WO2007097691A1

WO2007097691A1 - Bending apparatus

Info

Publication number: WO2007097691A1
Application number: PCT/SE2007/000157
Authority: WO
Inventors: Bo Claesson; Sonny Evaldsson
Original assignee: Evolator Ab
Priority date: 2006-02-22
Filing date: 2007-02-22
Publication date: 2007-08-30
Also published as: SE529669C2; SE0600391L

Abstract

The invention concerns a bending apparatus (20) , which is adapted to bend an edge flange of a workpiece (21/22) , that is of sheet metal and is clamped by a sheet holder (24) in a bed (30) . The bending apparatus (20) comprises at least one prebending tool (31) , which is arranged on a first tool holder (29) and is movable relative to the same by a parallelogram linkage, and at least one final bending tool (27) , which is arranged on a second tool holder (28) . According to the invention, the bending apparatus (20) is arranged in a press (23) , which has a first and a second press unit which are displaceable toward and away from each other, the first tool holder (29) being mounted on the first of said press units together with said bed (30) and the second tool holder being mounted on the second of said press units, and both the prebending tool (31) and the final bending tool (27) being driven by the displacing movement of the second press unit relative to the first press unit.

Description

BENDING APPARATUS

Field of the Invention

The invention relates to a bending apparatus, which is adapted to bend an edge flange of a work piece, that is of sheet metal and is clamped by a sheet holder in a bed, and which comprises at least one prebending tool, which is arranged on a first tool holder and is movable relative to the same by a parallelogram linkage, and at least one final bending tool, which is arranged on a second tool holder. Background Art

In production in the vehicle industry, a method is used which is referred to as folding. The exterior and the visible surfaces of the car are assembled with the inner structure consisting of reinforced inner metal sheets. A bonnet or door consists of, for instance, an inner panel with various reinforcements for hinges, locking mechanisms, and, above all, beams for crashworthiness, and an outer panel which constitutes the visible surface. These panels are assembled by the metal sheets being "married to each other", intermediate glue and sealing compound being applied to the inner metal sheet (see Fig. 1) by a robot once the metal sheets are fitted in the correct position. Then the edge of the outer metal sheet is folded, pressed or rolled inward over the edge of the inner metal sheet.

In the current technique of assembling there are three different methods: lock rolling, table-top folding and press folding. In all three methods, both the inner metal sheet and the outer metal sheet must be geometrically secured within narrow tolerances in respect of position as well as shape. This is ensured by the inner metal sheet being introduced by docking and guiding and being held or clamped with a sheet holder. In all three principles, the fold flange of the outer metal sheet must be folded over the perpendicular toward the inner metal sheet in a first step. Before performing the actual folding, the sheet metal parts must be correctly positioned. Here a folding bed is used, in which the outer metal sheet to be folded is placed. This occurs using an industrial robot. In order to fix the outer metal sheet in the correct position in the bed, guide pins are used for correct positioning. With the outer metal sheet positioned, the inner metal sheet, glue and sealing compound are put in place by the robot. To prevent the inner metal sheet from moving over the outer metal sheet during folding, a sheet holder is used to fix the inner metal sheet in the correct position. With everything fitted, it is now time for the actual folding, in which the fold flange of the outer metal sheet is pushed, folded or pressed against the inner metal sheet by one of the above mentioned three methods, which will be described in more detail below. Lock Rolling

The fold flange is rolled inward over the inner metal sheet by means of rolls that are moved over the fold flange by a robot. The motion of the robot is repeated in several steps to achieve the desired rolling- in. This concept can be compared with the rolling-out of dough in baking. The great drawback of this method is that it requires a long time. Table-top Folding Here the fold flange is folded over the inner metal sheet by means of two folding tools (one prebending tool and one final bending tool) , which in two steps move the flange inward and downward. In this method the motive force comes from electric motors or individual hydraulic pistons, which drive a link arm system and, thus, the folding tools during their movement toward the outer metal sheet. A great drawback of this method is that it takes up a lot of space in production and is flexible only in a limited way. Press Folding

The folding process resembles to a certain degree table-top folding, but the motion is limited to a purely linear motion. Here a mechanical or hydraulic press is used. This method has a high production capacity, but results in inward rolling that is difficult to control (insufficient quality) . Components Included in a Table-top Fixture

