EP0025469A1 - Method and hydraulic device for adjusting the stroke depth of the ram of a hydraulic bending press - Google Patents

Abstract

The invention adjusts the stroke depth of the ram (6) by permitting a modification of the position of the stops (3) without having to raise the block (4) from the part being shaped. The stops (3) are temporarily unloaded there by a thrust opposite to that of the block (4) - the counterthrust being obtained for example by double action cylinders (2) - without releasing the pressure on the part being shaped. This permits a fine adjustment to the stroke depth in a single operation. The method is applicable to bending presses comprising mechanical means (3) for stroke limiting as well as those comprising hydraulic means for stroke limiting. <IMAGE>

Description

The present invention relates to a method for correcting the penetration depth of the punch of a hydraulic press brake comprising means for limiting stroke as well as at least one double-acting hydraulic cylinder or pair of opposite single-acting hydraulic cylinders. . It also relates to a hydraulic circuit installation for the execution of the process.

It is known that the folding of a rigid material calls upon considerable forces which cause a deflection of the slide and the corresponding fixed deck of a hydraulic press. The deflection of the slide is observable during the folding of a given material, but can hardly be calculated beforehand with precision. However, even slight differences in the penetration depth of the punch can, when distributed over the entire length of the fold, cause measurable and often annoying variations in angle between the middle part and the extremi tees of a fold.

Swiss patent 411755 to Willy BEYELER describes a hydraulic press in which the deflection of the slider and the wear of the tool are compensated by means of two stops serving as rigid support at the ends of the slider while the middle part thereof continues its course under the effect of median cylinders, thereby undergoing a bending of its median portion. Variations in angle observed during folding can thus be corrected during this same single folding operation, without returning the slide to the rest position. The folding angle obtained will be the same over the entire length of the workpiece.

However, the machined sheet reacts _. to a certain extent elastically at the pressure of the punch, so that its folding angle reopens somewhat when the pressure ceases; this reaction too can be seen during machining, but can hardly be calculated in advance. This means that the desired angle cannot generally be reached from the start and requires a displacement of the stops to correct the penetration depth of the punch. However, the forces acting on the stops are such, during the folding operation, that it is generally excluded to then move the stops. In the known technique, the precise adjustment of the penetration depth of the punch is generally carried out in two or more stages, the position of the stops being modified between each folding operation until the desired folding angle is obtained. This setting Accurate neutral point of maximum penetration is inevitable when machining the first part of a series and causes considerable loss of time when machining single parts or small series. Thus in the press brake described in the aforementioned Swiss patent 411755, the mechanical stops preferably used can only be moved when the slide is returned to the rest position; in other words, the correction of the folding angle is obtained there, after a first folding operation and a displacement of the stops, in a subsequent folding operation which we are entitled to think will achieve , sincn to approach, the desired precision. The actual movement from the neutral point of maximum penetration of the punch is effected there by the displacement of sliding sleeves inside cylinders of cylinders, driven by worms. It should be noted that, in this known technique, the displacement of the stops takes place while, the slide being returned to the rest position, the punch no longer transmits to the machined sheet of thrust from the jacks.

In press brakes comprising hydraulic means for limiting the stroke of the jacks, movement of the stops remains possible during the folding operation, as long as the latter only uses small and medium pressures; it then suffices to partially reduce the pressure in the chambers containing the stroke limitation means, in order to increase the extensior maximum that the cylinders can reach. However, the fluids used for the stroke limitation are to some extent compressible, so that the adjustment of the penetration depth of the punch is less precise than for mechanical stops. When the hydraulic stops are moreover under the pressure of the slide, their displacement by simple reduction of the pressure causes additional inaccuracies of adjustment, rendering such an adjustment unusable at great pressures.

