DE102015102174A1 - Punch rivet and method of making a riveted joint - Google Patents

Abstract

Punch rivet (10) for connecting two workpieces, with a rivet head (14) and an adjoining rivet shank (16), wherein the rivet shank (16) is formed as a hollow shank, and wherein the punch rivet (10) consists at least partially of a duplex steel.

Description

The present invention relates to a punch rivet for connecting two workpieces, with a rivet head and an adjoining rivet shank, wherein the rivet shank is designed as a hollow shank. Such punch rivets are also referred to as semi-hollow punch rivets.

Examples of such punch rivets are from the DE 10 2005 052 360 B4 as well as from the DE 10 2009 039 936 A1 known.

The invention further relates to a method for producing a stamped-riveted joint of at least a first and a second workpiece, in which the stamped rivet according to the invention is used.

Punch rivets is a reshaping joining process and can be carried out by means of so-called solid rivets and / or so-called semi-tubular rivets or semi-hollow punch rivets. In the present case, it is about the punch riveting with semi-hollow punch rivets, which are formed with a hollow shaft. This method is characterized in that the semi-hollow punch rivet is driven into an arrangement of two workpieces, a first and a second workpiece, wherein the first (upper workpiece) is pierced (punched) by the hollow shaft of the semi-hollow punch rivet. A die, on which the second (lower) workpiece rests, is designed so that the hollow shaft is subsequently spread radially and is driven radially into the second or lower workpiece, so that an undercut is formed. In this case, the second or lower workpiece is usually not severed, so that the side facing the die of the workpiece remains closed and therefore is less susceptible to rust. This punch riveting method with Halbhohlstanzniet has been used for several years in the automotive industry increasingly. The punch riveting method is particularly suitable for joining workpieces of different materials (for example steel and aluminum or fiber composite material and metal). Since there is a trend towards a combination of different materials adapted to the respective application, in particular in body construction, the stamped riveting method is in this case a preferred joining method compared to welding methods.

It goes without saying that at least the material of the second or lower die-side workpiece should be readily cold-workable and should have the most homogeneous possible material properties.

Another trend in the automotive industry is the increased use of fiber composite materials, such as fiber reinforced plastic (FRP), carbon fiber reinforced plastic (CFRP), carbon fiber reinforced plastic (CFRP) and glass fiber reinforced plastic (GRP). The use of such materials also makes completely new demands on the punch riveting or on the technical properties of a punch rivet. Although it is already known to rivet FRP materials, however, the rivets usually fail in the corrosion tests. The previous rivets or in particular the previously known semi-hollow punch rivets were not developed for FRP materials and are usually made of pure austenitic steels. Although semi-hollow punching rivets made of pure austenitic steels have the necessary corrosion resistance, they do not have the necessary hardness, since they can not be hardened. With such punch rivets the punching of FRP materials is not possible. Therefore, a special approach is needed to open these fiber composites for punch riveting.

Accordingly, it is an object of the present invention to provide an improved semi-hollow punch rivet and an improved method for producing a stamped rivet connection, by means of which fiber composites can be added reliably.

The above object is achieved in a punch rivet of the type mentioned in that the punch rivet consists at least partially of a duplex steel.

• – Bereitstellen eines erfindungsgemäßen Stanzniets, und
• – Durchführen eines Stanznietvorganges, wobei wenigstens das erste Werkstück zumindest teilweise durchstanzt wird.

Furthermore, the above object is achieved by a method for producing a punched-riveted joint of at least a first and a second workpiece, with the steps:

• - Providing a punch rivet according to the invention, and
• - Performing a stamped riveting process, wherein at least the first workpiece is at least partially punched.

By using duplex steels in semi-hollow rivets, it is possible to add FRP sheets by means of punch rivets and to ensure the desired corrosion resistance. Duplex steels are characterized not only by their special corrosion resistance, but also by their extremely high strength. Compared to stainless chromium steels they have a higher ductility.

A duplex steel is a steel which has a two-phase structure consisting of a ferrite matrix with austenite islands embedded in it.

In tests, which have already been carried out by the applicant, half-hollow punch rivets made of duplex steel have proved to be surprisingly advantageous, although a use of Duplex steel for semi-hollow punching rivets is by no means considered obvious. On the contrary, because of the special punch riveting method described above, half-punched rivets must have good deformability because the semi-hollow rivet is subjected to cold working during the joining process. Duplex steels, however, already have a Vickers hardness of over 300 HV when clamped. In addition, duplex steels solidify very strongly during cold forming, so that they do not actually offer themselves for cold forming processes with high degrees of deformation, since the forces for forming become too high. However, the Applicant was able to show by simulations that duplex steels can also be used for semi-hollow punch rivets by a suitably coordinated cold forming process and this is even advantageous.