In table-top folding, a folding fixture is used, consisting of a cast unit, which is fixedly mounted in a bedplate which in turn is secured to the "floor" by chemical anchors. The function of the fixture (link arm system) is, as stated above, driven electrically or hydraulically . Thus, there are link arms which move the prefolding tool and the final folding tool toward the fold flange of the outer metal sheet during the actual folding . Analysis of an old Table-top Unit

To give the sets of tools in table-top folding the correct movement pattern in the fixture, a system of link arms is used. The two sets of tools, prefolding tool 1 and final folding tool 2, are integrated in a complicated link arm system (see Fig. 2) The prefolding tool 1 is attached by a prefolding holder 3 to an attachment plate 4 which is moved back and forth by means of a link arm 5. To obtain a circular path in prefolding, two separate link arms 6 and 7 are used. Two shafts are arranged on each link arm β and 7. One shaft is attached by ball bearings at a point of attachment A. The other shaft is connected to ball bearings in the actual attachment plate 4 at a point of attachment B. Once prefolding is completed, the link arm 5 pulls back the attachment plate 4 with its prefolding tool 1, and after that the final folding tool 2 finishes the actual folding. The final folding tool 2 is attached to a final folding holder 8 which in turn is attached to an attachment plate 9. The attachment plate 9 is moved by a link arm 10. By moving the points of attachment A of the link arms 6 and 7 on the fixture, the desired angle of attack toward the outer metal sheet can be obtained. The points of attachment A are fixed in the folding fixture 11 while the points of attachment B move forward and downward in a rotary motion when prefolding occurs by means of an electric/hydraulic drive means 12 and, driven by the same, a connecting rod 13.

Advantages and Drawbacks of Today' s Table-top Method

What should above all be emphasised as one of the advantages of the method is that it produces an excellent folding result. This is due to the fine and even rolling- in. The rolling-in determines to a great extent the total result in folding. This means that table-top folding is the method that produces the best result.

A drawback of this method is that it is in many cases not economically sustainable due to its specialisation and relative slowness. In addition, it requires a large production surface and causes a clearly limited flexibility. However, the industry requires in general small and flexible machines which are optimised both in respect of size (available shop surface) and flexibility (different production runs) . The time required for the actual folding is today also a problem, and here, too, it is desirable to shorten the cycle times for folding of more units per unit of time. Object of the Invention In view of that stated above, the object of the invention is to improve a bending apparatus according to the preamble so that the drawbacks of prior art techniques are eliminated. Summary of the Invention According to the invention, this object is achieved by the bending apparatus being arranged in a press, which has a first and a second press unit which are displaceable toward and away from each other, the first tool holder being mounted on the first of said press units together with said bed and the second tool holder being mounted on the second of said press units, and both the prebending tool and the final bending tool being driven by the displacing movement of the second press unit relative to the first press unit.

Preferably, the prebending tool is arranged to cooperate with a cam mechanism, by means of which the displacing movement of the second press unit is transferred to the prebending tool for controlled driving of the same.

The cam mechanism preferably comprises a pin means, which is arranged on the prebending tool, and a cam groove in the second tool holder, in which cam groove said pin means is to be inserted for said controlled driving.

According to the invention, the final bending tool is suitably rigidly connected to the second tool holder. Moreover, the final bending tool is preferably column shaped and directed toward the first press unit. Brief Description of the Drawings

A preferred embodiment of the bending apparatus according the invention will be described in more detail in the following with reference to the accompanying schematic drawings, in which

Figs 1 and 2 illustrate examples of prior art technique;

Fig. 3 illustrates the entire bending apparatus; and Figs 4 - 8 illustrate parts of the same.

Detailed Description of the Preferred Embodiment

The object of the invention is to further develop prior art folding tools, and an analysis of these tools demonstrated that the operation of the actual folding tools causes problems. These were solved by taking the necessary force for operating the folding tools directly from a hydraulic press. Then the same geometric movements that are available in table-top folding were used. This ensures high quality of the folding result.

