Self-piercing rivet, method for manufacturing self-piercing rivet, and method for connecting two elements with self-piecing rivet

Abstract

To provide a self-piercing rivet that enables or improves joining of two elements, at least one of which has high hardness and / or strength, with less failure.SOLUTION: Provided is a self-piercing rivet (10) for connecting at least two elements, where the self-piercing rivet (10) is coated with a coating (15), at least one component of the coating (15) has a melting point of 450°C or higher, and / or the coating (15) contains nickel.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] FIELD OF THE DISCLOSURE The present disclosure relates to a self-piercing rivet, a method for manufacturing a self-piercing rivet, and a method for connecting two elements with a self-piercing rivet. [Background technology]

[0002] For example, punch rivets are known for connecting two metal sheets. Compared to other riveting methods, punch riveting eliminates the need for pre-drilling holes in the metal sheets. In this case, the rivet element (punch rivet) functions as a disposable cutout punch, and the rivet element itself is formed in its case. The metal sheets to be connected are placed on a die. The rivet element is fed to the joining point, and a holding device is arranged to fix the joining point during feeding. During the subsequent joining process, the punch rivet penetrates at least the upper metal sheet and plastically deforms the lower metal sheet, forming a closing head.

[0003] In recent years, the use of ultra-high strength steels (UHSS) and advanced high strength steels (AHSS), which have high hardness or strength, has increased. To connect these steels to other materials using punch riveting, the punch riveting operation can be facilitated by heating the steel plate.

[0004] DE 112007001331 A1 relates to a method for connecting elements, in which one of the elements to be connected is heated by a laser to improve its formability.

[0005] EP 4253771 A1 relates to a fastening element for connecting at least two parts without pre-drilling, where the fastening area is heated with plasma.

[0006] DE 19630488 A1 relates to a method and device for joining by forming, in which the parts to be joined are arranged one on top of the other and are locally plastically formed with or without an auxiliary joining part using a joining tool consisting of a punch, a holding device and a die. The parts to be joined may be heated by induction heating.

[0007] Known punch rivets can break due to the temperature rise of the metal sheets during joining, which can result in an incomplete joining of the metal sheets. Summary of the Invention

[0008] It is an object of the present disclosure to provide a self-piercing rivet that enables or improves a connection between two elements with reduced failure, where at least one element has high hardness and / or high strength.A further object of the present disclosure is to provide a self-piercing rivet that enables or improves a connection between two elements with reduced failure, where at least one element becomes hot during use of the self-piercing rivet.A further object of the present disclosure is to provide a method for improving the connection of two elements, particularly where at least one element has high hardness and / or high strength, or where at least one element becomes hot during use of the self-piercing rivet.

[0009] At least one of the objects is solved by the features of each of the independent claims. Preferred embodiments are specified in the dependent claims and in the description.

[0010] A self-piercing rivet for connecting at least two components is identified. The self-piercing rivet is provided with a coating. At least one component of the coating has a melting point of 450°C or greater. Alternatively or additionally, the coating includes nickel.

[0011] Additionally, a method for manufacturing a self-piercing rivet is identified, the method comprising the steps of providing a self-piercing rivet blank, applying a coating to the self-piercing rivet blank by a chemical coating method, and obtaining a self-piercing rivet.

[0012] The self-piercing rivet may be any of the self-piercing rivets disclosed herein.

[0013] Also specified is a method for connecting at least two elements with a self-piercing rivet. The self-piercing rivet is coated with a coating. The self-piercing rivet may be any of the self-piercing rivets disclosed herein. The method includes providing at least two elements, heating a surface of at least one of the elements, and connecting the two elements with the self-piercing rivet. At least one component of the coating has a melting point higher than the melting point of the at least one element. Alternatively or additionally, the melting point of the at least one component of the coating is higher than the recrystallization temperature of the at least one element.

