GB2178986A

GB2178986A - Drill screw

Info

Publication number: GB2178986A
Application number: GB08619508A
Authority: GB
Inventors: George Jesson; Frank Piacenti
Original assignee: USM Corp
Current assignee: USM Corp
Priority date: 1985-08-14
Filing date: 1986-08-11
Publication date: 1987-02-25
Also published as: AU582457B2; IT1197865B; JPS6241416A; FR2586275B1; GB8619508D0; CA1275840C; DE3626627A1; DE3626627C2; IT8621477A0; GB2178986B; IT8621477A1; AU6110986A; FR2586275A1

Abstract

A drilling and thread forming fastener is provided having a pilot end 16 in which flutes 18 (and 20) are formed to provide cutting surfaces 22 (24) extending along a major axis. Lands having arcuate surfaces 36 (and 38) defining a minor axis of cross section of the pilot end lie in opposite quadrants between the flutes 18 (and 20), and lead to a substantially wedge shaped cutting tip 34. The inner arms dimension increases away from the tip to define a taper. <IMAGE>

Description

SPECIFICATION Drill screw The present invention relates to a rotary threaded fastener of the self-drilling and threading type, and more particularly to a fastener of that type which is manufactured by a pair of forging dies.

Various threaded fasteners of the self-drilling and thread forming type are known in the art, some of which are particularly adapted for manufacture by a milling process, while others are manufactured by a forging process which employs a pair of matched dies.

A typical example of the type of drilling and thread forming fastener which is preferably formed by the forging process is shown in U.S. Patent No. 3395603.

Fasteners manufactured in accordance with the teachings of this patent have met with wide acceptance as they provide a fastener which is simple to use, requiring no pre-drilling of the structure to which it is assembled, and fasteners of this type have proven to be easy to manufacture by mass production methods.

Recently, however, there has been a demand for self-drilling fasteners to be manufactured from high carbon steel, stainless steel, or metallic alloys which are of a hardness exceeding those of normal requirements. In some instances, it has been found that the forging dies employed to manufacture a drill point on these fasteners is susceptible to prernature breakage, when these harder materials are employed. It is considered that the stresses inherent in present point forging die configurations trap the harder material of the headed blank being worked on during the point forging operation, and that the entrapment of the blank material and its subsequent cold flow generates excessive stresses in the point forging die, causing in some instances, a premature point forging die breakage.

With the wide use of self-drilling and thread forming fasteners there has also been a requirement for the reduction in drilling time of the fastener. While existing point configurations which contain two flutes provide a satisfactory drill time in most applications, it is considered that they do not have sufficient clearance for chip flow to remove drilled material from the resultant hole, and thus to reduce drilling time. This occurs particularly when multi-layered assemblies of similar and dissimilar materials are operated upon.

Such failure to remove drilled material can result in binding between the point and drilled hole surface causing excessive heat generation and resultant slower drill times.

The present invention therefore has as an object to provide a drilling and thread forming fastener of the type manufactured by a die forging process, which is effective to facilitate an increase in point forging die life.

Another object of the present invention is to provide a drilling and thread forming fastener wherein a greater clearance for escape of drilling chips is provided in the resultant drilled hole, during the drilling process.

Another object of the present invention is to provide a drilling and thread forming fastener which is susceptible to a reduction in drilling time over those drilling and thread forming fasteners of the prior art.

The aforementioned objects and other objectives which will become apparent as the description proceeds are accomplished by providing a drilling and thread forming fastener comprising a threaded shank and a pilot end, said pilot end having a transverse major axis and a transverse minor axis intersecting at the centre line of said fastener, a pair of flutes extending longitudinally over the extent of said pilot end to form a pair of cutting surfaces, in cross-section defining said major axis, a pair of lands concentric with the centre line of said shank, each formed of a convex arcuate surface to define said minor axis at its radial extent on any cross-section of said pilot end and a substantially wedge shaped cutting tip formed at the terminal portion of said pilot end, wherein said minor axis increases in a linear progression from adjacent said cutting tip to a point remote from said cutting tip to thereby form an angular portion of said pilot end having a longitudinal outer surface which defines an angle with said fastener centre line.

