The object of the invention is a method for bending a plate in which a plate is positioned into a gap between an upper tool and a lower tool, and a fold is formed to the plate by pressing the plate against the tool. The object of the invention is also a plate bending machine used in the method.

Mainly two bending methods are used in bending, for example, of window flashings or generally of thin plates. In so-called squaring, an angle is bent to thin plates to the whole length of the plate, whereby the plate is first pressed between an upper and a lower jaw. Bending takes place by turning the level alongside the pressing point upwards either by hand or mechanically. Because of the structure of bending machines, the bending may be done only upwards. If one wants to bend the plate to opposite directions, one has to remove the plate from the bender between bendings and to turn the plate upside down by hand or mechanically. Performing the work is especially difficult if there are several bendings to different directions. Because of the need for turning the plate, the automation of the work phases is laborious.

Another known thin-plate bending method is so-called edging in which a horizontal plate rests on a lower tool. The lower tool has a narrow slot in which the plate is pressed with an upper tool of suitable profile. The upper tool is pressed into a determined depth for accomplishing a desired angle. Also with this method, the problem of automation is the need for turning the plate when bending to different direc- tions. In addition, automation is complicated by the upward bending of the plate from the stopper according to which the plate has been positioned before bending.

The object of the invention is to introduce a method and a machine which enable bending of thin plates so that the plate is not turned upside down between bend- ings to different directions, but the plate bending machine according to the method positions the plate and bends it to a desired direction, either upwards or downwards, irrespective of the direction of the previous bending. Thus, the invention enables easy automation of the bending process.

The method according to the invention uses a plate bending machine which has an upper and a lower tool and a stopper for supporting the edge of the plate to be bent. The upper and the lower tool are arranged rotatable around their longitudinal axes, and they are provided with both a slot and a pressing stem. The plate to be

bent is first arranged to a gap between the upper and the lower tool. After this, the plate to be bent is pressed with the upper tool to the slot of the lower tool, and simultaneously, the upper and the lower tool are rotated around their longitudinal axes. The rotation takes place around the midpoint of the radius of rounding of the pressing surface of the pressing stem of the upper tool. During rotation, the upper and the lower tool remain parallel in relation to each other, and the edge of the plate remains stationary supported by the stopper. Said midpoint of the upper tool radius of rounding remains, seen in elevation, substantially stationary in relation to the plate during the whole pressing and rotational motion when the pressing stem of the upper tool simultaneously contacts the plate surface. The rotational motion may take place in both directions in relation to the horizontal level of the plate. After bending, the tools pull away from each other, after which the stopper positions the plate in a new position, and the tools rotate back to the upright position. If the angle to be bent next is to a different direction than the previous one, the tools are rotated so that the tasks of the upper and the lower tool are interchanged. The slot becomes the pressing stem, and the pressing stem becomes the slot. The bending takes again place in a manner described above, but the rotational point is now the midpoint of the radius of rounding of the pressing surface of the pressing stem of the lower tool, and the rotation direction is reversed.

The present invention solves problems mentioned above, eliminates disadvantages of known prior art and accomplishes an effective method for bending a plate. Said advantages are accomplished with a method and a plate bending machine according to the invention which method and machine are characterised by what is said in the enclosed claims.

Next, the invention is described in detail by means of some advantageous embodiments and with reference to the accompanying drawings.

Figure 1 is a side view of a machine implementing the method according to the invention.

Figure 2 is an enlargement of the upper and the lower tool of the plate bending machine according to the invention in a first position in which the pressing stem of the upper tool is pressed to the slot of the lower tool.

Figure 3 is an enlargement of the upper and the lower tool of the plate bending machine according to the invention in a second position in which the pressing stem of the lower tool is pressed to the slot of the upper tool.

Figure 4 shows a picture sequence of the different steps of the method according to the invention.

Figure 5 shows by way of an example an advantageous embodiment of the bending machine according to the invention.

Figures 6a and 6b show by way of an example a second advantageous embodiment of the bending machine according to the invention.

Figures 1-3 show a plate bending machine according to the invention which ma- chine includes an upper tool A, a lower tool B and a stopper D against which the edge of the plate Sh to be bent is positioned during bending. Figure 1 shows a side view of a machine according to the invention, and Figures 2 and 3 show an enlargement of a detail 1 shown in Figure 1 when the upper and the lower tool are in different positions. With a method and a machine according to the invention, the plate Sh may be bent to both directions, that is, upwards from the plate level and downwards from the plate level without turning the plate upside down between bendings. The figures show only those functional parts of the plate bending machine which are relevant from the point of view of the invention. It is evident that the plate bending machine in its operating condition must also have different sup- port structures and actuator and regulating devices for supporting the functional parts shown in figures and for changing their position. However, they may be implemented by applying commonly known prior art, so they have been omitted from the figures for clarity.

