Self-piercing rivet and self-piercing riveting method and self-piercing riveted joint

Abstract

A self-piercing rivet for connecting high-strength steels. The rivet having a head which has a head diameter (DH); a shank which has a shank diameter (DS); and, located at the foot end of the shank opposite the head, the shank has radially outward a flat surface section and radially inward an axial recess defining an axial depth (LB). The ratio of axial depth (LB) of the recess to the shank diameter (DS) is smaller than 0.3.

Claims

1. Self-piercing rivet (10) for connecting high-strength steels, with a head (12) which has a head diameter (DH), and with a shank (14) which has a shank diameter (DS), wherein, at the foot end (18) opposite the head (12), the shank (14) has an axial recess (22) which has an axial depth (LB), and wherein, at the foot end (18), the shank (14) has a flat surface section (20), characterized in that the ratio of axial depth (LB) of the recess (22) to shank diameter (DS) is smaller than 0.3.

2. Self-piercing rivet according to claim 1, characterized in that the recess (22) is frustoconical in longitudinal section.

3. Self-piercing rivet according to claim 1, characterized in that the recess (22) is arch-shaped in longitudinal section.

4. Self-piercing rivet according to claim 3, characterized in that the recess (22) is in the shape of a pointed arch in longitudinal section.

5. Self-piercing rivet according to claim 1, characterized in that the recess (22) does not have a cylindrical section.

6. Self-piercing rivet according to claim 1, characterized in that the recess (22) has a recess volume, wherein a ratio of recess volume to volume of the shank (14) is smaller than 0.25, in particular smaller than 0.18 and/or is greater than 0.05, in particular greater than 0.1.

7. Self-piercing rivet according to claim 1, characterized in that the flat surface section (20) is designed as an annular surface section (20) and has a radial width (BF) in cross section, wherein the ratio of radial width (BF) of the annular surface section (20) to shank diameter (DS) is greater than 0.05 and/or is smaller than 0.25.

8. Self-piercing rivet according to Claim l, characterized in that the self-piercing rivet (10) is produced from a steel with a hardness of at least 500 HV10.

9. A self-piercing rivet for connecting high-strength steels, the self piercing rivet comprising: a head defining a head diameter (DH); a shank defining a shank diameter (DS) and including a foot end opposite the head, and radially outward at the foot end the shank further includes a flat surface section facing axially away from the head; an axial recess located radially inward of the flat surface section, partly defined in the foot end of the shank, open axially away from the head, and frustoconical in longitudinal cross section; the axial recess defining an axial depth (LB); and the ratio of axial depth (LB) of the recess to shank diameter (DS) is less than 0.3.

10. A self-piercing rivet according to claim 9, wherein the axial recess defines a recess volume (VB), and a ratio of recess volume to a volume of the shank (VS) is between 0.25 and 0.05.

11. A self-piercing rivet according to claim 9, wherein the flat surface section is an annular surface section and defines a radial width (BF) in cross section, and a ratio of radial width (BF) of the annular surface section to the shank diameter (DS) is between 0.25 and 0.05.

12. A self-piercing rivet according claim 9, wherein the self-piercing rivet is produced from a steel with a hardness of at least 500 HV10.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Exemplary embodiments of the invention are illustrated in the drawing and are explained in more detail in the description below. In the drawing:

(2) FIG. 1 shows a longitudinal sectional view through an embodiment of a self-piercing rivet according to the invention;

(3) FIG. 2 shows a longitudinal sectional view through a further embodiment of a self-piercing rivet according to the invention; and

(4) FIG. 3 shows a longitudinal sectional view through a self-piercing riveted joint produced by means of the self-piercing rivet of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(5) A rotationally symmetrical semi-tubular self-piercing rivet is illustrated schematically in longitudinal section and denoted in general by 10 in FIG. 1.

(6) The self-piercing rivet 10 is produced from a strong steel and preferably has a hardness of greater than 500 HV. The self-piercing rivet is in particular produced by pressure deformation.

(7) The self-piercing rivet 10 has a head 12 and a shank 14 adjoining the latter in the axial direction. The shank 14 merges into the head 12 via a transition section 16. An end of the shank 14 that is opposite the head 12 is designed as a foot end 18 in FIG. 1.

