AU669113B2 - Self-drilling hollow rivet - Google Patents

Description

0I1 DATE 24/01/94 APPLN. ID) 21521/92 AOJP [JAIL 14/04/94 PCI NUMBER PCT/EP92/01394 AU9221521 (51) Internationale lPatentklassifilkation 5 F16B 19/08 (11) Internationale \'eriiffentlichuingsntiiuert.

(43) lnernationailes Veriiffentlichungsdatum: 6.

WO) 94/00701 (2 1) Internationales Aktenzeichcn: (22) Internationales Anmeldedatuni: PCT, EP92 01394 20. Juni 1992 (20.06.92) (81) Best Imnmiungsstaten AU, CA. JP, KR. RU., US. europiische'. Patent (AT. BF. CHI IK, FS. FR. (G13 (MK IT, LU, MIC, NL, SE).

Ver6ffentlicht Alit internationale', RchelrchL'nlnric Ia.

(71) Anmelder (flir alle Bcstiniozungsswwei amser LTS,: NIAGE AG [CH 'CHI; Industriestrasse, Cl--1781 Courtaman (C G-.H.R4NG ,+4-nfTedjDE4DE]-, Herman n-Hesse- SrAe2,D-7290FL~rudenstmdttDE).

(72) Erinder-, und Erfinder/Aninelder (nur i US) SPON ER, Wolfgang [AT' CHI; Le Castel 16, CH-1700 Fribourg (CH).

(74) Anwalt: KOHLER SCHMI D PARTNER, Ruppmannstrafge 27, D-7000 Stuttgart 80 (DE).

669 13 (54) Title: SELF-DRI LLING HOLLOW RIVET (54) Bezeichnung: SELBSTBOH RHOHLNI ET (57) Abstract 4- A self-drilling hollow rivet (10) has a bit (11) and a rivet sleeve (12) to hold a first and a second component (16, 17) together. In order to secure the E components (16 and 17) rigidly together, a rivet hole (15) is drilled by the bit il H1 I I) i n a first operation. Thle bit I I) is given a positive a nd force fit i n th e rivet20-1/ sleeve f12) by means of ribs At the outer periphery of a set heat (20)18' there are flat surfaces with which a setting device engages. The setting device 1 2 1 rotates the self-drilling hollow rivet. The rotary forces are uniformly transferred by the self-drilling hollow rivet (12) to thle bit (11) via the ribs (19, 19") without the drill shaft's (18) breaking at the weakened point (19) during the drilling process. Once the drilling process is completed, the self-drilling hollow rivet (10) is set in a second operation in which the drill shaft (18) is pulled in the direction of thle arrow Here, the claws of the setting device engage inl the annular grooves In this setting process the drill head (14) is pulled in- 1 to thle rivet sleeve 12) and the latter almost completely surrounds the drill head 19 5 9 17 The closing head is made and the hollow rivet is hermetically sealed. 12 PCT/EP 92/01394 P 5942 PCT MAGE AG et al Replacement Pages 1 to 3b filed on June 7th, 1994 Self-Drilling Hollow Rivet The invention concerns a self-drilling hollow rivet comprising a rivet bushing and exhibiting a set-head on one end and a closing head capable of formation on the other end, with a drill shaft axially penetraing through the rivet bushing and exhibiting rotation carriers on either side of an intended breaking location and provided on one end with a drill head and on the other end of the drill shaft and with tensioning carriers for a setting apparatus, whereby the drill head tapers towards the rivet bushing or towards the rivet bushing section.

A self-drilling hollow rivet of this type has become known in the art through DE-OS 2554577.

With this type of rivet, construction components comprising the same or different materials can be permanently connected to each other. Rivets have the advantage, compared to other types of connecting means, that the construction components to be joined do not distort and do not undergo a structural change as can occur in welding. Construction components from differing materials can be easily, permanently and securely connected to each other. With modern riveting systems, economical connections of highest quality can be effected.

2 The self-drilling hollow rivet which is known in the art exhibits rotation carriers on both sides of an intended breaking location which comprise parallel opposing flat surfaces on the drill shaft which run in a longitudinal direction. The smooth surfaces of the drill shafts lie closely adjacent to corresponding opposing surfaces of the rivet bushing. When the drill shaft is rotated, the rivet bushing rotates therewith.

