Self-piercing rivet

Abstract

1. A self-piercing rivet (10) having a head (12) and a shank (14) having a shank diameter (Ds), wherein at a foot end opposite the head (12), the shank (14) has an axial recess (16) having an axial depth (LB), the recess having a recess volume, the ratio of the recess volume to the volume of the shank (14) and head (12) being between 0.06 and 0.08.

Description

Technical Field

[0001] The disclosure of the present invention relates to a self-piercing rivet having a head and a shank having a shank diameter. In particular, at the foot end opposite the head, the shank has an axial recess having an axial depth, and at the foot end, the shank includes an annular through-end for the generation of a connection portion that joins between at least two workpieces. The self-piercing rivet is particularly related to thin sheet metal applications, especially in thin sheet metal applications in the automotive industry.

Background Art

[0002] A self-piercing rivet has a partially hollow structure having a head and a cylindrical shank terminating in an annular edge. When the rivet is pushed into at least two overlapping sheets of material on a properly formed die, the shank is expanded outward. The sheets of material are deformed around the shank to create a ring that encloses the shank. The shank and the edge of the rivet remain embedded in the sheet material even after the rivet is fixed. The fastening operation by the self-piercing rivet enables the joining of sheet materials without the need to pre-drill or pre-punch holes in the material.

[0003] One important parameter for the joining operation and joining quality of a self-piercing rivet joint is the shape of the self-piercing rivet. In the prior art, many different shapes of self-piercing rivets are known. For example, see EP 0 720 695, EP 1 064 466, EP 1 229 254, EP 1 387 093, DE 44 31 769, DE 203 19 610 U1, DE 200 01 103 U1, US 2004 / 0068854 A1, JP 2001159409A, JP 09317730A, W2015086203, WO2014013232, or US9316243, etc.

[0004] The use of self-piercing rivets as a joining method is widely used in this industry and is the current major joining method for aluminum and lightweight material automotive structures.

[0005] WO2014013232 discloses a method of forming a joint within a stack of at least two sheets of a light metal alloy using a self-piercing rivet that is completely hollow. The rivet is coated with a lubricant along at least a portion of its bore, penetrates its upper surface, and has a shank that deforms outwardly to engage the material without penetrating to the die side of the material. The outer diameter of the shank of the rivet is 5.4 mm or less. The die has a volume that is less than 60% or 70% of the effective solid volume of the rivet.

[0006] US9316243 describes a self-piercing rivet that includes a head and a substantially cylindrical shank, the shank being at least partially hollow so as to define a bore that extends along at least a portion of its length, the outer diameter of the shank being at least 6 mm, the effective length of the rivet being at least 1.3 times the diameter of the shank, and the bore having a volume that is at least 38% of the effective solid volume of the rivet. Such a rivet is suitable for use with high-strength light metal alloys in thick stacks such as magnesium and aluminum alloys.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Patent Document 7

Patent Document 8

Patent Document 9

Patent Document 10

Patent Document 11

Patent Document 12

Patent Document 13

Summary of the Invention

Problems to be Solved by the Invention

[0008] However, for door applications in vehicles, especially for thin aluminum panels, other processes such as resistance spot welding compete with self-piercing riveting. Therefore, there is still a need to develop self-piercing rivets that increase joint quality and are suitable for a simple manufacturing process for joining workpieces such as door panels.

Means for Solving the Problems

[0009] The object mentioned above is achieved by the self-piercing rivet defined in independent claim 1.

[0010] The self-piercing rivet includes a head and a shank having a shank diameter. At the foot end opposite the head, the shank has an axial recess having an axial depth, and the shank further includes an annular through-edge. The self-piercing rivet is characterized in that the recess has a recess volume, and the ratio of the recess volume to the volume of the shank and the head is between 0.06 and 0.08.

