GB2428077A

GB2428077A - Self piercing rivet

Info

Publication number: GB2428077A
Application number: GB0613363A
Authority: GB
Inventors: Torsten Draht; Gerson Meschut
Original assignee: Boellhoff Verbindungstechnik GmbH
Current assignee: Boellhoff Verbindungstechnik GmbH
Priority date: 2005-07-07
Filing date: 2006-07-05
Publication date: 2007-01-17
Anticipated expiration: 2026-07-05
Also published as: GB2428077B; DE102005031916A1; GB0613363D0; DE102005031916B4

Abstract

A self piercing rivet (16) has a head (18) and a shank (20). The periphery of the rivet (16) is configured to diverge toward the head (18) in at least one area outside of the transition between the shank (20) and the head (18).

Description

1 2428077 Joining member for mechanical jointing The present invention

relates to ajoining member for mechanical jointing as well as a method for producing a joint between at least two plate-shaped joining portions. Joining members for mechanical jointing are in particular semi-hollow and solid self-piercing rivets, blind rivets, nails and screws.

Such joining members are used in a wide variety of industrial fields and usually consist of a head and a shank which is at least partly of cylindrical configuration. One difficulty which can occur when producing the corresponding joinings is that the cylindrical area of the joining member has a certain play in the hole of the plate-shaped joining portion. This can be of great disadvantage, in particular in the case of dynamically high-stressed joints such as those in e.g. automotive engineering.

The above-cited joining methods are frequently combined with adhesives resulting in a hybrid"bonding-adhesive" joining technique. This hybrid joining technique not infrequently suffers from the disadvantagethat the joint integrity of the bond is diminished due to flaws in the adhesive layer, in particular imperfect cohesive joint filling. In practice, this has necessitated various measures such as post-sealing the joints which, of course, requires the corresponding expenditure.

The present invention provides for avoiding such disadvantages. The object of the invention is in particular to provide a joining member for mechanical jointing as well as a method of producing a joint between at least two plate-shaped joining portions which does not allow any play between the joining member and the plate- shaped joining portions and in the case of bond-adhesive joinings, to avoid or at least minimize any diminishing of the joint integrity between the plate-shaped joining portions due to imperfect cohesive joint filling.

This object is achieved by ajoining member in accordance with claim 1.

In a joining member configured according to the invention, the peripheral surface of the shank is configured to diverge, i.e. widen, toward the rivet head at least over a given area. That means that the outer diameter of the shank enlarges toward the head in the associated area. The diverging area can extend over the entire length of the shank or also only over a portion of the length, whereby the diverging area can extend conically or be cambered.

The diverging area of the joining member ensures that the shank is upset during the joining procedure due to its frictional abutting against the material of the plate-shaped joining portion. This increases the compressive strength in both the joining member as well as the material of the plate-shaped joining portion which is of considerable advantage, in particular in the case of dynamically high-stressed joints such as those in e.g. automotive engineering.

A further advantage to joining members configured according to the invention consists of being able to lend a higher stability to their critical region. It is not infrequently the case in the prior art for self-piercing rivets of high-sirength materials to break or shear off in a middle region, since self-piercing rivets of rigid materials exhibit a particularly high rebound effect. The diverging form of the shank allows the shank of the joining member to be configured to be particularly stable in this critical region.

Particularly advantageous is using the joining member configured according to the invention in conjunction with the hybrid "bonding- adhesive" joining technique, and that for the following reasons.

As stated above, air pockets and channels can develop in the adhesive layer when producing the bond-adhesive joinings known in the Part. The inveitor recognized that in the case of e.g. self-piercing rivet joinings, after punching through the riveting die-side of the joining portion (sheet metal), same rebounds such that a cavity develops between the two joining portions (sheet metal). This cavity fills with air via the die clearance. Upon subsequent finish-setting of the self-piercing rivet, the two sheet metals are press-fit together and the pressurized air within expands into the adhesive layer. If a hot-setting adhesive is used, the air trapped in the adhesive layer expands further in the curing oven such that air shafts to the surrounding environment are formed through which corrosive media can compromise the self-piercing rivet.

It is now shown that using a joining member which has a shank of diverging configuration can prevent air pockets and channels in the adhesive layer. The inventor is of the assumption that designing the outer surface of the shank as provided according to the invention leads to preventing or at least reducing the rebounding of the riveting die- side of the sheet metal and thus the drawing in of air. In any event, using joining members having shanks configured to be divergent according to the invention results in no diminishing of the joint integrity to the self-piercing rivet bond due to air pockets or channels.

A method for manufacturing a joint between at least two plate-shaped joining members is defined in claim Ii. This method makes use of a joining member as described above in order to produce increased compressive strength in the joining member and in the joining region of the plate-shaped joining portion. In a further design of the invention, this joining method is used in conjunction with adhesives, as has already been described above.

Further advantageous designs and developments of the invention are defined in the depending claims.

