Punch rivet

Abstract

Punch rivet (6) for joining an upper molded part and a lower molded part (4), with a rivet head (14) and with at least one rivet shank (16) having a punched section (20), characterized in that the rivet shank (16) has at least one deformation section (24) for widening a punched hole at least partially, which is arranged behind the punched section (20) when viewed in the punching direction and has a larger outer diameter (d3) than the punched section (20), wherein at least one deformation section (24) is arranged behind a locking section (22) with a diameter (d2) when viewed in the punching direction, wherein the outer diameter (d3) of at least one deformation section (24) is constant, wherein the outer diameter d3 of the deformation section (24) is larger than the outer diameter d1 of the punching section (20) such that d3 > d1 > d2, wherein the locking section (22) serves to receive material of the lower molded part (4) and thus to lock the joining connection, wherein in a region of a surface (12) of the lower molded part (4) the punch rivet (6) further has an embossing ring (13) which can be inserted by a cutting embossing matrix during punching.

Description

[0001] The invention relates to a punch rivet.

[0002] A well-known method for joining molded parts is so-called self-piercing riveting with solid rivets. Self-piercing riveting is frequently used in automotive manufacturing and, more generally, in the sheet metal processing industry for thin sheets of various metallic materials. Suitable materials include, for example, light metals such as aluminum and magnesium, or ferrous metals such as steel. However, self-piercing riveting also allows the joining of a metallic molded part to a plastic-based molded part, thus enabling the production of hybrid joints.

[0003] Self-piercing riveting with solid rivets is based on a combined piercing and pressure forming of the formed parts, in which a rigid solid rivet creates a force and positive point connection. To create the connection, the formed parts are fixed to a die using a hold-down device, as shown, for example, in patent application DE 10 2009 044 888 A1 or in patent US 6,244,808 B1. The self-piercing rivet is then driven through the formed parts using a riveting punch, thus piercing them. Due to the contour of the die and the compressive force applied by the riveting punch and hold-down device, the material of the die-side formed part flows into a circumferential shank groove of the self-piercing rivet. The material flow is counter to or perpendicular to the punching direction. At the same time, the self-piercing rivet head is pressed against the punch-side formed part or, if it is a countersunk head, is impressed into the punch-side formed part.The main strength component of the connection is the positive locking, which results from the undercut on the self-piercing rivet head and the filling of the rivet's shank groove. A disadvantage of self-piercing rivet connections is that they have relatively low fatigue strength compared to bolted connections.

[0004] DE 102 59 370 B3 describes a punch rivet for joining sheets of metal together, with a shaft, with several circumferential ribs formed one above the other on the shaft, with a shaft end for punching through the sheets of metal to be joined together and with a head.

[0005] DE 102 59 369 B3 describes a device for setting a punch rivet in sheet metal, with an upper sleeve in which a punch is displaceable, with a fixed lower sleeve which is spaced from the upper sleeve.

[0006] DE 10 2008 014 840 A1 discloses a blind fastener that is constructed similarly to a screw. The fastener has a head located at one end of the shaft and a contact surface facing the shaft for engagement with the object to be fastened.

[0007] DE 1 962 383 A relates to an arrangement for fastening parts in a preferably plate-shaped workpiece by means of bolts, pins or similar elements which are firmly connected to the workpiece and which then serve as holders, spacers, etc. for the part to be fastened to the workpiece.

[0008] The object of the invention is to create a punch rivet which eliminates the aforementioned disadvantages and leads to an improved vibration stress of a joint.

[0009] This problem is solved by a punch rivet having the features of patent claim 1.

[0010] In a method for joining shaped parts with a punch rivet, at least in sections a punch hole is radially widened when punching the shaped parts.

