The present invention also relates to a method for flanging a first workpiece which, by hemming, is to be joined together to a second workpiece, comprising the steps that the workpieces are placed and positionally fixed against one another and against a bed so that an edge portion on the first workpiece extends outside and approximately in a plane with an edge portion on the second workpiece, and that the projecting edge portion is formed so that it will be transversely directed, possibly at right angles, in relation to the edge portion of the second workpiece.

BACKGROUND ART In the joining together of two sheet metal parts in such contexts where the requirements on surface finish are extremely high-as is the case in the automotive industry-use is often made of folding or hemming as a better alternative to welding. In hemming, one of the workpieces is given an edge portion which extends over the edge portion of the second workpiece and which is folded over the. second workpiece and urged against it so that the edge on the second workpiece will be accommodated between the first workpiece and its folded-over edge portion.

For the above-mentioned folding over of the edge portion of the first workpiece, use is made of a hem roller which, by means of a suitable movement device such as an industrial robot, for example, is displaced in the longitudinal direction of the edge portion. Before the hem rolling or folding, the first workpiece has its edge portion projecting approximately at right angles or at least transversely directed in relation to the plane of the portion of the workpiece

lying inside the edge portion. The hem roller is then passed as a rule three different times along the edge portion so that this is bent stepwise to a final bending of approximately 90°.

The two US Patent Specifications 5,224, 253 and 5,267, 387 described hemming of the above- intimated type. In addition, the Patent Specifications show how the hem roller may be guided along a guide path on the bed on which the two workpieces rest during the hemming operation. The precision in the hemming operation is hereby improved.

The upwardly projecting or transversely directed edge portion on the first workpiece is normally given its form in connection with the forming operation of the first workpiece in a press.

However, there are situations where the configuration of the workpieces in general is such that the second workpiece cannot be placed in or on the first workpiece if the first workpiece has been given its transversely directed flange. The reason for this may, for example, be that the space which the flange defines is undercut. In such situations, the flange must be given its direction once the second workpiece has been placed in the correct position on the first.

In order to realise such a flanging, apparatuses are previously known in the art which operate with a number of sliding jaws. An apparatus displaying such sliding jaws will be complex in design and construction since it must be specifically adapted in response to the configuration of the workpiece. Particular problems arise moreover in curved edge portions on the workpieces.

It is not inconceivable to imagine that a technology analogous to the above described hemming might also be used to provide the first workpiece with the transversely directed flange. However, this is not feasible for the simple reason that, today, there are no movement devices, in particular industrial robots, in existence which can, with the sufficient precision, guide the roller which is to be used in the flanging operation. Contemporary industrial robots are quite simply provided with far too great resilient suspension and flexing to be able to operate with the precision that is required.

SUMMARY OF THE INVENTION The present invention has for its object to design the apparatus intimated by way of introduction such that this may be employed for flanging from planar state to a transversely directed state whence the edge portion may subsequently be hemmed in a conventional manner or folded over in a different conventional manner. The present invention further has for its object to design the apparatus so that it will be economical in manufacture and operation and will also give the requisite high precision.

The objects forming the basis of the present invention will be attained if the apparatus is given the characterising features as set forth in appended Claim 1.

In that, as is disclosed in appended Claim 1, at least a part of the forces that occur because of the bending of the edge portion can be relieved from the movement device and directly absorbed by the bed on which rests the workpiece, there is quite simply no possibility for outward flexing or resilient movements in the movement device, at least not in this direction.

The present invention also has for its object to design the method intimated by way of introduction so that this may be employed for the relevant flanging under consideration here with high precision, high output productivity, and using simple and economical tools.

The object forming the basis of the present invention will be attained in respect of the method, if this is given the characterising features as set forth in appended Claim 8.

In that at least a part of the forming forces during the folding operation are absorbed directly by the bed on which rest the workpieces, considerably improved precision in the folding operation will be achieved.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS The present invention will now be described in greater detail hereinbelow, with reference to the accompanying Drawings. In the accompanying Drawings:

Fig. 1 is a cross section through an edge portion of a bed on which two workpieces rest during a flanging operation; Fig. 2 is a view corresponding to Fig. 1 in which, however, the workpiece has angled configuration from the outset; Fig. 3 shows the embodiment according to Fig. 2 when the flanging has been completed; Fig. 4 shows the embodiment according to Figs. 2 and 3 when a first step of the subsequent hemming has been completed; Fig. 5 is a view corresponding to Fig. 4 when a second hemming step has been completed; and Fig. 6 is a view corresponding to Fig. 5 when the final hemming step has been completed.

DESCRIPTION OF PREFERRED EMBODIMENT In Fig. 1, reference numeral 1 relates to a bed on which a first workpiece 2 and a second workpiece 3 rest. The two workpieces 2 and 3 consist of sheet metal and may, for example, comprise components which are to be included in an automobile body. The first workpiece 2 has an edge portion 4 which extends outside an edge portion 5 on the second workpiece 3 and which, before the folding, lies approximately in a plane with this edge portion 5, as is illustrated by the broken line 6.

The second workpiece 3 has an edge line 7 which lies one or a few millimetres inside the corner edge line 8 of the bed 1. The exact distance depends naturally on material dimensions, but in one practical embodiment in which the first workpiece 2 consists of an automobile body panel of a thickness of 0.8 mm and the second workpiece 3 consists of a reinforcement beam of a material thickness of 1.2 mm, the distance is of the order of magnitude of 2-2.5 mm.

