Metal mold for coupling punch rivet, tool for coupling punch rivet and punch rivet joint formation method

Abstract

To provide a metal mold which is used during fitting of a self-drilling type rivet.SOLUTION: A metal mold for coupling punch rivet is used for a tool for coupling punch rivet for installing a semi-hollow punch rivet having a rivet shank inner diameter to a punch rivet joint. The metal mold for coupling punch rivet comprises a base part body having a metal plate support surface, and a recess for forming a bottom surface of the punch rivet joint. The recess is located in rotational symmetry with respect to a central axis of the metal mold for coupling punch rivet, and has a first annular base part, a second annular part, and a central cavity which extends in an axial direction below the second annular base part of the recess. A projection is provided at a midship part of the cavity. A first annular wall extends between the first annular base part and the metal plate support surface, a second annular wall extends between the first annular base part and the second annular base part, and a third annular wall extends between the second annular base part and a bottom of the cavity.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] This application relates to self-piercing rivet (SPR) technology. More specifically, this application relates to dies used during the installation of self-piercing rivets. [Background technology]

[0002] Self-piercing rivets (SPR) are a high-speed mechanical fastening process for joining two or more sheets of material without pre-drilled or punched holes. Typically, the SPR process is performed by driving a semi-hollow rivet through a top layer of workpieces and upsetting the rivet in a bottom layer of workpieces to form a durable mechanical joint. The hollow shank of the rivet expands radially as it is driven into the array of workpieces, thereby forming an undercut that results in a permanent joining of the workpieces. The end of the shank does not completely penetrate the bottom workpiece and does not protrude from the array of workpieces. Rather, a so-called residual base thickness of material of the bottom layer of workpieces remains between the end of the rivet shank and the bottom surface of the punch riveted joint thus formed. To realize the SPR process, the bottom layer of workpieces is supported by a die. The die is positioned opposite a punch adapted to drive the rivet into the array of workpieces.

[0003] Dies come in a variety of shapes and geometries, which may depend on the workpiece material, the rivet material and / or geometry, as well as the joint to be achieved. The die plays a key role in the formation of a robust joint.

[0004] For example, the applicant's EP 2 872 270 A1 discloses a die with a basic body having a recess for forming the bottom surface of the punch rivet joint, the recess having a base and an annular wall. An annular radial flow restriction device is realized in the central region of the base, which restricts the radial material outflow from its inner region. With such a die, an axially compact and robust joint can be realized.

[0005] EP 3423211 A1 discloses a die having a body with an upper surface and a recess formed therein, the recess comprising a radially outwardly disposed annular demolding section, a subsequent or adjacent annular groove section and a centrally disposed die bottom, and in a cross section of the self-piercing riveting die extending parallel to the central axis, the demolding inclination of the demolding section forms an angle α with an upper side of the self-piercing riveting die in the range of 5°≦α≦45°. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] European Publication No. 2872270 [Patent Document 2] European Publication No. 3423211 Summary of the Invention [Problem to be solved by the invention]

[0007] In vehicle assembly, the use of megacasting has increased the need to join materials of different strengths, especially workpieces of high or ultra-high strength steel with cast aluminum. More generally, there is an increased need to join brittle materials (and therefore not deformable) such as die cast aluminum without the risk of cracking in the rivet and in the workpiece of brittle material (especially on the outside and shank area of ​​the rivet when the workpiece of brittle material is the bottom workpiece). Also, a tool is needed that avoids crushing of the rivet during the upsetting process and allows high joining forces. [Means for solving the problem]

[0008] The present invention therefore provides a punch riveting die as claimed in claim 1. More specifically, the punch riveting die is for a punch riveting tool for setting a semi-hollow punch rivet having a rivet shank inner diameter in a punch riveted joint. The punch riveting die comprises a base body having a metal sheet support surface and a recess for forming a bottom surface of the punch riveted joint, the recess being arranged rotationally symmetrically with respect to a central axis of the punch riveting die, the recess having a first annular base, a second annular base and a central cavity extending axially below the second annular base of the recess. A protrusion is provided in the central part of the cavity, a first annular wall extending between the first annular base and the metal sheet support surface, a second annular wall extending between the first annular base and the second annular base and a third annular wall extending between the second annular base and the bottom of the cavity.

[0009] The protrusion in the cavity is such that it forms an annular groove. This geometry with three heights allows, for example, a joint between high-strength or ultra-high-strength steel and brittle cast aluminum without the formation of cracks or changing the performance of the joint. The cavity is such that the rivet is compressed as little as possible and can form a sufficient undercut.