[0014] It has been found that the use of special coatings can suppress or prevent cracking or breakage of self-piercing rivets. For example, if two elements, such as two metal parts, are connected with a conventional self-piercing rivet and at least one of the elements is heated by the self-piercing rivet before the elements are connected, reducing its hardness or strength, the conventional self-piercing rivet may crack or (partially) break. As a result, the connection strength of the elements is reduced or even lost. This problem is exacerbated because cracks and breakage of self-piercing rivets are not always visible. Cracks and breakage of self-piercing rivets can often only be reliably detected by destructive testing. As a result, connections made with conventional self-piercing rivets create uncertainty as to whether the connection is sufficiently strong. Furthermore, the connection may only fail over time or under load.

[0015] The elements (also referred to as joining elements) may be metal elements, in particular metal parts or metal plates. In particular, the elements are two different metal elements. The metal elements may differ by composition (e.g., alloy), physical properties, and / or shape (e.g., thickness). Preferably, at least one element is a steel element, in particular a UHSS or AHSS steel element. At least one element may be an aluminum element, for example an aluminum casting.

[0016] The self-piercing rivet may be completely covered with the coating. The entire surface of the self-piercing rivet may be coated with the coating. The coating may be thinner within one or more cavities of the self-piercing rivet than outside the cavities. Similarly, no coating may be present within one or more cavities. Preferably, at least the outer surface of the self-piercing rivet is completely covered with the coating.

[0017] The coating may contain different components, or the coating may contain exactly or at most one component.

[0018] The self-piercing rivet may be a solid self-piercing rivet, in which case the joining element is cut by the solid self-piercing rivet and the resulting recess is filled by the solid self-piercing rivet. The solid self-piercing rivet may not have a recess or cavity.

[0019] The self-piercing rivet may be a semi-hollow self-piercing rivet. In the case of a semi-hollow self-piercing rivet, one of the joining elements is cut and the lower joining element is deformed. At the same time, the semi-hollow self-piercing rivet is also deformed. The semi-hollow self-piercing rivet may have a recess or a cavity. In particular, the semi-hollow self-piercing rivet has a substantially cylindrical cavity. The cavity may be open to the surroundings on only one side or exactly one side.

[0020] The self-piercing rivet may be a hollow self-piercing rivet. In the case of a hollow self-piercing rivet, all joining elements are not cut. In contrast to a semi-hollow self-piercing rivet, a hollow self-piercing rivet has a continuous recess or a continuous cavity. The recess or cavity may be open to the surroundings on at least two sides.

[0021] The melting point of the at least one component may be 475°C or higher, preferably 500°C or higher, preferably 550°C or higher, preferably 600°C or higher, preferably 650°C or higher, preferably 700°C or higher, preferably 750°C or higher, preferably 800°C or higher, preferably 850°C or higher, preferably 900°C or higher, preferably 950°C or higher, preferably 1000°C or higher, preferably 1050°C or higher, preferably 1100°C or higher, preferably 1150°C or higher, preferably 1200°C or higher, preferably 1250°C or higher, preferably 1300°C or higher, preferably 1350°C or higher, preferably 1400°C or higher, preferably 1425°C or higher.

[0022] The melting point of the at least one component may be 3000°C or less, preferably 2900°C or less, preferably 2800°C or less, preferably 2700°C or less, preferably 2600°C or less, preferably 2500°C or less, preferably 2400°C or less, preferably 2300°C or less, preferably 2200°C or less, preferably 2100°C or less, preferably 2000°C or less, preferably 1900°C or less, preferably 1800°C or less, preferably 1700°C or less, preferably 1600°C or less, preferably 1500°C or less.

[0023] The melting point of the at least one component may be in the range of 450°C to 3000°C, preferably 500°C to 2800°C, preferably 600°C to 2600°C, preferably 700°C to 2400°C, preferably 800°C to 2200°C, preferably 900°C to 2100°C, preferably 1000°C to 2000°C, preferably 1100°C to 1800°C, preferably 1200°C to 1700°C, preferably 1300°C to 1600°C, preferably 1400°C to 1500°C.

[0024] The coating may include at least one component and at least one other component. The at least one component may be a metal. The at least one other component may be a (different) metal or a non-metal. In particular, the at least one other component is phosphorus.

[0025] The coating may include nickel. Nickel may be at least one component. Preferably, the coating includes nickel and at least one other component. The at least one other component may be a metal (other than nickel) or a non-metal. The at least one other component may be phosphorus.

