TO THE CURSOR OF A PRESS-BENDING MACHINE

The present invention regards a device for fixing a tool to the cursor of a press-bending machine,

The press bending machines are equipped with tools (punches) to bend e.g. metal sheet pressing it inside corresponding fixed matrices. To each working step of the sheet metal a special punch corresponds, which must be changed from time to time and removably fixed to a cursor via a fixing device.

The device comprises a massive central body and a clamping bracket movable with respect to it. Together they form a clamp structure to block the punch and keep it suspended vertically.

The punch is a heavy and blunt piece, which is replaced manually at every new setup of the press. It is therefore necessary a safety system against accidental fall.

One recurring solution is to provide stop teeth which engage in a groove of the punch.

U.S. 5,022,256 uses a flexible plate screwed to the back of the main body behind the bracket and provided with a detent. The plate can block the punch and can flex elastically toward the bracket to allow removal of the punch. But the plate is a rather weak structural element and very prone to shocks and stresses, that can deform it and render unsafe.

A more sophisticated device is described in WO 01 /39906. The device still comprises a massive central body and a clamping bracket attached to it. Between the central body and the bracket is a plurality of stop hooks. These have a curved tooth at the upper end, which can engage an inner lip inside the bracket for support, so that the punch hangs to the bracket during disassembly. In addition to the other end they have a tooth for engaging a groove of the punch in order to lock it on the main body. In the middle there is a spring that is pushed by a terminal tooth of the bracket when the device is to clamp the punch.

The shape of the stop hooks and the bracket is very complicated to make, due to a lot of working needed to obtain teeth and corresponding grooves. During the detachment the weight of the tool rests entirely on the curved tooth of the stop hooks, which must be sized appropriately along with the brackets they are suspended to. This imposes structural constraints on the bracket and its connecting means to the main body.

The bracket pushes a very small area of the stop hook with a tooth. The high pressure causes a deformation of the stop hook which weakens and wears it. The various stop hooks undergo different deformations, and different tolerances occurs in their clamping action. It may then happen that just a few stop hooks are actually pushing the punch, while others in practice do not cooperate. Note that in WO 01 /39906 the movement of the bracket can only be rotary because the stop hook must also push up the punch against an abutment. Therefore not only the tooth of the bracket presses the hook but it also will drag above, further stressing it.

Another problem is that while moving the punch during the assembly the hook is pulled or stressed, and its curved teeth often break. Unfortunately, the hooked configuration of those teeth and their modest thickness, limited by the overall size of the fixing device, do not allow structural strengthening.

The main object of the present invention is to improve this state of the art.

In particular, the object is to create a fixing device that is very robust, simple and inexpensive to build, and immune to stress deformation and positioning errors.

These and other objects are all achieved by the fixing device according to claim 1 , comprising

- a central body connectable to the cursor

- a fastening bracket placed in front of the central body and movably connected to it,

- a hook element for hooking the punch which is mounted to be able to move with play between the central body and the bracket and to be able to pull the punch toward the central body,

wherein the bracket can move to push the hook element against the punch to block it with respect of the central body, and is mounted linearly movable on the central body.

The advantages of the linear driving are primarily a simplification of the mechanism for moving the bracket, because a costly and complicated hinge is avoided. In addition, the pressure exerted by bracket on the hook element does not discharge on a point but on a flat surface or band, so the hook element spoils and wears less. That is, the use of a flat bracket or with flat contact portions on the hook element can be allowed, in order to better distribute the clamping pressure.

As a preferred variant, there are linearly guiding elements, e.g. pins, for supporting and linearly guiding the bracket, which has through-openings in which the pins are inserted with such a play as to let it slightly tilt (e.g. 5 to 20 degrees). This tilting is very useful during assembly or disassembly of the tool because it facilitates the tooling maneuvers by increasing the divarication of the hook elements. Note that instead the hinge used for the bracket in WO 01 / 39906 is necessarily rigid and limits the opening of the bracket. Preferably, the hook element has an anchoring point on the central body to keep the punch abutting against it. In this way, the hook element is anchored very firmly and heavy tools are firmly supported, which are never likely to fall. In addition, the anchoring is very simple to implement mechanically, e.g. by a recess or step.

Preferably a hook element, to keep the punch suspended and detached from the central body, has an anchoring point on the latter. In this case too, in which only to support the tool prior to removal is needed, one can very solidly anchor the hook element that keeps him suspended. This anchoring too is very simple to implement mechanically, e.g. by a recess or step.

