This application is a National Phase filing regarding International Application No. PCT/GB02/05661, which relies upon British Application No. 0129878.5 for priority.
The invention relates to a method of fastening, using fasteners such as those described in U.S. Pat. Nos. 4,642,010 and 4,701,993, to which the reader is referred for the background to the present invention.
On such prior art rivets, a clamping force in the components being joined is achieved by deforming the head of the rivet so as to move a radially outer part of the head towards the tail end of the rivet (claim 4 of U.S. Pat. No. 4,701,993). One problem with this is that in practice, to achieve the desired result, the rivet head undergoes severe deformation—the head geometry typically is 120° included angle countersunk, which is deformed to 120° conical form during installation of the rivet (compare FIGS. 3 and 4 of U.S. Pat. No. 4,701,993). This represents a complete inversion of the head form. This can have the effect of weakening or damaging the protective coating which is normally applied to the rivet e.g. zinc plating or nickel plating. Also, to some customers the resultant conical head shape is not acceptable from a cosmetic point of view.
On prior art rivets on applications where it is not necessary or desirable to provide clamping of the joint, a rivet which has a non-deforming head may be used (column 7, line 7 of U.S. Pat. No. 4,701,993).
The present invention seeks to reduce the need to provide different designs of fasteners for use in different applications, and also to provide improved resulting fastenings.
The invention provides, in one of its aspects, a method of fastening one or more apertured members to an apertured workpiece, as set out in the primary claim of the appended claims.
Further preferred features of the invention are set out in the remaining claims.
Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:
Referring to
The fastener has an axial bore 22 throughout the shank and head, the bore being substantially constant in diameter, but having a countersink 24 at the head end.
The fastener is made from carbon steel and is harder than, for example, aluminium, magnesium and a variety of engineering plastic materials such as might form a workpiece in which it might be desired to install the fastener.
The material of the fastener is sufficiently ductile for the shank to be deformed by radial expansion to an extent such that the major diameter of the shank (that is the diameter taken across the crest of the thread) after expansion is greater than before expansion by at least the depth of the thread.
Referring to
The mandrel 26 has an elongate stem 30 which is able to pass with clearance through the bore of the fastener, and an enlarged head 32 at one end of the stem. The mandrel head 32 has a conical tapering portion 34 in which the diameter of the mandrel increases progressively away from the stem 30 to a diameter substantially greater than that of the bore 22 of the fastener, and leads to a somewhat elongate portion 36 of the head in which the cross-sectional shape of the mandrel is circular, as shown, or may be the shape of a regular hexagon. The mandrel is formed from high tensile steel.
The annular anvil 28 has an axial passage 38 through which the stem of the mandrel can be passed into engagement with the gripping and pulling means, and an abutment face 40 at its forward end. In the embodiments illustrated in
The apparatus may be used to install fasteners in a manner substantially the same as that used in repetition riveting.
Thus, the fastener 10 is fed on to the stem of the mandrel so that the stem extends through the bore 22 and the mandrel head 32 is adjacent the tail end of the fastener but outside the bore, and with the stem of the mandrel passing through the passage 38 of the anvil into engagement with the pulling means so that the fastener is between the mandrel head and the abutment face 40 of the anvil.
A plurality of further fasteners (not shown) may at the same time be disposed on the stem behind the anvil, ready to be fed one at a time through the jaws into position between the mandrel head and the abutment face of the anvil.
The fastener 10 thus associated with the installing apparatus is offered to the work and the mandrel head and tail portion of the fastener are entered through the aperture 50 of the member 48 and into the aperture 54 of the workpiece 52 until the anvil pushes the head of the fastener into engagement with the near face of the member 48 and, in turn, urges the member 48 into abutment with the near face of the workpiece. The installing apparatus is then actuated to pull the mandrel through the fastener, thus drawing the head of the mandrel into the tail end and through the bore while the head of the fastener is supported by the abutment face of the anvil.
It will be appreciated that the tapered portion 34 of the mandrel head leads the cylindrical portion 36 into the bore of the fastener and as it does so expands the shank progressively from the tail end towards the head. As the expansion of the shank progresses towards the head of the fastener there comes a time when the crest 20 of the external thread 16 at the leading edge of the progressively expanding parts of the shank first engages the material of the workpiece 52 and begins to embed into the material. At this point the axial position of the engaged threads become substantially fixed.
It will be appreciated that the degree of penetration of the threads into the workpiece material is a function of the expanded diameter of the fastener and the diameter (d1) of the aperture 54 in the workpiece, and that the expanded diameter of the fastener, in turn, is a function of the diameter (d2) of the bore 22 of the fastener, the original diameter (d3) of the shank of the fastener, and the diameter (d4) of the cylindrical portion 36 of the mandrel head. The dimensions d1, d2, d3 and d4 are selected to provide a degree of thread penetration into the workpiece of not more than half of the overall height of thread 18. Thus, referring to
The dimensions d1 and d3 and the angle of the conical tapering portion 34 of the mandrel head are selected such that the progressively expanding part of the shank of the fastener first engages the material of the workpiece and therefore becomes substantially axially fixed, before the axial pulling load of the mandrel reaches a magnitude sufficient to axially compress the fastener.
