GB2417452A

GB2417452A - A self pierce die rivet

Info

Publication number: GB2417452A
Application number: GB0517164A
Authority: GB
Inventors: Stephen Kemosky
Original assignee: Ford Global Technologies LLC
Current assignee: Ford Global Technologies LLC
Priority date: 2004-08-24
Filing date: 2005-08-23
Publication date: 2006-03-01
Anticipated expiration: 2025-08-23
Also published as: GB2417452B; GB0517164D0; DE102005040258A1

Abstract

A die 16 and system 10 for driving a self pierce rivet 28 into a plurality of workpieces 30 is disclosed. The die 16 includes an anvil 40 and a collar 42 affixed to the anvil 40 which cooperate to reduce stresses thereby reducing the risk of die breakage.

Description

A SELF PIERCE RIVET DIE

The present invention relates to a die for self pierce riveting and a system for driving a self pierce rivet into a plurality of workpieces.

Self pierce rivets may be used to assemble a plurality of workpieces together and are commonly upset using a die assembly. Previous die assemblies utilized a one piece forming die. Under some conditions one piece forming dies are not durable and may easily crack and break due to the high forces involved in self pierce riveting.

One problem of known one piece dies is that they may fail due to the high localized stresses associated with the use of such a design.

It is an object of this invention to provide an improved die for use with self-pierce rivets that overcomes or minimises the problems associated with the prior art According to a first aspect of the invention there is provided a die for shaping a self pierce rivet when the self pierce rivet is driven into a plurality of workpieces, the die comprising an anvil having a perimeter surface and a collar having an inner surface that contacts the perimeter surface of the anvil wherein the collar is affixed to the anvil so that the anvil and collar cooperate to reduce stress induced breaking of the die.

Preferably, the anvil may be made from a first material and the collar is made from a second material.

The anvil may be made from a material having a Rockwell 'C' hardness in the range 60 to 62 and the collar is made from a material having a Rockwell 'C' hardness in the range 56-58. - 2 -

The anvil may comprise a first portion having the perimeter surface, a flange portion extending around the perimeter surface and having a lower surface and an upper surface disposed opposite the first surface and a second portion coaxially disposed with the first portion and extending away from the upper surface and the collar has the inner surface that contacts the perimeter surface and an end surface that mates with the upper surface of the flange lo portion.

The second portion may further comprise an end surface and a nub that protrudes from the end surface The second portion may further comprise an end surface having a conical configuration.

The upper surface of the flange portion may be concave.

8. A die as claimed in any of claims 4 to 6 wherein the upper surface of the flange portion is convex.

The upper surface of the flange may be disposed parallel to the lower surface.

The upper surface of the flange portion may be angled towards the lower surface in a direction extending toward a centre axis.

The upper surface of the flange portion may be angled toward the lower surface in a direction extending away from a centre axis.

At least a portion of the inner and perimeter surfaces may include mating threads for removably coupling the collar to the anvil. - 3 -

The second portion may further comprise a groove extending from the end surface toward the flange portion, the groove being spaced apart from the inner surface of the collar and is used to receive a solder material for joining together the anvil and collar.

The anvil may have an end surface and the perimeter surface may be a first perimeter surface disposed about a centre axis of the anvil and the inner surface of the collar lo may be affixed to the perimeter surface of the anvil.

The anvil may further comprise an end portion having a second perimeter surface having a smaller diameter than the first perimeter surface disposed concentrically with the first perimeter surface and the centre axis, a step surface extending between the first and second perimeter surfaces and the collar has a lower surface which contacts the step surface.

The end portion may further comprise a nub extending from the end portion.

The die may further comprise a flange portion disposed around the perimeter surface of the anvil which is spaced away from the end surface.

The collar may further comprise a first end surface, a second end surface disposed opposite the first end surface and a groove extending from the second end surface toward the first surface and spaced apart from the perimeter surface of the anvil to receive a solder material for joining together the anvil and the collar.

