PRESS-FIT CONNECTION BETWEEN A HIGH-STRENGTH COMPONENT AND A PRESS-FIT ELEMENT, METHOD FOR MAKING SUCH A PRESS-FIT CONNECTION, AND PRESS-FIT ELEMENT FOR SUCH A PRESS-FIT CONNECTION

Abstract

A press-fit connection between a high-strength component and a press-fit element is characterized by a non-circular previously made hole into which the press-fit element having a collar is inserted. Here, the collar is merely upset and pressed against a hole rim without embracing an underside of the component. Preferably, the hole rim is widened in a longitudinal direction such that a form-locking connection acting in opposition to the longitudinal direction is formed. The non-circular hole geometry is produced with the aid of a punch of circular cross sectional geometry, in that a cutter of the punch has leading and recessed cutting regions, with the result that disrupted partial regions are formed.

Claims

1. A press-fit connection, comprising: a high-strength component having a pre-shaped hole formed therein and an underside, and for providing resistance to twisting forces said pre-shaped hole being defined by a hole rim being other than circular in shape; and a press-fit element being pressed into said pre-shaped hole in said high-strength component, said press-fit element extending in a longitudinal direction and having a head part with a head contact face for lying on said high-strength component and a collar for providing resistance to extraction being effective in opposition to the longitudinal direction, said collar being pressed by an upset process against said hole rim and provides a press-fit without said collar embracing said underside of said high-strength component.

2. The press-fit connection according to claim 1, wherein said high-strength component has no deformation in a region of said pre-shaped hole.

3. The press-fit connection according to claim 1, wherein: said hole rim is widened in the longitudinal direction; and said collar forms, with said hole rim, a form locking engagement acting in opposition to the longitudinal direction.

4. The press-fit connection according to claim 1, wherein at least one of said press-fit element or said collar has a circular cross sectional geometry in a starting condition.

5. The press-fit connection according to claim 1, wherein: said pre-shaped hole extends along a line of a circle arc; and said hole rim is disrupted only in a partial region, as a result of which a cross sectional shape that is other than circular is formed.

6. The press-fit connection according to claim 5, wherein said pre-shaped hole in said partial region being a disrupted partial region has a diameter that is larger by only a few tenths of a millimeter.

7. The press-fit connection according to claim 1, wherein a strength of said press-fit element is less than that of said high-strength component, wherein said high-strength component has a strength of >600 MPa.

8. The press-fit connection according to claim 1, wherein a strength of said press-fit element is less than that of said high-strength component, wherein said high-strength component has a strength of >2,000 MPa.

9. The press-fit connection according to claim 1, wherein said press-fit element is a press-fit bolt having a shaft, wherein an inward curve is constructed between said shaft and said collar.

10. A method for making a press-fit connection between a press-fit element and a high-strength component, which comprises the steps of: making, with an aid of a punch and a punching die, a hole in the high-strength component with a hole rim that is other than circular in shape, the press-fit element having a head part with a head contact face for lying on the high-strength component and a collar; and introduced the press-fit element via the collar into the hole with an aid of a die and the collar is merely upset and pressed against the hole rim.

11. The method according to claim 10, wherein the die has a circular die flange.

12. The method according to claim 10, wherein the die has a die flange and a spring-urged inner support element that projects beyond said die flange and is supported against an annular face of said press-fit element.

13. The method according to claim 10, which further comprises producing the hole with the aid of the punch that has a peripheral cutter which has cutting regions that are recessed in a longitudinal direction, for producing a disrupted partial region.

14. The method according to claim 10, wherein the punch is in a shape of a roof at its front end face.

15. The method according to claim 10, which further comprises forming the punching die with a central aperture having a diameter corresponding to a diameter of the punch plus more than 15% of a thickness of the high-strength component.

16. The method according to claim 10, which further comprises forming the punching die with a central aperture having a diameter corresponding to a diameter of the punch and more than 18% of a thickness of the high-strength component.

17. A press-fit element for providing a press-fit connection with a previously pierced high-strength component of a predetermined thickness, the press-fit element comprising: a head part with a head contact face for lying on the high-strength component, said head contact face is free of any elements for resistance to twist; and a collar for providing a form-locking connection with the high -strength component that acts in a longitudinal direction, said collar having an axial height that is at most 20% greater than a thickness of the high-strength component.

