Punching and riveting die, punching and riveting tool and method for producing punching and riveting joint

Abstract

A punch riveting die (22) for a punch riveting tool for arranging a semi-hollow punch rivet having a rivet shaft inner diameter as a punch riveting head, the punch riveting die (22) comprising a base body (24) having a sheet metal support surface (30) and a recess (32) for forming an underside of the punch riveting head, the recess being arranged rotationally symmetrical with respect to a central axis of the punch riveting die (22), the recess (32) has 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, with a projection (40) implemented in a central portion of the central cavity (38), and with a first annular wall (42) extending between the first annular base and the sheet metal support surface (30), a second annular wall (44) extends between the first annular base and the second annular base, and a third annular wall (46) extends between the second annular base and a bottom (38A) of the central cavity (38).

Description

Technical Field

[0001] The present application relates to self-piercing riveting (SPR) technology. More specifically, the present application relates to a die used during the installation process of a self-piercing rivet. Background Art

[0002] Self-pierce riveting (SPR) is a high-speed mechanical fastening process for joining two or more sheets of material without pre-drilling or punching. Generally, the SPR process is carried out by driving a semi-hollow rivet through the topmost workpiece layer and upsetting the rivet in the bottommost workpiece layer to form a durable mechanical joint. When driven into the workpiece device, the hollow rod of the rivet widens radially to form an undercut, which causes a permanent joint of the workpiece. The end of the rod does not completely pierce the bottom workpiece and does not protrude from the workpiece device. On the contrary, the so-called residual base thickness of the bottom workpiece layer material is retained between the end of the rivet rod and the underside of the resulting punch riveted joint. In order to realize the SPR process, the bottom workpiece layer is supported on a die. The die is arranged to be opposite to a punch suitable for driving a rivet into the workpiece device.

[0003] The dies have different shapes and geometries, depending on the workpiece material, the rivet material and / or geometry, etc., but also on the type of joint to be obtained. The die plays an important role in forming a robust joint.

[0004] For example, EP2872270A1 from the applicant discloses a mold comprising a base having a recess for forming the underside of a punch-riveted joint, the recess having a base and an annular wall. An annular radial flow suppression device is implemented in the central area of ​​the base, which restricts the material from flowing radially out of the inner area of ​​the annular radial flow suppression device. Such a mold allows to realize an axially compact and strong joint.

[0005] EP3423211A1 discloses a mold comprising the following features: a main body having an upper side and a recess formed in the upper side. The recess comprises an annular demoulding portion arranged radially outward, a subsequent or adjacent annular channel portion, and a centrally arranged mold bottom, wherein in a cross section of the self-piercing riveting mold extending parallel to the central axis, the demoulding slope of the demoulding portion forms an angle ∝ with the upper side of the self-piercing riveting mold, and the range of the angle is 5°≤∝≤45°.

[0006] In vehicle construction, with the use of megacasting, there is an increasing need to join materials of different strengths, in particular the joining of high-strength steel or ultra-high-strength steel workpieces with cast aluminum. More generally, there is an increasing need to join brittle materials, such as die-cast aluminum (which is therefore non-deformable), but without the risk of cracking within the rivet, within the brittle material workpieces (in particular on the outside of the rivet and on the shank area when the brittle material workpiece is the lowermost workpiece). There is also a need to have a mold that avoids collapse of the rivet during the setting step and allows high joining forces. Summary of the invention

[0007] Therefore, the present invention provides a punch-riveting die according to claim 1, more specifically, a punch-riveting die for a punch-riveting tool, which is used to set a semi-hollow punch rivet with an inner diameter of a rivet shank into a punch-riveted joint. The punch-riveting die comprises a base. The base has a metal sheet support surface and a recess for forming the lower side of the punch-riveted joint. The recess is arranged to be rotationally symmetrical with respect to the central axis of the punch-riveting die. The recess has a first annular base, a second annular base, and a central cavity (hereinafter referred to as the cavity) extending axially below the second annular base of the recess. A protrusion is implemented in the central part of the central cavity. And a first annular wall extends between the first annular base and the metal sheet support surface. A second annular wall extends between the first annular base and the second annular base. And a third annular wall extends between the second annular base and the bottom of the central cavity.

