EP2813357A1 - Overload release device in a servo press - Google Patents

Abstract

The invention relates to a mechanical press for molding processes of molded parts, with an upper and a lower tool, which form a mold for the molding between them, and a hydraulically assisted drive for the upper tool and / or the lower tool between a top dead center and a bottom dead center , characterized in that an overload protection for lowering the hydraulic pressure for applying a pressing force to the upper tool and / or the lower tool is provided at least at the bottom dead center, and that a release device for targeted and preferably continuous lowering of the hydraulic pressure over a predetermined time and below a predetermined threshold is provided, wherein the release device is operable so that the structure of the hydraulic pressure for applying the pressing force from the threshold value to the nominal pressing force in the passage of the press from bottom dead center to top dead center is effected.

Description

1. Field of the invention

The invention relates to a mechanical press for molding processes of molded parts with a top and a bottom tool, which form a mold for the molding between them, and a hydraulically assisted drive for the upper tool and / or the lower tool and for movement between a top dead center and a bottom dead center and a method for molding of moldings in such a mechanical press.

2. State of the art

Mechanical presses, usually equipped as a servo eccentric with an electric drive or toggle presses with hydraulically assisted power transmission for at least one of the tools, are designed for various molding processes, such as embossing metallic bodies, mold hardening or even the production of composite and hybrid materials. Particularly in the automotive sector, the development of new lightweight technologies has progressed in recent years. In order to connect new material combinations economically, many different combinations of molding processes are used. As well as the resulting material properties Depending on the joining method used, one usually distinguishes mechanical, thermal and hybrid bonding techniques.

The number of materials used in lightweight construction also increases from year to year. While component production used to be limited mostly to steel or aluminum joints, the material range was expanded, in particular, with magnesium, plastic and a variety of fiber composites. Thus, in addition to the combination of dissimilar metallic, the connection of plastic material with metal plays a major role. These so-called hybrid or multi-material materials require precisely adapted joining technologies for their field of application in order to fully exploit their desired properties.

Mechanical presses generate the forming forces required for the molding process with appropriate design of frame and drive, wherein the pressing force on the upper and / or lower tool is performed periodically depending on the rotational speed of the flywheel used in the press. The stroke adjustment in turn takes place by means of a rotatable eccentric bushing between the eccentric pin and the connecting rod, and additionally by a plunger adjustment of the bottom dead center. Mechanical presses of the type in question, used for example in stamping machines, reach a maximum stroke rate of about 1500 strokes per minute.

However, there is also a need in certain molding processes to keep the press closed for a predetermined period of time while cooling the molding, for example in the mold, or molding a hybrid part. Forming processes of this type have hitherto been carried out with hydraulic presses and not with mechanical presses of the type mentioned at the outset, since such a shaping process entails the departure from the continuous periodic work process.

Mechanical presses, for example designed as eccentric and toggle presses, are usually designed as servo presses in which the drive of the tool (s) is electrically assisted. The pressing force is applied by means of a hydraulic system. The principle of operation of such mechanical presses usually provides a continuous forming process without interruption at bottom dead center, in which the forming tools are closed and the nominal pressing force is applied. At least, however, such mechanical presses only have an extremely short residence time in the area of bottom dead center.

In eccentric presses in particular, however, this leads to great problems due to unfavorable friction conditions in the dead center of the eccentric, since, after prolonged staying in the bottom dead center, poor friction conditions occur, in particular due to squeezing out of the lubricating oil from the bearing point. A start from the dead center under nominal pressing force is ultimately almost impossible and almost inevitably leads to damage in the usually hydrodynamic bearings of these presses.

Hydraulic overload devices on presses are already known from the prior art for this purpose, by means of which it is possible to abruptly reduce the pressure in the hydraulic cylinder (s). Such a hydraulic overload protection is usually provided for the bottom dead center mechanical servo presses. Hydraulic overload devices are for example in the DE 10015785 A1 , of the DE 3810490 C2 , of the DE 4436742 A1 , of the DE 19643104 A1 , of the EP 0114170 B1 , of the DE 4036470 A1 , of the GB 2235404 A or the DE 19805519 C1 disclosed.