[0026] Preferably, the coating comprises nickel and phosphorus.

[0027] The melting point of the coating may be 450°C or higher, preferably 475°C or higher, preferably 500°C or higher, preferably 550°C or higher, preferably 600°C or higher, preferably 650°C or higher, preferably 700°C or higher, preferably 750°C or higher, preferably 800°C or higher, preferably 850°C or higher.

[0028] The melting point of the coating may be 1700°C or less, preferably 1600°C or less, preferably 1550°C or less, preferably 1500°C or less, preferably 1450°C or less, preferably 1400°C or less, preferably 1350°C or less, preferably 1300°C or less, preferably 1250°C or less, preferably 1200°C or less, preferably 1150°C or less, preferably 1100°C or less, preferably 1050°C or less.

[0029] The melting point of the coating may be in the range of 450°C to 1400°C, preferably 500°C to 1350°C, preferably 550°C to 1300°C, preferably 600°C to 1250°C, preferably 650°C to 1200°C, preferably 700°C to 1150°C, preferably 750°C to 1100°C, preferably 800°C to 1050°C, preferably 850°C to 1000°C.

[0030] The coating may comprise 50% by weight or more, preferably 55% by weight or more, preferably 60% by weight or more, preferably 65% ​​by weight or more, preferably 70% by weight or more, preferably 75% by weight or more, preferably 80% by weight or more, preferably 85% by weight or more of said at least one component, in particular nickel.

[0031] The coating may comprise up to 95% by weight of at least one component as defined above, in particular nickel, preferably up to 92.5% by weight, preferably up to 90% by weight, preferably up to 87.5% by weight.

[0032] The coating may comprise at least one component as above, in particular nickel, in the range of 50% to 95% by weight, preferably 55% to 95% by weight, preferably 60% to 95% by weight, preferably 65% ​​to 92.5% by weight, preferably 70% to 90% by weight, preferably 75% to 90% by weight, preferably 80% to 80% by weight.

[0033] The coating may contain at least one other component, in particular phosphorus.

[0034] In particular, the coating may comprise 3% by weight or more, preferably 4% by weight or more, preferably 5% by weight or more, preferably 6% by weight or more, preferably 7% by weight or more, preferably 8% by weight or more, preferably 9% by weight or more, preferably 10% by weight or more, preferably 11% by weight or more, preferably 12% by weight or more, preferably 13% by weight or more, preferably 14% by weight or more of at least one further component, in particular phosphorus.

[0035] The coating may contain up to 40% by weight, preferably up to 35% by weight, preferably up to 30% by weight, preferably up to 25% by weight, preferably up to 20% by weight, preferably up to 18% by weight, preferably up to 16% by weight, preferably up to 15% by weight of at least one further component, in particular phosphorus.

[0036] The coating may comprise at least one further component, in particular phosphorus, in the range of 4% to 18% by weight, preferably 5% to 18% by weight, preferably 6% to 18% by weight, preferably 7% to 18% by weight, preferably 8% to 18% by weight, preferably 9% to 18% by weight, preferably 10% to 18% by weight, preferably 11% to 17% by weight, preferably 12% to 16% by weight, preferably 13% to 15% by weight.

[0037] The at least one other component may be boron. All features disclosed herein with respect to phosphorus are also applicable to boron. That is, phosphorus can be substituted for boron herein.

[0038] The coating density is 5g / cm 3 ~10g / cm 3 , preferably 6 g / cm 3 ~9g / cm 3 , preferably 7 g / cm 3 ~8g / cm 3 , preferably 7.5 g / cm 3 ~8.5g / cm 3 , preferably 7 g / cm 3 ~8g / cm 3 The range may be:

[0039] The coating may have a Knoop hardness, measured in particular according to ASTM E384 (100 g), in the range of 250 to 1500, preferably 300 to 1400, preferably 350 to 1300, preferably 400 to 1200, preferably 400 to 1100, preferably 400 to 1000, preferably 450 to 900, preferably 500 to 850.

