METHOD OF ATTACHING A FUNCTIONAL ELEMENT TO A SHEET METAL PART

Abstract

The invention relates to a method of attaching a functional element to a sheet metal part. The functional element has a head part having a ring-shaped support surface and a tubular rivet section that is designed as self-piercing and that extends at the side of the support surface of the head part and away from said head part.

Claims

1. A method of attaching a functional element to a sheet metal part of sheet metal material, wherein the functional element has a head part having a ring-shaped support surface and a tubular shaft part that is formed as self-piercing and that extends at the side of the support surface of the head part and away from the head part, wherein the support surface comprises a ring recess, and wherein the sheet metal part is supported on a perforated die that has a bore whose diameter at least substantially corresponds to the outer diameter of the shaft part or is somewhat larger than it, wherein the bore is surrounded at the side of the perforated die facing the sheet metal part by a ring nose that is raised with respect to a support surface of the perforated die and defines a planar circular ring-shaped end surface, wherein the functional element is pressed onto the sheet metal part supported on the perforated die such that a panel slug is punched out of the sheet metal part by means of the shaft part, wherein an undercut is produced at the shaft part on the attachment of the functional element to the sheet metal part, and a portion of the sheet metal material that surrounds the punched hole generated by the punching out of the panel slug is plastically pressed by means of the circular ring-shaped end face of the ring nose into the ring recess while completely filling it, and is pressed in the region of the transition from the head part into the shaft part radially into the shaft part and is further pressed into the undercut formed during the attachment process.

2. The method in accordance with claim 1, wherein the sheet metal part has a thickness of more than 3 mm.

3. The method in accordance with claim 1, wherein features providing security against rotation are provided that are located in the region of the ring recess and/or in the region of the transition of the ring recess into the shaft part and that selectively divide the ring recess into individual fields distributed about the longitudinal axis of the functional element.

4. The method in accordance with claim 3, wherein a portion of the sheet metal material that surrounds the punched hole generated by the punching out of the panel slug is plastically pressed by means of the circular ring-shaped end face of the ring nose into the individual fields.

5. The method in accordance with claim 3, wherein the features providing security against rotation are security against rotation noses.

6. The method in accordance with claim 1, wherein the undercut formed on the attachment of the functional element to the sheet metal part is present in the form of one of a crease and a constriction.

7. The method in accordance with claim 1, wherein the rivet shaft part is free of undercuts prior to the attachment of the functional element to the sheet metal part.

8. The method in accordance with claim 1, wherein the undercut is formed in the region of the transition from the ring recess to the shaft part.

9. The method in accordance with claim 1, wherein, during the punching of the sheet metal part, the ring nose also presses via its circular ring-shaped end surface toward the lower side of the sheet metal part and there forms a recess that extends around the shaft part in the region of its free end, wherein the material displaced by the formation of the recess is pressed into the undercut formed at the shaft part during the attachment process.

10. The method in accordance with claim 9, wherein the material displaced by the formation of the recess enlarges the undercut formed during the attachment of the functional element to the sheet metal part.

11. The method in accordance with claim 1, wherein the functional element is pressed onto the sheet metal part supported on the perforated die such that a portion of the sheet metal material that surrounds the punched hole produced by the punching out of the panel slug starts to flow plastically as a result of contact with the circular ring-shaped end surface of the ring nose and is plastically pressed into the ring recess while completely filling it.

12. The method in accordance with claim 1, wherein the functional element is pressed onto the sheet metal part supported on the perforated die such that a portion of the sheet metal material that surrounds the punched hole produced by the punching out of the panel slug is pressed radially into the shaft part in the region of the transition from the head part into the shaft part.

13. The method in accordance with claim 1, wherein a perforated die is used as the perforated die whose circular ring-shaped end surface of the ring nose has a radial extent that corresponds to approximately half the thickness of the sheet metal part and/or that is smaller than the radial extent of the ring recess, but larger than half the radial extent of the ring recess.

14. The method in accordance with claim 1, wherein a perforated die is used as the perforated die whose ring nose has a volume that substantially corresponds to volume of the ring recess of the functional element.

