PUNCH RIVET JOINT

Description

[0001] The invention relates to a punch rivet connection according to the preamble of claim 1. The invention is limited to the joining of components made of formable, metallic materials with a low strength of up to 300 MPa, in particular to the joining of aluminum materials.

[0002] The self-piercing rivet joint according to the invention is preferably used in automotive construction. In this case, the self-piercing rivet joint is specifically designed with regard to the dynamic loads and / or crash loads encountered in vehicles. In automotive construction, the production of a vehicle body takes place in a fully automated process chain in which, for example, aluminum semi-finished products (sheet metal and cast materials as well as profiles) are provided, joined using a self-piercing rivet joint, and then painted using, for example, a cathodic dip coating process.

[0003] In a punch rivet joint of this type, at least two components made of formable metallic materials with a strength of 300 MPa are joined together in a single riveting process. During the riveting process, a self-piercing rivet pierces the first, punch-side component with a setting force and is driven into the second, die-side component. This occurs while maintaining a residual base thickness in the second, die-side component and expanding the self-piercing rivet to an expansion diameter in the second component to create an undercut. The self-piercing rivet can be made of a wire material, such as cold-heading steel, and can be surface-coated with a corrosion-resistant layer.

[0004] Such a conventional self-piercing rivet has an inner bore with a comparatively deep bore. The self-piercing rivet can, for example, be manufactured in a total of five stages, two of which are required to create the inner bore. Furthermore, with the conventional self-piercing rivet (due to its scooping geometry caused by the deep inner bore) in the dip-spin process or other coating processes, there is the problem that the coating material flows into the inner bore of the self-piercing rivet and closes the inner bore. DE 10 2013 020 504 A1 discloses a self-piercing rivet for joining high-strength steels, which has an arc-shaped inner curvature at one end of the shank of the self-piercing rivet. EP 0 833 063 A discloses a self-piercing rivet for joining two aluminum sheets. DE 20 2016 102 528 U1 discloses a punch rivet for joining two workpieces, particularly those made of high-strength steel. BUDDE L ET AL: "FURTHER DEVELOPMENT OF PUNCH RIVETING TECHNOLOGY", SHEET METAL TUBES

[0005] PROFILE, MEISENBACH, BAMBERG, DE, Vol. 39, No. 4, 1 January 1992 (1992-01-01), pages 310-314, ISSN: 0006-4688 shows results of individual investigations on punch riveting of aluminum materials.

[0006] The object of the invention is to provide a punch rivet connection which is easy to produce compared to the prior art and which can be used for a larger number of material thickness combinations of the components to be joined.

[0007] The object is solved by the features of claim 1. Preferred developments of the invention are disclosed in the subclaims.

[0008] According to the characterising part of claim 1, the self-piercing rivet is designed such that an inner curvature in the undeformed state, starting from the shaft tip, projects into the rivet shaft with a curvature depth in the axial direction, and that the curvature depth is between 10% and 25% of the total length of the self-piercing rivet.

[0009] In a technical implementation, the still undeformed self-piercing rivet can have a cylindrical rivet shank with a flat inner curvature open towards the shank tip, as well as a rivet head with a larger diameter than the shank diameter. Compared to a conventional self-piercing rivet, the inner curvature is incorporated into the shank tip with only a shallow curvature depth, making it simple to manufacture. Due to the shallow curvature depth, unlike the state of the art, there is no scooping self-piercing rivet geometry. Therefore, no problems arise in the dip-spin coating process or other coating processes. The inner curvature can be dome-shaped, conical, or truncated cone-shaped.

[0010] Preferably, the base material of the self-piercing rivet can have a significantly lower hardness (or strength) compared to conventional self-piercing rivets, but a considerably higher ductility. The hardness of the self-piercing rivet in its initial state without work hardening can preferably be between 200 HV1 and 320 HV1, in particular between 250 HV1 and 300 HV1. This corresponds approximately to a strength between 600 MPa and 1000 MPa, in particular between 750 MPa and 900 MPa.

[0011] The core of the invention relates to the fact that the comparatively low strength of the self-piercing rivet, in combination with the self-piercing rivet geometry described later, results in a special self-piercing rivet compression behavior during the setting process. With a rivet and a die geometry, very different material thicknesses can be joined, especially on the die side. Regarding the material thickness of the punch-side component, we are rather limited compared to known self-piercing rivet elements due to the low hardness and the shallow internal bore depth. Preferably, the material thickness ratio between the punch-side component and the die-side component can be any ratio between 1:1 and 1:3.