[0011] In other words, the recess has a volume that is between 6% and 8% of the effective solid volume of the rivet or the total volume of the rivet. Some tests have surprisingly shown that a self-piercing rivet shape having a ratio between 0.06 and 0.08 of the recess volume to the volume of the shank and head enables, among other things, good joining quality for door panels and may be easy to manufacture at low cost. In fact, the geometry and shape of such fasteners are similar to those of clinch rivets or other conventional rivets, enabling easy manufacture, but the specific ratio of the rivets according to the disclosure of the present invention enables forming an engagement by penetrating sheet metal according to known self-piercing methods. The self-piercing rivets of the disclosure of the present invention are, that is, self-piercing rivets but simultaneously have the manufacturing advantages of clinch rivets and provide the joining quality and load-bearing capacity of self-piercing rivets known from the prior art. That is, such self-piercing rivets are coming to compete with other joining methods. Such a ratio enables linear bulging and ductility through an internal shape (rivet recess) rather than over an outer edge as known for rivets from the prior art. The special shape of the rivet and its recess enables bulging and ductility of the rivet without any special heat or surface treatment. More specifically, heat treatment of the rivet is not required.

[0012] Advantageously, the rivet is a cold-formed part without any heat or surface treatment. That is, such self-piercing rivets are easy to manufacture with a limited number of processing steps. The rivet obtains its strength using cold forming. According to an embodiment, the rivet is manufactured without any heat treatment step.

[0013] Preferably, the recess is arcuate in shape. For example, the recess is at least partially arcuate in shape in a recess base area positioned especially towards the head. This shape enables better forming, especially cold forming and limitation of the cold forming steps.

[0014] According to the embodiment, the ratio of the recess volume to the volumes of the shank and the head is in the range between 0.064 and 0.077.

[0015] According to the embodiment, the axial depth is defined to receive a determined amount of material (remaining at the bottom) and to weaken the self-piercing rivet over a certain height. The ratio of the axial depth to the shank diameter can be in the range between 0.05 and 0.66.

[0016] According to the embodiment, the annular through edge has a through diameter, and the ratio of the through diameter to the shank diameter is in the range between 0.85 and 0.99, for example, between 0.87 and 0.96. That is, the position of the through edge enables the correct expansion diameter and ductility of the rivet.

[0017] According to the embodiment, the rivet is made of steel, stainless steel, or an aluminum alloy. More specifically, a rivet made of an aluminum alloy is to be used for joining aluminum alloy workpieces. For example, the self-piercing rivet is made of precision steel 37MnB4.

[0018] According to the embodiment, the self-piercing rivet is made from a wire having a strength of 750 MPa. Such strength is different from the standard strength used for self-piercing rivets. It makes it possible, among other things, to avoid post-treatment of the rivet, but it increases the difficulty of generating sharp edges during cold forming.

[0019] According to the embodiment, the self-piercing rivet includes a first section near the head and a second section near the annular through edge, and the material strength of the second section is lower than the material strength of the first section. Due to cold forming and the recess shape, the second section is weakened relative to the first section.

[0020] According to an embodiment, the annular through-edge includes an outer edge, and the outer edge has a radius of less than 0.2 mm, particularly less than 0.1 mm, by which the edge is sharpened. This sharpened outer edge enables improved cutting through an aluminum alloy panel or workpiece and can be easily manufactured.

[0021] According to an embodiment, the recess is at least partially conical or frustoconical such that the recess includes a conical taper surface, and the conical taper surface has an included angle within a cross-section between 75 and 105 degrees, particularly 90 degrees. Such a recess shape enables a determined ductility within the workpiece.

[0022] The present invention also relates to a self-piercing rivet joint having an upper workpiece and a lower workpiece, at least one of which is realized from metal, and having a self-piercing rivet as described above, the head of which abuts against the upper workpiece.

[0023] According to an embodiment, the upper workpiece and / or the lower workpiece is made of an aluminum alloy. The lower side of the rivet shank is expanded in diameter, and an extension of the recess shape of the rivet occurs within the workpiece.

[0024] Hereinafter, specific embodiments of the present invention will be merely exemplarily described with reference to the accompanying drawings.

Brief Description of the Drawings

[0025]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0026] For different figures, the same reference numerals designate the same or similar elements.