A portion of the end surface disposed adjacent to the inner surface may be generally perpendicular to the inner surface. - 4

According to a second aspect of the invention there is provided a system for driving a self pierce rivet into a plurality of workplaces comprising a fixture having an aperture, a first die, a second die and an actuator disposed proximate the fixture, the actuator being configured to move the second die in an axial direction between a retracted position and an advanced position to axially drive the self pierce rivet wherein the first die is a die in accordance with said first aspect of the invention.

The first die may comprise an anvil having a first portion disposed in the aperture, a flange portion extending around a perimeter of the first portion having a lower surface that contacts the fixture and an upper surface disposed opposite the first surface, a second portion coaxially disposed with the first portion and extending away from the upper surface of the flange portion and a collar affixed to the anvil, the collar having an inner surface that contacts a perimeter of the second portion and a lower surface that contacts the upper surface of the flange portion.

The invention will now be described by way of example with reference to the accompanying drawing of which: Figure 1 is a schematic of a system for driving a self pierce rivet; Figure 2 is a magnified section view of a portion of the system taken along line 2-2 of Figure 1 illustrating a self pierce rivet prior to upsetting; Figure 3 is a magnified section view of the portion of the system shown in Figure 2 illustrating upsetting of the self pierce rivet; and - 5 - Figures 4A-4M illustrate various embodiments of a multi-piece die in accordance with this invention.

Those skilled in the art will appreciate that the

figures forming part of this specification are not

necessarily to scale and some features may be exaggerated or minimized to show details of particular components.

Referring firstly to Figure 1, a system 10 for driving lo a self pierce rivet into a plurality of workpieces is shown.

The system 10 includes a manipulator 12, a fixture 14, a die assembly 16 and an actuator 18.

The manipulator 12 may have any suitable configuration but, in the embodiment shown, the manipulator 12 is configured as a robot configured to move about one or more axes. The manipulator 12 permits the fixture 14 and die assembly 16 to be moved to various positions to facilitate riveting of a plurality of workpieces. Alternatively, the manipulator 12 may be omitted in various embodiments of the present invention.

Referring now to Figures 1 and 2, an exemplary embodiment of the fixture 14 is shown which may be configured to be mounted on the manipulator 12. Moreover, the fixture 14 may be adapted to receive the die assembly 16 and/or the actuator 18. The fixture 14 may have any suitable configuration.

In the embodiment shown, the fixture 14 is generally C shaped and includes an aperture 20 for receiving a portion of the die assembly 16 and a mounting portion 22 for receiving the actuator 18.

Referring now to Figures 1-3, an embodiment of the die assembly 16 is shown. The die assembly 16 may include a first die 24 and a punch or second die 26. The first and - 6 second dies 24, 26 cooperate to upset a self pierce rivet 28. More specifically, the second die 26 is adapted to exert force against the self pierce rivet 28 to drive the self pierce rivet 28 into a plurality of workplaces 30 while the first die 24 is adapted to help form the self pierce rivet 28.

As shown in Figures 2 and 3, the self pierce rivet 28 includes a plurality of protrusions 32 that extend away from lo the head of the self pierce rivet 28. The protrusions 32 pierce through some, but not all of the workplaces 30 and are deformed to help secure the self pierce rivet 28 and workplaces 30 together. More specifically, the protrusions 32 are deformed outwardly by the action of the die assembly 16, but do not penetrate completely through the workpiece disposed adjacent to the first die 24 when the self pierce rivet 28 is properly upset.

The first die 24 may have any suitable configuration.

Various exemplary embodiments are shown in Figures 3 and 4A- 4M and discussed in more detail below. The second die 26 may also have any suitable configuration and may include a generally planar surface that engages the self pierce rivet 28.

The actuator 18 may be configured to receive the second die 26 and provide force for upsetting the self pierce rivet 28. More specifically, the actuator 18 may be configured to move between a retracted position in which the first and second dies 24,26 are spaced apart from each other and an advanced position in which the first and second dies 24,26 are positioned closer together. The actuator 18 may be of any suitable type, such as a hydraulic, pneumatic, electric, mechanical, or other type of actuator.