Tension carriers are formed on the other end of the drill shaft opposite to the drill head in order to pull the drill shaft, under exercise of substantial tensioning force through the rivet bushing and in opposition to a resistant force produced by the drill head, through the rivet bushing.

In the course of this tensioning process the rivet bushing is deformed and a closing head forms. The drill shaft simultaneously shears at the predetermined breaking location and the drill head falls out of the closing head. The rotational carriers on both sides of the intended breaking location are provided in order to transmit a torque which is produced by the drilling procedure to the drill head without breaking the drill shaft.

In order to successfully transfer the torque to the drill head and to relieve the intended breaking location it is necessary for the parallel surfaces of the drill shaft to precisely seat on the opposing surfaces of the rivet bushing without play. This is in particular necessary for applications with which the rotation direction of the drill must be changed. For this reason the self-drilling hollow rivet known in the art is difficult and expensive to produce.

3 Since the outer wall of the rivet should be seated as closely as possible on the inner wall of an object into which the rivet is to be set, the overcoming of a certain amount of frictional force is necessary. In consequence of the rotation of the drill shaft, it is necessary for the rotation carriers of the self-drilling hollow rivet known in the art to already carry a substantial load during rotation, since the bore resistance as well as the frictional resistance between the rivet bushing and the adjacent wall must be overcome. For this reason the intended breaking location is not sufficiently relieved.

Furthermore, by means of the shoulder formed between the end of the rivet bushing and the drill head, one guarantees that the drill head does not sink into the rivet bushing during the setting procedure. For this reason the drill head either continues to hang loosely in the rivet bushing after the setting procedure or it falls out of the closing head.

The formed shoulder has, however, the disadvantage that a pulling back leads to the formation of cracks in the rivet bushing when setting the rivet and when forming the closing head.

Furthermore the self drilling hollow rivet known in the art has the additional disadvantage that the rotation carriers must already be formed during production and fabrication.

The rotational carriers of the drill shaft and their corresponding recesses in the rivet bushing require a difficult preorientation prior to each boring procedure.

An additional self-drilling hollow rivet is known in the art 3a fromra US-A 3,935,786 with which the rotational carriers comprise longitudinal ribs, which are difficult to fabricate, (on the drill shaft) and corresponding recesses in the rivet bushing.

The self-drilling hollow rivet can also be driven via the drill shaft.

A self-drilling hollow rivet which can be driven via the set-head is known in the art from DE-OS 2554577, whereby the rotation carriers are not configured on both sides of the intended breaking location.

It is therefore the purpose of the presently filed application to further improve a rivet of the above mentioned kind in such a fashion that the drilling and setting procedure can be securely enacted without waste to produce a tight rivet connection.

This purpose is achieved in accordance with the invention in that the rotation carrier penetrates into the material of the rivet housing, the rotation carriers border, without exhibiting a shoulder, on the taper of the drill head, and the set-head exhibits at least two flattened surfaces on the outer periphery which run parallel to the plane of a drill axis.

It is possible, using the self-drilling hollow rivet in accordance with the invention, for the drilling procedure to be securely carried out since the setting apparatus can tightly frictionally engage the set-head on its outer periphery. The torque occurring during the drilling procedure is securely transferred via the rotation carriers (>A1TC 3b formed on both sides of the intended breaking location without having an undesirable shearing on the drill shaft during the drilling procedure in the vicinity of the intended breaking location. Since the rotation carriers penetrate into the material of the rivet bushing, the fabrication of recesses in the rivet bushing is not necessary. Neither is it necessary to preorient the rivet bushing and the drill shaft prior to the setting procedure.

When the drilling procedure is ended it is possible for the self-drilling hollow-rivet to be securely set and the shoulder-free conical taper of the drill head guarantees that the rivet bushing is securely widened to an extent which depends on the conical shape without the formation of cracks to form a closing head. Thereby the drill head is pulled into the rivet bushing so that the rivet bushing nearly completely surrounds the drill head. The closing head is thereby stabilized and tightly closed.

)i 4 The drill shaft does not break at the provided intended breaking location until the drill head is pulled into the rivet bushing to undergo a secure connection therewith.

Even prior to the setting procedure the rotation carriers assure that the rivet bushing and the drill, comprising the drill head and the drill shaft, constitute a firmly joined unit.