[0011] According to the invention, during self-piercing riveting, a punched hole is created in the formed parts with a diameter smaller than the diameter of the actual punch rivet shank, so that the punch rivet is pressed directly into the punched hole in a press fit with corresponding cold deformation. The cold deformation or radial expansion causes work hardening in the expanded punched hole area, creating a residual stress state in the vicinity of the punched hole that has a beneficial effect on fatigue strength. After the respective punched hole area has been expanded, a compressive stress remains in it in the circumferential direction, which inhibits the formation and propagation of cracks and leads to increased fatigue strength of the joint.

[0012] Preferably, the radial expansion is limited to punched hole areas that are free from positive locking or crimping with the self-piercing rivet. This prevents the molded part areas to be crimped with the self-piercing rivet from being subjected to unnecessary work hardening, which would unnecessarily complicate crimping with the self-piercing rivet. Crimping can be performed conventionally using, for example, a cutting and stamping die. If the self-piercing rivet is crimped with a locking ring, the punched hole can be radially expanded over its entire axial length and thus hardened by the deformation section.

[0013] A self-piercing rivet according to the invention for joining molded parts, in particular for use in a method according to the invention, has a rivet head and at least one rivet shank having a punching section. According to the invention, the rivet shank has at least one deformation section for at least partially widening a punched hole, which is arranged behind the punching section when viewed in the punching direction and has a larger outer diameter than the punching section.

[0014] The self-piercing rivet automatically cold-forms the areas of the punched hole that are radially expanded by the deformation section. This strengthens these punched hole areas and increases the fatigue strength of the joint. Separate cold-forming, for example, by driving a mandrel into the punched hole to create at least partial plastic deformation of the punched hole, is not necessary.

[0015] According to the invention, the at least one deformation section is arranged behind a locking section of the rivet shank, viewed in the punching direction. This prevents cold deformation of the punched hole by the deformation section in the area where the punch rivet is positioned with its locking section. Thus, the material to be crimped with the punch rivet is unconsolidated and can be easily pressed with the locking section. The material pressed with the locking section is also consolidated during the pressing process, so that the formed parts are consolidated over the entire length of the punched hole.

[0016] In an alternative embodiment, the at least one deformation section extends from the punched section. This results in the punched hole being solidified over its entire axial length by means of the deformation section. Such a self-piercing rivet preferably has a locking section formed by the punched section, onto which a locking ring is crimped.

[0017] In order to be able to solidify the punched hole directly in the area of ​​the rivet head, in both embodiments the at least one deformation section advantageously extends to the rivet head.

[0018] In order to achieve constant work hardening over the entire length of at least one deformation section, this can have a constant outer diameter and thus be cylindrical in shape.

[0019] Alternatively, at least one deformation section can be radially widened towards the rivet head, thus forming a cone. This allows, for example, different levels of work hardening to be achieved. The highest work hardening could therefore be set in the area of ​​the rivet head, and thus in an outer region of the joint, while a lower work hardening could be set in an inner region of the joint, e.g., in the contact area of ​​the two molded parts.

[0020] An exemplary combination of these two geometries provides at least one deformation section, which, viewed in the punching direction, has a conical section and a downstream cylindrical section. Such a combined configuration is advantageous in that it facilitates the radial expansion of the punched hole, since no step or edge is formed at the deformation section in the transition area from the previous shaft section, but rather a gentle increase in the outer diameter can be achieved.

[0021] In one embodiment, the self-piercing rivet is a multi-section rivet with deformation sections between its locking sections. As a result, the deformation sections and the locking sections are arranged virtually alternately in the punching direction, resulting in cold deformation between the locking sections.

[0022] Other advantageous embodiments of the invention are the subject of further dependent claims.

[0023] Preferred embodiments of the invention are explained below with reference to schematic diagrams. The only Fig. Figure 1 shows a joining connection using a punch rivet according to the invention.