Preferably, a majority of the punch rivet is duplex steel. At least a part of the rivet head and / or at least a part of the rivet shank is preferably made of duplex steel. According to a further embodiment of the present invention, the punch rivet consists entirely of duplex steel.

According to the invention, it is particularly preferred that the duplex steel has 40 to 60% austenitic portions. As a result, the formability of the punch rivet can be positively influenced.

According to one embodiment, the duplex steel has fractions of chromium, nickel, molybdenum and nitrogen. As particularly advantageous, the use of X2CrNiMoN22-5-3 has been found. This duplex steel is highly corrosion resistant, has a very high strength, and yet is relatively cold-workable when used in a semi-hollow rivet.

According to a further embodiment, the rivet shank embodied as a hollow shank has a shank inner diameter and a shank outer diameter, wherein the ratio of shank inner diameter to shank outer diameter is smaller than 0.6, in particular smaller than 0.52.

When forming a ratio of shaft inner diameter to shaft outer diameter of less than 0.6, it can be achieved that the radial shaft thickness is relatively large. As a result, such a punch rivet achieves high rigidity during a punch riveting process and is suitable for penetrating high-strength materials, for example fiber composite materials. On the other hand, however, it still has a sufficient deformation ability to form an undercut and also a still sufficiently large internal shaft volume (borehole volume) to accommodate the stamping. In addition, a sufficiently high residual soil thickness can be achieved. Remaining floor thickness is understood as the axial thickness of the material of the punch-side workpiece, specifically where the axial height of this workpiece is the lowest, which is usually in the axial projection approximately in the region of the shaft end face between the shaft inner diameter and shaft outer diameter.

According to a further preferred embodiment, the rivet head has a shoulder which extends around the longitudinal axis of the punch rivet and projects radially over the rivet shank, a first joining material being arranged on a shoulder underside adjoining the rivet shank.

The use of such a joining material on the shoulder underside is particularly advantageous in the case of punched riveting of CFRP structures. With CFRP structures, the risk of delamination arises during punch riveting. Delamination refers to the detachment of layers in material composites, for example in fiber composites or the detachment of a corrosion protection layer on a steel part.

As a joining material, adhesive is preferably used, wherein a variety of different adhesives can be used here. The terminology "first joining material" is used in the present application merely to distinguish it from a "second joining material". However, this terminology does not imply a number or an order. Furthermore, it should be noted that in the present application between the first and second joining material is distinguished mainly with respect to their different arrangement on the punch rivet. However, both joining materials may be the same type of joining material, ie, for example, the same adhesive.

The first joining material is preferably arranged in a recess running around the longitudinal axis of the punch rivet, which recess is introduced into the shoulder underside. Alternatively or in combination with this embodiment, the rivet head has, within the rivet shank designed as a hollow shank, a head underside on which a second joining material is arranged. As already mentioned, this can also be a type of adhesive.

By means of the two joining materials mentioned above and their special type of arrangement on the shoulder underside and / or the head underside of the rivet head, the joining material is pressed between the punch rivet and the fibers of the CFRP structure during the joining process of CFRP materials. This bonds the fibers and seals the joints.

With regard to the last-mentioned embodiments in which one or more joining materials are arranged on the punch rivet, it may be particularly advantageous for the rivet shank to be rotationally symmetrical about a longitudinal axis of the punch rivet and to have a plurality of slots running parallel to the longitudinal axis which sever the rivet shank in the radial direction , As a result, an advantageous spreading of the punched rivet is achieved, which can be particularly advantageous in the case of punched riveting of CFRP materials. The joining material can thereby seal the leaks, which can occur during the spreading of the punch rivet.

When using joining material, which is arranged on the shoulder underside and / or the head underside of the rivet head, it may also be advantageous for the rivet shank to have a plurality of recesses extending parallel to the longitudinal axis, which are introduced into a shank outer surface and / or a shank inner surface , This is then not the rivet shank radially completely severing slots, but in this from the outside or from the inside introduced grooves or groove-shaped recesses. These also have an advantageous effect on the deformation of the punch rivet, but in contrast to the slots described above, prevent any undesired, excessive deformation.

According to a further embodiment of the present invention, the surface or at least a part of the surface of the punch rivet is surface hardened.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the particular combination given, but also in other combinations or in isolation, without departing from the scope of the present invention.