The upper tool has both a pressing stem A1 and a slot A2. Correspondingly, the lower tool has both a slot B1 and a pressing stem B2. The tip Sa of the pressing stem A1 has been rounded whereby the rounding midpoint is Ca. Also, the tip Sb of the pressing stem B2 has been rounded whereby the rounding midpoint is Cb. The upper tool A and the lower tool B are advantageously of identical form. The plate Sh to be bent is positioned in a gap between the upper tool A and the lower tool B. In a bending situation, the upper and the lower tool are always in such a position that the pressing stem and the slot point at each other whereby the gap is formed between the pressing stem and the slot. Figure 2 shows the upper and the

lower tool of the plate bending machine according to the invention in a first position in which the pressing stem of the upper tool and the slot of the lower tool point at each other, and Figure 3 shows them in a second position in which the pressing stem of the lower tool and the slot of the upper tool point at each other.

With the aid of a picture sequence, Figure 4 shows by way of an example the operation of the upper and the lower tool in the different steps of bending a plate. The plate to be bent is first brought to the gap between the upper and the lower tool, after which the upper and the lower tool are moved towards each other so that the upper tool contacts the upper surface of the plate and the lower tool contacts the lower surface of the plate.

When bending directed upwards from the plate level starts, the pressing stem A1 of the upper tool A starts to press the plate Sh in the slot B1 of the lower tool B (step 1), and simultaneously, the upper tool A and the lower tool B start to rotate around their longitudinal axes. The midpoint of rotation is the midpoint Ca of the pressing surface Sa of the pressing stem A1 of the upper tool A. During rotation, the upper and the lower tool remain parallel in relation to each other, and the edge of the plate Sh against the stopper D remains stationary (steps 2 and 3). The mid- point Ca of the radius of rounding of the pressing surface Sa of the pressing stem A1 of the upper tool A remains stationary in relation to the plate Sh during the whole pressing and rotational motion when the pressing-stem surface Sa simultaneously contacts the surface of the plate Sh.

After bending, the tools A and B pull away from each other (step 4). After pulling away has finished, the stopper D positions the plate Sh in a new position (step 5). The upper and the lower tool A, B rotate now back to the upright position (step 6) for starting a new bending movement.

If the angle to be bent next is to a different direction than the previous one, the upper and the lower tool are rotated so that their tasks are interchanged (steps 7- 9), whereby the pressing stem becomes a slot and the slot becomes a pressing stem. According to step 7, the upper and the lower tool A, B are rotated between bendings to different directions to a different position to correspond the form re- quired by the next angle to be bent, either as a slot or a pressing stem. Bending directed downwards from the plate level takes place in a manner described above, but now the rotational point of the upper and the lower tool is the midpoint Cb of

the radius of rounding of the pressing surface Sb of the pressing stem B2 of the lower tool B and the rotation direction is reversed (steps 9-12).

The pressing stem used in the invention may also be of such structure that it has no radius of rounding definable without ambiguity, or that the edge of the pressing stem may be extremely sharp, whereby radiuses of rounding Ca and Cb are extremely small. Then, the position of the rotational midpoint during the pressing and rotational movement is approximately in the point of contact of the pressing stem and the plate to be bent.

Figure 5 shows by way of an example a side view of an advantageous embodiment of the plate bending machine according to the invention. For implementing the method according to the invention, the upper or the lower tool of the plate bending machine may be formed as especially compact, 90-degree rotatable parts, whereby the space and force requirements for rotating them decrease. Advantageously, at least the slot (A2, B1 ) affecting bending may be manufactured of an elastic material or be coated with an elastic material, such as polyurethane, whereby there will be less possible traces of the tools during bending of coated plate. The rigidity required of the upper and the lower tool is accomplished with support structures 1 , 2 supporting the tools. In this advantageous embodiment of the invention, also support structures 1 , 2 take part in the pressing and rotational movement.

Figures 6a and 6b show by way of an example a side view of another advanta- geous embodiment of the plate bending machine according to the invention. In this embodiment, the upper tool A comprises a support structure 1 to the end of which a slot A2 is fixedly attached. In the same end of the support structure, there is additionally a pressing stem A1 which is attached to the side of the end of the support structure with an L-formed support 5. The support is fastened to the support structure with a pivot mounting 6 so that the pressing stem A1 may be rotated either on the slot A2 (Figure 6a) or off the slot (Figure 6b). Thus, changing the upper tool to function as either a slot or a pressing stem takes place by changing the positions of the support and the pressing stem connected to it. Naturally, the upper tool may also be implemented so that the pressing stem is fixedly fastened to the support structure, whereby the slot is fastened to the support structure by means of a pivot-mounted support. Advantageously, the lower tool is formed similar of structure.

In an advantageous embodiment of the method and the bending machine according to the invention, the depth of the slot B1 , A2 is in unloaded state essentially zero, that is, the "counterpart" of the pressing stem is essentially a flat surface. Unloaded state means here that no pressing force of the pressing stem is directed to the slot. In this advantageous embodiment, the pressing stem or at least a part of it is manufactured of a compressible material or it is coated with such a material, whereby a slot is formed to the pressing stem when the pressing force of the pressing stem is directed to it in a bending situation.

The figures and the description linked to them are only intended for illustrating the present invention. By details, the plate bending machine and the method may vary within the scope of the accompanied claims and the inventive idea described. It is well known by those skilled in the art that the technical solutions of the device may vary depending on use. The embodiment of the invention may vary depending on operating conditions and customer requirements and within the scope of manufacturing solutions implemented in connection with its production.