Method for the punching in and attachment of a fastener element and corresponding die button

Abstract

The present invention relates to a method for the punching in and attachment of the fastener element to a planar workpiece, in particular to a sheet metal part. During the punching in of the fastener element in the workpiece a movably arranged die plunger of the die button is pressed with a predetermined pressing force against the workpiece. The pressing force is adapted such that the die plunger first moves once a slug has been cut out of the workpiece by a piercing section of the fastener element.

Claims

1. A method for punching in and attaching a fastener element (10) to a workpiece (12) in particular to a sheet metal part, wherein during the punching in of the fastener element (10) into the workpiece (12) a movably arranged die plunger (28′) of a die button (18′) is pressed with a predetermined pressing force against the workpiece (12), with the pressing force being adapted such that the die plunger (28′) first moves when a slug (34) has been separated from the workpiece by a piercing section (14) of the fastener element (10) and prior to completion of deformation of the fastener element.

2. A method in accordance with claim 1, wherein the die plunger (28′) is movable in the direction parallel to a piercing movement of the fastener element (10).

3. A method in accordance with claim 1, wherein the pressing force which biases the die plunger in the direction towards the workpiece is directed antiparallel to a piercing movement of the fastener element (10).

4. A method in accordance with claim 1, wherein the pressing force is selected such that the die plunger (28′) first moves when a fastener section (14) of the fastener element is deformed by a shaping surface of the die plunger (28′).

5. A method in accordance with claim 1, wherein the die plunger (28′) includes a cutting edge (32′) which lies at the start of the piercing process in a plane which is defined by a rim of an opening (16′) of the die button (18′).

6. A method in accordance with claim 1, wherein the die plunger (28′) includes a raised portion (44) which, at the start of the piercing process, projects out of the plane which is defined by a rim of the recess (16′) of the die button (18′).

7. A method in accordance with claim 1, wherein a movement of the die plunger (28′) opposite to and/or in the direction of the pressing force is restricted by an abutment.

8. A method in accordance with claim 1, wherein the die plunger (28′) has a shaping surface (46) by which the piercing section (14) is at least regionally deformed radially outwardly, with the shaping surface (46) in particular being conically and/or concavely shaped at least regionally.

9. A method in accordance with claim 1, wherein a depression is generated which at least partly accommodates a flange (38) of the fastener element (10) contacting the workpiece (12) in an end state.

10. A method in accordance with claim 1, wherein the predetermined pressing force is selected in dependence on at least one of the characteristics of the workpiece (12), the characteristics of the fastener element (10) and a pressing force generated by a press unit and exerted on the fastener element (10).

11. A method in accordance with claim 1, wherein an adjustable biasing device (42), with which a predetermined pressing force can be set, is associated with the die plunger (28′).

Description

(1) The present invention will now be described purely by way of example in the following with reference to an advantageous embodiment of the invention and to the accompanying drawings. There are shown:

(2) FIGS. 1 to 10 a customary method for the punching in and attachment of a fastener element to a planar workpiece and

(3) FIGS. 11 to 22 an embodiment of the method of the present invention.

(4) More precisely, there is shown:

(5) FIG. 1 a bolt element which is punched into a planar sheet metal part 12,

(6) FIG. 2 the section characterized in broking lines in FIG. 1 in an enlarged representation,

(7) FIG. 3 a representation similar to FIG. 1 but in a further advanced state of the attachment of the bolt element,

(8) FIG. 4 an enlarged representation of the central region of FIG. 3,

(9) FIG. 5 the tearing of the sheet metal part in accordance with a further advanced state of the attachment of the bolt element,

(10) FIG. 6 an enlarged representation of the central region of FIG. 5,

(11) FIG. 7 the creation of a burr in an advanced state of the attachment of the bolt element,

(12) FIG. 8 an enlarged representation of the central region of FIG. 7,

(13) FIG. 9 the completion of the connection of the bolt element to the sheet metal part,