[0024] In Fig. 1 shows a joining connection 1 of two formed parts 2, 4 by means of a self-piercing rivet 6 according to the invention. Of course, more than two formed parts 2, 4 can also be joined by means of the self-piercing rivet 6 according to the invention. The formed parts 2, 4 are plate-shaped in the area of ​​the joining connection 1 and each consist of a cold-formable material such as aluminum, magnesium, steel or a corresponding metal alloy. The self-piercing rivet 6 is completely received in a punched hole 8 formed thereby and is flush in the entry area with a surface 10 of the according to the illustration in Fig. 1 upper molded part 2 off. In the exit area of ​​the punched hole 8, i.e. in the area of ​​a surface 12 of the as shown in the illustration in Fig. 1 lower mold part 4, a stamping ring 13 is formed between the punch rivet 6 and the punch hole 8. This stamping ring runs coaxially to the punch hole axis and is inserted during punching by a cutting and stamping die. The punch rivet 6 is preferably made of a metallic material such as steel or a non-metallic material such as an oxide ceramic. It has a head 14 and a shank 16.

[0025] The head 14 is designed as a countersunk head with a conical taper 18, viewed in the punching direction. Alternatively, the head 14 is designed, for example, as a universal head.

[0026] The shaft 16 has a punching section 20, a locking section 22, and, in the illustrated embodiment, a deformation section 24. If the self-piercing rivet 6 is designed as a multi-region rivet, it can have a plurality of deformation sections 24 spaced apart from one another in the punching direction. Viewed in the punching direction, the locking section 22 is arranged behind the punching section 20, and the deformation section 24 is arranged behind the locking section 22. The locking section 22 is thus arranged between the punching section 20 and the deformation section 24, with the punching section 20 being arranged upstream of the locking section 22, viewed in the punching direction, and the deformation section 24 being arranged downstream of the locking section 22.

[0027] The punched section 20 serves to form the punched hole 8. It may, for example, be hardened by local heat treatment and / or have an unnumbered axial cutting edge. It has, in the case of the Fig. In the embodiment shown in Figure 1, the stamped section has a cylindrical shape with a constant outer diameter d1 and transitions directly into the locking section 22. In an alternative embodiment not shown, the stamped section tapers conically towards the head 14.

[0028] The locking section 22 serves to receive material from the lower mold part 4 and thus to lock the joint 1. To receive the crimped material, it has an annular groove 26 with a concave groove wall. It has a minimal outer diameter or core diameter d2 and transitions into the deformation section 24 via an enlarged diameter. Alternatively, a plurality of parallel annular grooves 26 can be provided in the locking section 22. Likewise, the locking section 22 can be provided with an external thread instead of the at least one annular groove 26.

[0029] The deformation section 24 is used for cold forming the upper mold part 2 in the area of ​​the punched hole 8. It has a cylindrical shape with a constant outer diameter d3 and merges directly into the conical taper 14 of the head 8. According to the invention, the outer diameter d3 of the deformation section 24 is greater than the outer diameter d1 of the punched section 20, so that d3 > d1 > d2 applies. A desired degree of press fit, with which the punch rivet 6 is received in the area of ​​its deformation section 24 in the punched hole 8, can be set by an appropriately selected diameter ratio d1:d3. In particular, the diameter ratio d1:d3 depends on the material of the molded part 2 to be hardened in the punched hole area and on the degree of hardening desired. The deformation section 24 preferably has an extension in the punching direction oran axial length which is greater than the axial length of the punching section 20 and that of the locking section 22. Advantageously, the deformation section 24 has an axial length which corresponds approximately to the thickness of the upper mold part 2 in the joining area, so that the upper mold part is solidified over its entire punch hole area when the punch rivet 6 is driven in.

[0030] In a method according to the invention for joining at least two molded parts 2, 4, these are clamped between a hold-down and a cutting die. The self-piercing rivet 6 is then driven through the molded parts 2, 4 by means of a rivet punch, thereby forming a punch hole 12. A so-called punch slug is ejected from the die side. The self-piercing rivet 6 is driven through the molded parts 2, 4 until its head 14 is flush with the surface 10 of the molded part 2. Due to the conical taper 18, the head 14 is thereby pressed into the surface of the upper molded part 2.