The drawings will be used to describe exemplary embodiments of the invention in greater detail. Shown is: Fig. I is a schematic cross-section through a self-piercing rivet adhesive-

bonded joint in accordance with the prior art;

Fig. 2 is a view colTesponding to Fig. I of a self-piercing rivet adhesive- bonded joint when using a self-piercing rivet configured according to the invention; Fig. 3 is a side view of the self-piercing rivet in Fig. 2; Figs. 4 to 7 are modified embodiments of the self-piercing rivet.

Fig. 1 is a highly schematized view of a self-piercing rivet adhesivebonded joint according to the prior art which uses a conventional selfpiercing rivet 2 during the joining process. The self-piercing rivet 2 has a conventional rivet head 4 and a rivet shank 6 with a cylindrical outer surface. The self-piercing rivet 2 serves to join Iwo plate-shaped joining portions 8, 10 (sheet metal), in the abutting region of which an adhesive layer 9 is provided. The setting tool for setting the self- piercing rivet 2 conventionally comprises a counter die 12 as well as a blank holder 14 to exert a blank holding force. Since such setting tools and their functioning are well-known, they will not be described any further here.

As is shown in Fig. I in exaggerated manner, the joining portion S facing the setting punch (not shown) rebounds after being punched by selfpiercing rivet 2, whereby a gap S develops between the two joining portions 8 and 10. Air can encroach into the area of the adhesive layer 9 through gap S. When the self-piercing rivet 2 is set and the rivet head 4 thereby pressed into the riveting die-side joining portion 8, both joining portions 8, 10 are force-fit together. The enclosed and pressurized air then expands into the adhesive layer 9. If a hot-setting adhesive is used, the air trapped in the adhesive layer expands further in the curing oven and air shafts form to the surrounding environment through which corrosive media can reach the rivet.

Figs. 2 and 3 show an exemplary embodiment of a self-piercing rivet 16 configured according to the invention in which the formation of a gap S, and thus air pockets and channels in the adhesive layer 9, can be avoided or at least minimized.

As shown, the peripheral surface of rivet shank 20 in the area 22 is configured to diverge slightly (widen) toward the rivet head 18. To put it more precisely, the peripheral surface has the shape of a cone having the tapered angle a.

When the setting punch (not shown) drives the self-piercing rivet 16 with the tapered peripheral surface into the joining portions 8, 10 (Fig. 2), the rivet shank 20 exerts a downward force on the riveting die-side joining portion 8 due to its tapering, which prevents a rebounding of the riveting die-side joining portion 8. The result of which is that joining portions 8, 10 remain abutted in the joint zone such that no gap S develops. The formation of air pockets and shafts as seen in the prior art (Fig. I) and the thereby resultant diminishing ofjoint integrity is thus prevented.

The optimum tapered angle a is contingent upon different factors such as, for example, the type and material of the joining members, the material of the joining portions and the like. The tapered angle a is in any case greater than zero and also greater than the manufacturing-related tapered angle and is in the range of e.g. 0.2 to 30 , preferably 0.5 to 20 , and most particularly preferred at 1 to 10 .

While the self-piercing rivet 16 is preferably a semi-hollow rivet, it can also be a solid rivet. The rivet head 18 can be of arbitrary configuration, for example a countersunk head, a dome head, a truss head, a large flange head or the like. All usual materials are applicable as the material for the self-piercing rivet 16. While steel is used most frequently, other materials such as aluminum alloys, high-grade steel, titanium and the like are also just as applicable.

The self-piercing rivet can otherwise be provided with studs, necks or other similar appendages, as is fundamentally known from the prior art.

All usual materials are likewise applicable as the material for the joining portions 8 and 10. The same type or also different materials can be used for the joining portions 8 and 10 in all other respects as well.

All the usual adhesives can likewise be used as the adhesive for the adhesive layer 9 such as, for example, a cold-setting two-component adhesive or a hot-setting one-component adhesive.

In the exemplary embodiment shown in Figs. 2 and 3, the entire area 22 of the peripheral surface of the rivet shank 20 is configured to be divergent, respectively conical. The diverging area can, however, also have a form deviating from that of a cone and does not need to extend over the entire axial length of the shank, as the embodiments of Figs. 4 to 7 show.

In the exemplary embodiment of Fig. 4, the self-piercing rivet 16a has a shank 20a in which the diverging area 22a is of cambered or arcuated configuration and abuts the base of the shank 20a. The diverging area 22a gives way to a cylindrical area 24a which abuts the transition between the shank 20a and the head 18.

The cambered diverging area 22a could, however, also run the entire length of the shank 20a. The diverging area 22a cambers convexly outwardly in Fig. 4; it could, however, also be of concave configuration.

The embodiment of Fig. 4 can be manufactured relatively simply. In addition, this form to the self-piercing rivet allows the self-piercing rivet to penetrate the plate-shaped joining portion relatively easily without any abrupt changes in the riveting force applied.

In the embodiment of Fig. 5, while the diverging area 22b of the selfpiercing rivet 1 6b is of conical configuration, it is positioned between a cylindrical area 24b abutting the rivet base and the transition between the shank and the head.

