JOINING ELEMENT, CONNECTION STRUCTURE WITH THE JOINING ELEMENT, MANUFACTURING METHOD OF THE JOINING ELEMENT AND CORRESPONDING CONNECTION METHOD

Abstract

A joining element for manufacturing a connection between at least two components, which includes: a head at a first axial end, an end portion at a second axial end opposite the first axial end, and a shaft arranged between the end portion and the head, wherein the shaft defines a longitudinal axis of the joining element between the first and the second axial end. At least the shaft and the end portion of the joining element comprise a hardened edge layer so that a material of the shaft and the end portion has in the interior a lower hardness compared to an adjacent surface of the edge layer.

Claims

1. A joining element for manufacturing a connection between at least two components, which comprises: a. a head at a first axial end, b. an end portion at a second axial end opposite the first axial end as well as c. a shaft arranged between the end portion and the head, wherein the shaft defines a longitudinal axis of the joining element between the first and the second axial end, wherein d. at least the shaft and the end portion of the joining element comprise a hardened edge layer, so that a material of the shaft and the end portion has in the interior a lower hardness compared to an adjacent surface of the edge layer.

2. The joining element according to claim 1, wherein at least the material of the shaft and the end portion is quenched and tempered.

3. The joining element according to claim 1, selected from the group consisting of: setting bolts, semi-hollow self-piercing rivets, solid self-piercing rivets, blind rivets and screws.

4. The joining element according to claim 1, wherein the hardening of the edge layer was achieved by nitriding, induction hardening, flame hardening, laser beam hardening, electron beam hardening or carburizing.

5. The joining element according to claim 1, wherein at least the shaft and the end portion of the joining element comprise a coating of a material providing a hardness greater than the material of the shaft and the end portion.

6. The joining element according to claim 2, selected from the group consisting of: setting bolts, semi-hollow self-piercing rivets, solid self-piercing rivets, blind rivets and screws.

7. The joining element according to claim 2, wherein the hardening of the edge layer was achieved by nitriding, induction hardening, flame hardening, laser beam hardening, electron beam hardening or carburizing.

8. The joining element according to claim 2, wherein at least the shaft and the end portion of the joining element comprise a coating of a material providing a hardness greater than the material of the shaft and the end portion.

9. The joining element according to claim 3, wherein the hardening of the edge layer was achieved by nitriding, induction hardening, flame hardening, laser beam hardening, electron beam hardening or carburizing.

10. The joining element according to claim 3, wherein at least the shaft and the end portion of the joining element comprise a coating of a material providing a hardness greater than the material of the shaft and the end portion.

11. The joining element according to claim 4, wherein at least the shaft and the end portion of the joining element comprise a coating of a material providing a hardness greater than the material of the shaft and the end portion.

12. A connection structure comprised of at least a first component and a second component connected by a joining element according to claim 1.

13. The connection structure according to claim 12, in which the first component is arranged adjacent to the head and the second component is arranged adjacent to the end portion of the joining element, wherein the second component is comprised of a steel, in particular a hot forming steel, having a tensile strength of at least 800 MPa, in particular having a tensile strength between 800 MPa and 2,000 MPa or at least between 800 MPa and 1,500 MPa.

14. A manufacturing method of a joining element according to claim 1, comprising the following steps: a. providing, in particular by cold forming or turning, the joining element having a head at a first axial end, an end portion at a second axial end opposite the first axial end, as well as a shaft arranged between the end portion and the head, wherein the head defines a longitudinal axis of the joining element between the first and the second axial end, and b. hardening of at least the shaft and the end portion of the joining element so that the shaft and the end portion comprise a hardened edge layer, whereby a material of the shaft and the end portion has in the interior a lower hardness compared to a radially adjacent surface.

15. The manufacturing method according to claim 14, which comprises the further step before the hardening of the joining element: c. quenching and tempering of at least the shaft and the end portion of the joining element.

16. The manufacturing method according to claim 14, wherein the step of hardening comprises: d1. nitriding, induction hardening, flame hardening, laser beam hardening, electron beam hardening or carburizing; or d2. applying a coating at least at the shaft and the end portion of the joining element.

17. The manufacturing method according to claim 14, wherein the joining element is selected from the group consisting of: setting bolts, semi-hollow self-piercing rivets, solid self-piercing rivets, blind rivets and screws.

18. The manufacturing method according to claim 14, wherein a material for the joining element comprises a cold-formable steel.

19. The manufacturing method according to claim 15, wherein the step of hardening comprises: d1. nitriding, induction hardening, flame hardening, laser beam hardening, electron beam hardening or carburizing; or d2. applying a coating at least at the shaft and the end portion of the joining element.