[0040] The Rockwell hardness (Rockwell C) of the coating may be in the range of 30-80, preferably 35-75, preferably 40-70, preferably 45-65.

[0041] The coating can be applied by painting or by chemical coating methods, which may involve redox reactions.

[0042] The chemical coating method may involve at least one chemical reaction. By means of the chemical coating method, nickel, preferably a nickel alloy, particularly preferably a nickel-phosphorus alloy or a nickel-boron alloy, can be applied to the surface of the self-piercing rivet. For this purpose, the self-piercing rivet may be introduced into a solution. The solution may contain a nickel salt (e.g., nickel sulfate) and a reducing agent. The reducing agent may contain phosphorus or boron. For example, hypophosphite (H2PO2 - ) or borohydride (BH4 - ) can be used as a reducing agent.

[0043] Prior to coating the self-piercing rivet, the surface of the self-piercing rivet may be chemically and / or mechanically cleaned. Similarly, the surface of the self-piercing rivet may be activated by making it hydrophilic. Similarly, the surface of the self-piercing rivet may be activated by providing a (thin) metal layer on the surface of the self-piercing rivet.

[0044] After coating, the coated surface may be provided with an anti-oxidation layer and / or an anti-oxidation initiation layer.

[0045] Chemical coating methods may include electroless nickel plating.

[0046] After the coating is applied, the self-piercing rivet or self-piercing rivet blank may be heat treated. The heat treatment may be carried out in a furnace. Similarly, the heat treatment may be carried out in a bath, such as an oil bath.

[0047] The self-piercing rivet or self-piercing rivet blank may be heat treated at a temperature of not more than 350°C. In particular, the self-piercing rivet or self-piercing rivet blank is heat treated at a temperature of not more than 300°C, preferably not more than 250°C, preferably not more than 200°C. Preferably, the self-piercing rivet or self-piercing rivet blank is heat treated in the temperature range of 100°C to 300°C, more preferably 150°C to 250°C, more preferably 180°C to 220°C.

[0048] The self-piercing rivet or self-piercing rivet blank may be heat treated for a period of at least 6 hours, preferably at least 12 hours, preferably at least 18 hours, preferably at least 24 hours. The self-piercing rivet or self-piercing rivet blank may be heat treated for a period of at most 48 hours, preferably at most 42 hours, preferably at most 36 hours, preferably at most 30 hours, preferably at most 26 hours.

[0049] Preferably, the self-piercing rivet or self-piercing rivet blank is heat treated for a period of from 6 hours to 42 hours, more preferably from 12 hours to 36 hours, more preferably from 18 hours to 30 hours, more preferably from 22 hours to 26 hours.

[0050] The heat treatment of the self-piercing rivet or self-piercing rivet blank can be initiated or carried out within 24 hours after the coating is applied to the self-piercing rivet or self-piercing rivet blank. In particular, the heat treatment of the self-piercing rivet or self-piercing rivet blank is initiated or carried out within 18 hours, preferably within 12 hours, preferably within 6 hours after the coating is applied to the self-piercing rivet blank.

[0051] As a non-limiting example, the self-piercing rivet or self-piercing rivet blank may be heat treated at a temperature of 200° C.±5° C. for 24 hours within 6 hours of coating.

[0052] Heat treatment allows hydrogen to escape from the self-piercing rivet, reducing the risk of hydrogen embrittlement of the elements connected by the self-piercing rivet. However, the coating is sealed and hardened. By heat treating the self-piercing rivet in a timely manner after coating, the hydrogen can escape before the coating is (fully) hardened, and the sealing makes it difficult for the hydrogen to escape.

[0053] The self-piercing rivet blank can be formed from wire, for example by cold forming, in particular cold solid forming. The wire can be steel wire. This allows the self-piercing rivet blank to obtain a basic shape. This basic shape can be substantially identical to the shape of the subsequent (finished) self-piercing rivet. The formed blank can be subjected to a heat treatment. The self-piercing rivet blank is hardened by the heat treatment. The surface of the self-piercing rivet can be treated, for example by a blasting method, in particular sandblasting or granulate blasting.

[0054] A coating as described herein can then be applied to the surface of the self-piercing rivet.

