Method for making a building board

(54) (56) (57)

Välinge Aluminum AB, Kyrkogränd 1 260 Darko Pervan, Viken SE

AWAPATENT

Method of

Viken SE

PATENT INVENTOR INVENTOR'S OFFICE NAME

QUOTES PUBLISHED: SUMMARY:,. .

The invention /

AB manufacture of building board such as a floorboard refers to a method of manufacturing a building board (2) which has a sheet body (S) which is formed with a gripping pin (24), and a sheet strip (10) extending from the body (S). which is formed partly by gripping members (26, 28) which are bent around the gripping pin (24) for mechanical attachment of the strip (10) to the frame (S) and partly by a locking part (12) for enabling mechanical joining of the disc (2) with similar discs . The method is characterized in that the gripping details (26, 28) of the mold (10) are preformed before being bent around the grip pin (24), and the preformed gripping details (26, 28) are then bent around the gripping pin (24), the preform being such that the preformed gripping details ( 26, 28) as a result of if the bending bumps against the gripping pin (24) and thereby undergoes a deformed opposite directed deformation during a final phase of the bending.

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The numbers in brackets indicate international identification code, iNID code. Letters in clamps indicate international document code.

509 060

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AWAPATENT

Manager Sören Giver

Technical area

The present invention relates generally to a method of manufacturing a building board, such as a floorboard, which board is intended to be mechanically joined together with similar building boards and which board comprises, on the one hand, a board body and, partly on the mechanical joint, a metallist mechanically connected to and projecting from the disc body and formed with a locking member intended to engage a complementary locking groove of an adjacent building board.

More particularly, the invention relates to an improved technique for the mechanical connection between the metal strip and the disc body.

Background of the invention, features and advantages

A building board, for example a floorboard, provided with a projecting sheet metal molded with a locking detail for mechanical jointing is described in WO 94/26999. The content of that document is to be considered as part of the present description, and describes in detail how such building slabs can be designed and joined together. The background, features and advantages of the invention will be described in particular for this known type of floorboards, but it should be emphasized that the invention is useful for the manufacture of types of building boards other than floorboards, such as wall panels and roofing. Any reference to the term floor slab should therefore be considered to apply to building slabs in general.

WO 94/26999 thus describes a system for mechanical joining of floorboards. A first mechanical joint provides a mutual vertical locking of the joint edges and may be in the form of a groove / tongue joint along the joint. A second mechanical joint provides one

509 060 mutually horizontal locking of the discs in a direction perpendicular to the joint edges of the discs.

In order to illustrate the situation underlying the present invention, reference is now made to Fig. 1, which shows in section a joint between two identical, mechanically joined floorboards 2. The method according to the invention is useful in the manufacture of such floorboards. The design and function of the floorboards 2 are substantially in accordance with what is previously known from WO 94/26999. However, there are some differences with the prior art regarding the geometric shapes of a grip pin and a locking detail.

Each sheet 2 has an upper side 4 and a lower side 6 and may, for illustrative purposes, be assumed to be made of a sheet frame S of a laminated wood fiber board, plastic composite, wood or the like. The thickness of the body S can, for example, be 7 mm. To enable a mechanical joint, opposing joint edges 8 of the discs 2 are formed with an integrated, factory mounted sheet strip 10 and a lock groove 16, respectively. The strip 10 is preferably made of aluminum sheet and extends horizontally from the underside 6 of the sheet 2 in the direction of the second floor sheet and runs continuously along the length of the joint. However, the strip 10 may be divided into smaller parts which cover most of the length of the joint.

In order to achieve the required joint tolerances as well as simple laying, the molding 10 is integrated with the sheet, ie it is factory mounted and especially should not be mounted in connection with laying. As a non-limiting example, the width of the mold 10 can be about 30 mm, and its thickness is about 0.6 mm. Metal sheet materials other than aluminum sheet are conceivable.

The strip 10 is formed along its one side edge with a locking member 12 bent from the sheet material, which has an active locking surface 14, the height of which is, for example, 1.0 mm. In the joined state, the locking member 12 is accommodated in a locking groove 16 which is formed the underside 6 of the second disk and which runs parallel to and spaced from the joint edge 8. The locking member 12 and the locking groove 16 together form the above-mentioned other mechanical joints, which lock the discs 2 mutually in the direction marked with D2. More specifically, the locking surface 14 of the locking member 12 acts as a stop stop against the surface 18 of the locking groove 16 which is closest to the joint edges 8.

