DOUBLE FLUSH CLINCH STUD

RELATED APPLICATIONS The present application is related to provisional patent application serial number 60/620,345 entitled "Double Flush Clinch Stud" filed on October 21, 2004,

priority from which is hereby claimed. FIELD OF THE INVENTION The present invention relates to fasteners for securing two sheets of metal face-to-face. It further relates to fasteners that provide a flush attachment to the sheets by deformation of the sheet material. BACKGROUND OF THE INVENTION AND PRIOR ART

Most commonly, metal sheets are fastened together using rivets or spot

welds. These methods of fastening, however, have their drawbacks inasmuch as the spot welds leave a weld scale and burn the surface of the sheets. Spot welding is also not effective in sheet materials which are not easily welded, such as is the case with very thin or dissimilar materials. Furthermore, the burned sheets may

leave an unacceptable aesthetic appearance. Rivets can perform a similar function

but they do not leave a finish flush with the surface of the sheets which may be a

requirement in some applications. As yet another alternative, adhesives or other bonding agents such as epoxies can be used, however these are often very messy

and very costly. Additional methods such as Tog-L-Loc® which forms sheets

together and Henrob style fasteners deform the sheets being attached. Allowing for rotation is also possible. Of the technologies discussed above, the additional

feature of rotation can only be accomplished by a rivet which does not install flush.

U.S. Patent 3,242,962 to Dupree discloses a double-sided clinch type insert which installs between the sheets being joined. However, there are many problems and disadvantages of the Dupree fastener. For example, it allows for installation of

only one fastener, due to the fact that once the sheets are joined nothing additional can be inserted between them. This also negates the advantage of autofeeding and installing the Dupree fastener using more efficient, modern techniques. In addition, the Dupree fastener must be the same thickness as the width of the combined sheets. And finally, while the Dupree fastener may be modified to permit rotation by removing a knurl in one of the undercuts, the rotating clinch would significantly

weaken and fail after numerous cycles. There is therefore a need in the art for means for securing two metal sheets together which provides flush finish on both metal sheets, with the additional feature of providing a pivot for rotation, and avoids the weld scale or epoxy mess

of the aforementioned fastening methods. SUMMARY OF THE INVENTION

The present invention provides an extremely simple solution to the above-

stated need in the art for a fastening method which secures two metal sheets face-

to-face. The device is a clinching stud having adjacent fastening means of differing diameter so that the stud may be pressed into suitably dimensioned holes of aligned

sheets in a single pressing operation. As will be more fully described herein,

double flush attachment is provided without the need for the heat of welding or the

mess and expense of bonding adhesives, or deformation of the surface of the sheets being bonded.

More specifically, the applicant has devised a clinch-type fastener for

joining parallel sheets having aligned apertures comprising a shank having a head at one end and an endcap at the opposite end, the head being a first displacer, a top surface, and being of the largest diameter of the fastener. A first undercut groove on the shank is located immediately below the first displacer having a first diameter and a second displacer on the shank located immediately below the first undercut

groove having a second diameter less than the first diameter. A second undercut groove on the shank is located immediately below the second displacer, and the endcap is located immediately below the undercut groove and is of lesser diameter than the second displacer. The fastener preferably includes opposing planar circular top and bottom surfaces. The inventive fastener is advantageously employed in forming an assembly

wherein two metal sheets are joined in face-to-face contacting relationship, the first sheet having a first hole therein including sidewalls which occupy substantially all of the first undercut groove of the fastener and wherein the second planar sheet is joined in face-to-face relationship with the first sheet. The second sheet has a second hole therein of lesser diameter than the first hole in the first sheet and is

concentric therewith. The second hole is of lesser diameter than the first hole and

includes sidewalls which occupy substantially all of the second undercut groove of

the fastener. This assembly provides flush attachment with a top surface of the first sheet being coplanar with a top surface of the head of the fastener and the

endface of the endcap of the fastener being flush or sub-flush with the bottom surface of the second sheet. This results in an assembly whereby the top undercut groove can alternatively be underfilled with the material of the top sheet

