DE102022127385B3 - Rivet connection - Google Patents

Abstract

The invention relates to a rivet connection with at least two joining partners (1, 2), which can be connected to one another in a setting process, in which a rivet element (7) with its rivet shank (13) passes in the setting direction through the at least one setting-side joining partner (2) into the The joining partner (1) facing away from the setting side can be driven in, namely by spreading the rivet shaft (13), so that the joining partners (1, 2), viewed in the setting direction, are under compressive stress between a rivet head (9) and a shaft tip of the rivet element (7 ) are clamped. According to the invention, in order to avoid contact corrosion, the joining partner (2) on the setting side is arranged in a contact-free manner, i.e. in an electrically insulating manner relative to the rivet element (7) and relative to the joining partner (1) facing away from the setting side.

Description

The invention relates to a rivet connection according to the preamble of claim 1 or according to the preamble of claim 19 and a rivet element according to claim 20.

The use of CFRP mixed construction, consisting of a carbon fiber composite component and an aluminum die-cast component, offers the following advantages, especially in vehicle construction: Both materials are lightweight materials. In addition, the carbon fiber composite component has a very high component rigidity, which offers advantages in terms of crash safety. In addition, the aluminum die-cast component can be produced using the casting process with extremely low component and manufacturing tolerances and with high repeat accuracy. Therefore, in CFRP mixed construction, the different properties of the carbon fiber composite component and the aluminum die-cast component can be ideally combined with regard to the requirements in vehicle construction.

The starting point of the invention is a rivet element setting process in which the carbon fiber composite component and the aluminum die-cast component can be connected to one another. In the setting process, a rivet element is driven through the carbon fiber composite component (i.e. the joining partner on the setting side) into the die-cast aluminum component (i.e. the joining partner facing away from the setting side) by spreading its rivet shank in the setting direction. After the setting process has taken place, the joining partners, viewed in the setting direction, are clamped under compressive tension between a rivet head and a shaft tip of the rivet element.

In a conventional setting process, the rivet element is driven in with a high setting force (for example 50 kN), whereby the tip of the rivet foot expands radially outwards over an expansion path. This creates an undercut between the rivet head and the expanded rivet base tip, which is filled with component material. The tip of the rivet base is framed in a form-fitting manner by the component material. In this way, a relative movement, for example caused by springing back of the rivet foot after spreading, is prevented because this would require a deformation of the component.

• Erstens weist das Aluminiumdruckgussbauteil im Vergleich zu einem herkömmlichen Aluminiumblech eine sehr geringe Duktilität auf. Bei Verwendung eines Aluminiumdruckgussbauteil als von der Setzseite abgewandten Fügepartner ist daher das oben beschriebene formschlüssige Umfassen der Nietfußspitze - aufgrund der geringen Duktilität - nur eingeschränkt möglich, so dass es nach dem Setzvorgang zu einer Rückfederung des Nietfußes (nach dem Spreizen) kommen kann. Von daher ist das Nietelement nicht ausreichend gegen ein Lösen gesichert. Zudem besteht bei dem Aluminiumdruckgussbauteil aufgrund der geringen Duktilität die Gefahr von Kerbbildung, die zu einem frühzeitigen Bauteilriss oder-bruch führen kann.

The following problem arises particularly with the rivet connection described above between a carbon fiber composite component and a die-cast aluminum component:

• Firstly, the aluminum die-cast component has very low ductility compared to a conventional aluminum sheet. When using an aluminum die-cast component as a joining partner facing away from the setting side, the form-fitting gripping of the rivet base tip described above is only possible to a limited extent - due to the low ductility - so that the rivet base can spring back (after spreading) after the setting process. Therefore, the rivet element is not sufficiently secured against loosening. In addition, due to the low ductility of the aluminum die-cast component, there is a risk of notch formation, which can lead to premature component cracking or breakage.

Secondly, the aluminum die-cast component has a very pronounced thermal expansion compared to the carbon fiber composite component, while the carbon fiber composite component is subject to almost no thermal expansion. A joining partner combination of aluminum die-cast component and carbon fiber composite component is therefore susceptible to component stresses aligned transversely to the setting direction, which are caused by the different thermal expansions. However, due to the high setting force usual in the prior art (for example 50 kN), such a high connection strength is achieved that does not allow any relative movement within the riveted connection in order to enable tension compensation.

Thirdly, the aluminum die-cast component and the carbon fiber composite component have a very high potential difference in the electrochemical voltage series, so that there is a risk of contact corrosion.

In CFRP mixed construction connections known from the prior art, contact corrosion is prevented as follows: For example, the carbon fiber composite component can be covered with an electrically insulating coating, such as a paint. In this way, direct contact between the carbon fibers in the carbon fiber composite component and the auxiliary joining element (i.e. screw or rivet element) or the aluminum die-cast component is prevented.

Alternatively, the carbon fiber composite component can have a glass fiber insert part. The glass fiber insert part can form the connection points that are in contact with the aluminum die-cast part and the auxiliary joining element, so that direct contact of the carbon fibers with adjacent metal is prevented. However, the above two possible solutions involve a lot of manufacturing effort.

From the DE 10 2012 204 131 A1 a generic method for joining joining partners using a punch rivet is known. From the DE 100 15 239 A1 a functional element arrangement is known. From the DE 10 2012 015 183 A1 a joint connection between two components and a method for producing such a joint connection are known. From the DE 10 2018 122 200 A1 a joint connection is known. From the WO 95/35174 A1 a punch riveting process is known. From the DE 10 2015 014 941 A1 a method for producing a connection between a functional element and a plate-shaped component is known.

The object of the invention is to provide a rivet connection in which, compared to the prior art, contact corrosion between the joining partners of the rivet connection is prevented in a simple manner, in particular in a rivet connection made of a metal die-cast part, especially aluminum die-cast component, and a carbon fiber composite component.

The task is solved by the features of claims 1, 19 or 20. Preferred developments of the invention are disclosed in the subclaims.

The invention is based on a rivet connection with at least two joining partners, which can be connected to one another in the setting process. In the setting process, a rivet element with its rivet shank can be driven in the setting direction through the at least one joining partner on the setting side into the joining partner facing away from the setting side, thereby spreading the rivet shank. As a result, the joining partners, viewed in the setting direction, are clamped under compressive stress between a rivet head and a shaft tip of the rivet element. According to the invention, in order to avoid contact corrosion, the joining partner on the setting side is arranged in a contact-free manner, that is to say is arranged in an electrically insulating manner relative to the rivet element and relative to the joining partner facing away from the setting side. Contact corrosion is particularly problematic in a CFRP hybrid construction consisting of an aluminum die-cast component and a carbon fiber composite component, since aluminum and carbon fibers have a very high potential difference in the electrochemical voltage series and therefore, with this choice of material, the aluminum die-cast component is extremely susceptible to contact corrosion.