[0055] After coating, a heat treatment as described herein may be carried out, which allows the production of a self-piercing rivet.

[0056] After the plurality of self-piercing rivets are manufactured, the self-piercing rivets may be inspected and sorted. For example, inspection and sorting may be performed using one or more cameras (e.g., four cameras) and / or lasers. The self-piercing rivets may then be packaged in hermetically sealed bags, e.g., with each bag containing approximately 2000 self-piercing rivets.

[0057] The melting point of at least one component of the coating may be higher than the melting point of at least one element to which it is connected, preferably at least 50°C higher, more preferably at least 100°C higher, more preferably at least 150°C higher, more preferably at least 200°C higher, more preferably at least 300°C higher, more preferably at least 400°C higher than the melting point of the element.

[0058] Similarly, the melting point of at least one component of the coating may be higher than the melting points of each of the (two) elements to be connected. Preferably, the melting point of at least one component of the coating is at least 50°C higher than the melting points of the (two) elements, more preferably at least 100°C higher, more preferably at least 150°C higher, more preferably at least 200°C higher, more preferably at least 300°C higher, more preferably at least 400°C higher.

[0059] The melting point of at least one component of the coating may be higher than the recrystallization temperature of at least one element to be connected, preferably at least 50°C higher, more preferably at least 100°C higher, more preferably at least 150°C higher, more preferably at least 200°C higher, more preferably at least 300°C higher, more preferably at least 400°C higher than the recrystallization temperature of the element.

[0060] Similarly, the melting point of at least one component of the coating may be higher than the recrystallization temperature of each of the (two) elements to be connected. Preferably, the melting point of at least one component of the coating is at least 50°C higher than the recrystallization temperature of the (two) elements, more preferably at least 100°C higher, more preferably at least 150°C higher, more preferably at least 200°C higher, more preferably at least 300°C higher, more preferably at least 400°C higher.

[0061] The recrystallization temperature refers to the temperature at which the material completely recrystallizes within the observed time. The recrystallization temperature can be 40% or 50% of the melting point of the material.

[0062] The melting point of the coating may be higher than the melting point of at least one element to be connected, preferably at least 50°C higher, more preferably at least 100°C higher, more preferably at least 150°C higher, more preferably at least 200°C higher, more preferably at least 300°C higher, more preferably at least 400°C higher than the melting point of the element.

[0063] Similarly, the melting point of the coating may be higher than the melting points of each of the (two) elements to be connected, preferably at least 50°C higher, more preferably at least 100°C higher, more preferably at least 150°C higher, more preferably at least 200°C higher, more preferably at least 300°C higher, more preferably at least 400°C higher than the melting points of the (two) elements.

[0064] The melting point of the coating may be higher than the recrystallization temperature of at least one of the elements to be connected, preferably at least 50°C higher, more preferably at least 100°C higher, more preferably at least 150°C higher, more preferably at least 200°C higher, more preferably at least 300°C higher, more preferably at least 400°C higher than the recrystallization temperature of the elements.

[0065] Similarly, the melting point of the coating may be higher than the recrystallization temperature of each of the (two) elements to be joined, preferably at least 50°C higher, more preferably at least 100°C higher, more preferably at least 150°C higher, more preferably at least 200°C higher, more preferably at least 300°C higher, more preferably at least 400°C higher than the recrystallization temperature of the (two) elements.

[0066] At least one element or both elements to be connected may have a yield strength measured in accordance with ISO 6892-1 of at least 1000 MPa, preferably at least 1300 MPa.

[0067] At least one or both elements to be connected may have a tensile strength measured in accordance with ISO 6892-1 of 1200 MPa or more, preferably 1600 MPa or more.

[0068] The coating of the self-piercing rivet allows the self-piercing rivet to be advantageously used to connect high strength and / or high hardness elements, even if one or both of the elements are heated prior to use of the self-piercing rivet, reducing the strength and / or hardness of the elements to facilitate use of the self-piercing rivet.