[0012] The starting point of the invention is therefore a self-piercing rivet that is considerably easier to manufacture than a conventional semi-tubular self-piercing rivet and that, instead of a deep internal bore, merely has a flat internal curvature at the shank tip. The self-piercing rivet with the flat internal curvature at its shank tip has been further developed with regard to the pronounced compressibility described above. The self-piercing rivet material, the shape of the self-piercing rivet head (for the introduction of setting force), and the geometry of the self-piercing rivet foot (for the dissipation of setting force) are particularly relevant for this compressibility: The head shape can be a countersunk head with a flat rivet head upper surface. The rivet head upper surface can merge radially on the outside at a head upper edge into a circumferential head rim, which extends axially over a head side height down to a head lower edge.The rivet head's underside adjoins the lower edge, which merges into the reduced-diameter rivet shank toward the shank tip. The shank tip has a ring-shaped, circumferential contact edge that defines the inner curvature, where the wall of the inner curvature converges with the outer circumference of the rivet shank. The inventive compressibility can preferably be enhanced by a self-piercing rivet material that is softer than the prior art. Particularly preferred dimensions, which are also important for the compressibility, are set forth in the inventive aspects listed in detail below.

[0013] Thus, the inner curvature, starting from the shaft tip in the undeformed rivet state, protrudes into the rivet shaft with a curvature depth in the axial direction .The crown depth is between 10% and 25%, particularly 15%, of the total length of the self-piercing rivet. This results in a rivet head material thickness (meaning the material thickness of the self-piercing rivet along the longitudinal axis of the rivet) of between 75% and 90%, particularly 85%, of the total length of the self-piercing rivet. The rivet head material thickness is measured along the longitudinal axis of the rivet between the top surface of the rivet head and the dome-shaped inner crown. The rivet head can thus provide a sufficiently large amount of material for the material flow during the riveting process.

[0014] To ensure sufficient strength of the self-piercing rivet joint, it is advantageous if, after the setting process (i.e., the riveting process), the inner concavity of the self-piercing rivet is essentially completely filled with the self-piercing rivet material due to material flow. Therefore, the shank tip preferably has a substantially flat end face after the riveting process.

[0015] During the setting process, the material stress is greatest at the transition between the rivet shank and the rivet head. To avoid material cracks at the rivet head-rivet shank transition, this can preferably be implemented as follows: The transition can have a rounded rivet head underside with a consistent head radius. The rounded rivet head underside can transition tangentially radially outwards into a flat, conical rivet head underside that extends to a rivet head edge. The flat, conical rivet head underside can be angled upwards towards the rivet head top at a conical angle with respect to a transverse plane. It is preferred if the above head radius is between 0.8 mm and 2.0 mm. The conical angle can be on the order of 20°.Between the rivet head underside and the rivet head top side, a radially outer rivet head edge can extend over a head side height, which can in particular be approximately 0.3 mm.

[0016] To further support flawless upsetting behavior, it is preferable for the self-piercing rivet to be designed not as a round-head rivet with a mushroom-shaped rivet head, but as a countersunk head rivet (or flat head rivet) with a flat rivet head surface. In the self-piercing rivet connection, the top surface of the flat head rivet can be flush with the surface of the first, punch-side component, i.e., without any protrusion, and not raised above the overall component surface.

[0017] The cutting edge geometry formed at the rivet base, i.e., at the shank tip, can have a ring-shaped, circumferential contact edge that limits the inner curvature. During the setting process, the contact edge acts as a cutting edge, which, on the one hand, prevents premature compression of the self-piercing rivet and, on the other hand, controls the radial outward expansion of the self-piercing rivet by a predefined amount. Preferably, an inner wall of the self-piercing rivet's inner curvature and the outer circumference of the rivet shank can converge at an acute angle at the contact edge, with a cutting angle of, for example, 45°. The contact edge can be rounded with a radius of curvature in the range of 0.15 mm.

[0018] In the undeformed rivet state, the total length of the self-piercing rivet can range from 4 mm to 8 mm, in particular between 4.5 mm and 6.0 mm. The rivet head diameter can range from 4.5 to 8.5 mm, in particular 5.5 mm or 7.75 mm, while the rivet shank diameter can range from 2.8 mm to 6.6 mm. Such a rivet shank diameter can be processed with known riveting machines.

[0019] With the self-piercing rivet, the material thickness ratio between the first, punch-side component and the second, die-side component can be between 1:1 and 1:3. The material thickness of the first, punch-side component can preferably be less than or equal to 1.3 mm.

[0020] An embodiment of the invention is described below with reference to the attached figures.

[0021] They show: Figure 1 shows a micrograph of a self-piercing rivet in the undeformed state; Figure 2 shows a roughly schematic representation of a self-piercing rivet in a setting tool before the setting process; and Figure 3 shows a self-piercing rivet connection.