[0027] Figure 1 shows a self-piercing rivet 10 including a rivet head 12 and a rivet shank 14 extending along a longitudinal axis X. The self-piercing rivet 10 is suitable for creating a joining connection between at least two components or workpieces C1, C2, as depicted in Figure 2. For example, one or both of the workpieces may be aluminum workpieces, such as vehicle door panels.

[0028] The rivet shank includes an axially recessed portion (or central bore) 16 having a base 18. The recess 16 is positioned at the foot end opposite the head 12. The rivet shank 14 further includes an annular through edge 20 facing outward from the rivet head 12. The recess 16 includes an axial depth LB between the base 18 of the recess 16 and the annular through edge 20. More specifically, the axial depth LB is the maximum distance along the longitudinal axis X between the base 18 and the annular through edge 20. For example, the axial depth LB is the distance between the uppermost point of the surface of the base (in other words, the point of the base closest to the upper surface of the head) and the lowermost point of the annular through edge. The axial depth is, for example, 1 mm.

[0029] The recess 16 has a volume, and the shape of the self-piercing rivet is such that the ratio of the recess volume to the volume of the shank and the head (in other words, the total volume of the solid rivet) is between 0.06 and 0.08 or between 0.064 and 0.077. More specifically, the ratio can be about 0.07. In another embodiment, the ratio can be about 0.065. The recess volume in this case is calculated starting from the foot end of the self-piercing rivet. The volume of the solid rivet is the volume of the rivet shank 14 and that of the rivet head 12, including the possible transition section to the head of the self-piercing rivet and excluding the recess volume that is not finally contained in the volume of the shank.

[0030] The rivet shank 14 includes a cylindrical shank outer surface 22. The shank outer surface has a shank diameter Ds. The shank has a uniform shank diameter. For example, the shank diameter can be between 3 and 5 mm, for example, it can be 3.3 mm or 3.5 mm. The ratio of the axial depth LB to the shank diameter Ds can range between 0.05 and 0.66.

[0031] The rivet head 12 extends radially outward from the rivet shank 14. The rivet head 12 has an upper portion 26 and a transition region defined between the upper portion 26 and the rivet shank 14. The transition region has a radius of curvature R1 in the range from 0.5 to 2 mm, for example, a radius of curvature of 1 mm or between 0.9 and 1.1 mm. The upper portion 26 has an upper surface opposite to the base 18. The thickness of the upper portion 26 is included between 0.1 and 0.3 mm, in particular 0.25 mm.

[0032] The rivet has a length along the longitudinal axis X. The length of the rivet from the annular through edge 20 to the head (more specifically, the upper surface of the upper portion of the head 12) is between 3 and 6 mm or between 3.5 and 5 mm, for example, it is 5 or 5.5 mm.

[0033] As shown in the drawings, the base 18 can be arc-shaped. For example, the base can have a radius between 0.05 and 4 mm of the shank diameter. The radius of the base is, for example, 1.3 mm. The base 18 can also be conical in the middle. More specifically, the base can be arc-shaped and the recess can be partially frustoconical. The recess can include a conical tapered surface having an included angle within the cross-section between 75 and 105 degrees, more specifically 90 degrees.

[0034] The annular through-edge 20 can be a flat shank end face as depicted in FIG. 1. As shown in FIG. 1, the annular through-edge includes an outer edge. The outer edge has an edge sharpened by a radius of less than 0.1 mm. The inner edge forms a cutting line including a cutting or through diameter. The cutting line is as sharp as possible so that the penetration through the workpiece can be performed without excessive fitting force. The ratio of the through diameter Dp to the shank diameter Ds ranges between 0.85 and 0.99, more specifically between 0.87 and 0.95.

[0035] The annular through-edge 20 can also be an arcuate shank end face. For example, the annular through-edge may include a circular cutter having a cutting diameter, and the circular cutter is formed by a cutting line between a radius or chamfered surface in the region of the inner surface of the axial recess and a radius facing the radially outer surface of the shank.

