SELF-PIERCING RIVET, METHOD FOR PRODUCING A SELF-PIERCING RIVET, AND METHOD FOR CONNECTING TWO ELEMENTS BY A SELF-PIERCING RIVET

Abstract

The invention relates to a self-piercing rivet for connecting at least two elements. The self-piercing rivet has a coating. At least one component of the coating has a melting temperature of at least 450 C., and/or the coating comprises nickel. A method for producing a self-piercing rivet includes, providing a self-piercing rivet blank, applying a coating to the self-piercing rivet blank by a chemical coating method, and obtaining the self-piercing rivet.

Claims

1. A self-piercing rivet for connecting at least two elements, wherein the self-piercing rivet has a coating, and wherein: (i) at least one component of the coating has a melting temperature of at least 450 C., and (ii) the coating comprises nickel.

2. The self-piercing rivet according to claim 1, wherein the self-piercing rivet is a solid self-piercing rivet, a semi-hollow self-piercing rivet or a hollow self-piercing rivet.

3. The self-piercing rivet according to claim 1, wherein the melting temperature of the at least one component of the coating is at least 1300 C.

4. The self-piercing rivet according to claim 1, wherein the melting temperature of the coating is at least 850 C.

5. The self-piercing rivet according to claim 1, wherein the coating contains nickel to an extent of at least 80% by weight.

6. The self-piercing rivet according to claim 1, wherein the coating contains phosphorus to an extent of at least 12% by weight.

7. The self-piercing rivet according to claim 1, wherein the coating is applied by a chemical coating method.

8. A method for producing a self-piercing rivet, the method comprising: providing a self-piercing rivet blank; applying a coating to the self-piercing rivet blank by a chemical coating method; and obtaining the self-piercing rivet.

9. The method according to claim 8, wherein the chemical coating method comprises electroless nickel plating.

10. The method according to claim 8, wherein the self-piercing rivet blank is thermally treated after the application of the coating at a temperature of at most 350 C. and for a duration of at most 48 hours.

11. The method according to claim 10, wherein the thermal treatment begins at most 24 hours after the application of the coating to the self-piercing rivet blank.

12. A method for connecting at least two elements by a self-piercing rivet with a coating, the method comprising: providing the at least two elements, heating a surface of at least one of the elements, and connecting the two elements by the self-piercing rivet, wherein a melting temperature of at least one component of the coating is above a melting and recrystallization temperature of at least one of the elements.

13. The method according to claim 12, wherein a melting temperature of the coating is above the melting and recrystallization temperature of at least one of the elements.

14. The method according to claim 12, wherein at least one of the elements has a yield strength, determined according to ISO 6892-1, of at least 1300 MPa, and a tensile strength, determined according to ISO 6892-1, of at least 1600 MPa.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0070] The invention is described in detail below with reference to figures.

[0071] FIG. 1 shows a cross section of a self-piercing rivet.

[0072] FIG. 2A shows schematically a work step when connecting two elements by means of a self-piercing rivet 10.

[0073] FIG. 2B shows schematically a work step when connecting two elements by means of a self-piercing rivet.

[0074] FIG. 3A shows a connection of two elements by means of a self-piercing rivet 10 from the prior art.

[0075] FIG. 3B shows a connection of two elements by means of a self-piercing rivet 10 of the disclosure.

DETAILED DESCRIPTION

[0076] FIG. 1 shows a cross section of a self-piercing rivet 10. The self-piercing rivet 10 shown in FIG. 1 is a semi-hollow self-piercing rivet, but the disclosure is not limited thereto. The self-piercing rivet 10 can likewise be a solid self-piercing rivet or a hollow self-piercing rivet.

[0077] The self-piercing rivet 10 can have a self-piercing rivet head 11. A self-piercing rivet shank 12 can adjoin the self-piercing rivet head 11. The self-piercing rivet shank 12 can be formed substantially in the shape of a hollow cylinder. A self-piercing rivet foot 15 can be formed at an axial end of the self-piercing rivet 10 which lies opposite the self-piercing rivet head 11. The thickness (in particular the wall thickness) of the self-piercing rivet shank 12 at the self-piercing rivet foot 15 can be less than in a region in the vicinity of the self-piercing rivet head 11. The thickness (in particular the wall thickness) of the self-piercing rivet shank 12 can decrease towards one end.