Such a contact-free arrangement can preferably be provided by means of an insulating layer, in particular a plastic intermediate layer, which is arranged between the joining partner facing away from the setting side and the joining partner on the setting side. In the same way, such an insulating layer can also be arranged between the underside of the rivet head and the joining partner on the setting side.

The joining partner on the setting side can have a through hole. During the setting process, the rivet element is driven through the through hole into the joining partner facing away from the setting side. In this way, a build-up of tension transverse to the setting direction in the setting-side joining partner can be reduced or eliminated completely. For a contact-free passage of the joining partner on the setting side, the rivet shank is preferably guided through the pre-hole of the joining partner on the setting side with sufficiently large hole play. Within the hole clearance, a later-described compensating movement of the setting-side joining partner transverse to the setting direction is also possible in order to reduce component stresses.

As described in the introduction to the description, there are considerable advantages in vehicle construction, especially through the use of CFRP composite construction, consisting of a carbon fiber composite component and an aluminum die-cast component. However, the following is problematic with this type of material selection: On the one hand, the aluminum die-cast component has very low ductility compared to a conventional aluminum sheet. When using an aluminum die-cast component as a joining partner facing away from the setting side, the form-fitting gripping of the rivet base tip described above is only possible to a limited extent - due to the low ductility - so that the rivet base can spring back (after spreading) after the setting process. Therefore, the rivet element is not sufficiently secured against loosening. In addition, due to the low ductility of the aluminum die-cast component, there is a risk of notch formation, which can lead to premature component cracking or breakage.

On the other hand, the aluminum die-cast component has a very pronounced thermal expansion compared to the carbon fiber composite component, while the carbon fiber composite component is subject to almost no thermal expansion. A joining partner combination of aluminum die-cast component and carbon fiber composite component is therefore susceptible to component stresses aligned transversely to the setting direction, which are caused by the different thermal expansions.

To compensate for different thermal expansions of the joining partner, the joining partner on the setting side (i.e. in particular the carbon fiber composite component) can be clamped in floating storage between the rivet head of the rivet element and the joining partner facing away from the setting side (i.e. die-cast aluminum component). As a result, a component tension transverse to the setting direction, caused by different thermal expansions, can be caused by a transverse movement of the the joining partner on the setting side can be reduced or dismantled.

The floating support of the setting-side joining partner is additionally supported by the insulating layers, preferably plastic intermediate layers, arranged on both sides of the setting-side joining partner. The insulating layers therefore have a dual function, not only providing electrical insulation, but also reducing the coefficient of friction between the joining partner on the setting side and the rivet head or the joining partner facing away from the setting side.

The insulating layer acting as a sliding element can, for example, be pre-assembled as a washer on the rivet element. In this case, a one-piece pre-assembly unit consisting of a rivet element and washer can be provided. The washer can preferably be pushed onto the rivet shank in a slight press fit. Alternatively, the insulating layer can be designed as a plastic coating molded onto the underside of the rivet head or onto the joining partner facing away from the setting side.

The insulating layer made of plastic ensures easy processing. In addition, the processing is gentle on the surface and electrically insulating. Furthermore, contact corrosion can be prevented.

The floating bearing according to the invention is, as indicated above, particularly preferred for a joining partner combination in which the joining partner on the setting side is generally a plastic component and/or the joining partner facing away from the setting side is generally a metal component which, in comparison to the plastic component, has a very pronounced or at least has different thermal expansion. According to the invention, the different thermal expansions can be compensated for by the transverse mobility of the joining partner on the setting side.

As stated above, the aluminum die-cast component (or generally a metal die-cast component) not only has a very pronounced thermal expansion (compared to the CFRP component), but also a low ductility compared to a conventional sheet metal part. Due to the low ductility, there is a risk of notch formation in metal die-cast components, which can lead to a component crack or breakage in a conventional setting process.

Against this background, according to the invention, a conventional rivet setting process is dispensed with when connecting the two joining partners, that is, in particular, a positive gripping of the expanded rivet shaft tip is dispensed with (as described in the introduction to the description). Instead, the following operating principle is used to secure the rivet element to the joining partner facing away from the setting side: The rivet shaft forms a bistable spring section that has two states of equilibrium. A first equilibrium state corresponds to the reduced cross-section, undeformed rivet shank state. As a result of the setting force, the rivet shank changes to the second equilibrium state, in which the rivet shank is spread with an expanded cross section in the pre-hole of the first joining partner. The changeover to the expanded state occurs essentially without the build-up of a springback force, which prestresses the rivet element in the direction of the undeformed state.

According to the invention, the deformation of the rivet element takes place in the setting process using the so-called buckling effect (also known as the cracking frog effect). The spring buckling effect is a physical effect in which the shape of the rivet element has two stable states that can be converted into one another by applying a suitable force.

A particular advantage of this new operating principle is the following fact: The setting force required to transfer it to the spreading state is far less than the setting force required in the conventional setting process. Due to the lower setting force compared to the prior art, the joining partner on the setting side is subjected to significantly lower compressive stress than would be the case in a conventional setting process. This makes a setting process of the assembly consisting of rivet element and sliding element possible. It is only because of this lower compressive stress - in interaction with the sliding element - that the compensating movement of the two upper joining partners to equalize the tension is made possible. In contrast, in the conventional setting process, the rivet element is driven into the joining partner with such a large setting force that there is no transverse mobility of the setting-side joining partner with respect to the joining partner facing away from the setting side.

As mentioned above, the joining partner facing away from the setting side is not completely formed without pre-holes in the undeformed state, but rather has a pre-hole at the joint to be produced. When assembled, the rivet shank of the rivet element is spread apart against the inner circumference of the pre-hole.

The rivet element can be designed to be rotationally symmetrical with respect to a rivet element longitudinal axis. In addition, the rivet element can have one have an expanded rivet head that merges into the rivet shaft in the axial direction. Another functional element, for example a threaded bolt, can also be formed on the top of the rivet head. The rivet shank can have an inner curvature that is open to the rivet shank tip; In addition, the rivet shank can end with a ring-shaped cutting edge at the tip of the shank.