[0022] In the Figure 3 A finished punch rivet joint is shown, in which a punch-side aluminum sheet part 1 and a die-side aluminum sheet part 3 are connected to each other by means of a punch rivet 5. The two aluminum sheet parts 1 have in the Figure 2 or 3 approximately equal material thicknesses s 1 , s 2 . The punch rivet 5 has a rivet head 7 and a rivet shank 9. In the figures, the punch rivet 5 is realized as a flat head rivet with a flat, plane-parallel rivet head upper side 17. The rivet head upper side 17 is in the Figure 3 aligned flush with the surface of component 1.

[0023] To prepare for the setting process, the two components 1, 3 are placed one on top of the other on a die 11 of the setting tool and pressed together with a hold-down force by means of a hold-down system (not shown). Subsequently, the self-piercing rivet 5 is driven into the two components 1, 3 by means of a punch 13 with a setting force F. During the setting process, the self-piercing rivet 5 pierces the material of the punch-side component 1 and is driven into the second component 3, while maintaining a residual base thickness r ( Figure 3 ) of the punch-side component 3 and by spreading the punch rivet 5 to a spreading diameter d A in the second component 3 in order to create an undercut.

[0024] The following is based on the Figure 1The self-piercing rivet 5 is described in isolation: Accordingly, the rotationally symmetrical self-piercing rivet 5 has a dome-shaped inner curvature 15 open towards the shaft tip, which projects into the rivet shaft 9 with a curvature depth t in the axial direction. The curvature depth t is in the Figure 1 15% of the total length of the punch rivet I. Conversely, the rivet head material thickness m K , which extends along the rivet longitudinal axis L between a rivet head top 17 and the inner curvature 15, is 85% of the total length of the punch rivet I. The transition between the rivet shank 9 and the rivet head 7 is in the Figure 1by a rounded rivet head underside 16 with a constant head radius d K , which is, for example, 1 mm. The rounded rivet head underside 16 merges tangentially radially outwards into a flat, conical rivet head underside, which extends to a rivet head edge 19. In Figure 1, the flat, conical rivet head underside is angled by a cone angle α ( Figure 1 ) of approximately 20° upwards towards the rivet head top side 17. The radially outer circumferential rivet head edge 19 extends with a head side height IK of approximately 0.3 mm between the rivet head bottom side 16 and the rivet head top side 17.

[0025] At the shaft tip facing away from the rivet head 7, a ring-shaped contact edge 21 is formed which borders the inner curvature 15. At the contact edge 21, an inner wall 23 of the punch rivet inner curvature 15 and a rivet shaft outer circumference converge at an acute angle, with an edge angle β of approximately 45°. The contact edge 21 is in the Figure 1 rounded with a rounding radius ra of 0.15 mm.

[0026] In the Figure 1 The total length l of the self-piercing rivet 5 in the undeformed state is 5 mm, the rivet head diameter d K is 5.5 mm, and the rivet shank diameter d s is 2.9 mm. The base material of the self-piercing rivet 5 is cold heading steel. Its strength in the initial state without work hardening is between 750 and 900 MPa.

[0027] The comparatively low strength of the punch rivet 5 in combination with the punch rivet geometry described above results in a special punch rivet compression behavior, in which the punch rivet 5 shrinks to 60% of its initial length I ( Figure 2 ) is compressed and the expansion diameter d A is increased to 135% to 150% of the rivet shank diameter ds, without causing material cracks in the punch rivet 5. As can be seen from the Figure 3 As can be seen further, after the setting process, the inner bulge 15 of the punch rivet is essentially completely filled with the punch rivet material due to material flow. The shaft tip of the punch rivet 15 is therefore in the Figure 3 a substantially flat frontal surface. LIST OF REFERENCE SYMBOLS:

[0028] 1Punch-side component 3Die-side component 5Self-piercing rivet 7Rivet head 9Rivet shank 11Die 13Punch 15Inner curvature 16Rivet head underside 17Rivet head top side 19Rivet head edge 21Set edge 23Inner wall dsRivet shank diameter d K Rivet head diameter d A Spreading diameter r K Head radius αCone angle βSet edge angle r A Rounding angle of the seat edge lSelf-piercing rivet total length l K Head side height m K Rivet head material thickness tCurvature depth of the inner curvature rRemaining base thickness LSelf-piercing rivet longitudinal axis s 1 , s 2 Material thicknesses FSetting force