When the disks 2 are joined according to Fig. 1, they can assume a mutual position in the direction D2 where there is a small clearance Δ as small as 0.01 mm between the locking surface 14 and the locking groove 16. This clearance allows the discs 2 to be moved in the direction of the joint without tools. This slidability provides a simplified lay-out and enables the short sides to be joined by snap-in. For a more detailed description of the function and benefits of this design, see WO 94/26999.

The strip 10 is mounted in a tolerance equalizing groove in the underside of the disc 2. In this embodiment, the width of the strip is approximately equal to half the width of the strip 10, ie around 15 mm. The function of and different ways of designing the leveling track are described in detail in WO 94/26999 and therefore need not be repeated here.

The strip 10 is mechanically attached to the frame S as follows. A groove 20 is received in the underside 6 of the disc body S at a distance from a recess 22 at the joint edge 8. The groove 20 can be formed either as a continuous groove along the entire length of the disc body S, or as a number of separate grooves. This groove 20, together with the recess 22, defines a salmon-tailed gripping pin 24 of the disc body S. In its attached state in Fig. 1, the strip 10 has a plurality of punched and bent tongues 26 and one or more lips 28, which are bent around opposite sides of the grip pin 24. The term grip detail will hereinafter be used as a general term for tongues, lips and corresponding

509 060 elements of the mold formed from the sheet material and bent around the disc frame S gripping pin 24.

Summary of the Invention

It is a principal object of the invention to provide a technique for improving building slabs of the above mentioned kind.

A particular object of the invention is to provide a technique for improving the mechanical attachment of the strip to the disc body.

It is also an object of the invention to provide a technique for improving a manufacturing method for building boards of the above mentioned kind.

In order to achieve these and other objects, according to the invention, a method of manufacturing a building board with the features set forth in the claims is provided.

Thus, according to the invention, a method is provided for the manufacture of a building board showing a sheet body formed with a gripping pin, and a sheet strip extending from the frame, from which molding parts are formed which are bent around the gripping pin for mechanical fastening of the molding to the frame and partly as a locking detail for enabling of mechanical jointing of the disc with similar discs. The method is characterized in that the gripping details of the mold are preformed before being bent around the gripping pin, and the preformed gripping details are then bent around the gripping pin, the preforming being such that the preformed gripping details impinges on the gripping pin and thereby undergoes a deforming opposite of a directed shape bending.

The preforming that occurs during said final phase of the bend preferably results in a bias of the grip details of the mold against the grip pin.

Both the preforming and the bending of the gripping details are preferably carried out by means of punching means which operate substantially perpendicular to a main plane of the lis509 060 tenon / building board, and in a particularly preferred embodiment, such punching means are arranged in one and the same punching tool so that they are stationary relative to each other. and the bend.

In order to achieve a good fastening, and to eliminate tolerance problems, it is preferred that the grip details are preformed to such a degree that said shape change that occurs during the final phase of the bend consists partly of a permanent bending of the gripping details and a resilient return of the grip details. The back bending can thereby compensate for tolerances regarding, for example, the position of the gripping pin relative to the disc body or relative bending punching means, while a biasing force provided by the resilient return can be kept substantially constant.

As is already known from the above-mentioned WO 94/26999, the gripping pin is suitably provided with undercut gripping edges around which bending is performed. A particularly strong grip pin, suitable for the inventive biasing technique, can be obtained if the grip edges of the grip pin are formed with first, non-cut grip edge portions closest to the strip and associated, second, undercut grip edge portions. During the bending, the unsupported gripping edge portions provide a reinforcement of the gripping pin, while the preformed gripping members are biased substantially only against the undercut gripping edge portions.

Undercut gripping edges of the gripping pin preferably have an undercut angle of 10 ° -45 ° relative to the normal to a main plane of the building board, and the gripping details are preferably preformed at a pre-angle of 15 ° -90 ° relative to a main plane of the molding. However, in order to achieve the bias, the undercut angle should be smaller than the pre-bias angle, and preferably so much smaller that, even in the event of tolerance-caused deviations in the gripping pin position, there is always a permanent rebound of the gripping details and a resilient return thereof. A return angle of the order of 45 ° has proven to be suitable.