In the expanded state, the rivet shaft wall can be folded against the setting direction, i.e. towards the rivet head. In this case, the cutting edge can be in spreading engagement with the inner circumference of the component pilot hole. In addition, the rivet shaft wall surrounds the rivet shaft solid material section in a plate shape and in the circumferential direction without interruption or continuously.

In a preferred technical implementation, the first joining partner can be a metal die-cast part, for example an aluminum die-cast part, while the rivet element can be made of a cold-forming material. The rivet connection according to the invention is particularly advantageous in this case, since the first joining partner is stressed during the setting process essentially without plastic deformation, that is to say in particular only elastically. According to the invention, the first joining partner remains largely undeformed after the setting process has taken place.

With regard to a perfect transfer of the rivet element from the undeformed state to the expanded state, it is advantageous if the component pre-hole has a corresponding activation contour. By means of the activation contour, the rivet element can be transferred from the undeformed state to the expanded state in a process-safe manner during the setting process.

According to a first embodiment variant, the activation contour can be implemented as an expansion cone projecting from the pre-hole bottom. With the help of the activation contour, the foot-side shaft section of the rivet shank can be folded into the expanded state in the setting process against the setting direction. After folding into the expanded state, a radially inner head-side shaft section of the rivet shaft merges at a folding edge away from the rivet head into the foot-side shaft section which projects in the direction of the rivet head and which wraps around the head-side shaft section radially on the outside.

The activation contour formed in the component pre-hole can additionally have an annular groove that surrounds the expansion cone at its cone base. The annular groove can merge radially outwards into the pre-hole peripheral wall at an, in particular rounded, inner corner area. In particular, the expansion cone in combination with the annular groove and the pre-hole inner corner area lead to a folding of the foot-side shaft section of the rivet shaft, as described above.

A setting process that can be carried out with the activation contour specified above is described below: At the beginning of the setting process, the rivet element can sit with its cutting edge on the conical surface of the expansion cone. By applying the setting force, the rivet element can slide with its cutting edge along the surface of the cone in the direction of the ring groove without penetrating the material of the joining partner. In this way, the foot-side shaft section of the rivet shaft is pre-spread while thinning the material. As the setting process continues, the material-thinned, base-side shaft section of the rivet shaft is guided from the expansion cone into the ring groove. To complete the setting process, the base-side cutting edge of the rivet element is driven into the material on the pre-hole peripheral wall.

As mentioned above, the rivet shank is pre-expanded during the setting process on the expansion cone. The pre-spreading causes the rivet shank to expand conically from its dimensionally stable, cylindrical, undeformed state. The conical expansion of the rivet shank occurs while reducing the wall thickness of the shank wall. This reduces the dimensional stability of the rivet shank. In the further course of the setting process, the rivet shank can reliably change to its expanded state.

For a reliable setting process, it is important that the rivet element's cutting edge does not penetrate the material of the first joining partner at the expansion cone at the beginning of the setting process. Against this background, a cutting flank on the cutting edge can have a cutting angle that approximately corresponds to a cone angle that is spanned between the conical surface of the expansion cone and a rectangular plane. This ensures that the rivet element can slide with its cutting edge along the lateral surface of the expansion cone in the direction of the ring groove without penetrating the material of the first joining partner.

The pre-hole peripheral wall can merge into a seating-side surface of the first joining partner at a pre-hole opening edge. The pre-hole peripheral wall can expand conically or run cylindrically from the bottom pre-hole inner corner area to the pre-hole opening edge. The pre-hole diameter is preferably larger than the outside diameter of the rivet shank. In this way, the rivet element can move smoothly with hole play in preparation for the setting process be pre-positioned in the pre-hole of the first joining partner.

In a further embodiment variant, the activation contour can be designed as follows: The blind hole-like pre-hole of the first joining partner can have an insertion section with a large diameter. This merges into a small-diameter depression at a circumferential ring shoulder. The cutting edge of the still undeformed rivet element can have a diameter that is larger than the inner diameter of the ring shoulder. This allows the rivet element to be positioned with its cutting edge on the annular shoulder of the component pilot hole (in preparation for the setting process).

When the setting force is applied, the rivet element can expand with its cutting edge radially outwards until it reaches a maximum outside diameter. As the setting process continues, the rivet shank can be driven into the pre-hole depression by an additional over-center stroke. This causes the rivet shank to be over-expanded, in which the rivet shank changes to the expanded state.

Preferably, the rivet element can be made from a cold impact material, in which a deformation limit is exceeded, particularly during over-expansion, at which a solidification of the rivet element material occurs, which is advantageous in terms of increased connection strength between the rivet element and the component. Therefore, according to the invention, there is no need for a die whose die shape supports spreading of the rivet shank. Instead, the first joining partner can be clamped between a hold-down device and a flat anvil.

The setting process according to the invention can be part of a fully automatic process chain in which a setting device is attached to the distal end of a robot arm of an industrial robot, which works autonomously using a program control. In order to ensure a perfect setting process, it is preferred if the outer diameter of the rivet shank is smaller than the outer diameter of the ring shoulder. In this way, the still undeformed rivet element can be positioned with its cutting edge in floating bearing, that is, with transverse play, on the ring shoulder, whereby component and/or manufacturing tolerances can be compensated for.

If the joining partner facing away from the setting side is designed as a die-cast part, the pre-hole can be created in the first joining partner during the casting process. In this case, the pre-hole can have a cone-like inner circumference, which serves as a demolding slope. The cone-like inner circumference also acts as an insertion bevel during the setting process in order to ensure perfect positioning of the rivet element on the annular shoulder of the component pilot hole.

In a specific embodiment, the rivet element can have a rivet element length of, for example, 2 to 5 mm in the undeformed state. The wall thickness of the shaft wall of the rivet shaft in the undeformed state can be in a range between 0.3 and 0.7 mm, in particular 0.5 mm. In addition, depending on the application, the rivet element can be made, for example, from a wire material suitable for welding, or from a conventional cold impact steel, in which a forming limit is exceeded, in particular during over-expansion, i.e. when folded over during the setting process, at which the rivet element material solidifies occurs, which is advantageous in terms of increased connection strength between the rivet element and the component. According to the invention, a die can be dispensed with during the setting process, the die engraving of which supports the spreading of the rivet shank. Instead, the component can be clamped between a hold-down device and a flat anvil during the setting process.