The setting apparatus can engage the self-drilling hollowrivet in an optimum rotation-transferring fashion by means of the surfaces on the set-head running parallel to the rivet bushing.

In further configurations of the invention, the drill shaft and the drill head are manufactured as integral parts and both the drill head as well as the drill shaft are made from a hardened material.

This has the advantage that no additional weak locations on the drill can be formed during the drilling procedure itself. The drill can break only at the intended breaking location when the tensioning forces exceed a predetermined amount. In the event that the drill shaft, along with the drill head, is uniformly hardened, it is possible for it to withstand even larger loads during the drilling procedure without damage.

In a further manifestation of the invention a sealing film is provided for on an inner wall of the rivet bushing or the rivet bushing section and a seal is arranged below the sethead. This has the advantage that the rivet connection can be sealed to a further extent in the event that same is 141 5 needed.

In a further manifestation of the invention, the rotation carriers are configured as ribs exhibiting a triangular shaped cross section which are evenly separated from the surface of the drill shaft in the longitudinal direction over nearly the entire length. The drill shaft is securely held in the rivet bushing.

This has the advantage that on the one hand the drill cannot unintentionally fall out of the rivet bushing, and, on the other hand, the rotational forces occurring during the drilling procedure can be uniformly transferred from the rivet bushing onto the drill shaft. Should the self-drilling hollow rivet in accordance with the invention be configured with rotation carriers on both sides of the intended breaking location as well as on the outer periphery of the sethead, it is not necessary to directly drive the drill shaft during the drilling procedure. It is sufficient to cause rotation of the rivet housing via the set head, that is to say, via the at least two flattened surfaces provided therein.

The conically formed drill head allows for the possibility of not only setting the self-drilling hollow rivet in one working step, rather also to permanently and securely spread out same. The hollow-rivet in accordance with the invention is, due to a relative motion between the drill shaft and the rivet bushing, sufficiently strongly spread in the vicinity of the closing head that the rivet bushing not only tightly fills the rivet hole over the entire length but the rivet bushing is also sufficiently widened on the end having the closing head that the drill head section with the conically 4' i running cross-section permanently seals the rivet hole.

In this fashion the self-drilling hollow rivet in accordance with the invention fulfills all extended requirements posed in high rise steel construction, crane construction, bridge construction with support carrier connections, supports, joints in steel frame work of trusswork and crane girdering, plate girders, in the construction of containers and in binding connections associated with automotive body, automotive and airplane construction. The self-drilling hollow rivet in accordance with the invention is particularly advantageous in the construction of facades and in the area of roof construction. Sheet metal overlaps of all kinds can be joined in a secure and rapid fashion. The self-drilling hollow rivet is not only easily handled but can also be worked in a rapid and secure fashion and can be equipped with all conventional set-head shapes. A leak proof rivet connection can be effected with the self-drilling hollow rivet. Furthermore, it is possible to also form holding grooves on the drill shaft or in the vicinity of the rotation carrier which are arranged neighbouring the drill head into which the plastic-deformed rivet bushing material flows during the setting procedure to effect an even stronger connection between the drill head and the closing head.

Should the drill shaft itself exhibit a triangular shaped cross-section this has the advantage that the drill shaft cannot slip in the setting apparatus during the drilling procedure, e.g. cannot twist or rotationally slip in an undesired fashion and the triangular shaped cross sectional form also guarantees that the conformed rivet bushing securely drives the drill shaft during the drilling procedure.

7 Further advantages can be derived from the description of the accompanying drawing. Likewise the above mentioned features and those which are to be explained further below in accordance with the invention can be utilized individually or collectively in arbitrary combination. The embodiments mentioned are not to be considered as exhaustive enumerations rather have exemplary character only.

The invention is represented in the drawing and will be further described with reference to embodiments.

Fig. 1 shows a cut through a self-drilling hollow rivet in accordance with the invention having a rivet bushing between a first and a second construction component; Fig. 2 shows a set and closed self-drilling hollow rivet in accordance with Fig. 1; Fig. 3 shows a cut through a section of a rivet bushing of a self-drilling hollow rivet with a drill shaft exhibiting holding and rotation carriers on both sides of a intended breaking location; Fig. 4 shows a further embodiment of a self-drilling rivet in accordance with the invention having a sidewards flattened set-head and a drill shaft exhibiting carriers which engage into the rivet bushing; Fig. 4a is a view in accordance with IVa IVa of Fig. 4; Fig. 5 shows an additional embodiment of a self-drilling 4 8hollow rivet in accordance with the invention having a shaft with an oval cross-section; Fig. Sa shows a view Va Va of Fig. Fig. 6 shows a further schematic representation of a sethead in accordance with the invention.