[0069] The present invention will now be described in detail with reference to the accompanying drawings. [Brief explanation of the drawings]

[0070] [Figure 1] 1 is a cross-sectional view of a self-piercing rivet 10. FIG. [Figure 2a] 1A-1C are diagrams showing a schematic illustration of the process of connecting two elements 30, 40 using a self-piercing rivet 10. [Figure 2b] 1A-1C are diagrams showing a schematic illustration of the process of connecting two elements 30, 40 using a self-piercing rivet 10. [Figure 3a] FIG. 1 shows a prior art self-piercing rivet 10 used to connect two elements 30, 40. [Figure 3b] FIG. 1 shows a self-piercing rivet 10 of the present disclosure used to connect two elements 30, 40. DETAILED DESCRIPTION OF THE INVENTION

[0071] Figure 1 is a cross-sectional view of a self-piercing rivet 10. The self-piercing rivet 10 shown in Figure 1 is a semi-hollow self-piercing rivet, although the present disclosure is not limited thereto. The self-piercing rivet 10 may also be a solid self-piercing rivet or a hollow self-piercing rivet.

[0072] The self-piercing rivet 10 has a self-piercing rivet head 11. A self-piercing rivet shank 12 is formed adjacent to the self-piercing rivet head 11. The self-piercing rivet shank 12 is formed in a substantially hollow cylindrical shape. A self-piercing rivet foot 15 is formed at the axial end of the self-piercing rivet opposite the self-piercing rivet head 11. The thickness (particularly the wall thickness) of the self-piercing rivet shank 12 at the self-piercing rivet foot 15 may be thinner than on the self-piercing rivet head 11 side. The thickness (particularly the wall thickness) of the self-piercing rivet shank 12 may decrease towards one end.

[0073] The self-piercing rivet 10 has a cavity 16. The cavity 16 is bounded or defined by the self-piercing rivet head 11 and the self-piercing rivet shank 12. The cavity 16 is open on one side to the surroundings. The opening of the cavity 16 may be formed in the region of the self-piercing rivet foot 12.

[0074] The self-piercing rivet 10 may be formed with rotational symmetry.

[0075] The diameter of the self-piercing rivet 10 may be 15 mm or less, preferably 12.5 mm or less, more preferably 10 mm or less, more preferably 8 mm or less, more preferably 5 mm or less.

[0076] In particular, the diameter of the self-piercing rivet head 11 may be 15 mm or less, preferably 12.5 mm or less, more preferably 10 mm or less, more preferably 8 mm or less. The diameter of the self-piercing rivet shank 12 may be 15 mm or less, preferably 12.5 mm or less, more preferably 10 mm or less, more preferably 8 mm or less, more preferably 6 mm or less.

[0077] The length (perpendicular to the diameter) of the self-piercing rivet 10 may be 30 mm or less, preferably 25 mm or less, more preferably 20 mm or less, more preferably 15 mm or less, more preferably 10 mm or less, more preferably 7.5 mm or less, more preferably 5 mm or less.

[0078] The surface of the self-piercing rivet 10 is preferably provided with a coating 20. The coating 20 may be any of the coatings disclosed herein. The coating 20 may be provided at least in the region of the self-piercing rivet shank 12 of the self-piercing rivet 10. Preferably, the coating 20 is provided on the entire surface of the self-piercing rivet 10. Similarly, the coating 20 may be provided only on the outer surface of the self-piercing rivet 10. One or more cavities of the self-piercing rivet 10 may be free of the coating 20, or the thickness of the coating 20 within the cavities may be less than the thickness of the coating 20 on the outer surface of the self-piercing rivet 10.

[0079] It is particularly preferred that the coating 20 is a nickel-phosphorus coating. The coating 20 can be applied by electroless nickel plating.

[0080] The self-piercing rivet 10 may comprise steel. Preferably, the self-piercing rivet 10, excluding the coating 20, is constructed from steel.

[0081] 2a and 2b show process steps in the connection of at least two elements 30, 40. FIG.

[0082] 2a, a first element 30 and a second element 40 are provided. The first and second elements 30, 40 are positioned relative to each other and optionally held. The first element 30 may be in at least partial contact with the second element 40.