[0008] The protrusion in the cavity allows the formation of an annular groove. The geometry of the invention with three levels allows, for example, the joining of high-strength steel or ultra-high-strength steel with brittle cast aluminum without the formation of cracks or without changing the properties of the joint. The cavity allows the rivet to be compressed as small as possible and sufficient undercuts can be formed.

[0009] In an embodiment, the first annular base is inclined relative to a plane defined by the metal sheet support surface. This improves material intake to avoid cracking and increases the die volume.

[0010] In an embodiment, the first annular base is curved.Thereby, an optimization of the flow behavior of the aluminum casting is achieved.

[0011] In an embodiment, the first annular base comprises a convex flow barrier. The flow barrier positively affects the material behavior and reduces the tension on the rivet, the die and the workpiece.

[0012] In an embodiment, the first annular base comprises a first end connected to the first annular wall and a second end opposite to the first end and connected to the second annular wall. And wherein the second end is a circular portion. And wherein the second end is above the first end. The circular portion forms a convex flow obstacle. The second end is above the first end, which means that the second end is axially closer to the metal sheet support surface than the first end. In other words, the second annular base is inclined so that its end near the cavity is axially higher than the first end. The second annular base forms a slope.

[0013] In an embodiment, the first annular wall is realized in the form of a truncated cone surface. In an embodiment, the second annular wall is realized in the form of a truncated cone surface. In an embodiment, the third annular wall is realized in the form of a truncated cone surface.

[0014] In an embodiment, the first annular wall has a first taper angle, and the second annular wall has a second taper angle. The second taper angle is smaller than the first taper angle. The first annular wall and the second annular wall with the taper angles allow for better demoulding.

[0015] In an embodiment, the bottom of the central cavity comprises a concave flow barrier which positively influences material behavior and reduces tension on the rivet, die and workpiece.

[0016] The present invention also relates to a punch riveting tool for setting a semi-hollow punch rivet into a punch riveted joint, comprising a frame, a punch riveting head and a punch riveting die according to the above. The punch riveting head can move in the punching direction and comprises a punch riveting punch. The punch riveting punch can be operated to install the punch rivet to be set into the punch riveted joint.

[0017] The punch riveting tool is suitable for performing self-piercing riveting joining of workpieces made of brittle materials without degrading the joint characteristics.

[0018] The invention also relates to a method for producing a punch riveted joint comprising at least two workpieces arranged on the top side of a punch riveting die as described above, the method comprising the steps of driving a semi-hollow punch rivet into the uppermost workpiece, the hollow rod of the semi-hollow punch rivet also penetrating into the lowermost workpiece and widening radially in the lowermost workpiece, forming the lower side of the punch riveted joint using the punch riveting die. In an embodiment, the uppermost workpiece (W2) is made of high-strength steel or ultra-high-strength steel, and wherein the lowermost workpiece (W1) is made of brittle cast aluminum. The geometry of the die limits or avoids cracks in the rivet or the workpiece during setting.

[0019] In an embodiment, the uppermost workpiece has a first thickness Tw. Wherein, the recess has an axial depth TA between the metal sheet support surface and the second annular base. And wherein, the axial depth TA ranges such that Tw < TA < 1.5Tw, and specifically ranges such that Tw < TA < 1.35Tw. Thus, the undercut remains axially compact.

[0020] In an embodiment, the semi - hollow stamping rivet has a rivet shank diameter Dr. And the second annular wall has a second recess diameter DA2. And wherein, the second recess diameter DA2 ranges such that 0.8Dr < DA2 < 1.2Dr. This contributes to the compactness of the undercut and limits cracking and stress within the materials of the rivet and the workpiece.

[0021] It should be understood that, without departing from the scope of the present invention, the above - described features and the features to be described below can be applied not only in the specifically - specified combinations, but also in other combinations or individually. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] With reference to the accompanying drawings, other features and advantages of the present invention will become apparent from the following description of embodiments provided as non - limiting examples.

[0023] In the drawings:

[0024] Figure 1 A schematic view of a riveting tool according to the present invention having a riveting die according to the present invention is shown;

[0025] Figure 2 Shows Figure 1 a perspective view of the riveting die of

[0026] Figure 3 Shows Figure 2 a cross - sectional view of the upper part of the base body of the riveting die of DETAILED DESCRIPTION

[0027] In the different drawings, the same reference numerals denote the same or similar elements.