18. The press-fit element according to claim 17, wherein the press-fit element is a press-fit bolt having a shaft that adjoins said head part in the longitudinal direction, said collar has a peripheral inward curve, wherein said peripheral inward curve has a radial width that lies in a range between 0.5 times and 1.2 times a radial width of said collar.

19. The press-fit element according to claim 17, wherein: the press-fit element is a press-fit nut having a central internal hole formed therein and an annular face disposed between said central internal hole and said collar; said head contact face adjoins said collar; said annular face has a radial width being greater than or equal to a radial width of said head contact face; and said head contact face is recessed from said annular face in the longitudinal direction.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0055] FIG. 1 is a diagrammatic, cross sectional view through a press-fit connection between a press-fit bolt and a high-strength component;

[0056] FIG. 2 is a sectional view of the press-fit connection at an end of the press-fit operation between the press-fit nut and the component, with a punching die;

[0057] FIG. 3A is a cross sectional view of the press-fit bolt;

[0058] FIG. 3B is a cross sectional view on a larger scale of a detail of the press-fit bolt according to FIG. 3A, in a region of a collar;

[0059] FIG. 4 is a cross sectional view of the press-fit nut;

[0060] FIGS. 5A, 5B are cross sectional view for explaining the press-fit operation during press-fitting of the press-fit bolt;

[0061] FIGS. 6A, 6B are illustrations for explaining the hole-punching operation, with a punch according to a first variant embodiment; and

[0062] FIGS. 7A, 7B are two side views, turned through 90° in relation to one another, of a punch according to a second variant embodiment.

DETAILED DESCRIPTION OF THE INVENTION

[0063] In the figures, parts having a like action are provided with like reference numerals.

[0064] Referring now to the figures of the drawings in detail and first, particularly to FIGS. 1 and 2 thereof, there is shown a press-fit connection 2 in each case of a connection between a press-fit element, which in FIG. 1 is constructed as a press-fit bolt 4 and in FIG. 2 as a press-fit nut 6, and a high-strength sheet-metal component 8. Here, the respective press-fit element 4, 6 has in each case a head part 10, on an underside whereof there is constructed a head contact face 12 by which the respective press-fit element 4, 6 lies on an upper side 14 of the component 8. The respective press-fit element extends in a longitudinal direction 16, with in each case a collar 18 adjoining the head part 10 in the longitudinal direction 16. In the case of the press-fit bolt 4, a shaft 20 adjoins the head part 10. The shaft has a peripheral inward curve 22 in the region of the collar 18. The press-fit nut 6 has a central internal hole 24 that is in particular provided with an internal thread. The shaft 20 is preferably provided with an external thread.

[0065] The respective press-fit element 4, 6 is press fit into a previously made hole 26 (in this regard, see in particular FIGS. 6A and 6B) of the component 8.

[0066] The hole 26 is delimited by a hole rim 28. The hole rim 28 has an enlargement 32 at an underside 30 of the component 8, with the result that the hole rim 28 and hence also the hole 26 widen toward an underside 30. In addition, a narrowing may be made toward the upper side 14. As a result, and as seen in cross section, the shape of the hole rim is made approximately convex overall. However, the crucial point is the enlargement 32, with the increasing hole diameter toward the underside 30.

[0067] As can furthermore be seen from FIGS. 1 and 2, the collar 18 is pressed radially against the hole rim such that it is adapted in particular to the widening hole rim 28. As a result, a resistance to axial extraction that is effective in the longitudinal direction 16 is provided by the provision of a positive engagement that is effective in opposition to the longitudinal direction 16. It is particularly important here that the collar 18 does not project beyond the underside 30 or embrace it. The collar 18 merely forms a way of engaging behind the widened hole rim 28.

[0068] In addition to this resistance to axial extraction, a resistance to twist is furthermore provided. For this, the pre-punched hole 26 is made non-circular, so has a peripheral contour other than circular in shape, such as is seen in particular from FIGS. 6A and 6B (lower region of the drawing). During the press-fit operation, the collar 18 is adapted in the radial direction to this non-circular peripheral contour, for the purpose of providing the resistance to twist, by solid forging during an upset process, and is pressed against the hole rim 28, forming a press fit.