[0031] At the same time, the deformation section 24 radially widens the punch hole 8 in the area of ​​the molded part 2 according to the diameter ratio d1 : d3 and thus the molded part 2 is subjected to work hardening in the punch hole area. As shown in the Fig.As shown in Figure 1, in this embodiment the deformation section 24 extends into the punched hole area of ​​the lower molded part 4 after the head 14 has been countersunk, so that this part of the lower molded part 4 is also hardened by the deformation section. At the same time, the lower molded part 4 is crimped in the area of ​​the punched hole 8 with the locking section 22 or with the annular groove 26, thus locking the self-piercing rivet 6 in the punched hole 8.

[0032] The radial expansion is limited to the punched hole areas that are not subject to squeezing or stamping by the cutting and stamping die. In the exemplary embodiment shown here, a radial expansion according to the invention is not even intended in the stamping area, i.e., in the area of ​​the locking section 22, since this would, on the one hand, impede pressing or stamping, and, on the other hand, during the stamping process itself, compressive stresses are introduced into the lower mold part 4 in the punched hole area, which lead to work hardening. The mold parts 2, 4 are work hardened virtually seamlessly over the entire length of the punched hole 8 by combining the deformation section 24 with the stamping in the area of ​​the locking section 22.When the punch rivet 6 according to the invention is designed as a multi-range rivet with a plurality of locking sections 22 and deformation sections 24 arranged alternately one behind the other in the punching direction, a punch hole area is first radially widened and then radially tapered or embossed, so that an embossing of a punch hole area that has already been cold-formed by means of a deformation section 24 can indeed take place.

[0033] The process or setting of the self-piercing rivet 6 according to the invention can be carried out using the same tools as in conventional self-piercing riveting processes. However, the punching die must be adapted to the outer diameter d1 of the punching section 20 so that the punching slug can be freely removed from the die side.

[0034] Disclosed are a method for joining molded parts with a punch rivet, wherein in molded parts to be punched a punched hole is widened radially at least in sections, as well as a punch rivet having a deformation section having a larger outer diameter than a punched section. List of reference symbols 1 joining connection 2 molded part 4 molded part 6 punch rivets 8 punched holes 10 Surface 12 Surface 13 embossed ring 14 heads 16 shaft 18 conical taper 20 punching sections 22 Locking section 24 Deformation section 26 ring groove d1 Outer diameter of punching section d2 Outer diameter of locking section d3 Outer diameter of deformation section

Claims

[1] Punch rivet (6) for joining an upper molded part and a lower molded part (4), with a rivet head (14) and with at least one rivet shank (16) which has a punching section (20), characterized by that the rivet shank (16) has at least one deformation section (24) for at least partially widening a punched hole, which is arranged behind the punched section (20) when viewed in the punching direction and has a larger outer diameter (d3) than the punched section (20), wherein the at least one deformation section (24) is arranged behind a locking section (22) with a diameter (d2) viewed in the punching direction, wherein the outer diameter (d3) of the at least one deformation section (24) is constant, wherein the outer diameter d3 of the deformation section (24) is greater than the outer diameter d1 of the punching section (20), so that d3 > d1 > d2 applies, wherein the locking section (22) serves to receive material of the lower mold part (4) and thus to lock the joint, wherein in a region of a surface (12) of the lower mold part (4) the punch rivet (6) further comprises an embossing ring (13) which can be introduced by a cutting embossing matrix during punching. [2] Punch rivet according to claim 1, wherein the at least one deformation section (24) extends to the rivet head (14). [3] A punch rivet according to claim 1 or 2, wherein the deformation section (24) has a conical section and a downstream cylindrical section when viewed in the punching direction. [4] A punch rivet according to claim 1, wherein the punch rivet is a multi-region rivet with deformation sections (24) arranged between the locking sections (22).

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