15. The method in accordance with claim 1, wherein a larger portion of sheet metal material of the sheet metal part is deformed than material of the shaft part of the functional element on attachment of the functional element to the sheet metal part.

Description

[0015] The invention will be explained in more detail in the following with reference to the enclosed drawings, where

[0016] FIGS. 1 to 3 show a sequence of snapshots during the carrying out of the method in accordance with the invention; and

[0017] FIG. 4 shows a detail from FIG. 3 in an enlarged representation.

[0018] FIG. 1 shows in an axial section a so-called RND rivet element 10 of the company Profil Verbindungstechnik GmbH and Co. KG. wherein the element 10 is sectioned in an axial plane that comprises the middle longitudinal axis 12 of the element 10. The element 10 shown is fastened to a sheet metal part 14 using the method in accordance with the invention.

[0019] The functional element 10, that is configured as a nut element here, has a head part 18 having a ring-shaped support surface 16 and a tubular punching and rivet section 20 located at the side of the support surface 16 of the head part 18. In the region of the transition from the head part 18 to the rivet section 20, the support surface 16 comprises a ring recess 22 having a ring surface 24 inclined with respect to the longitudinal axis 12 of the functional element 10, wherein the ring recess 22 has its greatest depth in the axial direction of the rivet element 10 adjacent to the rivet section 20 and the inclined ring surface 24 runs out in a further ring-shaped support surface region 27 that lies in a radial plane and that itself merges into a rounded portion 21 or chamfer of the head part 18.

[0020] In this example, features providing security against rotation in the form of security against rotation noses 26 are provided in the region of the ring recess 22, with the security against rotation noses 26 extending in the radial direction and bridging the ring recess 22. In this example, a total of six such security against rotation noses 26 are provided that divide the ring recess 22 accordingly into six fields following one another about the longitudinal axis 12. Fewer than six or more than six such security against rotation noses 26 can be provided and the noses 26 can additionally, if desired, also be provided in raised form in the region of the transition of the ring recess 22 into the rivet section 20. This is, however, not necessary and can also result in complications in the attachment of the element so that such security against rotation noses have been omitted in this representation.

[0021] The ring-shaped region of the ring-shaped support surface 16 that stands in a plane perpendicular to the longitudinal axis 12 and that is preferably not interrupted by security against rotation features 26 is therefore located around the ring recess 22.

[0022] The functional element 10 in this example has a center bore 28 that is provided with an internal thread 30. The head part 18 additionally has a ring-shaped cut-out 32 that defines a cylindrical region 34 of the head part 18 that is surrounded by a ring-shaped pressure surface 36. The functional element 10 does not have to be configured as a nut element. Instead, the cylindrical region 34 could merge over the ring surface 38 into a shaft part that would extend upwardly in the representation in accordance with FIG. 1 so that a bolt element is present. The functional element 10 could also have other functions. The bore 28 could, for example, be configured as a cylindrical support surface for a rotatable support of a shaft or are realized as a clip mount to receive a clip fastening. If the element 10 is provided with a shaft part, the shaft part cannot only be provided with a threaded cylinder, whereby a bolt element is present, but the shaft part could have a cylindrical support surface, e.g. for a rotatable support of a lever, or it could, for example, be provided with a ring groove to receive a clip. What is important is that the ring surface 36 is configured as a pressure surface so that a pressure in the longitudinal direction of the longitudinal axis 12 by means of a suitable tool, here shown by 40, can be exerted onto the pressure surface 36 to bring the element 10 into the sheet metal part 14 without the forces exerted on the functional element 10 resulting in an impermissible deformation of the functional element 10. It can additionally be seen from FIG. 1 that the tubular rivet section 20 has an internal diameter that is considerably larger than that of the bore 28 or than that of the outer diameter of the thread 30 and that the free end face of the tubular rivet section 20, i.e. the lower end in FIG. 1, is equipped with punching and rivet features that will be explained in more detail below.