[0069] FIG. 3A shows once again a cross sectional illustration of the press-fit bolt 4, and FIG. 3B shows an illustration on a larger scale of a detail in the region of the collar 18. An inward curve 22 is very readily visible from this detail illustration on a larger scale. It has a radial width b1 which lies approximately in the range of the radial width b2 of the collar 18. The radial width b1 of the inward curve 22 corresponds to the radial extent of the inward curve 22 from the shaft 20 to the transition to the substantially horizontal end face of the collar 18. The radial width b2 of the collar 18, which is in the shape of an annular flange, here corresponds to the radial extent of the end face of this collar 18.

[0070] Furthermore, the collar 18 has an axial height a that is adapted to a thickness D (see FIG. 1) of the component 8, such that in the press-fit condition the collar 18 does not project beyond the underside 30. Preferably, in the incorporated condition, the collar 18 ends flush with the underside 30 or is at most slightly recessed therefrom. Here, the axial height a is the spacing in the longitudinal direction 16 from the head contact face 12 to the end face of the collar 18.

[0071] It can be seen from the cross sectional illustration in FIG. 4 that in the case of the press-fit nut 4 the collar 18 is radially spaced from the internal hole 24 and thus from the internal thread. Adjoining the internal hole 24 there is first provided an annular face 34 that has a radial width b3. This is defined by the spacing in the radial direction from the internal hole 24 or a thread root, to the start of the collar 18. In general, in the respective press-fit element 4, 6, the internal surface of the collar 18 is inclined obliquely in relation to the longitudinal direction 16, and so is provided overall in the manner of a conical surface.

[0072] Finally, the collar 18 is adjoined in the radial direction by the head contact face 12. The latter has a radial width b4, which in the exemplary embodiment corresponds approximately to 1.5 times the radial width b3 of the annular face 34.

[0073] As an alternative to the one-part die 36 illustrated in FIG. 2, a preferably two-part die 36 (not illustrated in more detail here) is used, which has an outer, rigid annular die flange 38 over which the collar 18 is upset. In addition, the die 36 has a support punch that is arranged concentrically in relation to the die flange 38 and is in particular spring-urged, that is to say is pressed forward by means of a spring. The support punch—or indeed a support ring—is supported under spring load against the annular face 34. This prevents damage to the internal thread of the press-fit nut 6 and ensures that the thread is true to gage.

[0074] For the purpose of providing the press-fit connection 2—and as can be seen in FIGS. 5A, 5B—the press-fit bolt 4 is inserted into the hole 26 and pressed against a die 36. The die 36 has a planar die surface with a peripheral die flange 38 that in particular rises conically toward a center axis. During the press-fit operation, the die flange 38 is pressed against the collar 18, with the result that the latter is upset, and material of the collar is pressed, as a result of solid forging, at least partially radially outward and against the hole rim 28.

[0075] Here, the die flange 38 engages in the inward curve 22 by its conically tapering end face, and results in the desired upset process with solid forging.

[0076] For the purpose of providing the hole 26 having the non-circular geometry, a specific punch 40 is used, in combination in particular also with a specific punching die 42 in a hole-punching operation. This will be explained below with reference to FIGS. 6A, 6B and in addition in combination with FIGS. 7A, 7B:

[0077] Here, FIGS. 6A, 6B show a first embodiment of the punch 40, and FIGS. 7A, 7B show a second variant embodiment. The respective punch 40 is rotationally symmetrical and has a circular cross sectional surface. On its end face, it has a peripheral cutter 44 on the rim. It is of crucial importance that this cutter has cutting regions that are arranged at different axial heights in the longitudinal direction 16, that is to say that the cutter 44 has leading cutting regions 46A and cutting regions 46B that are recessed in the longitudinal direction. In the case of the punch 40 according to FIGS. 6A, 6B, the end face takes the overall shape of a roof with a roof angle a of approximately 120°. The leading cutting region 46A is in this case arranged centrally and so the external regions are recessed. Here, FIG. 6B shows a view that has been turned through 90° in relation to FIG. 6A.