A disadvantage of such hydraulic overload protection devices, however, is that, according to their purpose, they abruptly reduce the pressure in the hydraulic cylinder, whereby it is not possible to keep molded parts under defined press force ratios over a defined period of time within the mold and if necessary to cure, shape and / or cool under precisely defined conditions.

3. Object of the invention

It was therefore an object of the invention to provide a mechanical press, which allows a controlled relaxation of the press, thus reducing the pressing force at the bottom dead center. This object of the invention is achieved with a mechanical press comprising the features of claim 1. Advantageous embodiments of the invention are laid down in the dependent claims.

4. Summary of the invention

According to the invention, an overload protection for lowering the hydraulic pressure for applying a pressing force to the upper tool and / or the lower tool at least at the bottom dead center, but preferably at the bottom dead center, is provided on the device side. This overload protection is in operative connection with at least one release device for targeted and preferably continuous lowering of the hydraulic pressure over a predetermined time and below a predetermined threshold. As "bottom dead center" in the context of the invention, the dead point is understood in which the pressing tool is completely closed, but at least provides a minimum distance between the tool parts. According to the invention, the release device is designed and operable such that the structure of the hydraulic pressure for applying the pressing force from the threshold value to the nominal force in the passage of the press from bottom dead center to top dead center can be effected.

As a result, the object of the invention to ensure a targeted release of the press by reducing the pressing force at least at the bottom dead center by means of the hydraulic overload protection, solved by simple means. This makes it possible that mechanical presses can be used in applications that were previously reserved for hydraulic presses. In particular, the production of composite and hybrid materials in which a persistence of the press at bottom dead center over a predetermined time and possibly also applying a predetermined pressing force is required, can with the invention using a mechanical press of the type in question be realized.

It is preferred if the drive for the upper tool and / or the lower tool comprises at least one eccentric and / or a toggle lever. As a result, the desired nominal pressing force is applied specifically to the molded part with particularly simple and controllable means, it being particularly preferred if the force distribution on the lower and / or upper tool is applied symmetrically or asymmetrically as required by a toggle lever arrangement or the use of several eccentrics becomes.

In a further preferred embodiment of the invention, the predetermined threshold under which the hydraulic pressure is lowered over a predetermined time, adjusted so that no more than 10% of the nominal pressing force can be achieved, preferably the nominal pressing force at bottom dead center and after completion of the lowering process at least almost zero is.

It is also preferred if the predetermined time over which the hydraulic pressure is lowered by means of the overload safety device and the release device is at least one second, preferably at least three seconds. hereby the desired slow and controlled lowering of the hydraulic pressure is achieved particularly advantageous.

In the mechanical press according to the invention, the release device is operable so that the structure of the hydraulic pressure for applying the pressing force from the threshold value to the nominal pressing force in the passage of the press from bottom dead center to top dead center is effected. Thus, a mechanical press is provided which provides the nominal pressure force at least from reaching the top dead center again without delay, whereas the process of the press from bottom dead center to top dead center, in which the provision of the nominal pressing force is not mandatory, the structure of the nominal press force of the threshold, preferably close to zero. It is thus obtained a mechanical press, in which the cycle times or the stroke speed can be optimally adjusted.

Process side, the invention is operable by a method comprising the steps of separating upper and lower tool at top dead center of the press, the introduction of the molding or its starting materials in at least a part of the mold, the driving of the press to its bottom dead center, the residence of the press at bottom dead center for a predetermined time, the targeted reduction of the pressing force by lowering the hydraulic pressure and the driving of the press to its top dead center, in which case the biasing pressure is specifically increased.

It is particularly preferred if at the bottom dead center, the nominal pressing force is applied to the molding at least over a predetermined period of time and then selectively the hydraulic pressure for applying the pressing force is reduced.

It is particularly preferred if the targeted reduction of the pressing force at the bottom dead center takes place only after a predefined time interval of preferably more than two seconds, in particular more than three seconds. This ensures that under defined conditions with respect to the applied pressing forces and the time that the defined pressing forces act on the molding, there is sufficient time for cooling and / or curing and / or connection of the materials or moldings to be molded.