[0083] The first element 30 may be a steel component. The second element 40 may be an aluminum component. The thickness of the first element 30 may be in the range of 1.0 mm to 2.0 mm. Preferably, the thickness of the first element 30 is about 1.5 mm. The thickness of the second element 40 may be in the range of 2.0 mm to 6.0 mm, preferably 2.0 mm to 3.0 mm. Preferably, the thickness of the second element 40 is about 2.5 mm.

[0084] At least one of the first and second elements 30, 40 may be heated by the heating device 50 before the self-piercing rivet 10 is used to connect the first and second elements 30, 40.

[0085] The heating device 50 may include a laser. The heating device 50 may be configured to generate a laser beam 51 and 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 irradiated or irradiated with the laser beam 51 is heated. Furthermore, the area near the surface of the element irradiated or irradiated with the laser beam 51 is heated. When the laser beam 51 is irradiated onto the surface of the element, the surface of the element not irradiated with the laser beam 51 is also heated, for example, by (electrically conductive) heat conduction.

[0086] The heating device 50 may include a resistive element that can be heated by an electrical current and that can contact and heat the surfaces of the first and / or second elements 30, 40.

[0087] Similarly, the heating device 50 may include an inductive element configured to generate a magnetic field, which may heat the first and / or second elements 30, 40.

[0088] The first and / or second elements 30, 40 may be heated to a temperature below the melting point of the first and / or second elements 30, 40. Preferably, the first and / or second elements 30, 40 are heated to a temperature below 80% of the melting point of the first and / or second elements 30, 40. The first and / or second elements 30, 40 may be heated to a temperature above 500°C, preferably above 600°C, preferably above 700°C, preferably above 800°C, preferably above 900°C, preferably above 1000°C, preferably above 1100°C, preferably above 1200°C.

[0089] The first and / or second elements 30, 40 may be heated to a temperature above the recrystallization temperature of the first and / or second elements 30, 40. Preferably, the first and / or second elements 30, 40 are heated to a temperature that is 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 the recrystallization temperature of the first and / or second elements 30, 40.

[0090] Heating can reduce the strength and / or hardness of the first and / or second elements 30, 40.

[0091] The self-piercing rivet 10 may be held by a holding device (not shown), and further, a die (not shown) may be located opposite the holding device.

[0092] 2b shows elements 30, 40 connected by a self-piercing rivet 10. To connect the elements 30, 40, the self-piercing rivet 10 is inserted into the surface of the first element 30. For this purpose, a punch surrounded by a holding device may apply force to the self-piercing rivet 10, in particular the self-piercing rivet head 11, to force the self-piercing rivet 10 into the first element 30. By inserting the self-piercing rivet 10 into the first element 30, 40, a part of the first element 30 is punched out. The punched part of the first element 30 is forced towards the second element 40. The self-piercing rivet 10 penetrates only partially, or at most partially, through the second element 40. A part of the second element 40 is plastically deformed. When the self-piercing rivet 10 is driven into the first and second elements 30, 40, a protrusion 41 (also called a closing head) is formed on the second element 40. The protrusion 41 protrudes from the surface of the second element 40. The shape of the protrusion 41 is substantially determined by the shape of the die. When the self-piercing rivet 10 is inserted into the first and second elements 30, 40, the die is in contact with the surface of the second element 40. The shape of the protrusion 41 may substantially match the shape of the recess in the die.

[0093] The process of inserting the self-piercing rivet 10 into the first and / or second elements 30, 40 can be performed without the need for prior drilling of a pilot hole.

[0094] Heating the first and / or second elements 30, 40 reduces the strength and / or hardness of the first and / or second elements 30, 40, thereby facilitating or enabling insertion of the self-piercing rivet 10. For this purpose, a relatively thin or relatively small self-piercing rivet 10 may be used, although the self-piercing rivet 10 will also heat up as a result.

[0095] Figures 3a and 3b show two elements 30, 40 connected using a self-piercing rivet 10. In Figure 3a, a known method or a known self-piercing rivet 10 was used, while in Figure 3b, a method or a self-piercing rivet 10 of the present invention was used.

[0096] The first element 30 of the connection shown in Figures 3a and 3b is a steel element approximately 1.5 mm thick. The second element 40 of the connection shown in Figures 3a and 3b is an aluminum element approximately 2.5 mm thick. 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.