The individual figures of the drawings show the object in accordance with the invention in a strongly schematized fashion and are not to be taken to scale. The objects of the individual figures are represented partially in a greatly enlarged fashion so that their construction can be better shown. The cut surfaces of the drill head are represented in an oversimplified fashion.

Fig. 1 shows a self-drilling hollow rivet 10, represented in cross section, holding a drill 11 in a guided fashion. A rivet bushing 12 exhibits a shaft end 13 which is directed towards a drill head 14. The shaft end 13 borders on the drill head 14. The drill head 14 drills a rivet hole 15 in a first construction component 16 and a second construction component 17 which are to be permanently connected to each other. The drill head 14 exhibits, in the embodiment of Fig. 1, a diameter which is slightly larger than the outer diameter of the rivet bushing 12. When closing the set selfdrilling hollow rivet 10, the rivet bushing 12 is plastically deformed in the direction of the active sealing forces and the material-of the rivet bushing can flow into the free space between the rivet bushing outer diameter and the rivet hole diameter. In the embodiment of Fig. 1, the drill 11 exhibits a drill shaft 18 which is equipped with an intended breaking location 19 which is more or less distant from the 0 9 drill head 14. Rotation carriers are formed for the drilling process on both sides of the intended breaking location 19 as longitudinal ribs 19', 19'' having rectangular shape which tightly and securely press into the inner wall of the rivet bushing 12 when the drill 11 is pulled into the rivet bushing 12 during the manufacture of the self-drilling hollow rivet. The drill 11 is securely connected to the rivet bush>ng 12 by means of the longitudinal ribs 19', Should an auxiliary tool (not shown), for example, a setting apparatus be applied to the set-head 20 in such a fashion that the set-head 20 is pushed in a direction of a first construction component 16 and the drill shaft 18 is pulled in the direction of the arrow 20', whereby the closing forces act in a direction of arrow 20', it is possible for the drill head 14 to be pulled into the rivet bushing 12. The drill head 14 slides into the shaft end 13 via a ring-shaped conical surface 21 configured on the drill head 14 and rivet bushi.j material 12 surrounds the drill head 14. The shaft end 13 is carefully and evenly widened via the conically shaped surface 21 so that the material of the shaft end 13 can jacket the drill head 14 without cracking. The conically formed surface 21 and the surfaces of all longitudinal ribs 19' can be coated with a sealing film. Likewise a seal 22 is brought onto the surface of the set-head 20 which faces the first construction component 16.

The inner wall of the rivet bushing 12 can likewise be provided with a sealing film coating.

A section 26 of the drill shaft 18, also shown in Fig. 1, is provided with ring-shaped grooves 27 which have exemplary character only. Gripping claws of a setting apparatus can engage into the ring-shaped grooves 27 so that a defined force component can be generated in a direction of arrow 10 The drill 11, consisting of a drill shaft 18 and a drill head 14, is manufactured as one piece and the material from which the drill 11 is made is uniformly hardened.

Surfaces are provided, preferentially over the entire material thickness of the set-head 20, on the outer periphery of the set-head 20 which are longitudinally anc axially parallel to the rivet bushing 12 and which likewise serve as rotation carriers for the self-drilling hollow rivet 10. These surfaces, which are not shown in Fig. 1, are surrounded by the setting apparatus in clc'e frictional engagement and the se]f-drilling hollow rivet 10 rotates during the drilling procedure. The roLating rivet bushing 12 can also drive the drill shaft 18 so that it is not absolutely necessary for the drill shaft 18 itself to be driven.

Tt is also possible for holding grooves to be fashioned in the vicinity of the drill head 14 or in the vicinity of the longitudinal ribs 19' to additionally fix the drill head 14 in the rivet bushing 12 in a secure fashion. These holding grooves provide extra security for a set rivet.

The drill axis is indicated in Fig. 1 as 24.