It is also preferred if the targeted and preferably continuous lowering of the hydraulic pressure takes place along a pressure curve, which is monotonically decreasing in the region of the lowering, preferably in a strictly monotonically decreasing manner. As a result, the targeted controlled lowering of the hydraulic pressure, of which the pressing force is directly dependent, achieved with particularly simple and easy to control means. The lowering of the hydraulic pressure is thus carried out over the entire process to below the predefined threshold under defined conditions and in particular while ensuring the predetermined minimum times both for maintaining the nominal pressing force or another predetermined pressing force, over a predetermined period, as well as for Lowering to below the threshold.

1. 1. Mechanische Presse für Formprozesse von Formteilen, mit einem Ober- und einem Unterwerkzeug, die zwischen sich eine Form für das Formteil ausbilden, sowie einem hydraulisch unterstützten Antrieb für das Oberwerkzeug und/oder das Unterwerkzeug zwischen einem oberen Totpunkt und einem unteren Totpunkt,
   dadurch gekennzeichnet, dass
   eine Überlastsicherung für das Absenken des Hydraulikdrucks zur Aufbringung einer Presskraft auf das Oberwerkzeug und/oder das Unterwerkzeug zumindest am unteren Totpunkt vorgesehen ist, und dass eine Lösevorrichtung zum gezielten und vorzugsweise kontinuierlichen Absenken des Hydraulikdrucks über eine vorab festgelegte Zeit und unterhalb eines vorgegebenen Schwellenwert vorgesehen ist.
2. 2. Mechanische Presse gemäß Absatz 1, dadurch gekennzeichnet, dass die Formprozesse das Prägen, Formhärten und/oder das Herstellen von Verbund-und Hybridwerkstoffen umfassen.
3. 3. Mechanische Presse gemäß einem der Absätze 1 oder 2, dadurch gekennzeichnet, dass der Antrieb für das Oberwerkzeug und/oder das Unterwerkzeug einen Exzenter und/oder einen Kniehebel umfasst.
4. 4. Mechanische Presse gemäß einem der voranstehenden Absätze, dadurch gekennzeichnet, dass der vorgegebene Schwellenwert höchstens 10% der Nennpresskraft, vorzugsweise zumindest nahezu Null, beträgt.
5. 5. Mechanische Presse gemäß einem der voranstehenden Absätze, dadurch gekennzeichnet, dass die vorab festgelegte Zeit mindestens 1 Sekunde, vorzugsweise mindestens 3 Sekunden, beträgt.
6. 6. Mechanische Presse gemäß einem der voranstehenden Absätze, dadurch gekennzeichnet, dass die Lösevorrichtung so betreibbar ist, dass der Aufbau des Hydraulikdrucks zum Aufbringen der Presskraft von dem Schwellenwert bis zur Nennpresskraft im Durchlauf der Presse vom unteren Totpunkt bis zum oberen Totpunkt bewirkbar ist.
7. 7. Verfahren zum Formpressen von Formteilen in einer mechanischen Presse gemäß einem der voranstehenden Absätze, gekennzeichnet durch die Schritte des Trennens von Ober- und Unterwerkzeug am oberen Totpunkt der Presse, des Einbringens des Formteils oder von dessen Ausgangsstoffen, des Fahrens der Presse bis zu deren unteren Totpunkt, des Verweilens der Presse im unteren Totpunkt für eine vorab festgelegte Zeit, des gezielten Abbaus der Presskraft durch Absenken des Hydraulikdrucks, und des Fahrens der Presse zu deren oberen Totpunkt, wobei hierbei der Vorspanndruck gezielt erhöht wird.
8. 8. Verfahren gemäß Absatz 7, dadurch gekennzeichnet, dass am unteren Totpunkt die Nennpresskraft auf das Formteil aufgebracht wird.
9. 9. Verfahren gemäß einem der Absätze 7 oder 8, dadurch gekennzeichnet, dass der gezielte Abbau der Presskraft am unteren Totpunkt erst nach einem vorab festgelegten Zeitintervall von vorzugsweise mehr als 2 Sekunden, insbesondere mehr als 3 Sekunden, erfolgt.
10. 10. Verfahren gemäß einem der Absätze 7 bis 9, dadurch gekennzeichnet, dass das gezielte und vorzugsweise kontinuierliche Absenken des Hydraulikdrucks entlang einer Druckkurve erfolgt, die im Bereich des Absenkens monoton fallend, vorzugsweise streng monoton fallend, ist.

The invention will be further defined in the following paragraphs, in which preferred embodiments are set forth.