In an embodiment specified above, the two joining partners can be connected to one another directly in the setting process, in which the rivet element with its rivet shank can be driven in the setting direction through the joining partner on the setting side into the joining partner facing away from the setting side. As a result, the two joining partners, viewed in the setting direction, are clamped under compressive stress between a rivet head and a cutting edge of the rivet shank of the rivet element.

In a second embodiment, in the setting process, the rivet element with its rivet shank can only be driven into a first joining partner in the setting direction. The second joining partner, on the other hand, can be attachable to the rivet element independently of the setting process, in particular in a clip, screw, snap or weld connection.

To implement the above second embodiment, it is advantageous if the pre-hole diameter at the pre-hole opening edge of the blind hole-like pre-hole of the first joining partner (corresponds to the joining partner facing away from the setting side) is dimensioned smaller than a head diameter of the rivet head, so that after the setting process has been completed, the rivet head -The underside is in contact with the opening edge area of the component pre-hole. A bolt can be attached to the top of the rivet head of the rivet element be designed to connect the second joining partner, in particular a threaded bolt or welding bolt. In the assembled state, the bolt can preferably be guided through a through hole in the second joining partner with sufficiently large hole play (in order to achieve a contact-free passage). A clip, locking, screw or welding element can be attached to the threaded bolt tip protruding from the through hole of the second joining partner. In this case, the second joining partner can be clamped between the clip, locking, screw or welding element and the first joining partner.

When welding, the welding stud can be guided through a through hole in the second joining partner when assembled. A third joining partner or a head element, such as a welding cap, to which a sliding element (for example sliding element ring disk) is firmly connected, can be welded onto the welding stud tip protruding from the through hole of the second joining partner by means of resistance spot welding. The second joining partner can therefore be clamped between the third joining partner or the welding cap and the rivet head.

According to the invention, the second joining partner is clamped in floating storage between the rivet head of the rivet element and the second joining partner. In this way, component tension transverse to the setting direction, in particular caused by different thermal expansion of the joining partners, can be reduced or eliminated by a transverse movement of the second joining partner. To avoid contact corrosion and to provide a floating bearing between the top of the rivet head and the second joining partner - analogous to the first embodiment - an insulating layer or sliding element, in particular a plastic intermediate layer, can be arranged, by means of which a coefficient of friction between the top of the rivet head and can be reduced by the second joining partner. The clip, locking, screw or welding element can also be designed, for example, with a collar to which a plastic intermediate layer, such as a plastic disk, is attached as a further insulating layer or sliding element, or a plastic ring is molded on, by means of which a coefficient of friction between the Clip, locking, screw or welding element and the second joining partner can be reduced. As in the first embodiment, the insulating layers have a dual function, not only reducing the coefficient of friction, which supports the floating bearing, but also electrically insulating the second joining partner (that is, in particular the carbon fiber composite component).

Exemplary embodiments of the invention are described below with reference to the attached figures.

• 1 bis 5 Ansichten einer Nietverbindung gemäß einem ersten Ausführungsbeispiel;
• 6 bis 9 Ansichten einer Nietverbindung gemäß einem zweiten Ausführungsbeispiel; und
• 10 bis 12 Ansichten einer Nietverbindung gemäß weiteren Ausführungsbeispielen.

Show it:

• 1 to 5 Views of a rivet connection according to a first exemplary embodiment;
• 6 to 9 Views of a rivet connection according to a second exemplary embodiment; and
• 10 to 12 Views of a rivet connection according to further exemplary embodiments.

In 1 a rivet connection is shown with a lower first joining partner 1 and an upper second joining partner 2 facing the setting side. The rivet connection is made in one using the 4 indicated setting process with the help of a rivet element 7 designed as a semi-hollow rivet, which has a large-diameter rivet head 9, which is realized as a flat head. The rivet head 9 merges into a small-diameter rivet shank 13 on the underside of its rivet head, which terminates at a circumferential cutting edge 15. The rivet element 7 is realized in the undeformed state as a component which is rotationally symmetrical about a longitudinal axis L and is shown in a cross-sectional view in the figures.

In the, in the 1 In the rivet connection shown, the rivet element 7 is driven through the setting-side joining partner 2 into the joining partner 1 facing away from the setting side, while maintaining a residual base thickness in the joining partner 1. In the 1 the rivet shaft 13 is spread open. The two joining partners 1, 2 are therefore clamped together under a compressive stress acting in the setting direction S.

In the present exemplary embodiment, a mixed construction connection is realized in which the joining partner 1 facing away from the setting side is an aluminum die-cast part, while the joining partner 2 on the setting side is a carbon fiber composite component.

Such a joining partner combination of aluminum die-cast part and carbon fiber composite component is, in comparison to a conventional joining partner combination made of conventional sheet metal parts, susceptible to contact corrosion and to component stresses oriented transversely to the setting direction, which are caused by different thermal expansions of the joining partners 1, 2. In addition, the joining partner 1 facing away from the setting side (i.e. the aluminum die-cast part) has very low ductility compared to conventional metal sheets. A conventional setting process in which the rivet shank is completely positively enclosed by the die-cast material of the joining partner 1 facing away from the setting side therefore cannot be carried out reliably. In addition, due to the low ductility of die-cast metal, there is a risk that notches will form during the setting process, which can lead to premature component cracking or breakage.

A core of the invention is that the setting-side joining partner 2 is arranged in a contact-free manner, that is to say electrically insulating, relative to the rivet element 7 and relative to the joining partner 1 facing away from the setting side, whereby contact corrosion can be avoided. To provide such a contact-free arrangement, an insulating layer 6, in particular plastic intermediate layers, is arranged between the joining partner 1 facing away from the setting side and the joining partner 2 on the setting side. In addition, an insulating layer 6, in particular a plastic intermediate layer, is also arranged between the underside of the rivet head and the joining partner 2 on the setting side.

A further core of the invention is that the upper joining partner 2 is clamped in floating storage between the rivet head 9 of the rivet element 7 and the joining partner 1 facing away from the setting side. In this way, a component stress transverse to the setting direction S, which is caused, for example, by different thermal expansion of the joining partners 1, 2, can be reduced or reduced by a transverse compensating movement of the upper joining partner 2.