In a preferred embodiment, the preform is accomplished by bending each gripping member at a predetermined bending angle at a first point away from a free end of the gripping member, and the bending is accomplished by bending the thus-formed gripping waist at a second point further from said free end than the first point. In particular, the bend can be performed against a punch pad separate from the grip pin, while the bend is performed only after the strip has been positioned against the grip pin, which thereby acts as a punch pad.

These and other embodiments of the invention will become apparent from the appended claims and from the following description of preferred embodiments.

With the inventive biasing technique with preforming and bending, a number of advantages of both manufacturing and product technical nature are obtained:

1st The sheet metal, which is typically made of wood or a wood-based material, or alternatively of plastic, can change its dimensions in moisture and temperature variations, while the sheet metal is only temperature sensitive. Such dimensional changes of the body and / or the sheet metal can adversely affect the mechanical connection between the body and the mold, and may in particular lead to undesirable joint gaps between the discs and poor strength.

A first advantage of the invention is that it ensures that such dimensional changes of the body and / or the strip do not impair the mechanical connection, since the mechanical connection between the mold and the disc body according to the invention can be biased and therefore can adapt automatically and

509 060 continuously to each dimensional change of these two components. Thus, it is ensured that the strip is always firmly and securely connected to the disc body, so that the mutual position relationship between these two components is maintained correctly and unchanged. The invention therefore avoids moldings that are loose and can be displaced relative to the disc body, and consequently eliminates unwanted joint cracking and poor strength due to loosely attached moldings.

2nd In addition to the aforementioned ambient-caused dimensional variations of the finished building board, a variation of the position of the grip pin relative to the disc body may also occur. This position variation is due to tolerances in the fabrication of the grip pin itself, especially if its gripping edges are formed by milling. The position of the gripping edges relative to the joint edge of the body may, as a result of these tolerances, vary slightly (for example on the order of ± 0.05 mm) from the disc body to the disc body. If the strip is positioned relative to the grip pin during manufacture, this position variation of the gripping edges can result in the strip being incorrectly positioned.

A second advantage of the invention is that the molding in combination with back bending and prestressing compensates for the above-mentioned position variation of the gripping edge, since an incorrect position of the gripping edges can be compensated by causing the gripping details of the mold to always bump against the gripping edges during its rebounding and rebounding to varying degrees. , depending on the position of the corresponding gripping edge.

Generally, it is desirable to be able to work with the highest tolerances possible during manufacture, as this reduces downtime, controls and tool grinding. A suitably designed

509 In this case, the 060 preform can withstand tolerances of, for example, 0.15 mm.

3rd A third advantage achieved with the invention is that the grip details of the mold, because they are preformed, can always be put in the correct position relative to the punches and yet bumped and rebounded by the grip pin positioned with a certain manufacturing tolerance relative to the punches. This advantage means that although the relative position between the gripping edges of the body and the bending punches would vary slightly between different punching operations, this does not adversely affect the quality of the mechanical connection between the strip and the disc body.

4th A further advantage achieved by the invention is that the biasing force exerted on the gripping pin by the mechanically fastened strip on the grip pin is substantially independent of both the punching force applied by the bending punches and the bending punch stroke length. The advantage of this is that (i) the bending punches and (ii) other punches required for the manufacture of the floorboard (such as bending punches, hollow punches, etc.) can be mounted in one and the same punching tool which during the production moves back and forth with one common to all punches. stroke length and joint press force. In particular, it becomes possible to allow the unbending punches as they move in the direction of the strip, to continue a bit past the point in the punching movement at which the fastening of the strip to the disc body is completed, whereby the other punches can complete their punching function in a final, inactive movement. at the bending punches. The biasing force can be controlled partly by the parameters of the sheet metal (plate thickness, layering ring, etc.) and partly by the position, angle and length of the preformed gripping details in relation to

509 060 the gripping edges and the undercut thereof, and partly by means of the mutual position between the gripping edges and the bending punches.

5th Forming of the locking detail of the mold is preferably carried out with punches which work substantially perpendicular to the main plane of the floorboard, and as mentioned above, it is advantageous if all punching steps can be carried out with the same punching tool. It follows that it is desirable that the fixing of the strip can also be carried out with punches that work perpendicular to the main plane of the floorboard. A further advantage of the invention is that the preform makes this possible, since the preform means that the punching equipment does not have to include any side bending punches for attaching the strip to the gripping pin.