Claims

1. Self-piercing rivet joint, with at least two components (1, 3) made of formable metallic materials with a strength up to 300 MPa, which are connected to one another by a riveting procedure, in which a self-piercing rivet (5) pierces the first, stamp-side component (1) with a setting force (F) and is driven into the second, die-side component (3), specifically while maintaining a residual base thickness (r) in the second component (3) and while spreading out the self-piercing rivet (5) to a spreading diameter (dA) in the second component (3), wherein the self-piercing rivet (5) is compressed after the riveting procedure down to 60% of its starting length (l) and the spreading diameter (dA) is enlarged up to 140% to 150% of the rivet shaft diameter (ds), specifically without damaging the self-piercing rivet (5) by self-piercing rivet material cracks, characterized in that an inner curvature (15) in the undeformed state projects starting from the shaft tip with a curvature depth (t) in the axial direction into the rivet shaft (9), and in that the curvature depth (t) is between 10% and 25% of the self-piercing rivet total length (l).

2. Self-piercing rivet joint according to claim 1, characterized in that the still undeformed self-piercing rivet (5) has a cylindrical rivet shaft (9) with an inner curvature (15), which is open toward the shaft tip and is spherical-cap-shaped and a rivet head (7) larger in diameter in relation to the rivet shaft diameter (dS), and in that after the riveting procedure the self-piercing rivet inner curvature (15) is completely filled up by self-piercing rivet material due to material flow during the riveting procedure, and in that the shaft tip has an planar end face after the riveting procedure, or a rounded end face with a large radius in relation to the rivet dimensions.

3. Self-piercing rivet joint according to claim 1 or according to claim 2, characterized in that the rivet head material thickness (mK), which extends along the rivet longitudinal axis (L) between a rivet head upper side (17) and the inner curvature (15), is between 75% and 90% of the self-piercing rivet total length (1).

4. Self-piercing rivet joint according to claim 2 or 3, characterized in that the transition between the rivet shaft (9) and the rivet head (7) is formed by a rounded rivet head lower side (16) with uniform head radius (rK), and in that the rounded rivet head lower side (16) merges tangentially radially outwards into a planar, conical rivet head lower side, which extends up to a rivet head boundary (19), and / or in that the planar, conical rivet head lower side is set diagonally upward in the direction of the rivet head upper side (17) by a cone angle (α) in relation to a horizontal plane, and in that the head radius (rK) is between 0.8 mm and 2.0 mm, and / or the cone angle (α) is in an order of magnitude of 20°.

5. Self-piercing rivet joint according to any one of the preceding claims, characterized in that the self-piercing rivet (5) is a flat head rivet with a planar rivet head upper side (17), and in that, in the self-piercing rivet joint, the rivet head upper side (17) is aligned surface flush, that is to say without head projection, with the surface of the first, stamp-side component (1), and in particular is not raised in relation to the integral component surface, and in that a circumferential rivet head boundary (19) extends radially outwards between the rivet head lower side (16) and the rivet head upper side (17) over a head lateral height (lK), and in that the head lateral height (lK) is in particular 0.3 mm.

6. Self-piercing rivet joint according to any one of the preceding claims, characterized in that on the shaft tip facing away from the rivet head (7), a ring-shaped circumferential placement edge (21) delimiting the inner curvature (15) is formed, and in that the placement edge (21) acts as a cutting edge during the riveting procedure, with which, on the one hand, early compression of the self-piercing rivet (5) can be suppressed, and, on the other hand, spreading out of the self-piercing rivet (5) by a predefined spreading amount radially outwards can be controlled, and in that a wall (23) of the self-piercing rivet inner curvature (15) and a rivet shaft outer circumference run together at an acute angle, in particular at an edge angle (β) of 45°, at the placement edge (21), and / or in that the placement edge (21) is rounded with a rounding radius (ra) in the region of 0.15 mm.

7. Self-piercing rivet joint according to any one of the preceding claims, characterized in that in the undeformed state, the self-piercing rivet total length (l) is 4 to 8 mm, the rivet head diameter (dK) is 4.5 to 8.5 mm, and / or the rivet shaft diameter (dS) is 2.8 mm to 6.6 mm.

8. Self-piercing rivet joint according to any one of the preceding claims, characterized in that the base material of the self-piercing rivet (5) is a wire material made of cold extrusion steel or cold heading steel, and / or in that the self-piercing rivet (5) has a low strength in comparison to conventional self-piercing rivets, but significantly greater ductility, and in that the strength of the self-piercing rivet (5) in the starting state without strain hardening is between 600 MPa and 1000 MPa.

9. Self-piercing rivet joint according to any one of the preceding claims, characterized in that the material thickness ratio between the first, stamp-side component (1) and the second, die-side component (3) is between 1:1 and 1:3, and in that the material thickness of the first, stamp-side component (1) is less than or equal to 1.3 mm.