The two insulating layers 6 not only provide electrical insulation in a dual function. In addition, the insulating layers 6 also act as sliding elements, with the help of which a coefficient of friction between the underside of the rivet head and the upper joining partner 2 or a coefficient of friction between the two joining partners 1, 2 can be reduced. The insulating layer 6 is, for example, a plastic washer or a plastic foil that can be pre-assembled on the rivet element 7 or on the second joining partner 2.

To further support the floating storage, the upper joining partner 2 has a through hole 17 through which the rivet element 7 can be driven into the joining partner 1 facing away from the setting side. The rivet shank 13 is guided with a hole clearance Δx through the through hole 17 of the second joining partner 2, so that the compensating movement B of the upper joining partner 2 transversely to the setting direction is possible within the hole clearance Δx. In addition, the hole clearance Δx is dimensioned sufficiently large to ensure a contact-free passage of the rivet element 7 through the second joining partner 2.

In this way, on the one hand, tension can be equalized between the joining partners 1, 2 in the event of thermal stress. On the other hand, electrical contact between the rivet shank 13 and the second joining partner 2 is prevented.

In the setting process ( 3 to 5 ), the rivet element 7 is guided through the pre-hole 17 of the upper joining partner 2 without any load and is then driven into the first joining partner 1 facing away from the setting side.

• Gemäß der 1 ist das Nietelement 7 in ein Vorloch 5 des von der Setzseite abgewandten ersten Fügepartners 1 eingetrieben, dass sich konusartig bis zu einer Vorlochtiefe t erstreckt und dort mit einem Vorloch-Boden abschließt.

A significant advantage of the invention is that the rivet connection can be realized with a joining partner 1 facing away from the setting side, whose flowability or ductility is reduced compared to the prior art (for example a component made of die-cast aluminum). According to the invention, the rivet element 7 is not secured by completely positively enclosing the rivet shaft 13 in the material of the first joining partner 1, but rather by means of the following 1 to 5 described security mechanism:

• According to the 1 the rivet element 7 is driven into a pre-hole 5 of the first joining partner 1 facing away from the setting side, which extends like a cone up to a pre-hole depth t and ends there with a pre-hole bottom.

In the pre-hole 5 of the first joining partner 1 an activation contour 31 ( 3 or 4 ) is designed, which controls the transfer of the rivet element 7 from the undeformed state to the expanded state in the setting process. The activation contour 31 has an expansion cone 33 projecting from the pre-hole base, which is surrounded at its cone base by an annular groove 35 formed in the pre-hole base. The annular groove 35 extends radially outwards at a rounded inner corner region 37 into a pre-hole peripheral wall 39 ( 4 or 5 ) above. In the 1 to 5 the smooth-surfaced pre-hole peripheral wall 39 extends from the pre-hole inner corner area 37 to a pre-hole opening edge 41 ( 2 ) slightly conically expanded on the setting-side surface of the first joining partner 1.

According to the 1 a foot-side shaft section 43 of the hollow rivet shaft 13 is driven into the material of the first joining partner 1 with its cutting edge 15 on the pre-hole peripheral wall 39.

Like from the 2 As can be seen, the pre-hole diameter dv is larger than the rivet shank outer diameter d _A , so that the rivet element 7 can be pre-positioned in preparation for the setting process with a hole clearance in the pre-hole 5 of the first joining partner 1. The pre-hole diameter ser dv is also dimensioned smaller than a head diameter d _K of the rivet head 9. After the setting process, its underside is in contact with the opening edge area of a through-hole 17 of the upper setting-side joining partner 2. As can be seen from the 2 As can be seen further, the rivet shank 13 is cylindrical on the outside in the undeformed state. The inner curvature 14 of the rivet shaft 13 is realized as a hollow cylindrical shape, which results in a constant wall thickness w of the shaft wall over the rivet element longitudinal axis L. Overall, the rivet element 7 is designed to be rotationally symmetrical to the longitudinal axis L of the rivet element.

The following is based on the 3 to 5 a setting process is described: At the beginning of the setting process ( 3 ) the rivet element 7 (guided through the upper joining partner 2) is brought with its cutting edge 15 into contact with the conical surface of the expansion cone 33. The rivet element 7 is aligned coaxially with the expansion cone 33. When the setting force F is initiated, the rivet element 1 slides with its cutting edge 15 along the lateral surface of the cone in the direction of the annular groove 35. In this way, the foot-side shaft section 43 of the rivet shaft 13 is pre-spread. On the one hand, the pre-spreading causes the cylindrical rivet shank 13 to expand conically. On the other hand, the conical expansion of the rivet shank 13 reduces the wall thickness w, especially on the foot-side shaft section 43. Due to the conical expansion and the reduced wall thickness w, the activation contour 31 can reliably transfer the rivet shank 13 into the expanded state in the further setting process. To complete the setting process ( 5 ), the cutting edge 15 of the rivet element 7 is driven into the material of the first joining partner 1 on the pre-hole peripheral wall 39.

In the 2 Two cutting flanks 45, 47 converge on the rivet shank 13 to form the cutting edge 15. The radially inner cutting edge 45 spans a cutting angle β with a plane perpendicular to the rivet element longitudinal axis L. This corresponds to a cone angle γ, which is spanned between the conical surface of the expansion cone 33 and a plane perpendicular to the rivet element longitudinal axis L. In this way it is ensured that during the setting process the cutting edge 15 slides reliably in the direction of the ring groove 35 without penetrating the material.

With the help of the activation contour 31, the foot-side shaft section 43 of the rivet shaft 13 is folded over against the setting direction S in the setting process. In the completed rivet connection, a head-side shaft section 49 merges into the foot-side shaft section 43, which projects in the direction of the rivet head 9, at a folding edge 51 remote from the rivet head. The folded foot-side shaft section 43 extends in the circumferential direction continuously and in a plate shape around the head-side shaft section 49. It should be emphasized that only the folded foot-side shaft section 43 penetrates into the material of the first joining partner 1 with its cutting edge 15 of the rivet shaft 13 on the pre-hole peripheral wall 39 , while the head-side shaft section 49 remains without material engagement with the first joining partner 1.

The rivet shank 13 thus acts like a bistable spring section, which changes to the expanded spreading state during the setting process. The spreading state ( 1 or 5 ) is characterized by the fact that, in contrast to the prior art, essentially no springback force is built up in the rivet shaft 13, which prestresses the rivet element 7 in the direction of the undeformed state. Therefore, according to the invention, an almost completely positive enclosing of the rivet shaft 13 in the material can be dispensed with.

According to the 3 to 5 The setting tool according to the invention does not have a die with die engraving as a counterholder 30, but rather a flat anvil.