[0028] Figure 1 A riveting tool 10 is schematically shown. The riveting tool 10 includes a frame 12, also referred to as a C - shaped frame. At one end of the frame 12, a carriage 14 is mounted in a known manner to be movable along a longitudinal axis X (the stamping axis). A punch 16 for performing the riveting process is arranged on the carriage 14. The stamping rivet 18 is held by a holding device.

[0029] The frame 12 further includes a riveting die receiving portion 20 for receiving a riveting die 22 at a second end opposite to the first end.

[0030] The punch riveting die 22 has a base body 24 and a shank 26 of smaller diameter extending axially from the base body. The shank 26 is adapted to be received in an opening of the die receiving portion 20. The radial surface at the transition between the base body 24 and the shank 26 bears on a shoulder 28 of the die receiving portion 20. The base body 24 is preferably of rotationally symmetrical form.

[0031] The punch riveting die 22, more specifically the base 24, comprises a sheet metal support surface 30 forming a first axial side. The sheet metal support surface 30 is adapted to face the punch 16 when the die 22 is mounted in the die receiving portion 20. The sheet metal support surface 30 is adapted to support the workpiece layers to be joined.

[0032] During the punch riveting process, two or more workpieces W1, W2 in sheet form are usually arranged between the punch 16 and the die 22, and more specifically, supported by the metal sheet support surface 30 of the die 22. In addition, the workpiece stack can be fixed in place relative to the metal sheet support surface 30. Then, the punch 16 is moved downward along the longitudinal axis X, so that the rivet 18 can be driven into the workpiece device. In this case, the hollow rod of the punch rivet 18 is radially deformed in the workpiece and deflected radially outward, resulting in a non-positive joint and / or a positive joint between the workpieces. A non-positive joint refers to a rivet that only pierces one of the sheets of the sheet forming the joint, that is, fails to pierce or completely pierces the second sheet. This joint relies on friction and clamping force to keep two or more sheets together. A positive joint refers to a rivet that pierces two layers of sheets forming a joint including two layers of sheets to form a mechanical interlock. This joint provides high strength as well as resistance to shear and tension.

[0033] The sheet metal support surface 30 includes a recess 32 (see Figure 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 arranged in the central part of the central cavity 38. Therefore, the central cavity 38 with the protrusion defines an annular groove.

[0034] The first annular base 34 extends axially below the metal sheet 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 sheet support surface 30 and the second annular base.

[0035] The first annular wall 42 extends between the sheet metal support surface 30 and the first annular base 34. The first annular wall connects the sheet metal support surface 30 and the first annular base. The first annular wall is realized in the manner of a truncated-conesurface.

[0036] The second annular wall 44 extends between the first annular base 34 and the second annular base 36. The second annular wall connects the first annular base and the second annular base. The second annular wall is realized in the form of a truncated cone surface.

[0037] The first annular wall 42 has a first taper angle A1. For example, the first taper angle A1 may be between 35 degrees and 80 degrees. The second annular wall 44 has a second taper angle A2. The second taper angle A2 may be between 5 degrees and 45 degrees. The second taper angle is smaller than the first taper angle.

[0038] The third annular wall 46 extends between the second annular base and the bottom 38A of the central cavity 38. The third annular wall connects the second annular base with the bottom 38A of the central cavity 38. The third annular wall is implemented in the form of a truncated cone surface. The third annular wall can have a cone angle substantially similar to the second cone angle A2.

[0039] The sheet metal support surface 30 extends along a substantially horizontal plane. The first annular base 34 is inclined relative to the plane defined by the sheet metal support surface 30. The first annular base 34 may also be slightly curved.

[0040] The first annular base 34 includes a convex flow barrier CXF. The convex flow barrier prevents brittle material from breaking at the shank of the rivet. The first annular base 34 includes 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 slope extending from the first end to the second end, wherein the second end is closer to the metal sheet support surface than the first end. The slope and / or the rounded portion can form a convex flow barrier CXF.

[0041] The second annular base 36 includes a first end that contacts the second annular wall and a second end that contacts the third annular wall. The first end and the second end are, for example, substantially in the same plane or horizontal plane, so that the axial distance between the first end and the metal sheet support surface and the axial distance between the second end and the metal sheet support surface are the same or substantially the same. The second end may also have a rounded portion. For example, the second annular base 36 extends in a plane substantially parallel to the metal sheet support surface 30.

[0042] The bottom 38A of the cavity 38 comprises, for example, a concave flow barrier CCF. The concave flow barrier CCF reduces stresses in the mould and provides additional volume for the deformed material. The concave flow barrier is formed, for example, by an annular groove.