Preferably, said cutting surfaces of a fastener in accordance with the invention are substantially parallel to one another over a greater portion of said pilot end angular portion. Each said land may be formed of a convex arcuate surface extending from the outer edge of one of said cutting surfaces to a similar diameter concave surface formed between said land and the inner edge of said other cutting surface and connecting the two. The minimum dimension of said minor axis of the fastener may be in the range of 20% to 50% of the maximum dimension of said minor axis, and the length of said angular portion of said pilot end may be in the range between 75% to 95% of said pilot end.

A pair of mating dies for forming the above described structure in a forged point process have inner surfaces substantially conforming to the configuration set forth above.

There now follows a detailed description of a fastener in accordance with the invention and illustrative thereof. This illustrative fastener has been selected for description by way of example and not of limitation of the invention.

In the accompanying drawings Figure 1 is a fragmentary elevational view showing a portion of the illustrative drilling and thread forming fastener aforementioned; Figure 2 is an elevational view showing the fastener portion of Figure 1 rotated through 90 ; Figure 3 is an end view showing further details of the fastener of Figures 1 and 2; Figure 4 is a sectional view taken along the lines IV-IV of Figure 3 showing details of the outer peripheral configuration of the fastener of Figures 1 though 3 at that section; Figure 5 is a sectional view taken along the lines V-V of Figure 3 showing details of the outer peripheral configuration at that section; Figure 6 is a sectional view taken along the lines IV-IV of Figure 3 showing details of the outer peripheral configuration of the fastener of Figures 1 through 3 at that section;; Figure 7 is an elevational view similar to Figure 2 showing the entire fastener of Figures 1 through 3 during the drilling operation; Figure 8 is a fragmentary elevational view similar to Figure 1 showing the fastener of Figure 7 rotated through 90 during the drilling operation; Figure 9 is a fragmentary elevational view showing an alternative embodiment of the structure of Figures 7 and 8; and Figure 10 is a perspective view showing one of a pair of dies which comprise the die set for manufacture of the fastener shown in Figures 1 and 9.

Referring now to the drawings, and in particular to Figures 1 through 3, there is shown a drilling and threaded forming fastener 10 having a shank 12 bearing the continuous thread 14 and a pilot end 16.

The fastener 10 is substantially symmetrical about the centre line of the shank 12 and has a transverse major axis XX and a transverse minor axis YY intersecting at the centre line. A pair of flutes 18 and 20 are formed in the pilot end 16 and extend longitudinally over the length of the pilot end to form a pair of cutting surfaces 22, 24 extending along the major axis and in general defining the extent of the major axis of the fastener at any section thereof.

Each of the cutting surfaces 22 and 24 defines a cutting edge 26, 28 running substantially parallel to the centre line of the fastener and terminating in an angular portion 30, 32. Each of the angular portions 30 and 32 of the cutting edge terminates at a wedge shaped cutting tip 34. The cutting tip is disposed for preliminary entry into the metal surface to provide a lead for the cutting edges 30, 32, 26 and 28.

A pair of arcuate surfaces 36 and 38 extend along the length of the pilot end and terminate at an angular surface 40 and 42, respectively, which extend toward the centre line of the fastener to join the cutting tip 34.

Referring now to Figures 4 through 6 it will be noted that as the cross section of the pilot end 16 progresses from the cutting tip 34 to the threaded shank 12, the major axis remains substantially constant while the minor axis increases, approaching the length of the major axis but remaining less throughout the length of the pilot end.

The taper of the pilot end 16 is considered to extend from the minimum dimension M as shown in Figures 2 and 3, to a maximum dimension W which is slightly less than the dimension of the X-X axis at that point.

The minimum dimension M is in the range of 20% to 50% of the dimension W, and the taper generally extends over a length L which is in the range between 75% to 95% of the pilot end 16.

In each of the sections shown in Figures 4 through 6, it can be seen that each of the arcuate surfaces 36, 38 is connected to a cutting surface 26 or 28 by a concave surface 44, 46 the concave surface forming the base of the flute 18 or 20 over the length of the pilot end 16.

Referring to Figures 7 and 8, a fastener 10 of the type described with reference to Figures 1 through 6 is shown having a hex head 50 for driving the fastener.