A particular advantage of this new operating principle is the following: The setting force F required to transfer it to the spreading state is far less than the setting force required in the conventional setting process. Due to the lower setting force F compared to the prior art, the rivet element 7 with the two insulating layers 6 and the upper joining partner 2 is subjected to significantly lower compressive stress than would be the case in a conventional setting process. Only because of this lower compressive stress - in interaction with the two insulating layers 6 - is the transverse compensating movement of the upper joining partner 2 possible to equalize the tension. In contrast, in the conventional setting process, the rivet element is driven into the joining partner with such a large setting force that there is no transverse mobility of the upper joining partner 2 with respect to the joining partner 1 facing away from the setting side.

In the 6 to 9 A rivet connection according to a second exemplary embodiment is shown, the structure of which essentially corresponds to the structure of the first exemplary embodiment 1 to 5 corresponds. As in the first exemplary embodiment, in the second exemplary embodiment the rivet shank 13 also acts as a bistable spring section which has the two states of equilibrium, namely the undeformed state of reduced cross-section ( 7 ) and an extended spreading state ( 6 or 9 ).

The following is based on the 6 to 9 the pre-hole geometry of the first joining partner 1, the rivet element geometry and the setting process according to the invention are described: This is according to 7 the still undeformed rivet element 7 is designed to be rotationally symmetrical with respect to its longitudinal axis L. The rivet shaft 13 is in the 6 or 7 divided into a head-side shaft section 49 and an adjoining foot-side shaft section 43, which delimits an inner curvature 14 which is open at the rivet shaft tip. The inner curvature 14 ends at an annularly circumferential cutting edge 15 of the rivet element 7.

The folding of the rivet shaft 13, which acts as a bistable spring section, is carried out by means of an activation contour 31 ( 7 ) in the pre-hole 5 of the first joining partner 1, which is designed as follows: The pre-hole 5 of the first joining partner 1 points in the 7 a large-diameter insertion section 21. This goes in the direction of the pre-hole bottom 22 on a circumferential ring shoulder 23 in steps into a small-diameter pre-hole depression 25. When the rivet element 7 is still undeformed, the cutting edge 15 extends over a diameter d ₁ that is larger than the inner diameter d ₂ of the ring shoulder 23. In addition, the rivet shank outer diameter is smaller than the ring shoulder outer diameter d ₃ .

The setting process is carried out with a setting device that is in the 7 to 9 has the hold-down device 27, in which a setting piston 29 is guided in a stroke-adjustable manner. The two joining partners 1, 2 are clamped between the hold-down device 27 and a flat anvil 30.

When the setting force F acts, the rivet shank 13 expands with its cutting edge 15 radially outwards until a setting stroke dead center T is reached ( 8th ). At the setting stroke dead center T, the cutting edge 15 of the rivet element 1 is expanded to a maximum diameter d _max and is in expanding engagement with the inner circumference of the large-diameter insertion section 21 of the component pilot hole 5. In addition, the end face of the rivet shank tip is in contact with the annular shoulder 23 over a large area.

According to the invention, the setting stroke is beyond the dead center T with an over-center stroke path s ( 8th ) extended. In the further course of the setting process, the head-side shaft section 49 is driven into the pre-hole depression 25 by the over-center stroke distance s. This results in an over-spreading of the foot-side shaft section 43, in which the foot-side shaft section 43 changes to the expanded state. The foot-side shaft section 43 is therefore folded over in the opposite direction to the setting direction, that is to say in the direction of the rivet head 9. The foot-side shaft section 43 extends continuously in the circumferential direction and in a plate shape around the head-side shaft section 49 of the rivet element 7.

Like from the 7 Furthermore, the inner circumference of the large-diameter insertion section 21 of the component pre-hole 5 is designed like a cone, so that the inner circumference acts as an insertion bevel, by means of which the rivet element 7 can be easily inserted into the pre-hole 5 of the first joining partner 1. In addition, the rivet element 7 is positioned in a floating position on the ring shoulder 23 ( 7 ), that is, positioned with transverse play, which allows component and/or manufacturing tolerances to be compensated for.

In the 10 Another rivet connection is shown, in which the first joining partner 1 can be connected to the second joining partner 2 with the aid of the rivet element 7. Analogous to the previous exemplary embodiments, the rivet element 7 is driven into the first joining partner 1 in a setting process with its rivet shank 13 in the setting direction. The second joining partner 2, on the other hand, is attached to the rivet element 7 in a separate assembly process, independent of the setting process. For this purpose, the rivet element 7 is formed on its top with a threaded bolt 53. In the assembled state, the threaded bolt 53 is guided through a through hole 55 of the second joining partner 2. At the in the 10 A threaded bolt tip protruding from the through hole 55 of the second joining partner 2 can be screwed on a collar screw nut 57, so that the second joining partner 2 can be clamped between the collar screw nut 57 and the rivet head 9.

The second joining partner 2 is in the 10 - analogous to the previous exemplary embodiment - electrically insulated both from the rivet element 7 and from the first joining partner 1 and clamped in floating storage between the rivet head 9 of the rivet element 7 and the second joining partner 2. As a result, component tension transverse to the setting direction, for example caused by different thermal expansion of the joining partners 1, 2, can be reduced or reduced by a transverse movement of the second joining partner 2.

The floating storage and electrical insulation is achieved, among other things, by the insulating layers 6. One of the insulating layers 6 is arranged between the top of the rivet head and the second joining partner 2 and also acts as a sliding element, by means of which a coefficient of friction between the top of the rivet head and the second joining partner 2 is reduced. The sliding element 6 is, for example, a plastic washer that can be pre-assembled on the threaded bolt 53 of the rivet element 7.

In addition, a further insulating layer 6 is arranged between the second joining partner 2 and the facing underside of the collar screw nut 57, which also acts as a sliding element, by means of which a coefficient of friction between the top of the rivet head and the second joining partner 2 can be reduced. This insulating layer 6 is, for example, a plastic coating sprayed onto the underside of the collar screw nut 57 or a permanently mounted plastic washer.

In addition, the second joining partner 2 has a through-hole 17 to support the floating bearing, through which the threaded bolt 53 is guided with a hole clearance Δx, so that the compensating movement of the second joining partner 2 transversely to the setting direction is possible within the hole clearance Δx and also the threaded bolt 53 is guided contact-free through the second joining partner 2.

