14 "and 14" 'are pressure-controlled in such a way that the force transmitter 15; 15 '; If the blank holder force decreases in regions below the respective preset desired value, the proportional valve is opened in the direction of the pressure source and the pressure in the associated pressure chamber 14 is increased. If, on the other hand, the sheet metal holder force partially increases beyond the predetermined setpoint due to the malfunction, the proportional valve opens in the direction of the working oil sump, so that the pressure in the force-determining pressure chamber 14 is reduced.

If the predetermined blank holder force is reached again during such a control intervention, then the associated proportional valve returns to the illustrated middle blocking position; The pressure then prevailing in the force-determining pressure chamber 14 is maintained. These processes take place very quickly thanks to the relatively small quantities of control and working oil to be pumped. The controlled system is only very short and operates hysteresis-free world-wide, so that the control processes are also reproducible Blank holder areas, the areas 17; 17 * and 17 "17"'to protect against overloading, is the single servohydraulic control circuit with a pressure relief valve 26; 26 '; 26 ^H or "'provided With excessive pressure in the working line or · at the associated pressure space. 14; 14';14" · 26 and 14 "'on a pre-settable maximum value flows on the upper pressure valve 26, working oil from · This high pressure flowing working oil a common emergency stop switch 27 for all four upper pressure valves

be pressed, which shuts down the press.

The embodiment of the hydraulic scheme illustrated in FIG. 8 differs from that according to FIG. 7 in that, instead of force-insulated force transmitters, each individual force-determining pressure chamber 14; 14 '; 14 "and" 14 "'in each case a separate pressure transducer 16; 16 '; It converts the pressure signal into a corresponding electrical signal which is applied to the input of the associated controller 19; 19 '; Incidentally, the mode of operation of the hydraulic reactor according to FIG. 8 is quite analogous to the mode of operation of the scheme according to FIG. 1, with the difference that the blank holder force of a particular blank holder area, the areas 17; 17 '; 17 "and 17" ', but the pressure in the force-determining

the pressure chamber 14; 14 * j 14 "and 14" * is adjusted to a pre-set nominal value «

A further modification is also indicated in Fig. 8, the possibility of a crank angle-dependent change in the setpoint "on the stylized indicated crankshaft 29 of the press is an angle encoder 30 rngekoppelt» represents a the instantaneous threat position of the crankshaft 29 corresponding electrical signal outputs «This is to four different function generator 31; 31 *) 31 "or 31 ^M> These function encoders are designed in such a way that a different function value can be output depending on the crank angles" with which the associated setpoint value generator 18; 18V; 18 "or" 18 "'are changed "Thanks to the rapid start of the controlled system, this can also be followed relatively quickly by changing the setpoint setting during the stroke." For example, in the individual sheet-metal holding areas, the sheet-metal holding forces can be increased within the range of 17, 17 *, 17 "and 17" * can be lowered "as needed" The individual function transmitters 31, 31 ', 31 "and 31"' can - after they have been optimized individually for a particular workpiece - taken out

and against other function transmitters that have been optimized for another workpiece »exchanged« This replacement of the function encoders can be effected by switching over to a control unit »where all functional encoders optimized for different workpieces are installed in groups and kept in standby«

Claims (6)

Berlin »19.1 * 1989 AP B 21 D / 320 865-1 71 288/25/39 Claims 1. Double-acting press for drawing sheet metal parts, with a guided in Preseenständer »hubretriebe symmetrically arranged connecting rod, the blank holder of a tool carrying blank holder ram and arranged with a within the blank holder ram« hubbewegetrieben relative to him and the hub hubbewegetrieben «the drawing punch of the same tool supporting Drawing plunger, further with one in the power flow between each of the connecting rods and the sheet holder mounted piston / cylinder unit, the transferable force-determining pressure chamber with a separately controllable for each piston-cylinder unit fluid pressure can be acted upon, characterized in that the Sheet metal holder force determining pressure chamber (14; X4n 14 "ι 14" *) each piston / cylinder unit (11; 11 ·; 11 "; JLlV) a pressure transducer (16; 16 ';16"; 16 "*) or one to one Connecting rod (6; 6 ') belonging portion (17; 17 ·; 17 ";17" *) of the accountant (7) on this area (17; 17 ', 17 ", 17"') of the sheet-metal holder, (7) proportion of the sheet-metal holder force respectively detecting force transmitter (15; 15 '; 15 ";15"'), each of which generates an electrical signal corresponding to the pressure or "force value" that for each pressure transducer (16; 16'; 16 ";16"') or force transmitter (15; 15'; 15 ";15" \) is associated with a setpoint generator (18, 18 ', 18 ", 18" *) emitting a similar signal "that, in addition, each pressure transmitter (16, 16', 16", 16 "') or force transmitter (16; 15, 15 ', 15 ", 15"') are assigned in each case the instantaneous actual signal and the associated reference signal of comparative controllers (19, 19 ', 19 ", 19"') which are each connected via a proportional valve (20, 20 '; 20 ", 20" *) and by means of a pressure source as required ZfSOtS the target / actual deviation increases the pressure in the piston-and-blind unit (11), and in the sense of a reversed return to the desired value increases it or keeps it constant. 2, press according to claim 1, characterized in «, that the setpoint value for each individual controller (19; 19 '; 19" j 19 "') is variable depending on the stroke or crank angle during each press cycle, in each case after a repetitive mueter. 3 · Press according to claim 1 or 2> characterized in that the force transmitter (15j 15 * j 15 "" 15 "') in the form of on carrying wall sections of the sheet holder (7) applied strain gauges (36) auegebildet is · Press according to claim 3, characterized in that at the location of the strain gauge (36) the wall (35) is weakly weakened locally with a low notch effect in the load bearing capacity. Press according to Claim 4, characterized in that in the wall (35) a pair of bores (32) lying horizontally next to one another is provided, which enclose between them a vertical biconcave web (33) at its thinnest point the strain gauges (36) are attached or are « 6 · Press according to claim 4 _9, characterized in that in the wall (35) at least on one side a cup-shaped recess (34) is incorporated on the smooth 'flat ^M floors ⁿ or the strain gauges (36) is mounted or S Su'kt ^ Icicle uUU