Another advantage of perpendicular bending punches is that the compression pressure on these can be optionally very high without the risk of the grip pin being broken, while the fastening force against the grip pin can be controlled precisely with the mold's shape change. If, on the other hand, the bending punches had worked against the edges of the grip pin, whose position in such a punching direction varies due to the aforementioned manufacturing tolerances, the pressure on the grip pin would have varied considerably with the risk of tearing the grip pin or loose attachment of the strip.

6th A further advantage of the invention is that the preforming means that the thickness of the disc body can be reduced, and thus of the finished building board, because the height of the gripping pin can be reduced since the grip details to be bent around the gripping pin are deformed when bending is performed.

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Brief description of the drawings

Figure 1 shows in section two mechanically joined edge portions of two identical floorboards.

Fig. 2 is an overview view of a production line for the manufacture of floorboards according to the invention.

Fig. 3 shows the central part of a press included in the production line of Fig. 3.

Figs. 4A-4C show three consecutive work steps in a work cycle of the press of Fig. 3.

Figures 5A-5F illustrate preforming, bending and backbending according to the invention.

Figures 6A and 6B illustrate the advantage of the invention when there are tolerances regarding the position of the grip pin relative to the disc body.

Description of embodiments

Referring now to Figures 2-6 of the accompanying drawing sheets, a production line will now be described which is useful for the manufacture of building boards, such as floorboards, of the kind described above with reference to Figure 1 and in which production line an embodiment of the method of the invention is implemented. For the components of the floorboard, the same reference numerals will be used as in Fig. 1.

In Fig. 2, a flexible and malleable sheet metal 40, preferably aluminum sheet, is wound on a reel 42.

The aluminum plate 40 is output from the reel 42 to a plate feeder 46. The plate feeder 46 has the task of incrementally feeding (arrow P1) the directed plate blank 40 into a press 48. On its opposite side, the press 48 (arrow 30 P2) receives machined (milled) frames. S of, for example, compact laminate from a disk feeder 50.

In the production line in Fig. 2, sheet metal 40 is cut into separate sheet molds 10, locking members 12 are formed in the moldings 10 and the moldings 10 are mechanically fastened to disc frames S with 35 partial gripping details formed from the moldings.

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Fig. 3 schematically shows a central part of the press

48th An upper press table 52 carries a punch holder 56, and a lower press table 54 carries an associated press pad and a tool table connecting to the press pad 58

60 forming an upper support surface 62 (see Fig. 4) for the body

S. The two press tables 52 and 54 are mutually movable in the direction shown by arrow P3.

Figures 4A-4C show the parts which are central to (i) the molding of the locking member 12 of the mold 10 and (ii) the mechanical attachment of the molding 10 to the frame S.

In Figures 4A-C, the press pad 58 and the tool table are shown on a larger scale. The molding pad 58 has at its top part a molding surface 64 against which the locking detail 12 of the mold 10 is formed, and a retaining surface 66. The molding surface 64 is formed by two part surfaces of a groove 68 which is formed with great precision in the molding pad 58 and extends perpendicular to the paper. plane along the entire width of the sheet metal 40. The tool table 60 has an abutment edge 70 extending transversely to the insertion direction P2 against which a predetermined portion of the body S is brought into contact as the body S is fed into the press 48. In the preferred embodiment, said predetermined portion is the upper joint edge 8 of the body S. The task of the abutment edge 70 is to act as a reference surface and for this purpose has an exact, predetermined position relative to the forming surface 64 which corresponds to a desired position on the upper joint edge 8 of the body S relative to the locking surface 14. The forming surface 64 and the reference surface 70 act together as a template against which the locking surface 14 and the upper joint edge 8, respectively, are positioned to achieve good tolerance values ​​of the finished building board.

Above the press pad 58 and tool table 60 are shown three punches S1, S2 and S3. In the embodiment shown, these punches operate in unison relative to the press pad 58, i.e. they are mutually stationary. Furthermore, two are shown from the punches

S1-S3 separate, vertically operating holders T1 and

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T2. The punches S1-S3 and the holders T1 and T2 are extended over the entire width of the sheet blank 40. However, S2 is made up of several mutually spaced modules.