20. The manufacturing method according to claim 15, wherein the joining element is selected from the group consisting of: setting bolts, semi-hollow self-piercing rivets, solid self-piercing rivets, blind rivets and screws.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In the following, the present disclosure is described in detail with reference to the drawings. The same reference signs in the drawings indicate the same components and/or elements. Showing:

[0032] FIG. 1 a cross-section of a joining element,

[0033] FIG. 2 a perspective view of a joining element set in a component made of high or ultra-high strength steel,

[0034] FIG. 3 a perspective view of a joining element set in a component made of high or ultra-high strength steel,

[0035] FIG. 4 a perspective view of a joining element set in a component made of high or ultra-high strength steel,

[0036] FIG. 5 a micrograph or microsection of an end portion of an embodiment of the joining element,

[0037] FIG. 6 a diagram for illustrating the hardened edge portion,

[0038] FIG. 7 a diagram of notched bar impact work as well as hardness,

[0039] FIG. 8 a flow chart of an embodiment of a manufacturing method of the joining element, and

[0040] FIG. 9 a flow chart of an embodiment of a method for connecting two components with the joining element.

DETAILED DESCRIPTION

[0041] Referring to FIG. 1, a joining element 1 is shown in the form of a setting bolt. With regard to the details of the form, reference is made to DE 10 2006 002 238 A1, the content of which is incorporated by reference in this respect.

[0042] Instead of the setting bolt as joining element 1, semi-hollow self-piercing rivets, solid self-piercing rivets, blind rivets, screws and the like can also be used as joining elements and the following description applies accordingly to these joining elements. With regard to the details of the shape, reference is made to DE 10 2012 102 860 A1, DE 10 2015 118 888 A1 and DE 10 2019 102 383 A1 for semi-hollow self-piercing rivets, DE 10 2018 128 455 and DE 10 2019 102 380 for solid self-piercing rivets and DE 20 2005 005 536 Ul and EP 1 710 454 A1 for blind rivets, which are also incorporated by reference in this respect.

[0043] Referring again to FIG. 1, the joining element 1 comprises in a known manner a head 10 at a first axial end, an end portion 20, in this case a tip, at a second axial end as well as a shaft 30 arranged in between. The shaft 30 defines a longitudinal axis L of the joining element 1 between the first and the second axial end, which due to its position can also be referred to as the central longitudinal axis.

[0044] The head 10 of joining element 1 comprises a flat upper side 12, a cylindrical circumferential face and a flat underside 14. The flat underside 14 has an annular groove 16 adjacent to the shaft 30 for receiving a bead- or bulge-shaped material accumulation of the head-side component, which is particularly advantageous when setting the joining element 1 into at least two components.

[0045] The annular groove 16 comprises a rounded circumferential face adjacent to the shaft 30, which transitions tangentially into the shaft 30 on the one hand and into a conical face on the other. In this way, especially when the material of the component facing the head rises against the joining direction, the material can be accommodated in the annular groove 16.

[0046] The shaft 30 is formed cylindrically and, at least in a subportion, has a surface profiling 32 for receiving material, of the component A facing away from the head. In this way, the joining element 1 may be reliably fastened in at least one component.

[0047] The end portion 20, in this case the tip, directly adjoins the shaft 30.

[0048] Now referring to FIG. 2, which shows a perspective view of a joining element set in the component made of high or ultra-high strength steel, the disadvantages of the known joining elements are explained. The joining element used comprises a hardness of 450 HV 10, that is, a Vickers hardness (HV) of 450 at a test force or applied force of 10 kilopond. Due to the high tensile strength of the component made of high-strength or ultra-high-strength steel, the use of the known joining element results in plastic deformation of the end portion 26 of the joining element. In addition, a slug 40 is separated from the component. However, this is disadvantageous due to the noise development even if the component is only accessible from one side. Overall, the connection made in this way can therefore be categorized as not being acceptable.

[0049] FIG. 3 shows a perspective view of another joining element set into a component made of high or ultra-high strength steel. The joining element used here comprises the hardness class 8 with a hardness of 600 HV 10. The increase in the hardness of the joining element resulted not only in an increase in brittleness, but also in a reduction of the deformation of the end portion. As can be seen from FIG. 3, the slugs remain at the eyelet. In this case, in particular dynamic loads could cause a loosening of the slug. This can in turn, especially with regard to the manufacturing of a motor vehicle body, lead to damage to the cathodic dip coating layer, so that there is no corrosion protection in this portion when the component is further processed with the joining element. Thus, this connection is also disadvantageous as it is not suitable for possible further processing steps or downstream processing steps.

[0050] Now referring to FIG. 4, a perspective view of a joining element according to an embodiment set into a component made of high-strength or ultra-high-strength steel is shown. Therefore, at least the shaft and the end portion of the joining element, which may be the entire joining element, comprises a hardened edge portion 24. The use of the hardened edge portion 24 results in hardnesses of up to 1,200 HV 10 being achievable, depending on the material used for the joining element.

[0051] FIG. 5 shows a micrograph or microsection of the end portion 20 of the joining element to illustrate the modification in the material. The hardening of the edge portion 24 was achieved by nitriding, especially gas nitriding. Apart from nitriding, any method in which the joining elements provided may be further processed as bulk material, i.e. where no individual processing is required.