[0010] In one embodiment, the first annular base is inclined relative to the plane defined by the metal plate support surface, which improves material intake to avoid cracks and increase mold volume.

[0011] In one embodiment, the first annular base is curved. In this way, an optimization of the flow behavior of the aluminum casting is achieved.

[0012] In one embodiment, the first annular base comprises a convex flow barrier that positively influences material behavior and reduces tension on the rivet, the die, and the workpiece.

[0013] In one embodiment, the first annular base comprises a first end connected to the first annular wall and a second end connected to the second annular wall opposite the first end, the second end being a rounded portion, the second end being above the first end. The rounded portion forms a convex flow barrier. The second end being above the first end means that the second end is axially closer to the metal plate support surface than the first end. In other words, the first annular base is inclined such that the end near the cavity is axially higher than the first end. The first annular base forms a slope.

[0014] In one embodiment, the first annular wall is realized in the form of a frustoconical surface. In one embodiment, the second annular wall is realized in the form of a frustoconical surface. In one embodiment, the third annular wall is realized in the form of a frustoconical surface.

[0015] In one embodiment, the first annular wall has a first taper angle and the second annular wall has a second taper angle, the second taper angle being less than the first taper angle. The first and second annular walls having tapered angles allow for better demolding.

[0016] In one embodiment, the bottom of the cavity is provided with a recessed flow barrier that positively influences material behavior and reduces tension on the rivet, die, and work piece.

[0017] Furthermore, the present invention relates to a punch rivet joining tool for installing a semi-hollow punch rivet at a punch rivet joint. The punch rivet joining tool includes: a frame, a punch rivet joining head including a punch rivet joining punch that is movable in the driving direction and operable to attach a punch rivet to be attached to a punch rivet joint, the above-described punch rivet joining die, and is provided with. The punch rivet joining tool is adapted to perform self-piercing rivet joining with a workpiece made of a brittle material without degrading the joining characteristics.

[0018] In addition, the present invention relates to a method for forming a punch rivet joint of at least two workpieces disposed on the upper surface of the punch rivet joining die as described above. The method includes the step of driving a semi-hollow punch rivet into the uppermost workpiece, wherein the hollow shank of the semi-hollow punch rivet penetrates into the lowermost workpiece and spreads radially therein, and the bottom surface of the punch rivet joint is formed by the punch rivet joining die.

[0019] In one embodiment, the uppermost workpiece is made of high-strength steel or ultra-high-strength steel, and the lowermost workpiece is made of brittle cast aluminum. The geometric shape of the die limits or avoids the generation of cracks in the rivet or workpiece during installation.

[0020] In one embodiment, the uppermost workpiece has a first thickness Tw, the recess has an axial depth TA between the metal plate support surface and the second annular base, and the axial depth TA is in the range of Tw < TA < 1.5Tw, and more specifically in the range of Tw < TA < 1.35Tw. Accordingly, the undercut remains axially compact.

[0021] In one embodiment, the rivet has a rivet shank diameter Dr, and the second annular wall has a second recess diameter DA2, and the second recess diameter DA2 is in the range of 0.8Dr < DA2 < 1.2Dr. This contributes to the compactification of the undercut and the limitation of cracks and stresses in the materials of the rivet and the workpiece.

[0022] It should be understood that the above-described features and the features described below can be applied not only in the specifically identified combinations but also in other combinations or alone without departing from the scope of the present invention.

[0023] Other features and advantages of the present invention will become apparent from the following description of embodiments presented as non-limiting examples with reference to the accompanying drawings.

Brief Description of the Drawings

[0024] [Figure 1] It is a schematic view of a punching-riveting tool according to the present invention provided with a punching-riveting die according to the present invention. [Diagram 2] It is a perspective view of the punching-riveting die of FIG. 1. [Diagram 3] It is a cross-sectional view of the upper part of the base body of the punching-riveting die of FIG. 2.

Modes for Carrying Out the Invention

[0025] In different figures, the same reference numerals indicate the same or similar elements.

[0026] FIG. 1 schematically shows a punching-riveting tool 10. The punching-riveting tool 10 includes a frame 12 also called a C-shaped frame. A reciprocating table 14 is displaceably attached to the first end of the frame 12 along the longitudinal axis X (punch axis) in a known manner. A punch 16 for performing a punching-riveting process is disposed on the reciprocating table 14. The punching-rivet 18 is held by a holding device.

[0027] The frame 12 further comprises a punch riveting die receiver 20 at a second end opposite the first end for receiving a punch riveting die 22 .