Referring to Figures 2, 3, and 4A-4M, various embodiments of the first die are shown. For convenience, - 7 common reference numbers are used to designate identical or similar features or components when possible.

In each embodiment, the first die includes multiple pieces. In a two piece embodiment the first die includes an anvil and a collar and in a three piece embodiment the first die includes an anvil, a collar, and a flange.

In these embodiments the anvil and collar may be lo coaxially disposed about a centre axis 34 as shown in Figures 2-3. Moreover, in each of these embodiments, the anvil may include an end surface having an optional protrusion or nub 36 that helps direct the protrusions toward the collar during upsetting of the self pierce rivet 28. Moreover, in each embodiment the end surface may be disposed generally perpendicularly to an adjacent surface of the collar so that the self pierce rivet is properly upset.

The first die may be made of any suitable material or materials. For example, the anvil may be made of a material with good wear resistance and compressive strength, such as an A8 or M2 grade steel, while the collar made be made of a material that having good fatigue resistance, such as an H13 VAR (vacuum arc re-melted) steel. In addition, the anvil and collar may each have different hardness to accommodate different types and/or magnitudes of stress. In at least one embodiment, the hardness of the anvil may be greater than the hardness of the collar to accommodate the compressive forces that occur when the self pierce rivet 28 is upset. For instance, the anvil and collar may be configured with hardness of Rockwell 'C' (Rc) 60-64 and Rc 56-61, respectively. Of course, larger or smaller hardness ranges that may or may not overlap may also be provided in various embodiments of the present invention.

Referring to Figures 2-3, an embodiment of the first die 24 is shown that includes an anvil 40 and a collar 42. - 8 -

The anvil 40 is configured to be received in the aperture 20 of the fixture 14. The anvil 40 includes an outside or perimeter surface 44 and an end portion 46. The collar 42 defines a hole and includes an interior surface 48 that is attached to the portion of the perimeter surface associated with the end portion 46.

Referring to Figure 4A, another embodiment of the first die is shown that includes an anvil 50 and a collar 52. The lo anvil 50 includes a first portion 54 that may be configured to be received in the aperture 20, a flange portion 56, and a second portion 58. The flange portion 56 includes an upper surface 60 and a lower surface 62 disposed opposite and generally parallel to the upper surface 60. The lower surface 62 may contact the fixture 14 when the first portion 54 is disposed in the aperture 20. The second portion 58 may extend from the upper surface 60 and may be coaxially disposed with the first portion 54. The collar 52 may include an interior surface 64 disposed adjacent to the perimeter of the second portion 58 and an end or mating surface 66 disposed adjacent to the upper surface 60.

Referring to Figure 4B, a three piece embodiment of the first die is shown that includes a collar 52, an anvil 70, and a flange portion 72. The flange portion 72 is disposed around and attached to the perimeter surface of the anvil 70. The flange portion 72 may be attached in any suitable manner as will be described in more detail below.

Referring to Figures 4C-4D, two piece embodiments are shown in which the upper and lower surfaces of the flange portion are disposed at an angle relative to each other.

In Figure 4C, the first die includes an anvil 80 and a collar 82. The anvil 80 has a flange portion 86 that includes an upper surface 90 that is angled toward the lower - 9 surface 92 in a direction extending away from a centre axis 34.

In Figure 4D, the first die also includes an anvil 80' and a collar 82'. The anvil 80' has a flange portion 86' that includes an upper surface 90' that is angled toward the lower surface 92' in a direction extending toward the centre axis 34. In these embodiments, the collar 82,82' includes a mating surface 96,96' that mates with the upper surface lo 90, 90'. These configurations help position the collar with respect to the anvil and may provide improved force distribution.

Referring to Figures 4E-4F, embodiments are shown in which the upper and lower surfaces of the flange portion are non-planar.

In Figure 4E, the first die includes an anvil 100 and a collar 102. The anvil 100 has a flange portion 106 that includes an upper surface 110 and a lower surface 112. The upper surface 110 is convex and slopes toward the lower surface 112 in a direction extending away from the centre axis 34.