The tool 20 functions according to the following movement pattern. With the tool 20 moved apart, an inner and an outer metal sheet 21/22 are placed in the tool 20. The hydraulic press 23 starts and moves down and the sheet holder 24 contacts the metal sheets 21/22. Subsequently, the wedge 25 of the prefolding unit 26 will hit the unit 26 and prefold the metal sheet 21/22. Finally, the final folding tool 27 will perform the final folding. After completion of the folding, the press 23 moves and goes up to allow a robot to remove the completed product and supply new parts. To give the gripping means of the robot enough space, it is desirable for the gap to be at least 600 mm when the tool parts 28, 29 are moved apart. The complete solution is shown in Fig. 3. Only one prefolding unit 26 is shown on one side; the prefolding units are in practise positioned around the entire bed 30. Of course, also wedges 25 and final prefolding tools 27 will be positioned around the entire bed 30.

Since it is unknown what factors in prefolding produce a good result, a well-tried prefolding movement is used. The movement pattern is the same as in the existing table-top folding. The first part of the task was to transfer the vertical movement of the hydraulic press 23 to the movement performed by the prefolding tool 31 in table-top folding. This was solved by a prefolding unit 26 and a wedge 25 which guides the same. The wedge 25 is placed in the upper part 28 of the tool and the unit 26 in the lower part 29 (see Figs 3-6) .

To keep the inner and outer metal sheets 21/22 correctly positioned during folding, a new sheet holder 24 has been constructed (see Figs 7-8) . This is controlled by ball bushings 32 and the sheet holding force is determined by gas springs 33. Gas springs 33 were chosen largely because they make it easy to change the sheet holding pressure.

The upper and lower parts 28, 29 of the tool 20 consist of frameworks of panels or beams. The final folding tool 27 has a fully new and simplified construction and is placed on the upper part 28 of the tool. That part of the folding tool 27 which is closest to the workpiece 21/22 and also hits the workpiece follows the geometry of the product. The prefolding tool 31 which is positioned in the unit 26 is completely unchanged compared to prior art. Moreover, the bed 30 has not been changed. Prefolding Unit and Wedge

A large amount of the work behind the invention consisted of analysing and developing the prefolding unit 26. The purpose of the unit 26 is to recreate the movement performed by the prefolding tool 31 in table- top folding. This movement is to be created by means of the vertical movement of the press 23. In Figs 4-6, the prefolding unit 26 and the wedge 25 are described in more detail. The unit 26 is made of welded steel plates which, after welding, have been worked in the positions where higher precision is required or there are to be holes. The unit 26 is, together with the bed 30, mounted in the lower part 29 of the tool.

The unit 26 can exist in a few variants, for instance one for an angle of attack of 30 degrees and one for an angle of attack of 46 degrees. Which unit 26 is used in a given situation depends on the appearance of the workpiece 21/22 that is to be folded. What is described in this text as a wedge 25 is rather a bracket with a cam 34 mounted on the same, which drives the unit 26 when it hits the upper bearing 35 of the unit. The wedge 25 mechanically guides the unit 26 back and forth. When the wedge 25 is not in contact with the unit 26, there are two springs in the unit that hold the unit in a retracted position. This function facilitates loading of the tool and maintenance of the same. The wedge 25 is mounted in the upper part 28 of the tool 20. The cam 34 of the wedge 25 is releasable to allow a slight change of the travel of the unit 26. To achieve a desired movement, a certain distance, for instance 100 mm, must exist between the centres of the link arms. This means that there is a limited space for attaching and mounting of the link arms in bearings between the upper and the lower part of the unit. The unit 26 has a horizontal travel of 20 mm for instance. The vertical travel depends on what variant is used (see above) . The travel in the horizontal direction is determined by the height of the wedge 25. When the wedge 25 begins to move down toward the unit 26, it hits the bearing 35 of the unit for instance about 65 mm before the press 23 reaches its bottom position. The unit 26 travels back and forth. After that the final folding tool 27 hits the workpiece 21/22 and performs the final folding. As the press 23 returns upward, the unit 26 performs the same movement once more, but without hitting the workpiece 21/22. This extra movement is due to the mechanical guiding and serves no purpose.