respectively, while maintaining a high pushout strength. With this alternative, the

top sheet is effectively constrained between the head of the fastener and the second

sheet while permitting a strong pivot joint. Pushout performance remains high due to the larger diameter, and hence, displaced volume, of the top displacer and

undercut. Compared with some of the prior art described above such as the Dupree

fastener, the present invention provides the advantage of installing from the top of the sheets and therefore can be installed in any pattern on multiple fasteners as desired. Additionally, the present invention only requires a minimum thickness of the second sheet and the second sheet can be thicker than the lower shank of the fastener if the fastener is installed blind in the second sheet. Also, according to the

invention as will be more fully described below, the top sheet is contained between

the head of the fastener and the second sheet. This permits the top sheet to rotate freely by underfilling the undercut while maintaining a high push-out force and flush installation. From the following drawings and description of the preferred embodiment,

it will be appreciated by those of skill in the art that the objects of the invention have been achieved. While the present invention will be described with the

reference to a specific embodiment, the following description is illustrative of the invention and is not to be construed as limiting the invention. Various

modifications to the present invention can be made to the preferred embodiment by

those skilled in the art without departing from the true spirit and scope of the

invention. It will be noted here that for better understanding like components are designated by the reference numerals throughout the various figures of drawing

which follow.

DESCRIPTION OF THE DRAWINGS Figure 1 is a side view of the clinch stud of the invention with the displacers

and undercuts indicated. Figure 2 is a right front top exploded assembly view of the clinch connector in alignment with the receiving apertures of two sheets to be fastened. Figure 3 is a partial side sectional view of the installation of the invention by pressing. Figure 4 is a side sectional view showing the resulting completed installation of the invention. Figure 5 is a side sectional view of an alternate embodiment of the invention in which the clinch stud is installed into a blind hole in the second sheet.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to Figure 1, the present invention is a clinch-type fastener which has two pairs of displacers 13 and 15 and related undercuts 14 and 16

coaxially adjacent one another, the first pair 13 and 14 being larger in diameter

than the other pair. The fastener is terminated at the bottom by endcap 17. These

structures lie along a shank of the fastener between a top surface 18 and a bottom

surface 19 of endcap 17.

As shown in Figure 2, two sheets 1 and 2 are held in alignment with the

clinch connector of the invention being forcibly applied from above. Sheets 1 and

2 are shown separated in this figure for illustration only. The top sheet and second

sheet include aligned holes 3 and 4 of different diameter which correspond to the

diameters of the respective displacers and undercuts of the connector. The

diameter of hole 3 in the top sheet is greater than the diameter of hole 4 in the

second sheet, allowing the first advancing clinching feature of the connector to pass through it.

As depicted in Figure 3, an installation force is applied to punch 21 which

forces the clinch connector of the invention 11 into sheets 1 and 2 against

installation anvil 23. The arrow shows the direction of application of force to the

clinch connector which is applied to the first and second sheets. The connector 11

is applied by a single application of force during a pressing operation against anvil

23 which achieves the resulting installation as shown in Figure 4 wherein the top

displacer and undercut clinch into the top of the two sheets 1 being bonded and the

lower displacer and undercut simultaneously clinch into the second sheet 2.

Referring now to Figure 4, after the pressing operation is complete, the

sheets become locked together by the cold flow of metal by the top head/displacer

13 forcing the cold flow of metal 25 of the top sheet into the top undercut and

similarly the cold flow of metal 26 is displaced by displacer 15 into the bottom undercut within the second sheet locking the clinch stud of the invention into both

sheets, thus joining them together. As depicted in Figure 5, the second sheet 2 can

have a blind hole. As a significant advantage of the invention, if the first and or

second undercut grooves are of sufficient diameter such that they are underfilled by

the material of their respective sheets, the present invention provides a locking pivot whereby the sheets may be attached flush in a controlled manner while

providing for relative rotation between the sheets.

It should be understood that there may be other modifications and changes

to the present invention that will be obvious to those of skill in the art from the

foregoing description, however, the present invention should be limited only by the

following claims and their legal equivalents.