Preferably there is an elastic means mounted on the hook element and pushing the bracket, e.g. placed, with respect to the connection/ sliding point between the bracket and the central body, in position opposite to the punch. So the elastic means can be arranged in sight and/ or in an easily accessible position, away from the punch, for example to replace it without removing the bracket. The elastic means is useful to compensate for tolerances or deformations in the hook element: the latter blocks when it abuts on the tool, and the elastic means absorbs any further push of the bracket. It is preferred that the elastic means is mounted in expansion between an inclined plane of the bracket and an inclined plane of the hook element, so that the bracket pushes and can be able to lift the hook element to raise the tool.

By preferably putting the elastic means at one end of the hook element, e.g. above, the benefits of having it in an accessible position are still retained. Furthermore, a lever pivoted at the center of the bracket is created, wherein the lever is the hook element. When the punch is released by moving towards the outside the bracket, the elastic means pushes a little outside the hook elements thereby facilitating the tool removal.

Preferably the hook element comprises a substantially flat head, an elongated and substantially flat body, and a terminal tooth for hooking the punch. The nail- or mushroom-shape of the hook element allows inserting it and letting it hang between the bracket and the central body in simple manner and with very simple geometries. Thanks to the abutting head that supports it, it never falls.

To compensate for superficial defects or mechanical stresses the bracket, on a surface facing the central body and adapted to contact the hook element, can comprise one or more adjustable-projection element. The tolerances of the pieces into contact can be thus compensated.

Preferably the bracket is operated linearly toward or away from the central body with a fluid-operated plunger. The plunger is, for example, sealingly housed in the central body and connected to the bracket to move it, and comprises a groove in communication with the ducts conveying the fluid. So a greater area to the fluid under pressure can be offered for a greater sprint.

These and other advantages will be better understood from the following description and the annexed drawings, given as an example in which:

- Figure 1 is a front perspective view of a device according to the invention in unlocked configuration;

- Figure 2 is a sectional view of the device of Fig. 1 along plane II-II in the unlocked configuration;

- Figure 3 is a sectional view of the device of Fig. 4 along the plane III-III in locked configuration;

- Figure 4 is an enlarged view of the dotted circle in Fig. 1 ;

- Figure 5 is a front perspective view of the device of Fig. 1 in locked configuration;

- Figure 6 is a rear perspective view of the device of Fig. 1 ;

- Figure 7 is a front perspective view of a component of the device of Fig. 1 ;

- Figure 8 is a rear perspective view of the component of Fig. 7; - Figure 9 is a side view of the component of Fig. 7;

- Figure 10 is an enlarged view of the dotted circle in Fig. 5;

- Figure 1 1 is an enlarged view of the dotted circle in Fig. 6;

- Figure 12 is a view of a variant of the device.

In the figures there is indicated as a whole by 10 a fixing device of a tool UT to the cursor of a bending press (not shown).

The device 10 comprises a central body 20, a clamping bracket or plate 40 and a plurality of hook elements 60 (shown together in Fig. 5).

The tool UT in known manner is shaped to abut against a plane 28 and a bottom support surface 30 of the body 20.

The body 20 has pass-through holes 18 in which are movably inserted horizontal pins 42 along an X axis that is perpendicular to the movement direction of the cursor.

The pins 42 at one side are fixed to a plunger 22 and at the other, where they have a head, they support and grip the bracket 40, to which they mate by pass-through openings of the same. These openings are large enough to form a little play around the pins 42, so that the bracket 40 can slightly oscillate in relation to them. The length of the pins 42 is such as to leave the bracket 40 at a distance from the body 20, so that between the two there is an empty space and a row of hook elements 60 can be inserted therein (Fig. 5). To adapt the elements 60 around the pin 42, the former can have pass- through openings through which the pins 42 can go through or lateral recesses 74 to give them space (see Fig. 7). Another function of the recesses 74 is to exploit the pins 42 for supporting the hook elements 60.

An element 60, see Figs. 7-9, comprises a substantially flat head 68, an elongated and substantially flat body 66 (along a Y axis) (except for an optional reference rib in relief), and a terminal tooth 62, to be turned toward the body 20, which serves to attach the tool UT. The Y-axis is parallel to the motion direction of the tool UT and orthogonal to the axis X.

The head 68 protrudes on two opposite sides from the plane in which the body 66 lies: on one side with an inclined plane 70, and on the other side with a nose 76 oriented as the tooth 62.

On the head 68 is mounted an elastic means, e.g. a leaf spring 72, arranged so as to be placed in front of the inclined plane 70.

The surface of the bracket 40 toward the central body 20 can contact the hook element 66 of device 10. This surface can comprise the entire inner side of the bracket 40 or only a portion thereof, like e.g. in the drawings in which only two flat bands 43, 45 separated by a slight depression give a push. The two flat bands 43, 45, one at the pins 42 and one near and behind the tooth 62, have e.g. a height between 2 and 8 mm, preferably about 4 mm. These height values were found experimentally effective and sufficient to assure a good thrust, preventing that too wide a flat contact surface suffers from tolerances and deformations affecting its operation. Indeed, it is good to avoid localized areas of pressure created by surface defects.