In the 11 Another rivet connection is shown, in which the first joining partner 1 can be connected to the second joining partner 2 with the aid of the rivet element 7. Analogous to the previous exemplary embodiments, the rivet element 7 is driven into the first joining partner 1 in a setting process with its rivet shank 13 in the setting direction. The second joining partner 2, on the other hand, is attached to the rivet element 7 in a separate welding process, regardless of the setting process. For this purpose, the rivet head 9 of the rivet element 7 is formed on its top with a welding bolt 53, which can be guided through a through hole 55 of the second joining partner 2. At the in the 11 The welding bolt tip protruding from the through hole 55 of the second joining partner 2 can be welded onto the third joining partner 3, which is formed as a sheet metal component, using resistance spot welding, so that the second joining partner 2 together with the two insulating layers 6 (for example plastic washers or a plastic foil) is between the third joining partner 3 and the rivet head 9 can be clamped.

Alternatively, in the 12 A welding cap 56 is welded onto the tip of the welding bolt protruding from the through hole 55 of the second joining partner 2 using resistance spot welding, so that the second joining partner 2 is clamped between the welding cap 56 and the rivet head 9. In order to ensure both electrical insulation and floating storage, an insulating layer 6 is arranged between the second joining partner 2 and the welding cap 57, by means of which a coefficient of friction between the welding cap 57 and the second joining partner 2 can also be reduced. The insulating layer 6 is in the 12 exemplified as a plastic coating ring sprayed onto the underside of the welding cap 56 or as a firmly connected sliding element ring disk.

Reference symbol list

1

first joining partner

2

second joining partner

3

third joining partner

5

pre-hole

6

Insulating layer

7

Rivet element

5

blind hole-like pre-hole in the first joining partner 1

9

Rivet head

13

Rivet shank

14

Internal curvature

15

cutting edge

17

Through pre-hole

22

pre-hole floor

21

large diameter insertion section

23

Ring shoulder

25

Pre-hole countersink

27

Hold-down device

29

Set piston

30

anvil

31

Activation contour

33

Expanding cone

35

Ring throat

37

Inside corner area

39

Pre-hole peripheral wall

41

Pre-hole opening edge

43

foot-side shaft section

45.47

cutting edges

49

head-side shaft section

51

Cover edge

53

bolt

55

through hole

56

Head element or welding cap

57

Clip, locking, screw or welding element

there

Shank outside diameter

dK

Head diameter

dv

Pre-hole diameter

w

Wall thickness

F

setting force

S

Setting direction

L

Rivet element longitudinal axis

β

Cutting angle

γ

cone angle

t

Pre-hole depth

Δx

Match play

Claims (20)