In Figure 4F, the first die also includes an anvil 100' and a collar 102'. The anvil 100' has a flange portion 106' that includes upper and lower surfaces 110',112'. The upper surface 110' is concave and slopes toward the lower surface 112' in a direction extending toward the centre axis 34.

Referring to Figure 4G, an embodiment similar to Figure 4A is shown. In this embodiment, the anvil 120 has an end surface 122 having a generally conical configuration that intersects the interior surface 64 of the collar 52 at an angle. As such, this configuration helps direct the protrusions of the self pierce rivet 28 during upsetting and help distribute forces.

Referring to Figure 4H, an embodiment is shown that includes an anvil 130 having first and second portions 134,138. The first portion 134 includes a first perimeter surface 140. The second portion 138 includes a second perimeter surface 142. A step surface 144 extends between the first and second perimeter surfaces 140, 142. The interior surface 64 and mating surface 66 of the collar 52 are disposed adjacent to the second perimeter surface 142 and step surface 144, respectively.

Referring to Figures 4I-4M, additional embodiments are shown that depict features that help facilitate assembly of the anvil and collar. Alternatively, the anvil and collar may be joined in other ways, such as with welding, an adhesive, an interference fit, and/or one or more fasteners.

In Figure 4I, at least a portion of the anvil 150 and collar 152 are provided with mating threads. In the embodiment shown, the second portion 154 of the anvil 150 and interior surface 156 of the collar 152 include mating threads 158 that permit easy assembly and disassembly of the anvil 150 and collar 152. As such, the anvil or collar may be replaced independently of each other, thereby reducing die assembly costs as compared to a one piece die design.

In Figures 4J and 4L, a groove is provided between the anvil and the collar.

In Figure 4J, the first die includes an anvil 160 and a collar 52. The anvil 160 includes a second portion 162 that includes a groove 164 that extends from the end surface 166 toward the flange portion 168.

In Figure 4L, the first die includes an anvil 50 and a collar 170. The collar 170 includes a groove 172 that extends from the lower surface 174 toward an upper surface 176. In each embodiment, the groove 164,172 may extend partially or completely around the anvil or collar. The groove 164,172 may receive a solder material 178 for joining the anvil and the collar as is shown in Figures 4K and 4M, respectively.

The embodiments of the first die described above may be combined in any suitable manner. For example, the various anvil and collar attributes may be combined in multiple combinations. For example, the upper and mating surfaces in lo Figures 4C-4F may be incorporated with a three piece design.

In addition, the mating threads shown n Figure 4I or the groove and solder combinations of Figures 4J-4M may be integrated with the embodiments shown in Figures 4A-4H.

The embodiments of the first die described above may be fabricated in any suitable manner. For example, the anvil and/or collar may be formed in a desired shape, such as by casting or material removal. For instance, the anvil and or collar may be rough cut, finish cut, and hardened in any suitable order and with any suitable techniques to achieve desired geometry and material properties.

The multi-piece die of the present invention helps improve die durability as compared to a one piece design and may do so with little difference in die cost. Improved durability may also provide one or more of the following benefits. First, downtime is reduced, which helps improve process throughput and efficiency. Second, product quality and process reliability is improved, which may help reduce inspection costs and scrap.

A multi-piece die in accordance with one or more embodiments of the present invention may also expand the operating window of self pierce riveting. More specifically, additional joint configurations (sheet thickness, number of sheets, rivet length, etc.) are economically feasible with a multi-piece design that were - 12 not economically feasible with the best one piece design.

In addition, a multi-piece design, which eliminates the continuous sharp inside corner of the one-piece design, is less sensitive to tooling marks that may impact die durability and product quality. Thus, a multi-piece design may improve die manufacturing robustness while easing the burden on die manufacture operations, such as machining, polishing, grinding, and inspection. - 13

Claims

1. A die for shaping a self pierce rivet when the self pierce rivet is driven into a plurality of workpieces, the die comprising an anvil having a perimeter surface and a collar having an inner surface that contacts the perimeter surface of the anvil wherein the collar is affixed to the anvil so that the anvil and collar cooperate to reduce stress induced breaking of the die.