[0052] As can be seen from FIG. 5 in connection with FIG. 6, the hardened edge portion 24 extends into the interior of the joining element to a depth of approx. 1.2 mm. The hardness curve or progression is shown in FIG. 6 for the two joining element materials 34Cr4 and 42CrMo4. By nitriding, hardnesses of up to 900 HV 0.3 were achieved for these materials, which decrease linearly towards the core. The nitriding depth, i.e. the depth of the hardened edge layer 24, can be reliably adjusted by means of the nitriding duration.

[0053] By using edge layer hardened joining elements, steel materials with a tensile strength of 1,200 MPa are joinable without separation of a slug and without deformation of the end portion. In addition, for example steels such as hot forming steels with a tensile strength of up to 2,000 MPa, for example 1,500 MPa, can be joined in thicknesses of approx. 1.2 mm.

[0054] In addition to that the process window has been extended when setting the joining element, there is also an increased notched bar impact work and thus an increased ductility. The notched bar impact work or notched bar impact strength is a measure for the abrupt and/or dynamic stress of the joining element. This stress occurs not only during the joining process but also in the later connection structure if the joining element has to hold the at least two components together under component loads. This increased notched bar impact work or notched bar impact strength can be attributed to the core 26 in the interior of the joining element 1, which is soft compared to the hardened edge portion 24. For example, by changing the material from C67 to 34Cr4 and using the nitriding process, the notched bar impact work can be increased tenfold, as shown in FIG. 7, taking into account different materials.

[0055] One advantage of this attribute has an effect on the later connection structure. The combination of a hard edge portion and a relatively soft core results in the joining element being reliably fastened in subsequent processing steps despite the hardened edge portion. This applies, for example, with regard to a later artificial ageing of two components joined by means of the joining element.

[0056] A connection structure in which the joining element is used, for example, is comprised of a first component facing the head and a second component facing away from the head. The components are connected by means of an embodiment of the joining element. Here, an end portion of the joining element can penetrate both components. Alternatively, the end portion of the joining element is arranged in the component facing away from the head. Similarly, the joining element can only be set into one of the components and subsequently be welded to the second component.

[0057] One of the components, in particular the component B facing away from the head, may be comprised of a steel with a tensile strength of at least 800 MPa. Thus, the component B facing away from the head or the lower component B was manufactured from a high-strength or ultra-high-strength steel. Due to the specific design of the joining element, the risk of plastic deformation of the end portion 20 as well as of a fracture of the joining element may be reduced or eliminated when setting the joining element in such a component B as well as when penetrating component B, as explained above. In addition, the joining element prevents a slug from being separated or cut off from the second component made of steel with a tensile strength of at least 800 MPa.

[0058] FIG. 8 shows a flow chart of an embodiment of a manufacturing method of a joining element. The joining element may be comprised of a cold-formable steel at least at the shaft and the end portion. In addition, the joining element was advantageously selected from the following group: setting bolts, semi-hollow self-piercing rivets, solid self-piercing rivets, blind rivets, screws and the like.

[0059] In the course of manufacturing, in a first step A, a providing, which may be by cold forming or turning, of the joining element having a head at a first axial end, an end portion at a second axial end opposite the first axial end, as well as a shaft arranged between the end portion and the head takes place, wherein the shaft defines a longitudinal axis of the joining element between the first and the second axial end.

[0060] In an optional step C, a quenching and tempering of at least the shaft and the end portion of the joining element, of the joining element as a whole, is then carried out. For details on quenching and tempering, reference is made to the above explanations.

[0061] In a final step B, hardening of at least the shaft and the end portion of the joining element, of the joining element as a whole, may take place so that the shaft and the end portion comprise a hardened edge layer, whereby a material of the shaft and the end portion has in the interior a lower hardness compared to a radially adjacent surface. The hardening step comprises either one of nitriding, induction hardening, flame hardening, laser beam hardening, electron beam hardening or carburizing (step D1) or the hardening step comprises applying a coating at least at the shaft and the end portion of the joining element (step D2). In this way, the joining element described above is manufactured according to one embodiment.

[0062] Finally, and with reference to FIG. 9, a flow chart of an embodiment of a method for connecting a first component A to a second component B by means of an embodiment of a joining element is shown. In a first step I, an arranging of the first A and the second component B one above the other is performed. In a subsequent second step II, a setting of the joining element into the arrangement of the first and the second component arranged one above the other takes place, wherein the setting of the joining element is essentially rotation-free. The essentially rotation-free setting can also be described as an exclusively translatory setting of the joining element.

[0063] The first component is arranged adjacent to the head and the second component is arranged adjacent to the tip of the joining element during setting and both components are not pre-punched in the joining portion, as already discussed. The second component may be comprised of a steel with a tensile strength of at least 800 MPa. A penetration of the second component B takes place without separation of a slug. It is precisely the specific design of the joining element that makes it possible that no slug is separated from the second component made of steel with a tensile strength of at least 800 MPa.