The aperture 50 in the member 48 is large enough to allow the fastener to expand within the aperture without any substantial radial constraint. Thus the diameter of the expanded thread portion 60 within the member is slightly larger than the diameter of the thread portion 62 within the workpiece, as shown by dimension ‘X’ in
It has been found by experiment that a fastener of the present example and manufactured with the following dimensions will function in the intended manner when installed in a workpiece of cast magnesium with a 5.42 mm hole diameter (d1) to which a steel member 4 mm thick and with a 6.3 mm diameter hole, is attached by the fastener, using a mandrel of diameter 3.5 mm (d4). The dimensions of the fastener being: diameter of bore 22 is 2.76 mm (d2), diameter of shank (diameter over crests of thread) is 5.3 mm (d3), length of shank 16 mm, thread pitch 1.0 mm. In this case between 30% to 40% of the thread depth is expanded into the workpiece. This is more than sufficient to support any tensile loads imposed on the fastener in service. In fact the retention of the fastener in the workpiece at this level of thread penetration is sufficient to cause the fastener to rupture, rather than the threads to strip, when an excessive tensile load is applied to the installed fastener. Also, for example, if a tightening torque is applied to the installed fastener, for example, in the case where an equivalent hexagonal head mandrel is used, and a hexagonal wrench is used, then the torque which causes the threads to strip is well in excess of the recommended maximum tightening torque of the equivalent screw or bolt (in this case an M6 setscrew, grade 8.8).
Of course, it will be realised that the thread stripping torque and the pull-out tensile load will depend to an extent on the amount of fastener shank (i.e. the length) which is engaged in the workpiece, this in turn being determined by the thickness of the member or members being attached to the workpiece. It has been found that the installed fastener strength characteristics described above are maintained when at least half the length of the shank is engaged in the workpiece, that is in this example 8 mm.
When the member 48 is very thin, that is less than 1.5 mm in the example above, then in order to obtain the clamping effect which is produced when the threaded position adjacent the head of the fastener expands without radial constraint, it may be necessary to produce a counterbore in the aperture 54 of the workpiece. For a fastener of the same construction as the example quoted, and a member with a thickness, for example, of 1 mm, then a counterbore depth of 2 mm would be sufficient
Referring to
In some applications it will be preferable to use the fastener in workpieces in which the aperture, for receiving the fasteners are produced by a casting operation. In which case, the apertures will preferably have a taper (or draft), the angle of the draft being typically 1° to 1.5° inclusive. The fastener of the present invention will function satisfactorily in such a tapered hole. Referring to
In applications where the member to be attached to the workpiece is manufactured from a non-rigid material, such as an elastomeric material, the reduction in length of the fastener which occurs during the installation process has the effect of compressing the member as shown in
It has been found in practice that in some applications there can exist a gap between the member and the workpiece which cannot be closed by the normal pushing action on an operator engaging the fastener into the member and the workpiece. When the gap is small, the foreshortening effect of the rivet shank, on a rivet according to this invention, may be sufficient to close the gap and to create a clamp force in the member. In those applications where a larger gap between the member and the workpiece might exist, a rivet as described above can be used in accordance with the present invention in conjunction with an anvil 82 (
Referring to
The embodiments described above show the example fasteners installed in blind holes in the workpiece which extend beyond the end of the fastener shank. This is not essential as the fastener will function in accordance with this invention even if the hole in the workpiece is non blind, and even if part of the threaded shank of the fastener projects beyond the end face of the workpiece, remote from the head of the fastener.
In the examples the mandrel head is illustrated as being of circular cross-section. It will be appreciated that a mandrel having a head cross-sectional shape which is polygonal, to provide a plurality of wrenching surfaces, and which provides an equivalent amount of ductile radial expansion of the shank, may be used.
It will be seen that the foregoing examples include the provision of a method of fastening which produces a high clamping force in the joined members without the need to severely deform the head of the rivet and such that the rivet head geometry of the initialled rivet is substantially unaltered from its original manufactured form.
Also provided is a method of fastening in which the shank is radially expanded and at the same time is axially reduced in length to provide compression, for example, of a non-rigid member being joined to the workpiece by the rivet.
Also provided is a method of fastening in which the rivet and its installation tool are configured such that during installation of the rivet, the head of the rivet is deformed towards the tail end of the rivet which is effective in closing any gaps which may be present between the member being joined and the workpiece.
It will be seen that the workpiece in which a fastener is to be installed should be of a material which is less hard than the material of the rivet. The rivet is intended for use in soft metals, such as aluminium and magnesium and in plastics.
The workpiece should have an aperture into which the shank of the rivet can be inserted, preferably with a minimum of clearance peripherally of the shank. The aperture should be a blind hole which may be of uniform diameter or with a shallow taper typical of holes produced by casting in aluminium or magnesium castings.
The member which is being attached to the workpiece by the rivet should have an aperture which is larger in diameter than the expanded diameter of the rivet.
The invention is not restricted to the details of the foregoing examples. For example, the bore of the fastener used need not be uniform in dimension along its length.
Number | Date | Country | Kind |
---|---|---|---|
0129878.5 | Dec 2001 | GB | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
---|---|---|---|---|
PCT/GB02/05661 | 12/13/2002 | WO | 00 | 1/24/2005 |
Publishing Document | Publishing Date | Country | Kind |
---|---|---|---|
WO03/051557 | 6/26/2003 | WO | A |
Number | Name | Date | Kind |
---|---|---|---|
4488843 | Achille | Dec 1984 | A |
4701993 | Bradley et al. | Oct 1987 | A |
Number | Date | Country |
---|---|---|
0725221 | Aug 1996 | EP |
0841491 | May 1998 | EP |
Number | Date | Country | |
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20050155212 A1 | Jul 2005 | US |