(14) FIG. 10 an enlarged representation of the central region of FIG. 9,

(15) FIG. 11 a representation of the start of the attachment of the bolt element to a sheet metal part using the method in accordance with the invention and using the die button in accordance with the invention,

(16) FIG. 12 an enlarged representation of the central region of FIG. 11,

(17) FIG. 13 a representation of the method in accordance with the invention directly after the formation of the piercing slug,

(18) FIG. 14 an enlarged representation of the central region of FIG. 13,

(19) FIG. 15 a representation similar to FIG. 13, but after the initial movement of the die plunger,

(20) FIG. 16 an enlarged representation of the central region of FIG. 15,

(21) FIG. 17 a representation similar to FIG. 15 but after a further movement of the die plunger,

(22) FIG. 18 an enlarged representation of the central region of FIG. 17,

(23) FIG. 19 a representation similar to FIG. 17 but shortly before the completion of the formation of the rivet bead,

(24) FIG. 20 an enlarged representation of the central region of FIG. 19,

(25) FIG. 21 a representation similar to FIG. 19 but after the termination of the formation of the rivet bead and the attachment of the bolt element to a sheet metal part,

(26) FIG. 22 an enlarged representation of the central region of FIG. 21.

(27) FIG. 1 shows a bolt element 10 which is to be punched into a planar sheet metal part 12 and secured to it. It will be understood that instead of the bolt element a nut element, a hollow rivet or another self-piercing element can be used.

(28) The piercing section 14 of the bolt element 10 starts in the state shown in FIG. 1 to press the sheet metal part 12 into a recess 16 of the die button 18 whereby the formation of a depression sets in.

(29) FIG. 2 shows the section shown in broken lines in FIG. 1 in an enlarged representation. The die button 18 includes a die button jacket 20 merges via a rounded section 22 forming the rim of the recess 16 into a sheet metal support surface 24 (see also FIG. 1). The sheet metal part 12 lies on the sheet metal support surface 24 during the punching in and attachment process.

(30) At the end of the recess 16 remote from the sheet metal support surface 24 the die button jacket 20 merges into a further rounded section 23 which is in turn followed at the radially inner side by a die plunger 28 surrounded by a ring groove 26.

(31) It can be seen from FIGS. 3 and 4 that with increasing depth of the depression a crack 30 forms in the sheet metal part 12 because the material here is particularly strongly extended by the piercing section 14.

(32) The crack 30 propagates—as shown in FIGS. 5 and 6—until it has completely passed through the sheet metal part 12. It can be seen that the crack 30 does not normally arise at the position where the piercing section 14 in conjunction with the cutting edge 32 of the die plunger 28 leads to a cutting through of the sheet metal part 12 and thus to the generation of a slug 34. Accordingly, a ring-like burr 36 arises which, during a beading over of the piercing section 14 acting as a rivet section through the section of the ring groove 26, is jammed between the piercing section 14 and a side of the sheet metal part 12 remote from a flange 38 of the bolt element 10 (see FIGS. 7 and 8).

(33) In many cases the burr 36 remains between the sheet metal part 12 and the surrounding piercing section 14. Often it is however forced outwardly by a further pressing action 10 against the die button 18 which is shown in FIGS. 9 and 10. The burr 36 then either remains in the recess 16 of the die button 18, where it disturbs the subsequent punching in processes, or it is likewise removed from the die button 16 during the removal of the component assembly consisting of the sheet metal part 11 and the bolt element 10 and then wanders through the tooling as a disturbing foreign body.

(34) The method which is described with reference to FIGS. 11 and 22 reliably prevents the creation of swarf 36.

(35) As in the customary method a bolt element 10 can be used which is provided with features 40 providing security against rotation at the flange 38 which is to be brought into contact with the sheet metal part 12. The method of the invention can however be carried out with any desired self-piercing elements.