[0023] A perforated die 42 is located beneath the sheet metal part 14 in FIG. 1, wherein the tool 40 and the perforated die 42 normally lie opposite one another and are provided aligned with one another in a station of a progressive tool. This means that the longitudinal axis 12 of the element 10 simultaneously represents the longitudinal axis of the tool 40 and the longitudinal axis of the perforated die 42 and the perforated die 42 is accommodated in a manner known per se in a lower plate of the progressive tool and the upper tool 40 is moved in accordance with the double arrow 44 to accept a further functional element 10 in the position shown on every upwardly directed movement and to provide the introduction of the functional element into the sheet metal part 14 in the manner to be explained in the following on every downwardly directed movement. In another respect, the tool 40 and the perforated die 42 could be arranged in a transfer press. The perforated die 42 would then have to be arranged in the lower tool of the press and the tool 40 is accommodated in a setting head that is installed at an intermediate plate of the press or at the upper tool of the press. The perforated die 42 could instead be installed on the intermediate plate of the press and the tool 40 could be fastened to the upper tool of the press. Reverse arrangements are also absolutely conceivable in which the lower tool 40 is arranged beneath the perforated die 42, for example in the lower tool of the press or at the intermediate plate of the press while the perforated die would then have to be arranged at the intermediate plate or at the upper tool of the press.

[0024] It can furthermore be seen from FIG. 1 that the functional element 10 is accommodated in a ring recess 46 of the tool 40 that has a ring-shaped shoulder 48 in the base region that presses toward the pressure surface 36 of the functional element 36. The cylindrical region of the head part 18 is accommodated in a further cylindrical recess 50 of the tool 40 and merges over the ring shoulder 48 into the cylindrical recess 46. The free end of the tubular rivet section 20 of the functional element 10 projects beyond the lower ring-shaped end face 52 of the tool, whereas the ring-shaped support surface 16 of the functional element 10 lies in the same radial plane as the lower ring-shaped end face 52 of the tool 40.

[0025] The perforated die 42 has a center bore 54 that can merge in the downward direction in FIG. 1 into a larger bore or can diverge downwardly to facilitate that a panel slug 66 that arises by means of the cooperation of the perforated die 42 and the rivet section 20 can fall out of the bore 54 of the perforated die 42, see FIG. 2. The bore 54 is designed as slightly larger than the rivet section 20 so that it fits into the bore 54 with a small clearance. The bore 54 could, for example, be approximately 0.01 mm larger in diameter in comparison with the rivet section 20.

[0026] The bore 54 is surrounded at the side of the perforated die 42 facing the sheet metal part 14 by a ring nose 80 that is raised with respect to a support surface 82 of the perforated die 42 and defines a planar circular ring-shaped end surface 84. The ring nose 80 has the same inner diameter as the bore 54. As can be seen from FIG. 1, the circular ring-shaped end surface 84 of the ring nose 80 has a radial extent that corresponds to approximately half the thickness of the sheet metal part 14. The circular ring-shaped end surface 84 of the ring nose 80 has a radial extent that is smaller than the radial extent of the ring recess 22, but larger than half the radial extent of the ring recess 22. It can furthermore be seen from FIG. 1 that the ring nose 80 has a volume that substantially corresponds to the volume of the ring recess 22 of the functional element 10.

[0027] If now the upper tool 40 is moved downwardly in accordance with the double arrow 44, the rivet section 20 in accordance with FIG. 2 punches a panel slug 66 out of the sheet metal part 14 that then falls through the preferably downwardly flaring bore 54 of the die 42 and can be removed from the press. The punching of the sheet metal part 14 takes place on the basis of shear forces that arise between the free end of the rivet section 20 and the inner margin of the ring nose 80 at the upper side of the die 42. Due to the huge force on the punching of the sheet metal part 14, not only the sheet metal part 14 is deformed, but the free end of the rivet section 20 can also be compressed slightly in the axial direction and can consequently be pressed slightly apart in the radial direction, see FIG. 4, whereby a kind of undercut 47 is produced at the rivet section 20 that is admittedly relatively small, but is very effective in the sense that a not inconsiderable resistance to pressing out is ensured.