[0078] In contrast hereto, in the case of the punch 40 according to FIGS. 7A, 7B, the recessed cutting region 46B is arranged in the center. This thus provides in particular approximately an inverted construction, by comparison with the variant according to FIGS. 6A, 6B, with a central inward curve of the punch 40. The latter also preferably has a geometry in the shape of a roof.

[0079] In principle, other geometries are also possible as an alternative to the roof geometry. The crucial point is that the cutter 44 has the different cutting regions 46A, 46B. Here, the individual cutting regions merge continuously into one another. As can be seen in particular with reference to a comparison between the views of FIGS. 6A, 6B and 7A, 7B, which are turned through 90°, the leading cutting regions 46A have a cutting edge that tapers to a very sharp point, whereas in the region of the recessed cutting edges 46B these are made at a markedly more obtuse angle.

[0080] During the punching operation, this has the result that in the region of the recessed cutting regions 46B cutting is not performed cleanly but is rather a disrupting of the edge. As a result, the hole 26 initially has a fundamentally circular basic contour that is adapted to the circle shape of the punch 40 and runs along the circle-arc line 48. In the region of the recessed cutting regions 46B, however, the hole 26 has partial regions 50 that are disrupted radially outward and in which the peripheral contour differs from the circle contour, so overall a non-circular contour is provided. In the region of the circle-arc line 48, the hole 26 has a diameter d1 that is somewhat smaller than the hole diameter d2 in the region of the disrupted partial regions. Specifically, the hole diameter d2 is at most a few tenths of a millimeter larger than the hole diameter d1 in the region of the circle-arc line.

[0081] Here, the hole diameter d1 corresponds at least broadly speaking to a punch diameter d3 of the punch 40.

[0082] During the hole-making operation, the punch 40 is punched through the (unpierced) component 8. Here, the hole 26 is provided with the specific hole geometry that is visible from the cross sectional illustration (upper part of the drawing) or plan view (lower part of the drawing) of the component 8 according to FIG. 6A or indeed 6B. In addition, in these two figures the punching die 42 against which the component 8 is supported during the punching operation is also illustrated. Here, the punching die 42 has a central aperture 54 with a diameter d4 that is larger than the punch diameter d3 by the size of a gap. The size of this gap (also called the blade clearance) depends here on the thickness D of the component 8: the diameter d4 is greater than or equal to the punch diameter d3 plus at least 15% of the thickness D, preferably plus approximately 20% of the thickness D.

[0083] As a result of this feature, an unclean hole 26 with the above-described enlargement 32 is deliberately produced. Because of the relatively large gap size between the punch 40 and the punching die 42, the hole 26 is made larger toward the underside 30.

[0084] In the application we recite a form-locking connection also known a positive engagement. A form-locking connection is a connection formed due to the shape of the objections such as a ball and socket.

[0085] The following is a summary list of reference numerals and the corresponding structure used in the above description of the invention: [0086] 2 Press-fit connection [0087] 4 Press-fit bolt [0088] 6 Press-fit nut [0089] 8 Component [0090] 10 Head part [0091] 12 Head contact face [0092] 14 Upper side [0093] 16 Longitudinal direction [0094] 18 Collar [0095] 20 Shaft [0096] 22 Inward curve [0097] 24 Internal hole [0098] 26 Hole [0099] 28 Hole rim [0100] 30 Underside [0101] 32 Enlargement [0102] 34 Annular face [0103] 36 Die [0104] 38 Die flange [0105] 40 Punch [0106] 42 Punching die [0107] 44 Cutter [0108] 46A Leading cutting region [0109] 46B Recessed cutting region [0110] 48 Circle-arc line [0111] 50 Disrupted partial region [0112] 54 Aperture [0113] α Roof angle [0114] a Axial height of collar [0115] b1 Radial width of inward curve [0116] b2 Radial width of collar [0117] b3 Radial width of annular face [0118] b4 Radial width of head contact face [0119] d1 Hole diameter of circle-arc line [0120] d2 Hole diameter of disrupted partial region [0121] d3 Punch diameter [0122] d4 Diameter of aperture of punching die [0123] D Thickness of component