Fig. 2 shows a self-drilling hollow rivet 10 in the set and closed state after the drill shaft 18, as represented in Fig. 1, has been strongly pulled in the direction of arrow to tear off the drill shaft 18 at the intended.breaking location 19. The end of the rivet bushing 12 facing away from the set-head 20 has been made into an enlargement 23 to form the closing head. The closing head overlaps the second construction component 17 and tightly surrounds the drill II head 14. The drill head 14 remains in the hollow region of the self-drilling hollow rivet 10 to stabilize the closing head. In this fashion, the first construction component 16 is permanently attached to the second construction component 17. The rivet bushing 12 has been enlarged via the conically running surface 21 and the longitudinal ribs 19' have pressed more firmly into the inner wall of the rivet bushing 12.

Fig. 3 shows a cross section of a rivet bushing section for example, the rivet bushing section 30 of a self-drilling hollow rivet. The drill shaft 30 is held in the rivet bushing section 30 and a drill head 32 is adjacent thereto.

The drill head 32 is arranged outside of an end 33 of the rivet bushing section 30. A conical expanded portion 34 is adjacent to the drill shaft 31 and points outwardly away from end 33. Longitudinal ribs 35,36 are formed as rotation carriers within the rivet bushing section 30 on the drill shaft 31 which additionally hold the rivet bushing section and the drill shaft 31 together. An additional contour 37 is formed on drill shaft 31. The contour 37 is dimensioned as an intended breaking location.

A surface section 39 is provided on the drill head 32 itself which works together with the end 33 of the rivet bushing section 30 when the drill shaft 31 is pulled back in the direction of arrow 40. The end 33 flows under plastic deformation about the drill head 32 and the two parts, the drill head 32 and the rivet bushing section 30, form a permanent connection. The hollow region of the rivet bushing section 30 is sealed by the drill head 32 and the longitudinal ribs 12 The conical expanded portions on the drill head 32 shown in Fig. 3 can exhibit differing angles for the dimensioning of the expanded portion. It is possible for the drill shaft 31 to exhibit, which is not shown in the figure, means on the end opposite to the drill head 32 to allow a setting apparatus, also not described, to grasp the drill shaft 31 in tight frictional engagement. The drill shaft 31 is manufactured from a hardened material. The drill shaft 31 and the drill head 32 are produced from a single material (mono-metal) Fig. 4 shows an additional embodiment of a self-drilling hollow rivet in accordance with the invention having a drill shaft 41 with ribs 42 formed as rotation carriers in the vicinity of the drill tip which engage into the inner walls 43 of a rivet bushing 44. The rivet bushing 44 is securely connected to the drill shaft 41 by means of the engagement of the ribs 42 which can be configured as guiding ribs. When the rivet bushing 44 is set into rotation, the drill shaft 41 and the drill tip rotate along therewith. In addition a first surface 46 and a second surface 47 are formed on the set-head 45 which are adapted to receive an auxiliary tool for the rotational motion. A contour 48 is provided for as an intended breaking location between, as viewed in the longitudinal direction, the ribs 42. Carriers 49 are provided for on the drill shaft 41 so that tensioning forces can be transferred in a defined fashion in the direction of arrow 49'. Setting apparatus claws securely engage the carrier 49' Fig. 4a shows a cut IVa IVa of Fig. 4. A plan view of the configuration of the set-head 45 is shown and the drill shaft 41 is cut. The surfaces 46,47 are visible.

X

13 The surfaces 46,47 can also form the peripheral surfaces of the set-head 45 configured in a four-, six- or eight-edged fashion.

Fig. 5 shows an additional manifestation of a self-drilling hollow rivet in accordance with the invention with an oval or triangular-shaped shaft cross section of a drill shaft 51 which engages into an opening of a rivet bushing 52 and penetrates from one end to the other end therethrough. The opening of the rivet bushing 52 has a cross section which is adapted to the cross sectional shape of the drill shaft 51 with necessary play. Should the cross sectional shape of the drill shaft 51 be adapted to the cross sectional shape of the rivet bushing 52, a frictional connection with regard to rotational motion in the direction of arrow 54 is guaranteed by this configuration. Likewise, a drill shaft 51 configured in this fashion cannot twist or slip in an undefined fashion in the setting apparatus. Ring-shaped grooves, which are not described further, are provided on the drill shaft 51 in order to pull the drill shaft 51 in the direction of arrow after completion of the drilling process to effect the formation of the closing head. Ribs or nubs 56, which also function as rotation carriers, serve to hold the drill shaft 51 securely within the rivet bushing 52. An intended breaking location 57 -s furthermore formed on the drill shaft 51.