[0028] During the punching of the sheet metal part 14, the ring nose 80 also presses via its circular ring-shaped end surface 84 toward the lower side of the sheet metal part 14 and there forms a recess 62 that extends around the rivet section 20 in the region of its free end. Due to the huge forces that are introduced in this respect as reaction forces over the circular ring-shaped end surface 84 into the material of the sheet metal part 14, the material of the sheet metal part exceeds its flow limit and starts to flow in the region around the rivet section 20, which has the consequence that the material displaced by the formation of the recess 62 is inter alia pressed into the undercut 47 at the rivet section 20—provided it has formed—and even enlarges it, whereby the sheet metal part 14 is connected in a manner secured against being pressed out to the element 10, see FIG. 3. At the same time, the material displaced by the formation of the recess 62 is pressed into the ring recess 22 such that it fills it completely in accordance with FIGS. 3 and 4, which becomes possible in that the volume of the ring nose 82 substantially corresponds to the volume of the ring recess 22 or is somewhat larger than it. The material displaced in the ring recess 22 in this respect tightly contacts the inclined ring surface 24 of the ring recess 22 and fills the ring recess 22 completely such that the security against rotation noses 26 are urged into the sheet metal material and the functional element is thus fastened in a manner secure against rotation at the sheet metal part 14. The engagement of the sheet metal material into the forming undercut 47 also provides that a more resistant engagement of the security against rotation noses in the sheet metal material is ensured, which considerably increases the security against rotation resistance. It must further be noted that the forces that are present on the attachment of the functional element to the sheet metal part substantially act between the ring-shaped pressure surface 36 and the circular ring-shaped end surface 84 of the ring nose that are opposite one another and therefore do not effect any deformation of the threaded cylinder. It must furthermore be mentioned that the flattened shape of the ring nose 80 of the die, whose radial extent is approximately the same in size as the radial extent of the ring recess 22, has a further special advantage. It is possible with this shape to move a relatively large volume of sheet metal material with a relatively small height of the ring nose above the planar surface of the die that engages around, and indeed such that the ring recess 22 can be completely filled. A height of the ring nose above the surrounding end surface of the die of approximately 0.8 mm or less, preferably 0.5 mm, is sufficient for this purpose. In another respect, the ring nose 80 provides that the slug 66 is cleanly separated from the remaining sheet metal material without the rivet section 20 having to project out of the lower plane of the sheet metal part 14, but remains set back by approximately 0.2 mm.

[0029] Due to the fact that the perforated die 42 contacts the sheet metal material 14 over its planar circular ring-shaped end surface 84, the sheet metal material that surrounds the punched hole 70 produced by the punching out of the panel slug 66 cannot be laterally or radially displaced. A compression stress can rather be built up over the planar end surface 84 of the ring nose 80 of the perforated die 42 that is used in the method in accordance with the invention in the sheet material that surrounds the punched hole 70 produced by the punching out of the panel slug 66 until the material exceeds the flow limit and starts to flow plastically such that it not only penetrates into the ring recess 22 at continued pressure, but rather produces a constriction 49 that is adjacent thereto in the rivet section 20 of the rivet element 10 and that is then covered by the sheet metal material. Due to this constriction 49, the undercut 47 produced by the compression of the rivet section 20 is increased therein—provided it has formed—whereby the rivet element 10 is particularly reliably secured against being pressed out at the sheet metal part 14. Not only high bearing stresses are in particular produced between the sheet metal part 14 and the rivet element 10 that also contribute to security against rotation by the material that is located in the construction 49; a shape matching is rather also produced such that the pressing of the rivet element 10 out of the sheet metal part 14 in the pressing-out direction is not possible or is only possible on the application of substantial destructive forces.

[0030] It must be noted at this point that the method in accordance with the invention works while using a rivet element that is, however, not deformed or is only slightly deformed within the framework of the application of the invention. The rivet element, preferably an RND rivet element, is therefore used as a force fitting element since primarily only the sheet metal part is deformed.