(8) A flat surface section 20 is formed at the foot end 18, said surface section being designed as an annular surface section, the outside diameter of which is limited by an outside diameter of the shank 14 and the inside diameter of which is limited by an edge of a recess 22 which extends from the foot end 18 in the direction of the head 12.

(9) In FIG. 1, the recess 22 is of frustoconical design and, starting from the foot end 18, has a conically extending recess transition section 24 and a recess base 26. The recess base 26 can be of flat design, as illustrated, but may also be of concave or convex design.

(10) Furthermore, the following dimensions are shown in FIG. 1, wherein the preferred values for said dimension are in each case also plotted in the table below:

(11) TABLE-US-00001 Designation Abbreviation Preferred value Note Axial length, self-piercing LR .sup. 5 mm rivet Length, shank LS 3.6 mm Axial height, head LH 0.5 mm Axial depth, recess LB .sup. 1 mm Diameter, head DH 7.75 mm  Outside diameter, shank DS 5.5 mm Recess diameter at the foot DB 4.5 mm end Recess diameter at the base DB′ ~2.5 mm  Radial width, annular BF 0.5 mm surface Section Cone angle, recess αB ~40° i.e. 25°-50° Cone angle, transition αH ~27° i.e. 20°-50° section
In the case of the self-piercing rivet of FIG. 1, the ratio of axial depth LB of the recess 22 to the shank diameter DS is approximately 0.18.

(12) The ratio of radial width BF to the shank diameter DS is approximately 0.09.

(13) Furthermore, the ratio of the recess volume to the volume of the shank is approximately 0.135, wherein the volume of the recess is approximately calculated at
VB=(LB.Math.π)/3.Math.[(DB/2).sup.2+DB.Math.DB′+(DB′/2).sup.2],
and wherein the volume of the shank is calculated at
VS=π.Math.(DS/2).sup.2.Math.LS.

(14) The volume VS of the shank consequently includes the recess volume VB.

(15) The values, which are indicated in the table above, for the respective dimensions and angles can preferably each deviate within the scope of the invention upwards and downwards by at least 20%, preferably upwards and downwards by 10% in each case.

(16) A radius RB which is formed at the transition between the recess transition section 24 and the recess base 26 is furthermore shown in FIG. 1. The value of RB can be, for example, 0.35 mm. The value of DB′ is an approximate value which lies approximately in the center of the recess RB, as seen in the radial direction.

(17) Furthermore, a radius RH which forms the transition between the conical transition section 16 and the shank 14 is shown in FIG. 1. The value of RH can be, for example, 0.5 mm or less.

(18) An alternative embodiment of a self-piercing rivet according to the invention is illustrated in FIG. 2 and is likewise generally denoted by 10. The self-piercing rivet 10 of FIG. 2 corresponds generally in respect of construction and function to the self-piercing rivet 10 of FIG. 1. Identical elements are therefore indicated by the same reference numbers. Essentially the differences are explained below.

(19) The recess 22 of the self-piercing rivet 10 of FIG. 2 is not frustoconical, as in the case of the self-piercing rivet 10 of FIG. 1, but rather is of arch-shaped design. In more precise terms, the recess 22 in FIG. 2 is in the shape of a pointed arch in longitudinal section, the pointed arch being assembled from two arcs of a circle which form a point on the longitudinal axis. The origins of the arcs of the circle lie in each case on that side of the longitudinal axis which is opposite the arc of the circle thereof. In the region of the point which is formed by the two arcs of the circle, the recess is rounded with a radius which can be, for example, 0.5 mm. This radius is indicated schematically in FIG. 2 by R1.

(20) The radius of the two arcs of the circle is indicated schematically in FIG. 2 by R2 and can be, for example, approximately 4 mm.

(21) In the case of the self-piercing rivet 10 of FIG. 2, the maximum axial depth LB of the recess 22 is preferably approximately 1.5 mm, and therefore a ratio LB/DS of approximately 0.273 is produced.

(22) The shank diameter DS and the shank axial length LS and also other dimensions can be identical to those of the self-piercing rivet 10 of FIG. 1.

(23) A self-piercing riveted joint 30 produced by means of the self-piercing rivet 10 of FIG. 1 is illustrated schematically in longitudinal section and is denoted in general by 30 in FIG. 3.