1. 1. Mechanical press for molding processes of molded parts, with an upper and a lower tool, which form a mold for the molding between them, and a hydraulically assisted drive for the upper tool and / or the lower tool between a top dead center and a bottom dead center,
   characterized in that
   an overload protection for lowering the hydraulic pressure for applying a pressing force to the upper tool and / or the lower tool is provided at least at the bottom dead center, and that a release device for targeted and preferably continuous lowering of the hydraulic pressure over a predetermined time and below a predetermined threshold is provided ,
2. 2. Mechanical press according to paragraph 1, characterized in that the molding processes include the embossing, molding and / or the production of composite and hybrid materials.
3. 3. Mechanical press according to one of the paragraphs 1 or 2, characterized in that the drive for the upper tool and / or the lower tool comprises an eccentric and / or a toggle lever.
4. 4. Mechanical press according to one of the preceding paragraphs, characterized in that the predetermined threshold is at most 10% of the nominal pressing force, preferably at least almost zero.
5. 5. Mechanical press according to one of the preceding paragraphs, characterized in that the predetermined time is at least 1 second, preferably at least 3 seconds.
6. 6. Mechanical press according to one of the preceding paragraphs, characterized in that the release device is operable so that the structure of the hydraulic pressure for applying the pressing force from the threshold to the nominal pressing force in the passage of the press from bottom dead center to top dead center is effected.
7. 7. A method for compression molding of molded parts in a mechanical press according to one of the preceding paragraphs, characterized by the steps of separating upper and lower tool at the top dead center of the press, the introduction of the molding or its raw materials, the driving of the press to their bottom dead center, the residence of the press at bottom dead center for a predetermined time, the targeted reduction of the pressing force by lowering the hydraulic pressure, and the driving of the press to its top dead center, in which case the biasing pressure is selectively increased.
8. 8. The method according to paragraph 7, characterized in that at the bottom dead center, the nominal pressing force is applied to the molding.
9. 9. The method according to any one of paragraphs 7 or 8, characterized in that the targeted reduction of the pressing force at the bottom dead center after a predetermined time interval of preferably more than 2 seconds, in particular more than 3 seconds, takes place.
10. 10. The method according to any one of paragraphs 7 to 9, characterized in that the targeted and preferably continuous lowering of the hydraulic pressure takes place along a pressure curve which is monotonically decreasing in the region of lowering, preferably strictly monotone decreasing.

5. Brief description of the figures

Fig. 1

eine schematische Ansicht auf eine erfindungsgemäße mechanische Presse in der Vorderansicht,

Fig. 2

die erfindungsgemäße mechanische Presse aus Figur 1 an ihrem oberen Totpunkt,

Fig. 3

zeigt die erfindungsgemäße mechanische Presse aus Figur 1 an ihrem unteren Totpunkt,

Fig. 4

die erfindungsgemäße mechanische Presse gemäß Figur 1 an ihrem unteren Totpunkt in einem weiteren Betriebszustand,

Fig. 5

zeigt die erfindungsgemäße mechanische Presse gemäß Figur 1 an ihrem oberen Totpunkt in einem weiteren Betriebszustand,

Fig. 6

zeigt ein Schaltschema einer hydraulischen Überlasteinrichtung gemäß dem Stand der Technik, und

Fig. 7

zeigt ein Schaltschema einer erfindungsgemäß verwendeten Überlast-Löseeinrichtung.

The invention will be explained in more detail below with reference to FIG. 7, wherein the structure or active principles of the device according to the invention emerge schematically from these figures. In the figures shows

Fig. 1

a schematic view of a mechanical press according to the invention in front view,

Fig. 2

the mechanical press according to the invention FIG. 1 at its top dead center,

Fig. 3

shows the mechanical press according to the invention FIG. 1 at its bottom dead center,

Fig. 4

the inventive mechanical press according to FIG. 1 at its bottom dead center in a further operating state,

Fig. 5

shows the inventive mechanical press according to FIG. 1 at its top dead center in a further operating state,

Fig. 6

shows a circuit diagram of a hydraulic overload device according to the prior art, and

Fig. 7

shows a circuit diagram of an overload release device used in the invention.