[0036] The self-piercing rivet is formed by cold forming. Heat or surface treatment is not applied to the self-piercing rivet 10 after cold forming. More specifically, quenching of the self-piercing rivet is not performed after cold forming. That is, cold forming gives the rivet its strength. The self-piercing rivet can be made, for example, from a wire having a strength of 750 MPa. The manufacturing process through cold forming of the self-piercing rivet is known to those skilled in the art and will not be described in detail accordingly.

[0037] More specifically, the self-piercing rivet 10 includes a first section near the head and a second section near the annular through-edge 20. The strength of the second section is lower than the strength of the first section.

[0038] The recess 16 forms a protruding surface S1 within the longitudinal cross-sectional illustration (as shown in FIG. 1). The solid rivet includes the protruding surface S1 within the same illustration. The protruding surface S2 is a surface formed by the shank 14 and the head 12 including a transition region.

[0039] The self-piercing rivet 10 is used for a self-piercing riveting joint as shown in Fig. 2. The self-piercing riveting joint includes an upper workpiece C1 and a lower workpiece C2, at least one of which is made of metal, especially an aluminum alloy. The head 12 abuts against the upper workpiece C1. The lower side of the rivet shank is expanded in diameter, and the extension of the concave shape of the rivet occurs within the workpiece. A clean cutting process is performed within the first workpiece through the cutting line.

[0040] The self-piercing rivet 10 of the present invention, as depicted in Fig. 2, does not include a determined ductility due to a thinly defined cutting edge (as known for prior art self-piercing rivets). Rather, the connection or joining of the two workpieces is effected through the expansion of the rivet by the die in its lower region and the ductility of the rivet through a concave shape having a determined tapered surface. The self-piercing rivet having the shape shown in Fig. 1 enables a clean cut during the joining operation. Its internal shape "slides" the workpiece material, i.e., forms an internal pressure. This ductility is assisted through a linear expansion in diameter.

Explanation of Reference Numerals

[0041] 10 Self-piercing rivet 12 Rivet head 14 Rivet shank 16 Concave portion S1, S2 Protruding surface

Claims

1. A self-piercing rivet (10) having a shank with an axial recess having an axial depth (LB) at a foot end opposite the head, the shank (14) further including an annular through-edge (20), and having a shank with a head and a shank diameter (Ds), wherein the recess has a recess volume, and the ratio of the recess volume to the volume of the shank and the head is between 0.06 and 0.08, and the self-piercing rivet (10) is a cold-formed part without any heat treatment, and the recess is in an arc shape, characterized by a self-piercing rivet (10).

2. The annular through-edge includes an outer edge, the outer edge has an edge sharpened by a radius of less than 0.2 mm, characterized by the self-piercing rivet according to claim 1.

3. characterized by the self-piercing rivet according to any one of claims 1 or 2, wherein the ratio of the axial depth (LB) to the shank diameter (Ds) is in the range between 0.05 and 0.

66.

4. The annular through-edge has a through diameter (Dp), and the ratio of the through diameter (Dp) to the shank diameter (Ds) is in the range between 0.85 and 0.99, characterized by the self-piercing rivet according to any one of claims 1 to 3.

5. characterized by the self-piercing rivet according to any one of claims 1 to 4, made of steel, stainless steel, or an aluminum alloy.

6. characterized by the self-piercing rivet according to any one of claims 1 to 5, made of 37MnB4.

7. characterized by the self-piercing rivet according to any one of claims 1 to 6, made of a wire having a strength of 750 MPa.

8. including a first section near the head and a second section near the annular through-edge, wherein the material strength of the second section is lower than the material strength of the first section, characterized by the self-piercing rivet according to any one of claims 1 to 7.

9. The recess is at least partially conical or frustoconical such that the recess includes a conical tapered surface, the conical tapered surface having an included angle in a cross-section between 75 and 105 degrees, characterized by the self-piercing rivet according to any one of claims 1 to 8.

10. having an upper workpiece and a lower workpiece, at least one of which is realized from metal, Having the self-piercing rivet according to any one of claims 1 to 9, and the head thereof abuts against the upper work piece, A self-piercing riveting joint characterized by this.

11. The self-piercing riveting joint according to claim 10, characterized in that the upper work piece and / or the lower work piece is made of an aluminum alloy.

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