The axial length of the cylindrical area 24b is preferably smaller or equal to the thickness of the riveting die-side joining portion 8. What this hereby achieves is that the rivet shank 20b force-fit frictionally abuts against the riveting die-side joining portion S after punching through same in order to prevent the joining portion 8 from rebounding. As is the case in the preceding exemplary embodiment, this thereby yields the advantage that punching through the riveting die-side joining portion 8, and in particular the spreading of the self-piercing rivet 16a upon the counter die-side joining portion 10 deforming, will facilitate the forming of the closing head.

In the exemplary embodiment of Fig. 6, the diverging area 22c of the selfpiercing rivet 16c is of conical configuration and abuts the rivet base. However, it only extends over a portion of the length of the rivet shank 20c. A cylindrical area 24c is provided between the diverging area 22c and the transition. This embodiment as well facilitates self-piercing rivet penetration into the plate-shaped joining portions.

Fig. 7 shows a further modified embodiment of a self-piercing rivet 16d, in which the diverging area 22d is positioned between a cylindrical area 24d abutting the s rivet base and a cylindrical area 25d abutting the transition between shank and head.

As mentioned above, the self-piercing rivets as shown can be semi-hollow or solid self-piercing rivets. In addition, the depicted and described shank geometries can also be used with other joining members for mechanical jointing such as e.g. blind rivets, nails, screws and the like since essentially the same advantages are occasioned with all these other joining members.

The joining method with the self-piercing rivets of Figs. 2 to 7 as based on hybrid "self-piercing rivet-adhesive" technology has already been described. As indicated at the outset, joining members having the depicted and described shank geometries can, however, also be advantageously used in corresponding joining methods without adhesives. Thus, Fig. 2 clearly shows that the self-piercing rivet 16 frictionally abuts against the riveting die-side joining portion 8 during the joining process. This thereby upsets the self-piercing rivet 16 somewhat, whereby a corresponding compressive strength is produced in both the self- piercing rivet 16 as well as in the abutting material of the joining portions 8, 10. Thus, no play or gap can develop between the peripheral surface 22 of the self-piercing rivet 16 and the joining portions 8, 10. This effect is particularly advantageous in the case of dynamically high- stressed joints such as those present in, for example, automotive engineering.

In all the embodiments described, the advantageous effect of the described shank geometry is based on a hole being formed in the riveting die-side joining portion which has a smaller diameter than the upper part of the shank, achieving a frictional fit between the shank and the joining portions and preventing a rebounding of the riveting die-side joining portion.

Claims

Claims 1. A semi-hollow self-piercing rivet having a head and a shank, its

peripheral surface configured to diverge toward the head in at least one given area outside of the transition between the shank and the head.
2. A semi-hollow self-piercing rivet according to claim 1, wherein the diverging area of the peripheral surface extends the entire length of the shank (20) to the transition into the head.
3. A semi-hollow self-piercing rivet according to claim 1, wherein the to diverging area of the peripheral surface extends only over a portion of the shank length.
4. A semi-hollow self-piercing rivet according to claim 3, wherein the diverging area abuts the base of the shank.
5. A semi-hollow self-piercing rivet according to claim 3, wherein the diverging area abuts the transition between the shank and the head.
6. A semi-hollow self-piercing rivet according to claim 3, wherein the diverging area is spaced from the base as well as from the transition between the shank and the head.
7. A semi-hollow self-piercing rivet according to any one of claims 1 to 6, wherein the diverging area extends conically.
8. A semi-hollow self-piercing rivet according to claim 7, wherein the tapered angle of the said diverging area amounts to 0.5 to 20 , more preferably 1 to 100.
9. A semi-hollow self-piercing rivet according to any one of claims I to 6, wherein the diverging area is cambered.
10. A semi-hollow self-piercing rivet according to any one of the preceding claims, wherein the peripheral surface of the shank is configured without recesses or elevations.
11. A method for producing ajoint between at least two plate-shaped joining portions in which a semi-hollow self-piercing rivet according to any one of the preceding claims is driven into the joining portions such that the diverging area of the shank of the semi-hollow self-piercing rivet exerts a frictional force on the riveting die-side joining portion to prevent a rebounding of the said riveting die-side joining portion.
12. A method according to claim 11, wherein the semi-hollow self-piercing rivet is driven into the joining portions so as to produce increased compressive strength in the semi-hollow self-piercing rivet and in the joint region of the plate- shaped joining portions.
13. A method according to claim 11 or 12, wherein an adhesive layer is provided between the plate-shaped joining portions at least in the joint region and the joining portions are then joined using a semi-hollow selfpiercing rivet according to any of claims I to 10.
14. A method according to any one of claims 11 to 13, wherein the plateshaped joining portions are pressed against one another during the joining process with no or only slight blank holding force.
15. A semi-hollow, self-piercing rivet substantially as described herein with reference to and as shown in the accompanying Figures.
16. A method for producing a joint substantially as described herein with reference to and as shown in the accompanying Figures.