6. Detailed description of the figures

• FIG. 1 shows a schematic front view of a mechanical press according to the invention, comprising a press body 1, in which a press ram 3 is slidably mounted via two connecting rods 5.1, 5.2 between a top dead center and a bottom dead center against a table top 2. On the press body 1, a hydraulic unit 12 is arranged, via which the maximum permissible pressing force of the press ram 3 can be adjusted. The connecting rods 5.1, 5.2 are mounted eccentrically via eccentric 4.1, 4.2, wherein in the position shown here the press ram 3 is at its top dead center. The hydraulic pressure is applied per connecting rod 5.1, 5.2 of the hydraulic unit 12 and displayed in the respective pressure displays 8.1, 8.2. Each connecting rod 5.1, 5.2 has its own pressure spindle 6.1, 6.2 and one pressure pad 7.1, 7.2. At the press ram 3 are also a central pressure storage unit 9 and each for each connecting rod 5.1, 5.2 a release unit 10.1, 10.2 and an overload unit 11.1, 11.2 assigned. The bearing load, represented by the plurality of arrows at the reference numerals 13.1, 13.2 for each connecting rod 5.1, 5.2 is very low in the illustrated top dead center position of the press ram.
• FIG. 2 shows the inventive mechanical press according to FIG. 1 in an operating condition at its top dead center. The eccentrics 4.1, 4.2 are in their upper dead center, thus the eccentric bushes are 37.1, 37.2 in their upper part of the eccentrics. In this operating state, the overload pressure pads 7.1, 7.2 are subjected to a biasing pressure PV, whereby the start of the pressing cycle of the mechanical press according to the invention is fixed. The biasing pressure PV denotes the pressure in the cylinder space of a pressure point without applying a pressing force.
• FIG. 3 shows the operating state of the mechanical press according to the invention at its bottom dead center, in which the mechanical press is loaded with the pressing force FP and the overload pressure pad 7.1, 7.2 are subjected to a load pressure PB. The load pressure PB denotes the pressure in the cylinder space of a pressure point, which sets under load under load. The height of the pressure pad is h and the force acting on the press body 1 causes an extension of the tool installation space height by a quantity change δL. This force acting on the press 1 also causes a deformation of the press body 1, which is shown oversubscribed by the deviation of the solid line from the contour of the press body 1 shown in dashed lines. The bearing load 13.1, 13.2 per connecting rod 5.1, 5.2 is in turn shown with arrows, but different than in FIG. 1 with a downward orientation. The greater length of the arrows indicates the higher bearing load due to the pressing force Fp.
• FIG. 4 shows the mechanical press according to the invention in an operating state at its bottom dead center, in which the pressure pad 7.1, 7.2, however, are depressurized, which is shown on the pressure displays 8.1, 8.2 with the display P0. PO thus designates the relief pressure, after the deliberate discharge of an amount of oil from the cylinder chamber of a pressure point with simultaneous reduction of the pressing force Fp to zero. The pressing force has thus been reduced according to the invention at the bottom dead center shown to zero. The height of the pressure pad is h - δL, wherein the rebound of the press and its press body 1 is reduced by the pressure reduction in the pressure pad 7.1, 7.2 to 0 and a part of the oil volume in the pressure pad 7.1, 7.2 is displaced. The bearing load 13.1, 13.2 per connecting rod 5.1, 5.2 has the same orientation as in the operating state according to FIG. 3 on, but a much lower level than in the operating state according to FIG. 3 ,
• FIG. 5 shows the mechanical press according to the invention in an operating state at its top dead center, wherein during the upward stroke of the press ram 3 of the eccentrically mounted connecting rods 5.1, 5.2, the displaced from the overload pressure pad 7.1, 7.2 oil quantity from the pressure storage unit 9 is fed back to the biasing pressure PV , shown on the pressure displays 8.1, 8.2, to provide again. As a result, the end of the forming cycle of the mechanical press according to the invention is achieved.
• FIG. 6 shows a mechanical press with 2-point drive via the eccentric 4.1, 4.2, equipped with an overload protection according to the prior art. In the power flow between the connecting rods 5.1, 5.2 and the press ram 3 are the oil pads or pressure pad 7.1, 7.2, biased by the biasing pressure Pv are. The pressing force generated at each operation, a pressure increase, which is still below the set cut-off pressure Pa. In case of overload opens when the cut-off pressure Pa reaches the valve 11.1, 11.2. The pressure in the pressure pad 7.1, 7.2 breaks abruptly and makes the ram force-free. The overload protection described above consists essentially of the elements hydraulic unit 12, consisting of the components 14-20, and the overload units 11.1, 11.2, which are arranged directly on the pressure pad 7.1, 7.2. Eccentric presses of various designs are usually equipped with a hydraulic overload protection according to the above-described prior art.
• FIG. 7 shows a mechanical press as in FIG. 6 described, however, was extended to the components release units 10.1, 10.2 and accumulator unit 9 and the oil supply 36 of the accumulator unit 9. The function of the classic overload protection as press protection is given in equal measure. A controlled pressure reduction in the pressure pad 7.1, 7.2 is made possible by the release device 10.1, 10.2. Via the pressure sensors 21.1, 21.2, the prevailing cushion pressure is detected, and a pressure reduction can take place via the throttles 22.1, 22.2 and the discharge valves 23.1, 23.2 in the tank. This can be done independently depending on pending pad pressure. A symmetrical relief of the prestressed press is to be striven for. When relieving the pressure pad 7.1, 7.2, a certain amount of oil is discharged into the tank. This amount of oil must be returned to the pressure pad to produce the biasing pressure Pv. This is advantageously done during the upward stroke of the press ram 3 to top dead center. In order to refill the pressure pads in a relatively short time with the oil volume started to relax, a pressure storage unit 9 with the individual components 8, 24-32 is provided. This provides the required amount of oil by means of a pressure accumulator 25 in sufficient quantity available. The required amount of oil is the pressure pad 7.1, 7.2 via the hydraulic valves 29 - 31 during the upstroke supplied to the press. The pressure storage unit 9 is supplied by an oil supply 36, consisting of the components oil pump 35, pressure relief valve 34 and pressure filter 33.