Rivet connection with at least two joining partners (1, 2), which can be connected to one another in a setting process, in which a rivet element (7) with its rivet shank (13) in the setting direction through the at least one joining partner (2) on the setting side into the one facing away from the setting side Joining partner (1) can be driven in, namely by spreading the rivet shaft (13), so that the joining partners (1, 2), viewed in the setting direction, are clamped under compressive tension between a rivet head (9) and a shaft tip of the rivet element (7), wherein, to avoid contact corrosion, the setting-side joining partner (2) is arranged in a contact-free manner, that is to say electrically insulating, relative to the rivet element (7) and relative to the joining partner (1) facing away from the setting side, characterized in that the rivet shaft (13) is designed as a bistable spring section is designed, which has two states of equilibrium, namely the cross-sectionally reduced, undeformed state and the expanded expansion state, and that due to the action of the setting force (F), the rivet element (7) changes from the undeformed state to the expansion state, in which the rivet shaft (13) has an expanded cross-section is spread in the joining partner (1) facing away from the setting side, in particular without a springback force being built up in the rivet element (7) when it is turned into the expanded state, which prestresses the rivet element (7) in the direction of the undeformed state. Rivet connection after Claim 1 , characterized in that in order to provide the contact-free arrangement between the joining partner (1) facing away from the setting side and the joining partner (2) on the setting side, an insulating layer, in particular a plastic intermediate layer, is arranged, and / or that between the underside of the rivet head and the An insulating layer, in particular a plastic intermediate layer, is arranged on the set-side joining partner (2). Rivet connection after Claim 1 or 2 , characterized in that the joining partner (2) on the setting side has a through hole (17) through which the rivet element (7) can be driven into the joining partner (1) facing away from the setting side, and in particular to provide the contact-free arrangement of the rivet shank (13 ) is guided contact-free with hole clearance (Δx) through the through hole (17) of the joining partner (2) on the setting side. Rivet connection after Claim 1 , 2 or 3 , characterized in that the materials of the two joining partners (1, 2) have a potential difference in the electrochemical voltage series, so that there is a risk of contact corrosion upon contact, and / or that the joining partner (2) on the setting side is a plastic component, in particular a carbon fiber composite component, and /or the joining partner (1) facing away from the setting side is a metal component which has a very pronounced thermal expansion compared to the plastic component. Rivet connection according to one of the preceding claims, characterized in that , in particular to compensate for different thermal expansions of the joining partner, the joining partner (2) on the setting side is clamped in floating bearing between the rivet head (9) of the rivet element (7) and the joining partner (1) facing away from the setting side is, so that a component stress transverse to the setting direction, caused by the different thermal expansion (1, 2), can be reduced or dismantled by a transverse movement of the setting-side joining partner (2). Rivet connection according to one of the preceding claims, characterized in that the two insulating layers, in particular plastic intermediate layers, not only provide electrical insulation in a dual function, but also act as sliding elements, with the help of which the floating bearing is achieved by creating a coefficient of friction between the underside of the rivet head and the joining partner (2) on the setting side or between the two joining partners (1, 2) can be reduced. Rivet connection according to one of the preceding claims, characterized in that the joining partner (1) facing away from the setting side is a die-cast metal component, in particular die-cast aluminum, which in particular not only has a very pronounced thermal expansion, but also has low ductility compared to a sheet metal part, and that, particularly in die-cast metal components, due to the low ductility, there is a risk of notch formation, which can lead to premature component cracking or breakage. Rivet connection according to one of the preceding claims, characterized in that the joining partner (1) facing away from the setting side has, in the undeformed state, a particularly blind hole-like pre-hole (5) at the joint to be produced, and that in the expanded state a foot-side shaft section (43) of the rivet shank (13 ) is driven into the material of the first joining partner (1) with its cutting edge (15) on a pre-hole peripheral wall (39). Rivet connection according to one of the preceding claims, characterized in that the rivet element (7) is designed to be rotationally symmetrical with respect to a rivet element longitudinal axis (L), and/or that the rivet element (7) has an expanded rivet head (9) which extends in the axial direction merges into the rivet shank (13), which ends at the shank tip with the preferably ring-shaped cutting edge (15) and/or delimits an inner curvature (14) that is open at the rivet shank tip. Rivet connection according to one of the preceding claims, characterized in that in the setting process a foot-side shaft section (43) of the rivet shaft (13) turns over against the setting direction (S), so that in particular a radially inner head-side shaft section (49) on a turn-over edge (51) away from the rivet head into the radially outer foot-side shaft section (43) projecting in the direction of the rivet head (9), which wraps around the head-side shaft section (49) in a plate shape, and in particular only the folded-over foot-side shaft section (43) of the rivet shaft (13) with its cutting edge (15) on the pre-hole peripheral wall (39) penetrates into the material of the first joining partner (1), while preferably the head-side shaft section (49) and/or the folding edge (51) remain without material engagement with the material of the first joining partner (1). Rivet connection according to one of the Claims 8 until 10 , characterized in that an activation contour (31) is formed in the pre-hole (5) of the joining partner (1) facing away from the setting side, which controls a folding of the rivet element (7) from the undeformed state to the expanded state during the setting process. Rivet connection after Claim 11 , characterized in that the activation contour (31) has an expansion cone (33) projecting from the pre-hole bottom of the joining partner (1) facing away from the setting side, and in particular the activation contour (31) has an annular groove (35) formed in the pre-hole bottom , which surrounds the expansion cone (33) at its cone base, and that in particular the annular groove (35) merges radially outwards into the pre-hole peripheral wall (39) at a particularly rounded inner corner region (37). Rivet connection after Claim 12 , characterized in that at the beginning of the setting process, the rivet element (7) sits with its cutting edge (15) on the cone surface of the expansion cone (33) and then slides along the cone surface in the direction of the annular groove (35), so that the foot-side shaft section (43 ) of the rivet shank (13) is pre-expanded while thinning the material, and that, in particular in the further course of the setting process, the material-thinned foot-side shank section (43) of the rivet shank (13) can be guided from the expansion cone (33) into the annular groove (35), so that by the action of the setting force (F) the rivet element (7) changes into the expanded state, in which the foot-side cutting edge (15) of the rivet element (7) is driven into the material of the first joining partner (1) on the pre-hole peripheral wall (39). Rivet connection after Claim 13 , characterized in that in the undeformed state of the rivet element (7) on the rivet shank (13) two cutting flanks (45, 47) converge to form the cutting edge (15), and that one of the cutting edges (45) has a direction relative to the rivet element's longitudinal axis (L ) rectangular plane spans a cutting angle (β), and that the cutting angle (β) corresponds to a cone angle (γ) which is spanned between the cone surface and the rectangular plane. Rivet connection according to one of the preceding claims, characterized in that the pre-hole peripheral wall (39) merges at a pre-hole opening edge (41) into a surface of the joining partner (1) facing away from the setting side, and in particular the pre-hole peripheral wall (39) expands conically from the pre-hole inner corner area (37) towards the pre-hole opening edge (41) or runs cylindrically between the pre-hole inner corner area (37) and the pre-hole opening edge (41). Rivet connection according to one of the Claims 8 until 15 characterized in that the pre-hole diameter (dv) of the component pre-hole (5) is larger than the rivet shank outer diameter (d _A ), so that the rivet element (1) can be pre-positioned with hole play in the component pre-hole (5). . Rivet connection after Claim 11 , characterized in that to form the activation contour (31), the pre-hole (5) of the first joining partner (1) has a large-diameter insertion section (21), which merges step-like into a small-diameter pre-hole depression (25) on a circumferential annular shoulder (23). , and that in particular the cutting edge (15) of the still undeformed rivet element (7) lies on a diameter (d ₁ ) that is larger than the inner diameter (d ₂ ) of the ring shoulder (23), so that in preparation for the setting process, the rivet element (7) with its cutting edge (15) on the Annular shoulder (23) of the component pre-hole (6) can be positioned. Rivet connection after Claim 17 , characterized in that during a setting stroke the rivet element (7) can be driven into the component pre-hole (5) up to a dead center (T), and that at the dead center (T) the rivet element (7) with its cutting edge (15) is up to Reaching a maximum diameter (d _max ) is expanded radially outwards, and that the setting stroke is extended with an over-center stroke (s), with which the rivet shank (13) can be driven into the pre-hole depression (25), so that a Over-spreading of the foot-side shaft section (43) takes place, in which it changes to the spreading state. Rivet connection in which, in a setting process, a rivet element (7) with its rivet shank (13) can be driven into at least one joining partner (1) in the setting direction, namely by spreading the rivet shank (11), with the rivet base (11) in the still undeformed state is reduced in cross-section and has an expanded cross-section when driven in, a bolt (53) for connecting a second joining partner (2), in particular a threaded bolt or a welding bolt, being formed on an upper side of a rivet head (9) of the rivet element (7), whereby in the assembled state, the bolt (53) is guided through a through hole (55) of the second joining partner (2), and there is a further element (3, 56, 57) on the bolt tip protruding from the through hole (55) of the second joining partner (2). is fastened, so that the second joining partner (2) can be clamped between the further element (3, 56, 57) and the rivet head (9), the second joining partner (2) being contact-free, that is to say electrically insulating, in order to avoid contact corrosion the rivet element (7), the further element (3, 56, 57) and the joining partner (1) facing away from the setting side, and in particular between the second joining partner (2) and the further element (3, 56, 57) a first insulating layer, in particular a plastic intermediate layer, is arranged, and / or between the second joining partner (2) and the first joining partner (1) a second insulating layer, in particular a plastic intermediate layer, is arranged, characterized in that the rivet shank ( 13) is designed as a bistable spring section, which has two states of equilibrium, namely the cross-section-reduced undeformed state and the expanded expansion state, and that due to the action of the setting force (F), the rivet element (7) changes from the undeformed state to the expansion state in which the rivet shank (13) is spread with an expanded cross-section in the joining partner (1) facing away from the setting side, in particular without a springback force being built up in the rivet element (7) when it is turned over into the expanded state, which biases the rivet element (7) in the direction of the undeformed state. Rivet element for a rivet connection according to one of the preceding claims.

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