The first punch S1 forms the locking surface 14 of the locking member 12 against the forming surface 64. The second punch S2 and the third punch S3 serve to bend the tongues 26 and the lip 28, respectively, around the grip pin 24 of the body S to mechanically attach the strip 10 to the body S. The second punch As mentioned above, S2 is made up of modules, each module serving to rebound a corresponding tongue and can be, for example, 10 mm wide. To punch

SI to be able to perform the bending of the lip 28 is the latter preformed in the sheet blank 40 upstream of the production line, and in order for the punch S2 to be able to perform said bending of the tongues 26, the latter are preformed in the sheet blank 40 upstream of the production line so that there are openings 72 in the production line. plate blank 40 for receiving the second punch S2.

A working cycle of the production line described above will now be described in more detail. First, the portion of the sheet blank 40 which is to form the strip 10 is inserted over the press pad 58. During this feed, the lip 28 and the tongues 26 are preformed and the strip 10 is still contiguous with the remainder of the sheet blank 40. However, some partial release may have occurred previously, but in any case, the list 10 in this input step is not handled as a separate unit. Substantially at the same time, a frame 10 is inserted over the tool table 60 and positioned with its upper joint edge 8 to abut against the reference surface 70.

Thereafter, holders T1 and T2 are activated to the holding position shown in Fig. 4B. T1 fixes the strip 10 relative to the press pad 58. T2 fixes the strip 10 relative to the underside 6 of the body S and fixes the frame S relative to the tool table 60 and thus also to the reference surface

70th T1 and T2 are retained in this holding position until

509 060 that the locking member 12 has been formed and the strip 10 has been mechanically attached to the frame S.

As the next step, the punches S1-S3 are actuated unison according to Figures 4B and 4C so that (i) the locking surface of the locking member 12

14 is formed against the forming surface 64, (ii) the strip 10 is exposed from the sheet blank 40 by being cut with, for example, a punch, and (iii) the strip 10 is fastened to the frame S. These three steps thus occur substantially simultaneously. To ensure that SI goes to the bottom of groove 68, the punches S2 and S3 go slightly ahead of SI. Thus, after completing their re-bending of the tongues 24 and lip 28, the punches S2 and S3 may continue an additional piece during the final forming of the locking member 12 by the punch S1. All punching steps (cutting, shaping, bending) are clear when S1 reaches its bottom position against the forming surface 64.

As mentioned above, a preforming of the tongues 26 and of the lip 28 is performed. Before the strip 10 is positioned and fixed by the holders T1 and T2, both the tongues 26 and the lip 28 are pre-bent into the position shown in Fig. 4A. The pre-bending of both the tongues 26 and the lip 28 is accomplished in previous (not shown) manufacturing steps. When the punches S2 and S3 are activated (Figures 4B and 4C), a second bending will occur around the gripping pin 24. The pre-bent portion will then undergo some back bending, with the result that a bias occurs in both the tongues 26 and the lip 28.

Figures 5A-5F show in more detail the attachment of a tongue 26 to the grip pin 24. The corresponding technique is used for the lip 28 and is therefore not described. The angles of cutting and the pre-cutting angles may be the same on both sides of the base 24 or alternatively may be different.

The gripping edge of the gripping pin 24 about which the tongue is bent has an undercut gripping edge portion 24a which forms an undercut angle of about 30 ° relative to a normal N to the main plane of the strip 10, and one with the normal

509 060

N parallel, non-undercut gripping edge portion 24b, which provides a reinforcement of the end portion of the gripper pin 24 at the bend.

Fig. 5A shows how the tongue 26 has already been preformed when the strip 10 is positioned on the gripping pin 24. An outer part

26b of tongue 26 has been bent downward (by means of a notch upstream of the upstream line in the production line) with a pre-angled angle of about 70 ° relative to the main plane of the strip 10, around a point P1 which is distant from the gripping pin 24. The direction of the bent outer part 26b is marked with a line F in Fig. 5A. An unformed inner portion 26a of the tongue 26 is extended from the grip pin 24 to the point P1.

The preforming of the gripping details of the mold can alternatively be carried out in several stages, and the preforming can be achieved as here by bending, and / or by a more continuous curvature of the gripping details. Both the outer portion and the inner portion may be preformed, and no defined bending point between the inner portion and the outer portion need not be present.

Fig. 5B shows how the bending punch S2 has been brought into contact with the tongue 26 and started the bending around the grip pin 24 at a point P2. The direction of the preformed outer portion 26b hereby substantially coincides with the normal N, as shown by the line F.