[0078] The self-piercing rivet 10 can have a cavity 16. The cavity 16 can be delimited or defined by the self-piercing rivet head 11 and the self-piercing rivet shank 12. The cavity 16 can be open on one side with respect to the surroundings. The opening of the cavity 16 can be formed in the region of the self-piercing rivet foot 12.

[0079] The self-piercing rivet 10 can be formed rotationally symmetrically.

[0080] The self-piercing rivet 10 can have a diameter of at most 15 mm, preferably at most 12.5 mm, more preferably at most 10 mm, more preferably at most 8 mm, more preferably at most 5 mm.

[0081] In particular, the self-piercing rivet head 11 can have a diameter of at most 15 mm, preferably at most 12.5 mm, more preferably at most 10 mm, more preferably at most 8 mm. The self-piercing rivet shank 12 can have a diameter of at most 15 mm, preferably at most 12.5 mm, more preferably at most 10 mm, more preferably at most 8 mm, more preferably at most 6 mm.

[0082] The self-piercing rivet 10 can have a length (perpendicular to the diameter) of at most 30 mm, preferably at most 25 mm, more preferably at most 20 mm, more preferably at most 15 mm, more preferably at most 10 mm, more preferably at most 7.5 mm, more preferably at most 5 mm.

[0083] The surface of the self-piercing rivet 10 is preferably provided with a coating 20. The coating 20 can be any coating disclosed herein. The coating 20 can be applied to the self-piercing rivet 10 at least in the region of the self-piercing rivet shank 12. Preferably, the entire surface of the self-piercing rivet 10 is provided with the coating 20. Likewise, the coating 20 can be applied only to outer surfaces of the self-piercing rivet 10. One cavity or a plurality of cavities of the self-piercing rivet 10 cannot be provided with the coating 20 or the coating 20 can be thinner in the cavity or cavities than on the outer surfaces of the self-piercing rivet 10.

[0084] Particularly preferably, the coating 20 is a nickel-phosphorus coating. The coating 20 can be applied by electroless nickel plating (electroless nickel plating).

[0085] The self-piercing rivet 10 can comprise steel. Preferably, the self-piercing rivet 10, apart from the coating 20, consists of steel.

[0086] FIGS. 2A and 2B show method steps in the connection of at least two elements 30, 40.

[0087] In FIG. 2A, a first element 30 and a second element 40 are provided. The first and second elements 30, 40 can be positioned and possibly held relative to one another. The first element 30 can at least partially contact the second element 40.

[0088] The first element 30 can be a steel component. The second element 40 can be an aluminum component. The thickness of the first element 30 can be between 1.0 mm and 2.0 mm. Preferably, the thickness of the first element 30 is approximately 1.5 mm. The thickness of the second element 40 can be between 2.0 mm and 6.0 mm, preferably between 2.0 mm and 3.0 mm. Preferably, the thickness of the second element 40 is approximately 2.5 mm.

[0089] At least one of the first and second elements 30, 40 can be heated by a heating device 50. This is done before the self-piercing rivet 10 is used for connecting the first and second elements 30, 40.

[0090] The heating device 50 can comprise a laser. The heating device 50 can be configured to generate a laser beam 51 and to irradiate the laser beam 51 onto the surface of the first element 30 and/or the surface of the second element 40. As a result, the surface of the element onto whose surface the laser beam 51 is irradiated or has been irradiated can be heated. In addition, a region of the element onto whose surface the laser beam 51 is irradiated or has been irradiated can be heated in the vicinity of the surface. If the laser beam 51 is irradiated onto the surface of the element, the element onto whose surface the laser beam 51 is not irradiated can likewise be heated, for example by (conductive) heat conduction.

[0091] The heating device 50 can comprise a resistive element. The resistive element can be heated by electric current. The resistive element can contact a surface of the first and/or second element 30, 40 and heat the latter.

[0092] The heating device 50 can likewise comprise an inductive element. The inductive element can be configured to generate a magnetic field. The first and/or second element 30, 40 can be heated by the magnetic field.

[0093] The first and/or second element 30, 40 can be heated up to a temperature below the melting temperature of the first and/or second element 30, 40. Preferably, the first and/or second element 30, 40 is heated up to a temperature of up to 80% of the melting temperature of the first and/or second element 30, 40. The first and/or second element 30, 40 can be heated up to a temperature of at least 500 C., preferably at least 600 C., preferably at least 700 C., preferably at least 800 C., preferably at least 900 C., preferably at least 1000 C., preferably at least 1100 C., preferably at least 1200 C.