Since prior art table-top units had problems with lateral forces during folding, a solution to these problems has been developed. This involves two hardened steel plates sliding against one another to prevent the upper and lower parts of the unit 26 from being displaced. To prevent the unit 26 from falling forward and damaging the bed 30 if the springs in the unit 26 should break, there are also adjustable stops in the unit 26. Corresponding stops are also arranged so that the unit 26 cannot move too far backward. Since the wedge 25 does not act on the unit 26, the springs pull the unit 26 to cause abutment of the rear stops. Sheet Holder

When folding takes place, the workpiece 21/22 must be located on the bed 30. Therefore there is a sheet holder 24 which presses the workpiece 21/22 against the bed 30. In the preferred embodiment, the sheet holder 24 is mounted in the upper part 28 of the tool and moves together with the same during the major part of the movement of the press 23. The sheet holder 24 contacts the workpiece 21/22 for example 70 mm before the press 23 reaches its bottom position, which is just before prefolding. The sheet holder 24 then holds down the workpiece 21/22 using a pressure of about 1200 kg. Since the sheet holder 24 must move vertically and is not allowed to move horizontally relative to the tool upper part, it is mounted with ball bushings 32. The ball bushings 32 lock the sheet holder 24 in all degrees of freedom except the vertical. The own weight of the sheet holder 24 is not sufficient to generate the pressure required for the workpiece 21/22 to stay locked. To obtain this pressure, gas springs 33 are mounted with the ball bushings 32. Each gas spring 33 has a variable boost pressure to be able to generate exactly the desired holding-down pressure. To reduce the total height of the sheet holder 24, the springs 33 are lowered into the mounting plate by means of a fastening bracket. Figs 7-8 show the sheet holder 24 with ball bushings 32, associated shafts, springs 33 and framework. This entire package is mounted directly in the upper part 28 of the tool. Here also the fingers 36 holding the workpiece 21/22 are to be seen. This part of the sheet holder 24 is unchanged compared to prior art. An adaptation and improvement have been made to reduce the height of the sheet holder 24, which in turn reduces the height of the tool. Other Parts

In order not to affect the folding result, that part of the bending tool 31 which is in contact with the sheet holder 24 is unchanged compared to prior art. The remaining part 27 is adjusted to allow mounting in the upper part 28 of the tool. The part of the folding tool that remains cannot, however, be changed.

The upper and lower parts are suitably designed as frameworks either of thick steel plates or of some kind of beams, such as I beam. Such frameworks resist great forces without sagging.

The same bed 30 as used in traditional table-top folding is placed in the tool 20 to provide support to the workpiece 22. Thus no modifications have to be made to the bed 30 for it to function in the new concept. By using a press 23 to generate the required bending forces, it is, however, due to the invention possible to keep the press 23 slightly longer than is usual in table-top folding. In this way, the glue that is used for gluing the fold will have more time to flow out and fill the entire fold. This results in a closer fold than is usual and besides allows a certain reduction in the amount of glue .

Claims

1. A bending apparatus, which is adapted to bend an edge flange of a workpiece (21/22), that is of sheet metal and is clamped by a sheet holder (24) in a bed (30), and which comprises at least one prebending tool (31), which is arranged on a first tool holder (29) and is movable relative to the same by a parallelogram linkage, and at least one final bending tool (27), which is arranged on a second tool holder (28), c h a r a c t e r i s e d in that the bending apparatus is arranged in a press (23) , which has a first and a second press unit which are displaceable toward and away from each other, the first tool holder (29) being mounted on the first of said press units together with said bed

(30) and the second tool holder (28) being mounted on the second of said press units, and both the prebending tool

(31) and the final bending tool (27) being driven by the displacing movement of the second press unit relative to the first press unit.

2. A bending apparatus as claimed in claim 1, in which the prebending tool (31) is arranged to cooperate with a cam mechanism (25, 34, 35), by means of which the displacing movement of the second press unit is transferred to the prebending tool (31) for controlled driving of the same .

3. A bending apparatus as claimed in claim 2, in which the cam mechanism comprises a pin means (35), which is arranged on the prebending tool (31) , and a cam groove (34) in the second tool holder (28), in which cam groove (34) said pin means (35) is to be inserted for said controlled driving.

4. A bending apparatus as claimed in any one of claims 1-3, in which the final bending tool (27) is rigidly connected to the second tool holder (28) .

5. A bending apparatus as claimed in claim 4, in which the final bending tool (27) is column-shaped and directed toward the first press unit.