Fig. 5a shows a cut Va Va of Fig. 5 wherein it is clearly shown how the cross sectional form of the drill shaft 51 and the opening of the rivet bushing 52 or the opening through the set-head 53 are adapted to each other. Surfaces 58,59, which are additionally formed on set-head 53, serve as rotation carriers.

L

o .C 14 Fig. 6 shows an additional configuration of a set-head 63 having a rivet bushing 62. Surfaces 64,65 are configured on the outer periphery of the set-head 63 axis-parallel to rivet bushing 62 and function as rotation carriers. A shoulder 66 borders on the surfaces 64,65 to serve as a flat seating surface for the ends of the setting apparatus.

A self-drilling hollow rivet 10 exhibits a drill 11 and a rivet bushing 12 which are intended to hold together a first and a second construction component 16,17. In a first working step a rivet hole 15 is bored with the drill 11 in order to permanently connect the construction components 16 and 17 to each other. The drill 11 is held via ribs 19',19' in a tight and secure fashion in the rivet bushing 12.

Flattened surfaces are provided for on the set-head 20 at its outer periphery into which a setting apparatus engages.

The setting apparatus sets the self-drilling hollow rivet into rotation. The rotational forces are evenly transmitted from the self-drilling hollow rivet 12 to the drill 11 via the rotation carriers 19',19'' without having the drill shaft 18 tear at the intended breaking location 19 during the drilling procedure. After completion of the drilling procedure, the self-drilling hollow rivet 10 is set in a second working step in which the drill shaft 18 is pulled in the direction of arrow 20'. In this fashion setting apparatus gripping means engage into the ring-shaped grooves 27. In this setting procedure the drill head 14 is pulled into the rivet housing 12 and the rivet housing 12 nearly completely encloses the drill head 14. The closing head is formed and the hollow-rivet is tightly sealed.

7-iii

Claims (4)

1. Self-drilling hollow rivet comprising a rivet bushing (12;30;44;52;62) which exhibits a set-head (20;45;53;63) on one end and which can be shaped into a closing head (23) at the other end, with a drill shaft (18;31;41;51) axially penetrating through the rivet bushing (12;30;44;52;62) which exhibits rotation carriers (19';35;42;56) on both sides of an intended breaking location (19;37;48;57) and which is provided at one end with a drill head (14;32) and at the other end with tension carriers (27;49) on the drill shaft (28;41;51) for a setting apparatus, whereby the drill head (14;32) tapers towards the rivet bushing (12;44;52;62) or towards the rivet bushing section characterized in that the rotation carriers (19',19'";35,36;42;56) penetrate into the material of the rivet'bushing (12;30;44;52;62), the rootation carriers (19';35;42;56) border, without exhibiting a shoulder, on the taper, and the set-head (20;45;53) exhibits at least two flattened surfaces (46,47;58,59:64,65) on its outer periphery which run parallel to the plane of a drill axis (24)

2. Self-drilling hollow-rivet according to claim 1, characterized in that the drill shaft (18;31;41;51;62) and the drill head (14;32) are manufactured as a single piece and the drill head (14;32) and the drill shaft (18;31;41;51) are formed from a hardened material.

3. Self-drilling hollow-rivet according to claim 1 or 2, characterized in that the rivet bushing (12;44,52) or the rivet bushing section (30) exhibits a sealing film O' on an inner wall (43) and a seal (22) is arranged below the set-head (22).

4. Self-drilling hollow-rivet according to one of the claims 1 to 3, characterized in that the rotation carriers (19',19"';35,36;42;56) are configured as ribs which exhibit a triangular-shaped cross section and which are equally distanced from the surface of the drill shaft (18;31;41;51) along the longitudinal direction over nearly the entire length and the drill shaft (18;31;41;51) is securely held in the rivet bushing (12;30;44;51;62). Self-drilling hollow-rivet according to one of the claims 1 to 4, characterized in that the flattened surfaces (46,47;58,59) on the outer periphery of the set-head (20;45;53) extend along the entire material thickness of the set-head (45;53) axis-parallel to the rivet bushing (44;52) or the flattened surfaces (58,59) on the set-head (63) border on a shoulder (66). i