In particular in such situations where the second workpiece 3 is of greater material thickness than the first workpiece 2, the edge of the second edge portion 5 will function as an abutment or indication for the bending line between the first workpiece 2 and its edge portion 4.

The apparatus in which the flanging is carried out displays suitable devices, on the one hand for compression and relative positional fixing of the two workpieces 2 and 3 in relation to one another, and, on the other hand, for compression and positional fixing of the two workpieces against the bed with the orientation in relation to the bed which was described above.

In order to strengthen the above-described indication action, the device which positionally fixes the workpieces 2 and 3 to one another and holds them against the bed 1 may include means which compress the edge portion of the second workpiece 3 against the first workpiece 2.

A movement device, for example an industrial robot, carries a flanging roller 9 which rotates about a shaft 10. The flanging roller 9 has a flanging surface 11 and a"radial"support surface 12 and an"axial"support surface 13. Corresponding to the support surfaces 12 and 13 of the flanging roller, the bed 1 has a"radial"support surface 14 and an"axial"support surface 15.

During operation, the radial support surfaces 12 and 14 are, contrary to that which is described in Fig. 1, in abutment against one another, which also applies to the axial support surfaces 13 and 15. Further, the dividing line 18 between the flanging surface 11 of the roller and its support surface 12 lies flush with the corner edge line 8 of the bed 1.

The flanging roller illustrated in Fig. 1 is designed to carry out a first step of the flanging where the edge portion 4 on the first workpiece 2 is bent from the position according to the broken line 6 to the position illustrated in Fig. 1 or possibly somewhat more so that the bending angle may amount to 30-50°. From the position according to Fig. 1, the edge portion 4 is bent by means of a flanging roller of the type which is illustrated in Fig. 3 so that thereafter the edge portion will be in the position which is illustrated by means of the broken line 16. During the flanging operation, the flanging roller is pressed in a radial direction so that the radial surfaces 12 and 14 abut against one another. The force which, in this instance, is consumed is partly the desired compression force between the support surfaces and in addition also the radial component of the force which is consumed for the deformation of the edge portion 4 from the position along the broken line 6 to the position along the solid line 4.

On the other hand, in the axial direction the forces generated by the flanging operation will be considerably greater than the radial forces at least in the first flanging step. These axial force components exercised by the flanging operation assist in holding the axial support surfaces 13 and 15 in abutment against each other. Consequently, no abutment force generated by the movement device between these support surfaces 13 and 15 need hardly exist. Thus, the flanging force gives an additional force in the axial direction which assists in guaranteeing high precision.

The axial support surface 13 of the flanging roller 9 may be considered as a flank or end surface for the roller and is, in the illustrated embodiment, conical. With a corresponding modification of the configuration of the bed 1, the axial support surface 13 of the roller may also be substantially planar.

The embodiment according to Figs. 2 to 6 corresponds to the embodiment according to Fig. 1 if the two sheet metal workpieces 2 and 3 are seen as bent approximately 90° in the clockwise direction at the broken line 17.

In this embodiment, the support surfaces 14 and 15 of the bed 1 are disposed on an upwardly directed (on the Drawings) strip-shaped projection 19 which surrounds the two workpieces 2 and 3. As a result, the two workpieces are held positionally fixed in relation to one another and in relation to the bed 1 during the flanging and subsequent hemming.

In Fig. 2, which shows the first flanging step, the flanging surface 11 of the flanging roller 9 folds the edge portion 4 of the first workpiece approximately 45° in the clockwise direction.

In the second flanging step, which is shown in Fig. 3, the edge portion 4 is folded by a cylindrical flanging surface 11'so that the total bending angle of the edge portion 4 amounts to approximately 90°.

After the flanging which was carried out according to Fig. 3, the edge portion 4 is located transversely directed in relation to the plane of extent of the edge portion 5 of the second workpiece, for which reason a further bending of the edge portion 4 of the first workpiece 2 in a clockwise direction down into abutment against the edge portion 5 of the second workpiece 3 may be carried out as illustrated in Figs. 4-6 by the application of a hemming operation which is described, for example, in Swedish Patent Specification 9901397-1 under

publication number SE-C2 514 087. It will be apparent from Figs. 4-6 that the hemming is carried out inn accordance with Fig. 4 in a first step with a hemming angle of the order of magnitude of 45°. In addition, a second hemming step is carried out in accordance with Fig. 5 with an additional hemming angle of the order of magnitude of 40°, while the final hemming is carried out in accordance with Fig. 6 until such time as both of the edge portions 4 and 5 are urged tightly against one another.

In Fig. 1, the flanging roller 9 has been illustrated as a single roller of one piece manufacture which is rotary about a shaft 10. In connection with Figs. 2 and 3, a flanging roller 9 of one piece manufacture was also described. However, it is possible to employ two rollers where the one roller carries the two support surfaces 12 and 13 while the second roller carries the flanging surface 11 proper. Both of the rollers are rotary about a common axis which is illustrated by the ghosted line 10. In Figs. 2 and 3, the parting line between the rollers has been given reference numeral 20.