The present invention aims to allow the correction, during the folding operation, of the dead center of maximum penetration of the punch for press brakes having means of limitation of stroke. The correction method is characterized in that a thrust is maintained on the part of at least one cylinder, that a pressure is created in the opposite chamber of at least one cylinder which causes a opposite thrust of the starts from at least one double-acting cylinder, or pair of single-acting cylinders, and compensates for all or part of the forces opposed thereto, and then the stroke limitation means are displaced by suitable means which are known per se , despite persistent pressure of the punch on the sheet metal to be machined.

The method can be applied equally to press brakes comprising mechanical stroke limitation means and to those comprising hydraulic stroke limitation means.

The advantages of the process according to the invention are in particular the following: The limited opposite thrust is sufficient to allow the fold of the sheet to reopen; the operator can therefore observe a possible difference in angle with respect to that desired. This opposite thrust is also sufficient to unload the stops and allow them to be adjusted without returning the slide to the rest position, that is to say without wasting time. As for the maintenance of a thrust on the part of certain jacks, it prevents an untimely movement of the sheet during the correction of the penetration depth of the punch, regardless of the weight of the slide and the trigger force respectively (elasticity and thickness , weight acting as a lever) of the sheet.

For its part, the installation of a hydraulic circuit enabling the process to be carried out is characterized in that the pressure P contained in the chambers of cylinder of double-acting cylinders can be reduced in favor of a back pressure P 'in chambers opposite of such cylinders.

• La fig. 1 représente, de façon volontairement exagérée, une tôle dont le pli s'est ouvert plus qu'on ne s'y attendait, lors de la réduction de la pression : une pénétration plus profonde du poinçon s'avère nécessaire ;
• la fig. 2 représente la même tôle en cours de correction : le poinçon pénètre dans la matrice ;
• la fig. 3 est une vue de face d'une presse-plieuse hydraulique à quatre vérins et butées mécaniques, le coulisseau se trouvant en position de repos ; les vérins y sont représentés en coupe partielle ;
• la fig. 4 représente la même presse-plieuse lorsque le coulisseau se trouve en position d'opération pendant le pliage de la tôle à usiner (non représentée); le déplacement des butées latérales est effectué alors que le coulisseau se trouve dans cette position
• la fig. 5 représente schématiquement les cylindres d'une presse-plieuse à cinq vérins en cours d'opération de pliage de la tôle ;
• la fig. 6 représente ces mêmes cylindres au moment où il devient possible de déplacer les butées.

The appended drawings serve to explain the process and represent embodiments described below:

• Fig. 1 shows, in a deliberately exaggerated manner, a sheet whose fold has opened more than expected, when the pressure is reduced: a deeper penetration of the punch is necessary;
• fig. 2 represents the same sheet being corrected: the punch enters the die;
• fig. 3 is a front view of a hydraulic press brake with four jacks and mechanical stops, the slide being in the rest position; the jacks are shown in partial section;
• fig. 4 shows the same press brake when the slide is in the operating position during the folding of the sheet metal to be machined (not shown); the lateral stops are moved while the slide is in this position
• fig. 5 schematically represents the cylinders of a press brake with five jacks during the sheet bending operation;
• fig. 6 shows these same cylinders when it becomes possible to move the stops.

Figures 3 and 4 show a press brake conforming to that shown in the description of the aforementioned Swiss patent 411755. This press comprises two lateral cylinders 1 with single effect and two median cylinders 2 with double effect; the diameter of the cylinders (D) and the pistons (d) is assumed to be the same in the four cylinders. A socket actuated by an endless screw is housed in each of the cylinders of the two lateral jacks and forms a mechanical stop there. In a preferred embodiment of the process applied to such a press brake, it suffices to reduce the pressure in the thrust chambers of the cylinders of the median cylinders 2 and to create, in the opposite chambers of these same cylinders, a back pressure P 'corresponding to the pressure P remaining in the cylinders of the two lateral jacks 1. The opposite thrust exerted by the two lateral jacks is thus balanced by a thrust opposite of the central cylinders, so that the stops only have to support the weight of the slide 4. - In a preferred embodiment, the opposite thrust exerted by the middle cylinders 2 is increased relative to the thrust P of veri side 1, in order to decrease, or even completely remove the weight of the slide 4 and thus further facilitate the movement of the stops. A further increase in the back pressure P ′ would cause the punch 6 to be raised, which would then detach from the sheet 5 and the fixed apron 7 situated below; such an increase in the back pressure P ′ is possible, but does not contribute to facilitating the movement of the stops 3 and on the contrary has the drawback that the sheet 5 risks tilting, or even falling from the matrix 8 during lifting of the punch 6, unless the sheet is fixed, for example to punch 6. As for the actual movement of the stops, it is carried out in this case by means of the endless screws (cf. in particular fig. 4) above .