Embodiments of the invention are illustrated in the drawings and are explained in more detail in the following description. Show it:

1 a first embodiment of a punch rivet according to the invention in a plan view ( 1A ) and a longitudinal sectional view ( 1B );

2 a second embodiment of the punch rivet according to the invention in a plan view ( 2A ) and a longitudinal sectional view ( 2 B );

3 a third embodiment of the punch rivet according to the invention in a plan view ( 3A ) and a longitudinal sectional view ( 3B ); and

4 a fourth embodiment of the punch rivet according to the invention in a plan view ( 4A ) and a longitudinal sectional view ( 4B ).

In the 1A and 1B is a first embodiment of a punch rivet according to the invention in a plan view (see 1A ) and in a longitudinal sectional view (see 1B ). The punch rivet is in total with the reference numeral 10 designated.

The punch rivet 10 is preferably rotationally symmetric about a longitudinal axis 12 formed and has a rivet head 14 as well as a rivet shaft 16 on, which is at the bottom of the rivet head 14 followed. The rivet head 14 has a top 18 , which is preferably designed as a flat, circular surface.

Furthermore, the rivet head 14 a cylindrical head outer surface 20 on which transverse to the top of the head 18 runs. Within the riveting stock 16 points the rivet head 14 a head base 22 on, which is formed in the present case truncated cone or rounded tapered. The rivet shaft 16 in other words has a central hole 24 on, which is designed as a blind hole. The face of this blind hole 24 , which the head top 18 is present, is present as the head bottom 22 designated.

From the top of the head 22 to distinguish is another side of the rivet head 14 , which also from the top of the head 18 turned away. It becomes as shoulder lower side 26 designated. The rivet head 14 preferably has one about the longitudinal axis 12 circumferential shoulder 28 , which radially over the rivet shank 16 protrudes. The shoulder bottom 26 adjoins the top of the head towards the top 20 at and down to the shaft outer surface 30 , The shoulder bottom 26 is according to the in 1 shown first embodiment in a substantially conical surface 32 and a phase that follows downwards 34 divided, which is the transition to the shaft outer surface 30 forms.

The rivet shaft 16 is divided into a shaft section 36 , the rivet head 14 connects, and a cutting section 38 , The shaft section 36 is formed substantially hollow cylindrical. On the inside, this results in a cylindrical surface, which in the present case as a shaft inner surface 40 referred to as. The cutting section 38 is comparatively tapered towards the bottom, as the punched rivet 10 with this shaft end face 42 is punched during the riveting process in the workpieces to be joined.

The punch rivet 10 according to the in 1A and 1B shown first embodiment of the invention is preferably made entirely of duplex steel. This duplex steel preferably has 40 to 60% austenitic components. Particularly preferred is the use of X2CrNiMoN22-5-3.

As ratio between shank inner diameter D2 and shank outer diameter D1, a ratio of smaller than 0.6 has been found to be advantageous. Particularly advantageous is a ratio of less than 0.52.

The in the 2A and 2 B illustrated second embodiment of the present invention differs from the first embodiment substantially in that the rivet shank 16 several, parallel to the longitudinal or symmetry axis 12 running slots 44 which has the rivet shank 16 cut in the radial direction. These slots 44 preferably extend to the lower end of the rivet shank 16 , so to the shaft front side 42 , They preferably end in the region of the underside of the rivet head 14 ,

By slitting the rivet shank 16 becomes an advantageous spreading of the punch rivet 10 achieved during the punch riveting process. This is particularly advantageous in the case of stamped riveting of fiber composite materials, since it increases the strength and durability of the riveted joint.

Another difference compared to the first embodiment is that when in the 2A and 2 B illustrated second embodiment on the head bottom 22 a first joining material 46 is arranged. At the first joining material 46 it is preferably adhesive. In particular, it bonds the individual fibers to one another during punch riveting of CFRP structures and thus seals the joint sufficiently well, which in turn prevents delamination of the CFRP structures.

In the in the 3A and 3B shown third embodiment is the head top 18 at the transition to the head outer surface 20 rounded. In addition, the shoulder bottom 26 designed as a planar annular surface, that is not more than conical surface or phase, as is the case in the first two embodiments.

The fundamental difference from the first two embodiments, however, in the third embodiment is that on the shoulder bottom 26 one, around the longitudinal axis 12 circumferential recess 48 is provided, in which a joining material 50 is arranged. This circumferential recess 48 does not have to, as in 3B shown, have an oval cross-section, but in principle may also have a triangular, rectangular, square, polygonal or round cross-section. At the joining material 50 it is preferably also adhesive.