[0028] The punch riveting die 22 has a base body 24 having a smaller diameter die shank 26 extending axially therefrom. The die shank 26 is adapted to be received within an opening in the die receiver 20. The radial surface of the transition between the base body 24 and the shank 26 rests on a shoulder 28 of the die receiver 20. The base body 24 is preferably rotationally symmetric in shape.

[0029] The punch riveting die 22, and more particularly the base body 24, includes a sheet metal support surface 30 which defines a first axial surface and faces the punch 16 when the die 22 is mounted in the die receiver 20. The sheet metal support surface 30 is adapted to support the workpiece layers to be joined.

[0030] In the punch riveting process, two or more workpieces W1, W2, usually in sheet form, are placed between the punch 16 and the die 22, in particular supported by the sheet metal support surface 30 of the die 22. It is also possible to fix the stack of workpieces in position relative to the sheet metal support surface 30. The punch 16 can then move downward along the longitudinal axis X and drive the rivet 18 into the array of workpieces. In this case, the hollow shank of the punch rivet 18 deforms radially within the workpieces and deflects radially outward, resulting in a non-positive and / or positive joint between the workpieces.

[0031] The metal sheet support surface 30 is provided with a recess 32 (see FIG. 2 ). The recess 32 is arranged rotationally symmetrically with respect to the central axis of the punch riveting die. The recess has a first annular base 34, a second annular base 36 and a central cavity 38 extending axially below the second annular base 36. The central cavity 38 is provided with a protrusion 40. The protrusion 40 is located in a central portion of the central cavity 38. The central cavity 38 with the protrusion thus defines an annular groove.

[0032] The first annular base 34 extends axially below the metal plate support surface 30. The second annular base 36 extends axially below the first annular base 34. In other words, the first annular base extends axially between the metal plate support surface 30 and the second annular base.

[0033] The first annular wall 42 extends between the metal plate support surface 30 and the first annular base 34. The first annular wall connects the metal plate support surface 30 with the first annular base. The first annular wall is realised in the manner of a frustoconical surface.

[0034] The second annular wall 44 extends between the first annular base 32 and the second annular base 36. The second annular wall connects the first and second annular bases. The second annular wall is realized in the manner of a frustoconical surface.

[0035] The first annular wall 42 has a first taper angle A1. For example, the first taper angle A1 can be between 35 degrees and 80 degrees. The second annular wall 44 has a second taper angle A2. The second taper angle A2 can be between 5 degrees and 45 degrees. The second taper angle is smaller than the first taper angle.

[0036] The third annular wall 46 extends between the second annular base and the recess. The third annular wall connects the second annular base and the recess. The third annular wall is realized in the manner of a frustoconical surface. The third annular wall can have a taper angle substantially similar to the second taper angle A2.

[0037] The metal plate support surface 30 extends along a substantially horizontal plane. The first annular base 34 is inclined relative to the plane defined by the metal plate support surface 30. The first annular base 32 may be slightly curved.

[0038] The first annular base 34 comprises a convex flow barrier CXF. The convex flow barrier prevents brittle materials from cracking at the rivet shank. The first annular base 34 comprises a first end 48 and a second end 50. The first end 48 contacts the first annular wall. The second end 50 contacts the second annular wall. The second end is a rounded portion. The second end 50 extends axially above the first end 48. The first annular base 34 forms a beveled surface extending from the first end to the second end, the second end being closer to the metal sheet support surface than the first end. The beveled surface and / or the rounded portion can form a convex flow barrier CXF.

[0039] The second annular base 36 comprises a first end contacting the second annular wall and a second end contacting the third annular wall. The first end and the second end are, for example, substantially flush or flush, and the axial distance between the first end and the metal plate support surface and the axial distance between the second end and the metal plate support surface are the same or substantially the same. The second end can also have a rounded portion. For example, the second annular base 36 extends in a plane substantially parallel to the plane of the metal plate support surface 30.

[0040] The bottom of the cavity 38 is provided with, for example, a concave flow barrier CCF. The concave flow barrier CCF reduces stress in the mold and provides additional volume for the deforming material. The concave flow barrier is formed, for example, by an annular groove.

[0041] The protrusion 40 may extend axially at the same height as the second annular base or may be located slightly axially above the second annular base. The protrusion may be, for example, a rounded protrusion.

[0042] As described above, in order to form the punch rivet joints of at least two workpieces, the workpieces are first stacked and placed on the metal plate support surface 30 of the mold. The semi-hollow punch rivet is driven into the uppermost workpiece together with the punch. The hollow shank of the semi-hollow punch rivet penetrates into the lowermost workpiece and expands radially therein. Next, the bottom surface of the punch rivet joint is formed by a mold for punch rivet connection. In a specific embodiment, the uppermost workpiece is made of high-strength steel or ultra-high-strength steel, and the lowermost workpiece is made of brittle cast aluminum. More generally, at least one of the workpieces is made of a brittle material such as cast aluminum.