The method according to the invention can be used, with the installation of an adequate circuit, in all hydraulic press brakes which include a mechanical stop and at least one double-acting cylinder or torque opposed to single acting. When the surface area of the pistons is not the same from one cylinder to another, the pressure required in the double-acting cylinder chambers will be different from that remaining in the single-acting cylinders; for technical reasons different from the problem dealt with here, the rods of the pistons of double-acting cylinders are often of different diameter than those of single-acting cylinders.

The thrust exerted by each of the cylinders will also be different from the opposite thrust required of each of the double-acting cylinders when their respective number does not correspond. Thus, in an embodiment comprising two lateral cylinders 1 with single effect and a single median cylinder with double effect, the median cylinder 2 must exert the double thrust of a cylinder with single effect 1, in order to compensate for the presson P, and it must exert a greater thrust to also compensate for the weight of the slide 4. In press brakes comprising at least three double-acting central cylinders 2, the opposite thrust P 'of the middle cylinders 2 can be proportionally less to compensate for the pressure of the cylinders single acting; the distribution of the hydraulic fluid between the chambers of the different cylinders 2 is modified accordingly. In a preferred embodiment, shown in Figures 5 and 6, the press brake comprises a total of five cylinders whose cylinder chambers and pistons are assumed to be all of the same diameter; only two of the cylinders of the middle cylinders 2 there receive a back pressure P 'equal to the pressure P remaining in the side cylinders 1, while the pressure has simply been reduced in the cylinder of the third double-acting cylinder and that no back pressure is created there .- Of course, it would also be possible to maintain all or part of the pressure P in all or part of the cylinders of the double-acting cylinders 2 as in single-acting cylinders 1; in this case, the double-acting cylinders 2 in which a back pressure P ′ is created, should develop a contrary thrust all the more large.

In all the examples thus far described, the method applied to press brakes comprising at least three jacks and mechanical stops arranged inside two lateral jacks 1 with single effect. The invention is not limited thereto. It is applicable in particular when the press brake comprises only double-acting cylinders and the stops are arranged inside such cylinders. It is also applicable for press brakes, the stops of which are arranged outside the jacks (possibly in the axis of the lateral jacks) and thus constitute a stop for the punch itself; in this case also, double-acting cylinders 2 (or opposite single-acting cylinders) have the task of creating an opposite thrust making it possible to partially compensate for the thrust P exerted by jacks remaining under pressure, the weight of the slide and, optionally, that of the machined sheet (in the case where the stop is arranged under the die 8 carrying the sheet 5).

The invention can also find an application for press brakes in which the slide 4 is pushed from the bottom against an apron. In this embodiment, it is not only the expansion force of the workpiece 5 which opposes the thrust of the jacks, but also the weight of the slide, so that the displacement of the stops can be carried out by means of a somewhat reduced reverse thrust P ′ on the part of the middle jacks 2, compared with those necessary in the abovementioned embodiments.

The invention also finds application in press brakes which do not have systems for compensating for the deflections of the slide 4 and the deck 7.

The method can also be applied to press brakes comprising hydraulic means (stops) of stroke limitation. The opposite thrust exerted by double-acting cylinders 2 (or opposite single-acting cylinders) compensates for the thrust of the cylinders pressing against the hydraulic stop 3, which allows easy adjustment of the hydraulic stroke limitation means and therefore precise movement of the neutral point for maximum cylinder extension.