Figures 5C and 5D show how the direction line F then, during continued bending around the point P2, passes the normal N, with the outer portion 26b of the tongue 26 increasingly approaching the undercut gripping edge portion 24a.

In Fig. 5E, the outermost tip of the outer portion 26b of the tongue 26 has just abut against the undercut grip portion 24a of the gripping pin 24 at a point P3.

During the final bending around point P2, from the state of Fig. 5E to the state of Fig. 5F, the outer portion 26b of the tongue 26 is prevented from penetrating into the gripping pin 24 to the dotted line position.

509 060 illustrating the original bend angle. Instead, the outer portion 26b is forced to bend back around the point P1 in a clockwise direction in the figures, that is to say the opposite bend direction around the point P2. In the embodiment shown, the outer portion 26b is rebooked over a rebound angle of about 40 ° (70 ° -30 °). This rebound is so large that it consists of both a permanent rebound (for example, on the order of 39 °) and a resilient return (for example, on the order of 1 °). Because part of the return is resilient, a bias is obtained between the tongue 26 and the grip pin 24.

The tolerance in machining the frame S is in the order of 0.02-0.03 mm with today's technology, and in addition, machining tools will wear out more than punching tools, so the measurement accuracy in machining the frame S can in practice amount to ± 0.05 mm. Therefore, the relative position between the bending punches and the corresponding gripping edges of the gripping pin 24 may vary. Figures 6A and 6B illustrate how this position tolerance of the grip pin is compensated by the invention. It should be noted here that it can be a production-technical advantage to work with large tolerances for a number of reasons.

Figures 6A and 6B correspond to the final state of Fig. 5F and show the result after completed bending in two extreme cases. In Fig. 6A, the left gripping edge of the gripper pin 24, due to machining tolerances, is offset maximally from the punch S2. The position of the grip edge is marked with a line Lmax and the position of the punch S2 is marked with a line L2. In Fig. 6B, the same gripping edge, due to machining tolerances, is instead displaced minimally from the punch S2. The position of the gripping edge is thereby marked with a line Lmin.

Thanks to the preforming and return of the present invention, mechanical bonding in both of these extreme cases is certainly achieved. In the situation of Fig. 6A, the outer portion 26b of the tongue 26 is rebooked slightly less than the situation of Fig. 6B. However, the total bending angle in both cases is so large that the resilient return angle is the same in both cases, ie the magnitude of the biasing force is not affected by the position tolerances of the gripping edge.

In Fig. 5A there is inscribed a circle C, whose center coincides with the bending point P2 and whose radius corresponds to a greatest distance from the point P2 to the tip of the outer portion 26b. During the bending in steps 5B-5E, the outer portion of the tongue 26 moves within this circle C. As the radius of the circle C decreases as the bending angle increases, it will be appreciated that the thickness of the body S and thus the thickness of the finished building board 2 can be reduced thanks to the preform, since the depth of the recesses 20 and 22 in the underside 6 of the body S can be reduced.

As shown in Fig. 4C, the underside of the bending punches S2 and S3 is at a distance A from the disc body S, at the moment the bending operation is completed. Thanks to this spacing A, it is ensured that the final forming of the locking member 12 in Fig. 4C can be safely completed by the punch S1 in the bottom against the punch pad 58.

Since the lip 28 is continuously extended along the entire length of the strip 10, while the tongues 26 are spaced apart in the longitudinal direction of the strip 10, the pressure on the lip 28 from the punch S3 will be higher than the pressure on the tongues 26 from the punch S2. The horizontal force F3 generated by S3 (Fig. 4C) will thus be greater than the opposite force F2 from the punch S2. The effect of this force difference (F3-F2) is that any possible web shape of the body S, which could give rise to an undesirable gap in the joint between two interconnected discs, is rectified by pressing the disc against the impact edge 70 of the tool table 60.

The above-described embodiment examples can be varied in several ways within the scope of the appended claims. Example 509 060, for example, those parts of the locking members 26, 28 which in the embodiment lie horizontally before the bend may instead be slightly deflected when the bend is started. Furthermore, the undercut edge may be formed in ways other than those described above, for example with a step-step shape. Alternatively, the gripping edge may not be undercut, where fastening is done with only frictional force and / or penetration of the gripping pin.

509 060