(36) As can be seen in FIG. 11, the die button 18′ of the invention has a movable die plunger 28′ which, at the start of the punching in and attachment process is pressed against the sheet metal part 12 from the side remote from the bolt element 10. The pressing force which acts coaxially to a longitudinal axis L of the bolt element 10 and of the plunger 28′ is made available by a spring 42. It will be understood that instead of the spring 42 other devices can be used which can generate a predetermined pressing force, such as for example hydraulic and/or pneumatic systems.

(37) The sheet metal part is supported in a central region of the slug 34 to be punched out by the die plunger 28′. In FIG. 12 it can be seen that a raised portion 44 of the die plunger 28′ projects in the illustrated basic state somewhat beyond the sheet metal contact surface 24 or the rim of the recess 16 of the die button 18. The sheet metal part is thereby bent slightly in this region towards the bolt element 10 in order to assist the cutting out of the slug 34 by the piercing section 14 and the cutting edge 32′. The cutting edge 32′ lies in the illustrated state in the above-named plane.

(38) As can be recognized in FIGS. 13 and 14 the pressing force made available by the spring 42 is selected such that during the cutting out of the piercing slug 34 from the sheet metal part a movement of the die plunger 28′ downwardly does not take place. The die plunger 28′ does the latter deflect downwardly as is shown in FIGS. 15 and 16 only when a shaping of the piercing section 14 starts as a result of the shaping of the shaping surface 46 of the die plunger 28′ and thereby correspondingly large forces act between the piercing section 14 and the die plunger 28′.

(39) In other words, the pressing force is so selected, taking account amongst other things of the properties of the sheet metal part 12 and/or of the element 10, that the slug 34 which is created is supported throughout the entire piercing process. A movement of the die plunger 28′ is first provided only after the slug 34 has been completely cut out of the sheet metal part 12. When this first starts depends, amongst other things, on the shape of the peripheral surface 46 and the pressing force which is set. Provision can, for example, be made that the reshaping of the piercing section 14 first takes place comparatively late and a plunger 28′ is not set in movement directly after the punching out of the slug 34.

(40) The start of the reshaping process of the piercing slug 14 is shown in FIGS. 15 and 16. As a result of the thereby enhanced coupling of the section 14 and of the die plunger 28′ a larger proportion of the pressing force acting on the bolt element 10 is transmitted to the plunger 28′ so that the pressing force is overcome and the plunger 28′ starts to deviate downwardly.

(41) In FIGS. 17 and 18 a state is shown in which the die plunger 28′ has reached a lower end position. I.e. it has reached an abutment position, so that the plunger 28′ no longer moves. The piercing section 14 has been pierced over outwardly concave design of the reshaping surface 46 in the lower parts. The concave section of the reshaping surface 46 thus forms a component comparable with the ring groove 26 which serves for the beading over of the piercing section 14, which can also be seen in FIGS. 19 to 22. It will be understood that the design of the die button jacket 20′ of the die button 18′ can be matched to the respectively present requirements. The same also applies to the rounded rim portion 22′ which corresponds functionally to the rounded section 22 of the die button 18.

(42) It can be seen in FIGS. 21 and 22 that the final end state resembles the state shown in FIGS. 9 and 10 to the extent that the flange 38 is received in the axial direction by a depression formed by the punching in and attaching process. The method of the invention thus serves for crack avoidance and thus a burr—avoiding support of the slug 34 to be cut out at the start of the method and simultaneously permits the formation of a depression which receives the flange 38. In accordance with the invention it has been recognized that the pressing force of the supporting die plunger 28′ must be selected such that a movement of the die plunger 28′ is first permitted after the cutting out of the piercing slug 34.

REFERENCE NUMERAL LIST

(43) 10 bolt element 12 sheet metal part 14 piercing section 16 recess 18, 18′ die button 20, 20′ die button jacket 22, 23, 22′ rounded portion 24 sheet metal contact surface 26 ring groove 28, 28′ die plunger 30 crack 32 cutting edge 34 slug 36 burr, swarf 38 flange 40 feature providing security against rotation 42 spring 44 raised portion 46 reshaping surface L longitudinal axis