For carrying out the method according to the invention, a press brake comprising five jacks, as shown diagrammatically in FIGS. 5 and 6, is equipped with an installation comprising a single pump (not shown), capable of distributing the hydraulic fluid, in during work, between the different cylinder chambers and divert the excess fluid from the middle cylinder chamber to an expansion tank until the stops are set differently. The distribution of the fluid can be carried out by means of valves (not shown) of constant value distribution (Konstantstromteiler). In the embodiment shown in Figures 3 and 4, hydraulic fluid is derived from the thrust chambers to the opposite chambers of the two cylinders of the middle cylinders 2 to create the back pressure P '. It is obviously also possible to supply the cylinder chambers by separate circuits, as well as to supply one or the other chamber from the outside, in order to increase or reduce the pressure by an adequate adjustment of the circuit. interior, to obtain in each of the chambers the desired pressure making it possible to displace the stroke limitation means in accordance with the invention.

Claims (11)

1. Method for correcting the penetration depth of the punch of a hydraulic press brake comprising stroke limiting means and at least one double-acting hydraulic cylinder or pair of opposite single-acting hydraulic cylinders, during which reduces the pressure in cylinder thrust chambers, characterized in that one maintains a thrust on the part of at least one jack, which is created, in the opposite chamber of at least one cylinder , a pressure which causes a contrary thrust on the part of at least one double-acting cylinder or pair of single-acting cylinders and compensates all or part of the forces to it opposite, and that then the means for limiting the stroke are displaced by suitable means and known per se, despite persistent pressure of the punch on the sheet to be machined. 2. Method according to claim 1 for a press brake comprising stroke limiting means arranged at the two ends of the slide (4), characterized in that the back pressure (P ') is created only in cylinders ( 2) disposed between the stroke limitation means (3). 3. Method according to claim 1 for a press brake to at least two jacks comprising mechanical stops

arranged inside double-acting cylinders, characterized in that at least part of the opposite thrust

necessary is created in the opposite chambers of the side cylinders. 4. Method according to claim 1 for a press brake at least three cylinders comprising means of limitde stroke (3) disposed inside the two lateral cylinders (1) and fixing the maximum travel dead center

tones in their cylinders, characterized in that the necessary opposite thrust (P ') is created only in the opposite chambers of median cylinders (2). 5. Method according to claim 1 for a press brake at least four cylinders, the two lateral cylinders (1) single acting have mechanical stops (3)

and of which the middle cylinders (2) are double-acting, character-ized in that the necessary opposite thrust (P ') is supplied by at least part of the middle cylinders (2). 6. Method according to claim 1 for a press brake at least four cylinders, characterized in that reduces pressure in at least half of the thrust chambers and that creates a back pressure (P ') in a number of chambers corresponding to that of the chambers remaining under pressure (P), the opposite thrusts of the jacks equilibrating. 7. Method according to claim 1 for a sliding press brake (4) lowering against the deck (7), characterized in that the total opposite thrust produced in the chambers subjected to back pressure (P ') is greater to the thrust obtained in the chambers remained under pressure (P), but less than the thrust thereof joined to the weight of the slide (4). 8. Installation of a hydraulic circuit for implementing the method according to claim 1, characterized in that the pressure (P) contained in chambers of cylinders of double-acting cylinders can be reduced in favor of a back pressure ( P ') in opposite chambers of such cylinders. 9. Installation of a hydraulic circuit according to claim 8, characterized in that fluid extracted from a chamber at reduced pressure can be diverted to the opposite chamber of the same cylinder (2). 10. Installation of a hydraulic circuit according to claim 8, characterized in that the fluid extracted from a chamber at reduced pressure can be diverted to at least one expansion vessel. 11. Installation of hydraulic circuit according to claim 8, characterized in that the opposite cylinder chambers are capable of receiving an additional quantity of fluid from an expansion vessel.

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