The adhesive bags 48 . 50 under the rivet head 14 especially prevent delamination during the punch riveting of CFRP structures. From the adhesive bags 48 . 50 the glue is between the punch rivet 10 and pressed the fibers of the CFRP structure. As a result, an improved sealing of the joint is again achieved.

In contrast to the according to the second embodiment of the punch rivet 10 provided slots 44 (please refer 2A and 2 B ) shows the punch rivet 10 according to the third embodiment several, parallel to the longitudinal axis 12 extending, groove-shaped recesses 52 on, which in the shaft outer surface 30 are introduced. These also improve the deformability or Aufspreizbarkeit of Halbhohlstanzniets 10 ,

Although this is not explicitly shown in the present case, it should be noted that such, groove-shaped recesses 52 basically also in the inner surface of the shaft 40 can be introduced.

In the in the 4A and 4B illustrated fourth embodiment of the punch rivet according to the invention 10 it is largely a combination of the second and third embodiments. After that, the rivet shaft 16 again several, parallel to the longitudinal axis 12 running slots 44 on, the rivet 16 cut radially. In addition, the punch rivet 10 both joining material 46 on which at the head bottom 22 attached, as well as joining material 50 which are in the on the lower shoulder 26 attached recess 48 is introduced.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102005052360 B4 [0002]
• DE 102009039936 A1 [0002]

Claims (15)

Punch rivet ( 10 ) for connecting two workpieces, with a rivet head ( 14 ) and an adjoining rivet ( 16 ), whereby the rivet shank ( 16 ) is formed as a hollow shaft, characterized in that the punched rivet ( 10 ) consists at least partially of a duplex steel. Punch rivet according to claim 1, characterized in that at least a part of the rivet head ( 14 ) and / or at least part of the riveting body ( 16 ) consists of duplex steel. Punch rivet according to claim 1, characterized in that the majority of the punch rivet ( 10 ) consists of duplex steel. A punch rivet according to any one of claims 1 to 3, wherein the duplex steel has 40-60% austenitic portions. Punch rivet according to one of claims 1 to 4, wherein the duplex steel has fractions of chromium, nickel, molybdenum and nitrogen. A punch rivet according to any one of claims 1 to 5, wherein the duplex steel is X 2 CrNiMoN 22-5-3. Punch rivet according to one of claims 1 to 6, wherein the rivet shaft formed as a hollow shaft ( 16 ) has a shaft inner diameter (D2) and a shaft outer diameter (D1), and wherein the ratio of shaft inner diameter (D2) to shaft outer diameter (D1) is less than 0.6, in particular less than 0.52. Punch rivet according to one of claims 1 to 7, wherein the rivet head ( 14 ) a circumferential shoulder ( 28 ), which over the rivet shank ( 16 ) projects radially, wherein at one of the rivet shank ( 16 ) adjacent shoulder base ( 26 ) a first joining material ( 50 ) is arranged. A punch rivet according to claim 8, wherein the first joining material ( 50 ) in a circumferential recess ( 48 ), which are in the shoulder bottom side ( 26 ) is introduced. Punch rivet according to one of claims 1 to 9, wherein the rivet head ( 14 ) within the rivet shank designed as a hollow shank ( 16 ) a head bottom ( 22 ), at which a second joining material ( 46 ) is arranged. Punch rivet according to one of claims 1 to 10, wherein the rivet shank ( 16 ) rotationally symmetric to a longitudinal axis ( 12 ) of the punch rivet ( 10 ) and several, parallel to the longitudinal axis ( 12 ) running slots ( 44 ), which the riveting ( 16 ) in the radial direction. Punch rivet according to one of claims 1 to 11, wherein the rivet shank ( 16 ) rotationally symmetric to a longitudinal axis ( 12 ) of the punch rivet ( 10 ) and several, parallel to the longitudinal axis ( 12 ) extending recesses ( 52 ), which in a shaft outer surface ( 30 ) and / or a shaft inner surface ( 40 ) are introduced. Punch rivet according to one of claims 1 to 12, wherein a surface of the punch rivet ( 10 ) is surface hardened. A method of producing a butt joint of at least a first and a second workpiece, comprising the steps of: providing a punch rivet ( 10 ) according to one of claims 1 to 13, - performing a stamped riveting process, wherein at least the first workpiece is at least partially punched. The method of claim 14, wherein the first workpiece comprises a fiber composite.

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