2. A die as claimed in claim 1 wherein the anvil is made from a first material and the collar is made from a second material.

3. A die as claimed in claim 2 wherein the anvil is made from a material having a Rockwell 'C' hardness in the range 60 to 62 and the collar is made from a material having a Rockwell 'C' hardness in the range 56-58.

4. A die as claimed in any of claims 1 to 3 wherein the anvil comprises a first portion having the perimeter surface, a flange portion extending around the perimeter surface and having a lower surface and an upper surface disposed opposite the first surface and a second portion coaxially disposed with the first portion and extending away from the upper surface and the collar has the inner surface that contacts the perimeter surface and an end surface that mates with the upper surface of the flange portion.

5. A die as claimed in claim 4 wherein the second portion further comprises an end surface and a nub that protrudes from the end surface.

6. A die as claimed in claim 4 wherein the second portion further comprises an end surface having a conical configuration. - 14

7. A die as claimed in any of claims 4 to 6 wherein the upper surface of the flange portion is concave.

9. A die as claimed in any of claims 4 to 6 wherein the upper surface of the flange is disposed parallel to the lower surface.

10. A die as claimed in any of claims 4 to 6 wherein the upper surface of the flange portion is angled towards the lower surface in a direction extending toward a centre axis.

11. A die as claimed in any of claims 4 to 6 wherein the upper surface of the flange portion is angled toward the lower surface in a direction extending away from a centre axis.

12. A die as claimed in any of claims 4 to 11 wherein at least a portion of the inner and perimeter surfaces include mating threads for removably coupling the collar to the anvil.

13. A die as claimed in claim 4 wherein the second portion further comprises a groove extending from the end surface toward the flange portion, the groove being spaced apart from the inner surface of the collar and is used to receive a solder material for joining together the anvil and collar.

14. A die as claimed in any of claims 1 to 3 in which the anvil has an end surface and the perimeter surface is a first perimeter surface disposed about a centre axis of the anvil wherein the inner surface of the collar is affixed to the perimeter surface of the anvil.

15. A die as claimed in claim 14 wherein the anvil further comprises an end portion having a second perimeter surface having a smaller diameter than the first perimeter surface disposed concentrically with the first perimeter surface and the centre axis, a step surface extending between the first and second perimeter surfaces and the collar has a lower surface which contacts the step surface.

lo

16. A die as claimed in claim 14 or in claim 15 wherein the end portion further comprises a nub extending from the end portion.

17. A die as claimed in any of claim 14 further comprising a flange portion disposed around the perimeter surface of the anvil which is spaced away from the end surface.

18. A die as claimed in claim 14 wherein the collar further comprises a first end surface, a second end surface disposed opposite the first end surface and a groove extending from the second end surface toward the first surface and spaced apart from the perimeter surface of the anvil to receive a solder material for joining together the anvil and the collar.

19. A die as claimed in any of claims 14 to 18 wherein a portion of the end surface disposed adjacent to the inner surface is generally perpendicular to the inner surface.

20. A system for driving a self pierce rivet into a plurality of workplaces comprising a fixture having an aperture, a first die, a second die and an actuator disposed proximate the fixture, the actuator being configured to move the second die in an axial direction between a retracted position and an advanced position to axially drive the self - 16 pierce rivet wherein the first die is a die as claimed in any of claims 1 to 19.

21. A system as claimed in claim 20 wherein the first die comprises an anvil having a first portion disposed in the aperture, a flange portion extending around a perimeter of the first portion having a lower surface that contacts the fixture and an upper surface disposed opposite the first surface, a second portion coaxially disposed with the first lo portion and extending away from the upper surface of the flange portion and a collar affixed to the anvil, the collar having an inner surface that contacts a perimeter of the second portion and a lower surface that contacts the upper surface of the flange portion.

22. A die substantially as described herein with reference to the accompanying drawing.

23. A system substantially as described herein with reference to the accompanying drawing.