[0043] The uppermost workpiece W2 has a first thickness Tw. The recess 32 has an axial depth TA between the metal plate support surface 30 and the second annular base. In one embodiment, the axial depth TA is in the range of Tw < TA < 1.5Tw, and more specifically in the range of Tw < TA < 1.35Tw.

[0044] The rivet has a rivet shank diameter Dr, and the second annular wall has a second recess diameter DA2. The second recess diameter DA2 is in the range of 0.8Dr < DA2 < 1.2Dr.

Explanation of Reference Numerals

[0045] 10 Tool for punch rivet connection 22 Mold for punch rivet connection 24 Base body 30 Metal plate support surface 32 Recess 34 First annular base 36 Second annular base 38 Central cavity 40 Protrusion 42 First annular wall 44 Second annular wall 46 Third annular wall

Claims

1. A punch riveting die (22) for a punch riveting tool for installing a semi-hollow punch rivet having a rivet shank inner diameter into a punch riveted joint, the punch riveting die (22) comprising a base body (24) having a metal sheet support surface (30) and a recess (32) for forming a bottom surface of the punch riveted joint; The recess (32) is arranged rotationally symmetrically about a central axis of the punch riveting die (22), the recess (32) having a first annular base (34), a second annular base (36) and a central cavity (38) extending axially below the second annular base of the recess, the central portion of the cavity (38) being provided with a protrusion (40), a first annular wall (42) extending between the first annular base and the metal sheet support surface (30), a second annular wall (44) extending between the first annular base and the second annular base, and a third annular wall (46) extending between the second annular base and a bottom of the cavity (38).

2. The punch riveting die (22) of claim 1, wherein the first annular base (34) is inclined relative to a plane defined by the sheet support surface.

3. The punch riveting die (22) of claim 1 or 2, wherein the first annular base (34) is curved.

4. The punch riveting die (22) of any one of claims 1 to 3, wherein the first annular base (34) comprises a convex flow barrier (CXF).

5. 5. The punch riveting die (22) of claim 1, wherein the first annular base (34) has a first end (48) connected to the first annular wall and a second end (50) connected to the second annular wall opposite the first end, the second end being a rounded portion, and the second end being axially above the first end.

6. A punch riveting die (22) according to any of the preceding claims, wherein the first annular wall (42) is realised in the manner of a frusto-conical surface.

7. 7. A punch riveting die (22) according to any of the preceding claims, wherein the second annular wall (44) is realised in the manner of a frustoconical surface.

8. A punch riveting die (22) according to any of the preceding claims, wherein the third annular wall (46) is realised in the manner of a frustoconical surface.

9. 9. The punch riveting die (22) of claim 1, wherein the first annular wall (42) has a first taper angle and the second annular wall (44) has a second taper angle, the second taper angle being less than the first taper angle.

10. The punch riveting die (22) of any one of claims 1 to 9, wherein the bottom of the cavity (38) is provided with a concave flow barrier (CCF).

11. A punch riveting tool (10) for driving a semi-hollow punch rivet into a punch riveted joint, comprising: A frame, a punch riveting head including a punch riveting punch movable in a driving direction and operable to set a punch rivet in the punch riveted joint; A punch riveting die (22) according to any one of claims 1 to 10; A punch riveting tool (10) comprising:

12. 11. A method for forming a punch riveted joint of at least two workpieces (W1, W2) arranged on an upper surface of a punch riveting die (22) according to any one of claims 1 to 10, comprising the step of driving a semi-hollow punch rivet into the uppermost workpiece, a hollow shank of the semi-hollow punch rivet penetrates into the lowermost workpiece and expands radially, and a bottom surface of the punch riveted joint is formed by the punch riveting die.

13. 13. The method according to claim 12, wherein the top workpiece (W2) is made of high strength or ultra high strength steel and the bottom workpiece (W1) is made of brittle cast aluminium.

14. 14. The method of claim 12 or 13, wherein the top workpiece has a first thickness Tw and the recess has an axial depth TA between the metal plate support surface and the second annular base, the axial depth TA being in the range Tw<TA<1.5Tw.

15. 15. The method of any of claims 12 to 14, wherein the rivet has a rivet shank diameter Dr and the second annular wall (44) has a second recess diameter DA2, the second recess diameter DA2 being in the range 0.8Dr<DA2<1.2Dr.

Images