[0043] The protrusion 40 may extend at the same height as the second annular base in the axial direction, or may be slightly higher than the second annular base in the axial direction. The protrusion is, for example, a circular protrusion.

[0044] As described above, in order to produce a punch riveted joint comprising at least two workpieces, the workpieces are first stacked and arranged on the sheet metal support surface 30 of the die. A semi-hollow punch rivet is driven into the uppermost workpiece using a punch. The hollow shank of the semi-hollow punch rivet penetrates into the lowermost workpiece and widens radially therein. Then, the lower side of the punch riveted joint is formed by a punch riveting die. 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.

[0045] The uppermost workpiece W2 has a first thickness Tw. The recess 32 has an axial depth TA between the metal sheet support surface 30 and the second annular base. In an embodiment, the axial depth TA ranges from Tw<TA<1.5Tw, and specifically ranges from Tw<TA<1.35Tw.

[0046] 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.

Claims

1. A punch riveting die (22) for a punch riveting tool for arranging a semi-hollow punch rivet with an inner diameter of a rivet shank into a punch riveted joint, the punch riveting die (22) comprising a base (24) having a sheet metal support surface (30) and a recess (32) for forming the underside of the punch riveted joint, The recess is arranged to be rotationally symmetrical relative to the central axis of the punching and riveting die (22), and the recess (32) has 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, wherein a protrusion (40) is implemented in the central part of the central cavity (38), and wherein a first annular wall (42) extends between the first annular base and the metal sheet supporting surface (30), a second annular wall (44) extends between the first annular base and the second annular base, and a third annular wall (46) extends between the second annular base and the bottom (38A) of the central cavity (38).

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

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

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

5. The punch riveting die (22) according to any one of claims 1 to 4, wherein: The first annular base (34) includes a first end (48) connected to the first annular wall and a second end (50) opposite the first end and connected to the second annular wall, wherein the second end is a circular portion, and wherein the second end is axially above the first end.

6. The punch riveting die (22) according to any one of claims 1 to 5, wherein: The first annular wall (42) is realized in the form of a truncated cone surface.

7. The punch riveting die (22) according to any one of claims 1 to 6, wherein: The second annular wall (44) is realized in the form of a truncated cone surface.

8. The punch riveting die (22) according to any one of claims 1 to 7, wherein: The third annular wall (46) is realized in the form of a truncated cone surface.

9. The punch riveting die (22) according to any one of claims 1 to 8, wherein: The first annular wall (42) has a first taper angle, and the second annular wall (44) has a second taper angle, wherein the second taper angle is smaller than the first taper angle.

10. The punch riveting die (22) according to any one of claims 1 to 9, wherein: The bottom (38A) of the central cavity (38) includes a concave flow barrier (CCF).

11. A punch riveting tool (10) for arranging a semi-hollow punch rivet into a punch riveted joint, the punch riveting tool comprising: -frame; a punch rivet head which is movable in the punching direction and comprises a punch rivet punch operable to install the punch rivet to be set into the punch rivet joint; as well as - A punch riveting die (22) according to any one of the preceding claims.

12. A method for producing a punch riveted joint comprising at least two workpieces (W1, W2), wherein the at least two workpieces are arranged on the top side of a punch riveting die (22) according to any one of claims 1 to 10, the method comprising the following steps: driving a semi-hollow punch rivet into the uppermost workpiece, the hollow rod of the semi-hollow punch rivet also penetrating into the lowermost workpiece and widening radially in the lowermost workpiece, and forming the lower side of the punch riveted joint using the punch riveting die.

13. The method according to claim 12, wherein: The uppermost workpiece (W2) is made of high-strength steel or ultra-high-strength steel, and wherein the lowermost workpiece (W1) is made of brittle cast aluminum.

14. The method according to claim 12 or 13, wherein: The uppermost workpiece has a first thickness Tw, wherein the recess has an axial depth TA between the metal sheet support surface and the second annular base, and wherein the axial depth TA ranges from Tw <TA<1.5Tw。 15. The method according to any one of claims 12 to 14, wherein: The semi-hollow punch rivet has a rivet shank diameter Dr, and the second annular wall (44) has a second recess diameter DA2, and wherein the second recess diameter DA2 is in the range of 0.8Dr<DA2<1.2Dr.

Images