Clinch fastener with a spiral shank

Abstract

A press-in fastener has from top to bottom: a head, a clinch feature, and a spiral, knurled shank. The fastener can hold two parts together by first clinching with a first metal panel, and then being pressed into a hole in a second, less ductile panel having a uniform interference between the knurled fastener shank and the hole. The knurled shank has a helix configuration that allows for use in non-ductile materials and eliminates the need for tapered holes and screws for applications that do not require disassembly.

Claims

1. A press-in fastener, comprising: a head at a top being the largest diameter of the fastener; a cylindrical displacer of lesser diameter than the head and located immediately below the head; an undercut beginning immediately below the displacer and adapted to receive the cold flow of material from a first object caused by contact with the displacer such that the fastener is rigidly affixed to the first object; a spiral knurled shank extending downwardly from below the undercut to a distal bottom end of the fastener, said shank inwardly tapered beginning at the undercut and having a spiral helix knurled surface composed of helical crests, and corresponding valleys between the helical crests, said helical crests constructed at a uniformly consistent helix angle to provide a self-threading rotation to the fastener when pressed into a receiving hole of an object by interference fit, said crests and valleys winding in a continuous gradually tightening curve beginning at the undercut; and wherein an outer surface of the helical crests lie at a uniform helix angle of approximately 45 degrees to a central axis of the fastener.

2. The press-in fastener of claim 1 wherein an outer surface of the helical crests lie at a uniform helix angle of 45 degrees to a central axis of the fastener.

3. The fastener of claim 1 wherein the displacer is a single displacer which has an outer surface that spans 360 radial degrees.

4. The fastener of claim 1 wherein the undercut is a groove with an inner surface that spans 360 radial degrees.

5. An assembly, comprising: a first object composed of ductile material having a first hole for receiving a fastener; the fastener of claim 1 pressed into the first hole and affixed to the first object by the cold flow of material of the first object into the fastener undercut; and a second object having a second hole for receiving the spiral shank of the fastener whereby the shank is rigidly affixed to the second object by interference fit with the helical crests of the shank knurl such that the first and second objects are thereby rigidly affixed to each other.

6. The assembly of claim 5 wherein the first and second objects are positioned in abutment.

7. The assembly of claim 6 wherein the outer surface crests lie at a uniform helix angle of 45 degrees to a central axis of the fastener.

8. The assembly of claim 7 wherein the second object is composed of a material of less ductility than the ductility of the first object.

9. The assembly of claim 8 wherein the second object is an ABS plastic or a printed circuit board.

10. The assembly of claim 9 wherein the first object is composed of aluminum.

11. The assembly of claim 5 wherein the fastener is affixed to the second object without the fastener being deformed.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a partially-sectioned side elevation of a fastener in accordance with a preferred embodiment of the invention;

(2) FIG. 2 is a bottom plan view of the fastener of FIG. 1; and,

(3) FIG. 3 is a partially-sectioned view of the fastener of FIG. 1 joining two panels by pressing between a punch above and an anvil below.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(4) A fastener 10 in accordance with a preferred embodiment is shown in FIG. 1. The fastener generally comprises, in order from top to bottom, an enlarged head 11, a displacer 13, an undercut 15 and a helically, knurled shank 17. The helix angle A is approximately 45 degrees from the fastener axis 12 but may vary slightly depending upon its particular application.

(5) FIG. 2 is a view from below the fastener looking upward. It shows the diametric relationship between the head 11, the displacer 13, and the knurled shank 17.

(6) FIG. 3 shows the fastener 10 installed in two abutting panels 20 and 22, holding the panels together. The fastener 10 and panels are assembled by pressing between a punch 21 above and an anvil 23 below. Both panels have appropriately sized and aligned receiving holes to accept the fastener 10 in a single pressing stroke. The angle of the helix knurl of the fastener shank 17 of approximately 45 degrees will permit the rotation of the fastener as it is pressed in. This provides a self-threading action that reduces the required press force and provides a stronger connection. In the last portion of the press stroke the undercut 15 receives the cold flow of material from the top ductile panel 20 and thus the tack fastener 10 becomes rigidly attached to the top panel 20 which can be composed of metal such as aluminum. Simultaneously, the shank becomes rigidly attached to a bottom, less ductile panel 22 which may be composed of a plastic such as ABS or be a printed circuit board (PCB), thereby joining the two panels. In additional to the examples provided here, the panels may be composed of any suitable material according to the degree of ductility required by the particular dimensions of the fastener and the pressing force.

(7) It will be apparent to those of skill in the art that the object of the invention has been achieved and that many variations and adaptations of what has been disclosed are possible. For example, the fastener can be composed of any material suitable for its function. Likewise, the composition and dimensions of the panels as disclosed depict but one embodiment of the invention. There may be many other variations on the embodiment depicted herein that do not depart from the spirit and scope of the invention, which shall be determined only by the claims and their legal equivalents.