An advantageous arrangement of the pressure storage unit 9 would be as close as possible to the pressure pad 7.1, 7.2, in order to minimize the negative influence of long connecting lines and to reduce the pressure build-up time of the biasing pressure Pv. This leads to an increase in the cycle time of the press and has a positive effect on the availability.

LIST OF REFERENCE NUMBERS

1

press body

2

tabletop

3

press ram

4

eccentric

5

pleuel

6

jackscrew

7

caul

8th

pressure indicator

9

An accumulator assembly

10

release unit

11

Overload unit

12

Hydraulic power unit

13

bearing load

14

Pressure relief valve

15

Pressure relief valve

16

Air-hydraulic pump

17

Pressure control valve air

18

Shut-off valve air

19

air supply

20

pressure indicator

21

pressure sensor

22

throttle valve

23

drain valve

24

pressure switch

25

accumulator

26

drain cock

27

Pressure relief valve

28

safety valve

29

Memory-off valve

30

Memory-sequence valve

31

check valve

32

check valve

33

pressure filters

34

Pressure relief valve

35

oil pump

36

Oil supply pressure storage unit

37

eccentric

Claims (5)

Mechanical press for molding processes of molded parts, with an upper and a lower tool, which form a mold for the molding between them, and a hydraulically assisted drive for the upper tool and / or the lower tool between a top dead center and a bottom dead center, wherein an overload protection is provided for the lowering of the hydraulic pressure for applying a pressing force to the upper tool and / or the lower tool at least at the bottom dead center,
characterized in that
a release device for selectively and preferably continuously lowering the hydraulic pressure over a predetermined time and below a predetermined threshold is provided, wherein the release device is operable such that the structure of the hydraulic pressure for applying the pressing force from the threshold value to the nominal pressing force in the passage of the press bottom dead center up to the top dead center is effected. Mechanical press according to claim 1, characterized in that the molding processes include embossing, mold hardening and / or the production of composite and hybrid materials. Mechanical press according to one of claims 1 or 2, characterized in that the drive for the upper tool and / or the lower tool comprises an eccentric and / or a toggle lever. Mechanical press according to one of the preceding claims, characterized in that the predetermined threshold is at most 10% of the nominal pressing force, preferably at least almost zero. Mechanical press according to one of the preceding claims, characterized in that the predetermined time is at least 1 second, preferably at least 3 seconds.

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