Preferably on such surface there are adjustable-projection elements (not shown), e.g. adjustable dowels. The aim is to fine-tune the contact between the bracket 40 and the elements hook 60 and compensate for manufacturing tolerances or deformations that would prevent uniform contact on all of the elements 60. In fact, the pressure of the bracket 40 would be exercised only on the thicker element 60, and/or would not involve the thinnest elements 60.

On the inside and top part of the bracket 40, the one facing the body 20, an inclined plane 44 is obtained, with inclination complementary to the inclined plane 70 that stands in front of it.

The front part of the body 20, at the level at which the head 68 locates, has a step or anchoring structure 80 for the hook element 60, in particular for his nose 76. Just below the step 80, a few millimeters of distance along the X axis toward the tool UT, on the body 20 there is a second step or anchoring structure 82, again adapted for the nose 76 to be able to anchor thereon. The second step 82 is also closer to the bracket 40 along the axis X.

The plunger 22 is mounted on the rear of the body 20, and is controlled by fluid (e.g. compressed air or oil). The plunger 22 is sealingly housed inside a cavity of the body 20, using e.g. O-rings 26, and is connected to the bracket 40 by the pins 42 to move it linearly toward or away from the central body 20 along the X axis. The plunger 22 on the inner side of the body 20 comprises a groove 24 in communication with the conduits for the fluid which feed the device 10 from the outside.

The device 10 operates as follows.

When one wants to equip the press the plunger 22 is operated to push the bracket 40 away from the body 20. Between the body 20 and the bracket 40 is formed a separation space or play, in which all the hook elements 60, when unconstrained, can slightly oscillate and tilt remaining suspended to the body 20 and the bracket 40 by the head 68.

An operator then inserts the tool UT between the surface 30 and the elements 60, which first diverge to receive it and then, pushed by the spring 72, they hook it by the teeth 62.

Then the plunger 22 is operated to draw the bracket 40 to the body 20 for the clamping. The bracket 40 moves along the X axis and the inclined planes 44, 70 approach. The spring 72 is compressed, and pushes and lifts the respective element 60 along the Y axis with two effects: first, the tooth 62 moves the tool UT abutting it against the plane 28; second, the nose 76 reaches the step 80 and rests firmly above it. Now the tool UT is perfectly in contact with the body 20 and immobilized permanently (Fig. 3 and 5). After machining, to replace the tool UT the plunger 22 is operated in the opposite direction. The heads of the pins 42 move away from the body 20 and the bracket 40 can move away from the body 20 enough for the head 68 of the 60 items to leave its stable position. The operator handling the tool UT can tilt and move the elements 60, so that the nose 76 ends up in the lower step 82 thereby slightly lowering the relative element 60 (Fig. 1 and 2). In this position, every element 60 has moved away a few millimeters from the body 20 but without the tooth 62 leaving accidentally the tool UT to drop. To remove the tool UT an intentional operation of the operator is required, who must push it horizontally to tilt the bracket 40 on the pins 42 and move away enough the teeth 62.

The structure of the elements 60 is very simple to implement and very robust. Each protruding part destined to gripping or abutting is massive, without excessive bending and supported by not much weakened areas. It is e.g. possible and easy to produce the element 60 by cutting an extruded steel, or metallic in general, profile or bar.

The springs 72 are mounted easily in sight on the head 68, for example by screws, which facilitates the replacement of a spring 72 that can be done without removing the bracket (as opposed to WO 01 /39906). The construction of the springs 72 is easier than that in WO 01 /39906.

The groove 24 on the plunger 22 serves to give vent to the injected fluid behind the body 20. This increases the free surface on which the fluid can exert pressure when the piston is near the inner wall of the body 22. The result is a faster and stronger attraction of the bracket 40.

The device can also be operated manually, as shown in Figure 12 for a variant 100. Its construction is equal to the device 10 except for the drive of the clamping mechanism. The device 100 comprises in fact, inter alia, a central body 120, a bracket or plate 140 for clamping a tool UT and a plurality of hook elements 160. Numbers equal to the previous ones increased by 100 mean equal members to the previous version.

The body 120 has pass-through holes or seats in which is inserted a threaded horizontal pin 198, along an X axis, on which a swivel counter- threaded pin 197, which extends through the bracket 140, can be screwed.

The pin 197 has a head 199 able to push the plate 140 against the body 120. Therefore it is sufficient to turn manually, e.g. with a key, the head 199 to move the pin 197 along the X axis and tighten the plate 140 against th etool UT.

The device can also be equipped contemporarily with both manual and assisted drive.