(24) The self-piercing rivet joint 30 connects a workpiece arrangement 32 which contains at least one upper workpiece 34 and one lower workpiece 36, of which at least the upper workpiece can be produced in the form of steel sheet from high-strength or super-high-strength steels.

(25) It is illustrated in FIG. 3 that the self-piercing rivet 10* has cut a punched-out piece 38 out of the upper workpiece 34 and has pressed said punched-out piece in front of itself during the self-piercing riveting operation. The remaining base thickness between the lower side of the punched-out piece and the lower side of the lower workpiece 36 is denoted by 40. This may be, for example, greater than 0.5 mm.

(26) Furthermore, a radial undercut of the deformed shank 14* is shown in FIG. 3. The self-piercing rivet 10* has been upset, in particular in the region of the foot end, because of the relatively hard material of the upper workpiece 34, and therefore the material of said self-piercing rivet has flowed somewhat outwards radially in the region of the foot end. Owing to the great hardness of the self-piercing rivet 10* too, the undercut 42 is nevertheless very small and may be, for example, smaller than 0.5 mm, but is, as a rule, greater than 0.05 mm. Correspondingly, the ratio of undercut 42 to shank diameter DS is preferably within a range of 0.1 to 0.01.

(27) Finally, FIG. 3 shows a projecting length 44 by which the head 12* protrudes in relation to the upper side of the upper workpiece 34. The projecting length 44 is preferably smaller than the axial height LH of the self-piercing rivet 10 in the undeformed state.

(28) Furthermore, FIG. 3 shows the axial length LR* of the deformed self-piercing rivet 10*. In the example illustrated, said length can be, for example, approximately 4.4 mm. The ratio of axial length LR* of the self-piercing rivet 10* after deformation and axial length LR of the self-piercing rivet 10 before deformation is preferably greater than 0.8 and/or smaller than 0.95.

(29) As stated, the self-piercing rivet 10* has been upset in the region of the foot end, and therefore the remaining volume of the remaining recess 22* is relatively small. Accordingly, in the embodiment illustrated, at most a portion of 50%, in particular at most a portion of 25%, of the volume of the punched-out piece 38 is accommodated within the deformed recess 22*.

(30) The axial thickness of the upper workpiece 34 is denoted by L34. Said thickness can be greater than or equal to the axial depth LB of the self-piercing rivet 10 in the undeformed state. The axial thickness of the lower workpiece 36 is denoted by L36. Said thickness is preferably greater than L34. The lower workpiece 36 is preferably softer than the upper workpiece 34.

(31) FIG. 3 furthermore schematically illustrates a die 50 of a self-piercing riveting tool, by means of which an axial force (punching force) 52 is exerted on the upper side of the head 12 of the self-piercing rivet 10 during the self-piercing riveting operation. The recess of the die 50 is of approximately frustoconical design. The somewhat softer material of the second workpiece 34 is pressed away radially by the punched-out piece 38 and the die 50 and in this case flows behind the undercut 42 such that the self-piercing riveted joint 30 provides an interlocking connection between the workpieces 34, 36.

(32) The volume of the die recess is preferably greater than or equal to the volume of the self-piercing rivet 10 in the undeformed state. In particular, the ratio of the die volume to the volume of the self-piercing rivet 10 is preferably greater than or equal to 1.0 and/or smaller than or equal to 1.5.

(33) The minimum punching force 52 is preferably 8 kN.

(34) The minimum length of the self-piercing rivet 10 in the undeformed state is produced form the thickness L34 plus a value which can be, for example, 3 or 3.5 mm. The maximum length of the self-piercing rivet 10 in the undeformed state can be equal to the overall thickness L34+L36, or a value which is formed to be equal to the overall sheet thickness+a value of, for example, 1 mm.

(35) The upper workpiece 34 preferably has a tensile strength in the region of greater than 800 N/mm.sup.2, in particular greater than 1000 N/mm.sup.2. The lower workpiece 36 preferably has a tensile strength of smaller than 600 N/mm.sup.2. The self-piercing rivet 10 preferably has a (Vickers) hardness of more than 650 HV.

(36) Although exemplary embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes may be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.