[0097] The self-piercing rivet 10 in the connection shown in Figure 3a has a coating comprising zinc, tin, and aluminum, while the self-piercing rivet 10 in the connection shown in Figure 3b has a coating of the present invention, particularly comprising nickel and phosphorous, applied by electroless nickel plating.

[0098] As shown in Figure 3a, the self-piercing rivet 10 has a crack 17. The crack 17 in the self-piercing rivet 10 has been identified in multiple similar or identical studies. The stability of the connection between the elements 30, 40 is limited or impaired by the crack 17. The connection between the elements 30, 40 may fail, especially under load.

[0099] As shown in Figure 3b, no cracks are found in the self-piercing rivet 10 according to the invention. The connection of elements 30, 40 using the self-piercing rivet 10 according to the invention or the method of the invention appears to be error-free.

[0100] Without intending to be bound by theoretical explanation, it is believed that the cracks 17 in the known self-piercing rivet 10 are at least partially due to liquid metal embrittlement. Liquid metal embrittlement is a phenomenon in which certain ductile metals experience a sudden loss of tensile ductility and brittle fracture when exposed to certain liquid metals. This may have occurred because part of the coating on the known self-piercing rivet 10 melted, resulting in the self-piercing rivet 10 losing its mechanical properties. This effect can be avoided or mitigated by the coating 20 according to the present invention.

Claims

1. A self-piercing rivet (10) for connecting at least two elements (30, 40), comprising: The self-piercing rivet (10) is provided with a coating (15); (i) the melting point of at least one component of said coating (15) is 450°C or higher, and / or (ii) A self-piercing rivet (10) wherein said coating (15) comprises nickel.

2. 2. The self-piercing rivet of claim 1, wherein the self-piercing rivet (10) is a solid self-piercing rivet, a semi-hollow self-piercing rivet, or a hollow self-piercing rivet.

3. A self-piercing rivet according to claim 1 or 2, wherein at least one component of the coating (15) has a melting point of 500°C or higher.

4. 3. A self-piercing rivet according to claim 1 or 2, wherein the melting point of the coating (15) is 450°C or higher.

5. 3. A self-piercing rivet according to claim 1 or 2, wherein the coating (15) contains at least 50% by weight of nickel.

6. 3. A self-piercing rivet according to claim 1 or 2, wherein the coating (15) contains at least 5% by weight of phosphorus.

7. 3. A self-piercing rivet according to claim 1 or 2, wherein the coating (15) is applied by a chemical coating method.

8. A method of manufacturing a self-piercing rivet (10), comprising: providing a self-piercing rivet blank; applying a coating to the self-piercing rivet blank by a chemical coating method; and obtaining a self-piercing rivet (10).

9. The method of claim 8 , wherein the chemical coating process comprises an oxidation-reduction reaction.

10. The method of claim 8 , wherein the chemical coating method comprises electroless nickel plating.

11. A method according to any one of claims 8 to 10, wherein the self-piercing rivet blank, after applying the coating, is heat treated at a temperature of not more than 350°C and / or for a period of not more than 48 hours.

12. 12. The method of claim 11, wherein the heat treatment is initiated within 24 hours of applying the coating to the self-piercing rivet blank.

13. 10. A method for connecting at least two elements (30, 40) with a self-piercing rivet (10) provided with a coating (15) according to claim 1 or 2, comprising the steps of: providing said at least two elements (30, 40); heating the surface of at least one of said elements (30, 40); connecting said at least two elements (30, 40) with said self-piercing rivet (10); A method wherein the melting point of at least one component of said coating (15) is higher than the melting point and / or recrystallization temperature of at least one of said elements (30, 40).

14. 14. The method of claim 13, wherein the melting point of the coating (15) is higher than the melting point and / or recrystallization temperature of at least one of the elements (30, 40).

15. 14. The method of claim 13, wherein at least one of the elements has a yield strength measured in accordance with ISO 6892-1 of at least 1000 MPa and / or a tensile strength measured in accordance with ISO 6892-1 of at least 1200 MPa.

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