The fastener 10 is shown in its drilling position having progressed through the workpiece W forming an opening H therein by rotation during the yet incomplete drilling operation. As will be noted, when the fastener 10 rotates to its position shown in Figure 7 there is a substantial space formed between the fastener and the opening H providing for material to be moved into the flutes 18 and 20 and subsequently removed from the opening during the operation. The drilling itself takes place by the action of the cutting edges 26, 28 and 30, 32 of the fastener 10 as shown positioned in Figure 8.

Referring to Figure 9, there is an alternate embodiment of the invention similar to that shown in Figures 1 through 8. The fastener 1 Oa shown in Figure 9 is provided with threads 1 4a which extend down onto the pilot end 1 6a which is otherwise constructed in accordance with the description of Figures 1 through 8, above.

In Figure 10, there is shown a die which is constructed to form the fastener of Figures 1 through 9 by a forging process. The die 48 is one of a pair of dies, or a die set, similarly constructed, which when forced together under high pressure are capable of forming the pilot end 16 of the fastener 10.

With the above described fastener, the objective of the invention have been achieved since the resultant shape of the point forging dies which are employed to form the elliptical cross section forces the excess headed blank material to flow more naturally and easily from the point forging die contour, thereby reducing the resultant bursting stresses that accompany the compaction of material during the forging operation. Also, by forming the cutting surfaces 22 and 24 such that they meet the arcuate surfaces 36 and 38 of the lands at the concave surfaces 44 and 46, there are no sharp edges provided in the die structure to cause die failure. The elliptical reduction in cross sectional area also allows for a greater thickness of material in the forging dies at the point of greatest pressure, which strengthens the forging die and thus reduces breakage. As also is evident from Figures 7 and 8 of the drawing, the new configuration achieves nearly 360 of clearance for chip and material removal, that is, since the end points of the major axis of the elliptical cross section and the cutting edge of the point are the only points in contact with the material being drilled there is a reduced possibility of drilled material binding the drill point with the resultant slow down of drilling.

The fastener 10 has therefore provided an improvement over drilling and thread forming fasteners of the forged type which are known in the prior art and the configuration has proved to be advantageous in those applications where high carbon steels and stainless steel are employed in the manufacture of this type of fastener.

Claims

1. A drilling and thread forming fastener comprising a threaded shank and a pilot end, said pilot end having a transverse major axis and a transverse minor axis intersecting at the centre line of said fastener, a pair of flutes extending longitudinally over the extent of said pilot end to form a pair of cutting surfaces, in cross-section defining said major axis, a pair of lands concentric with the centre line of said shank, each formed of a convex arcuate surface to define said minor axis at its radial extent on any cross-section of said pilot end and a substantially wedge shaped cutting tip formed at the terminal portion of said pilot end, wherein said minor axis increases in a linear progression from adjacent said cutting tip to a point remote from said cutting tip to thereby form an angular portion of said pilot end having a longitudinal outer surface which defines an angle with said fastener centre line.

2. The fastener of claim 1 wherein said cutting surfaces are substantially parallel to one another over a greater portion of said pilot end angular portion.

3. The fastener of claim 1 wherein said land is formed of a convex arcuate surface extending from the outer edge of one of said cutting surfaces to a similar diameter concave surface formed between said land and the inner edge of said other cutting surface and connecting the two.

4. The fastener of claim 1 wherein the minimum dimension of said minor axis is in the range of 20% to 50% of the maximum dimension of said minor axis.

5. The fastener of claim 1 wherein the length of said angular portion of said pilot end is in the range between 75% and 95% of said pilot end.

6. The fastener of claim 2 wherein said land is formed of a convex arcuate surface extending from the outer edge of one of said cutting surfaces to a smaller diameter concave surface formed between said land the inner edge of said other cutting surface and connecting the two.

7. The fastener of claim 6 wherein the minimum dimension of said minor axis is in the range of 20% to 50% of the maximum dimension of said minor axis.

8. The fastener of claim 7 wherein the length of said angle of said pilot end is the range of 75% to 95% of said pilot end.

9. A drilling and thread forming fastener substantially as herein before described with reference to a) figures 1 to 8, or figures 1 to 6 and figure 9 of the accompany drawings.