[0094] The first and/or second element 30, 40 can be heated up to a temperature above a recrystallization temperature of the first and/or second element 30, 40. Preferably, the first and/or second element 30, 40 is heated up to a temperature of at least 50 C., preferably at least 100 C., preferably at least 150 C., preferably at least 200 C., preferably at least 250 C., preferably at least 300 C., preferably at least 350 C., preferably at least 400 C., above a recrystallization temperature of the first and/or second element 30, 40.

[0095] As a result of the heating, the strength and/or hardness of the first and/or second element 30, 40 can be reduced.

[0096] The self-piercing rivet 10 can be held by a hold-down device (not shown). Furthermore, a die (not illustrated) can be positioned opposite the hold-down device.

[0097] FIG. 2B shows elements 30, 40 connected by the self-piercing rivet 10. In order to connect the elements 30, 40, the self-piercing rivet 10 can be introduced into the surface of the first element 30. For this purpose, the punch which is enclosed by the hold-down device can apply a force to the self-piercing rivet 10, in particular the self-piercing rivet head 11, and drive the self-piercing rivet 10 into the first element 30. By introducing the self-piercing rivet 10 into the first element 30, 40, a portion of the first element 30 can be punched out. The punched-out portion of the first element 30 can be pressed in the direction of the second element 40. The self-piercing rivet 10 can penetrate only partially or at most partially into the second element 40. A portion of the second element 40 can deform plastically. As a result of the penetration of the self-piercing rivet 10 into the first and second elements 30, 40, a bulge 41 (also referred to as closing head) can form on the second element 40. The bulge 41 can protrude beyond the surface of the second element 40. The shape of the bulge 41 can be defined substantially by the shape of the die. The die can bear against the surface of the second element 40 when the self-piercing rivet 10 is introduced into the first and second elements 30, 40. The shape of the bulge 41 can correspond substantially to the shape of a recess of the die.

[0098] The introduction of the self-piercing rivet 10 into the first and/or second element 30, 40 can take place without pre-punching.

[0099] As a result of the heating of the first and/or second element 30, 40, the strength and/or hardness of the first and/or second element 30, 40 is reduced, with the result that an introduction of the self-piercing rivet 10 is facilitated or enabled. For this purpose, relatively thin or relatively small self-piercing rivets 10 can also be used. However, the self-piercing rivet 10 is also heated as a result.

[0100] FIGS. 3A and 3B each show a connection of two elements 30, 40 by means of a self-piercing rivet 10. In this case, a known method or a known self-piercing rivet 10 was used in FIG. 3A. In FIG. 3B, the method according to the invention or a self-piercing rivet 10 according to the invention was used.

[0101] The first element 30 of the connection shown in FIGS. 3A and 3B is a steel element with a thickness of approximately 1.5 mm. The second element 40 of the connection shown in FIGS. 3A and 3B is an aluminum element with a thickness of approximately 2.5 mm. The surface of the first element 30 has a temperature of approximately 1200 C. during the joining process and the second element 40 has a temperature of approximately 300 C. during the joining process.

[0102] The self-piercing rivet 10 of the connection shown in FIG. 3a is provided with a coating which contains zinc, tin and aluminum. The self-piercing rivet 10 of the connection shown in FIG. 3b is provided with a coating according to the invention which contains, in particular, nickel and phosphorus, and is applied specifically by electroless nickel plating (electroless nickel plating).

[0103] As can be seen in FIG. 3A, the self-piercing rivet 10 has cracks 17. Cracks 17 in self-piercing rivets 10 have been found in a plurality of comparable or identical investigations. The stability of the connection of the elements 30, 40 is restricted or defective as a result of the cracks 17. The connection of the elements 30, 40 can fail, in particular under load.

[0104] No cracks have been found in the self-piercing rivet 10 according to the invention, as shown in FIG. 3B. The connection of the elements 30, 40 using the self-piercing rivet 10 according to the invention or the method according to the invention appears to be error-free.

[0105] Without wishing to be bound by a theoretical explanation, it is assumed that the cracks 17 in the known self-piercing rivet 10 could have resulted at least partially from liquid metal embrittlement. Liquid metal embrittlement is a phenomenon in which certain ductile metals suffer a drastic loss of tensile ductility or break brittle when they are exposed to certain liquid metals. This could have taken place by partial melting of the coating of the known self-piercing rivet 10, as a result of which the self-piercing rivet 10 has lost its mechanical properties. This effect can be avoided or reduced by the coating 20 according to the invention.