Thread Rolling Die and Method of Thread Rolling

This invention relates generally to thread rolling and more particularly to a novel and improved method rolling a threaded fastener having an annular ridge suitable for retaining a washer, clip or the like, and to a novel and improved die for performing such method.

It is known to assemble a washer, a clip or the like on a blank for a threaded fastener, usually against its head, and to then roll a thread on the blank. During the rolling operation the blank diameter increases along the threads and therefore the threads function to retain the washer or clip in position. In some instances, however, the clip or washer tends to engage the ends of the threads and is jammed or locked so that the fastener cannot freely turn within the washer or clip. In other instances the washer or clip tends to tip in a manner allowing it to rotate down along the threads until it is substantially spaced from its desired position or is threaded off of the fastener.

In order to overcome these problems the thread rolling operation is sometimes arranged to produce an annular rib or shoulder to secure the washer or clip in position. This has been done in some instances by clamping a thin metal blade against the top edge of the die in position to form an annular groove adjacent to the head end of the threads. When the groove is formed by the blade, blank material is displaced to form the annular rib beneath the washer or clip and functions to retain the washer or clip in position.

Difficulty is encountered with such blade assemblies. First, it is difficult to properly position and retain the blade. Also, if the thread groove shape is extended to the edge of the die adjacent to the blade, the thread convolutions have very thin sections at their ends which tend to break or chip causing rapid die deterioration. Also, the intersection of such thread grooves with the blade forms narrow or thin pockets which do not uniformly fill and the ends of the threads tend to be ragged, jagged or have unduly sharp edges.

If the ends of the thread grooves adjacent to the blade are ground or chamfered to eliminate the breakage or chipping other problems are encountered. In such case an annular rib is formed on both sides of the groove produced by the blade and the end of the thread is not uniform. The annular ridge remote from the head tends to jam when the fastener is threaded in a female threaded part and sometimes prevents full tightening of the fastener.

In accordance with the present invention a novel and improved die is provided for rolling threads in a blank and for simultaneously producing an annular rib suitable, fr example, for retaining a washer, clip or the like. The threads extend to an end where the thread form blends down to the root diameter to provide the threads with well defined and smooth ends. Spaced from the ends of the thread by a small distance is an annular rib which is formed by displacing the material of the blank substantially to the root diameter of the thread and causing axial displacement of such material into the required rib.

The illustrated die is provided with the usual thread convolutions which extend to a base line parallel to the lateral edge of the die and are tapered to zero depth at such base line. Located between the base line and the lateral edge of the die is an unthreaded ridge which operates to produce an annular groove extending from the ends of the thread. Such ridge on the die functions to displace the blank material to form the annular rib on the fastener which functions to retain the washer or clip in position.

In the preferred embodiment the die is chamfered in an angulated manner so that the side of the groove forming ridge on the die is inclined toward the top edge of the die to cause a continued axial displacement of the blank material to form the annular rib. Because the thread grooves fade to zero depth at a location spaced from the edge of the die, thin weakened sections do not exist and the tendency for the die to chip or break is eliminated. Also, the structure of the thread forming grooves, which includes the ends, which fade gradually to zero depth, insures tht the ends of the threads are smoothly formed and fully filled. Further, since the rib forming ridge joins the ends of the thread forming grooves the annular groove adjacent to the ends of the threads is produced without a secondary rib on the finished part at the ends of the threads. Consequently, the finished part can be threaded into a mating part all the way to the rib which is provided to lock the washer or clip. Finally, because the die is an integral structure, it is not necessary to attempt to position two working parts with respect to each other and there is no danger of slippage between two parts of type used in the prior art.

In accordance with another aspect of this invention, a method is provided in which blank material is displaced from the zone at the ends of the threads axially of the blank to produce an axial flow of blank material into the required annular rib. Such axial displacement produces a more sharply defined rib which can if required have a relatively large diameter. In accordance with this method the die is provided with a ridge which initially has very little width and wherein the width increases toward the finish end of the die to produce an axial displacement of blank material.

These and other aspects of this invention are disclosed more fully in the following description and drawings.

FIG. 1 is a plan view of one of a pair of flat dies incorporating the present invention;

FIG. 1a is a fragmentary section taken along 1a--1a of FIG. 1;

FIG. 1b is an enlarged fragmentary section taken along 1b--1b of FIG. 1;

FIG. 1c is an enlarged fragmentary section taken along 1c--1c of FIG. 1;

FIG. 2 is an enlarged fragmentary prospective view of the edge of the die illustrating the thread forming grooves and the ridge which functions to produce the annular rib;

FIG. 3 is a fragmentary section taken along 3--3 of FIG. 2;

FIG. 4 is an enlarged prospective view of the head end of a fastener rolled by a die in accordance with FIGS. 1 through 3 and;

FIG. 5 is a side elevation of the fastener illustrated in FIG. 4.

FIGS. 4 and 5 illustrate a threaded fastener formed by a die and a method in accordance with the present invention. Such fastener is illustrated as provided with a typical slotted head 10 and a threaded shank 11. The threads on the shank 11 extend to an end at 12 spaced from the head 10. Located intermediate the head 10 and the ends 12 of the thread is an annular rib or ridge 13 which in the illustrated embodiment has a maximum diameter substantially equal to the major diameter of the threads 11. Between the rib 13 and the head 10 is an unworked cylindrical portion 14 which is the original diameter of the blank used to form the fastener. Located around the cylindrical portion 14 between the head and rib 13 is a washer or clip 16 of any suitable type. It should be understood that the particular form of the washer or clip forms no part of this invention and can be of any type desired.

As best illustrated in FIGS. 4 and 5 the end of the thread blends smoothly to the root diameter of the thread at 12 and the shank is formed with a groove 17 having a depth equal to the root diameter which extends from the end 12 of the thread to the rib 13.

As discussed in detail below the material required to form the ridge 13 is displaced from the zone of the groove 17 during the thread rolling process. It should be noted that the shank of the screw is free of any obstructions to the threading of the fastener into a mating threaded part until the mating threaded part reaches rib 13. Consequently, the member 16 can be used for example as a terminal to properly grip even relatively thin wire when a screw fastener with the terminal member 16 is threaded into the appropriate mating part.

Referring now to FIGS. 1 through 3, a preferred die in accordance with the present invention is provided with a working face 21 on the die body 22. A lateral face 23 extends along one lateral edge of the body 22 and is the lateral face against which the washer or clip engages during the thread rolling operation. The working face 21 is formed with the usual thread forming groove 24 which are angulated with respect to the lateral face 23 at the thread lead angle of the thread to be formed by the die.

In the preferred die however, the grooves 24a, 24b, and 24c do not extend the full width of the working face. Instead such grooves extend to a base line 26 which is parallel to the lateral face 23 but spaced therefrom. At the base line the thread forming grooves 24a through 24c fade out as best illustrated in FIGS. 3 to zero depth at their ends 27. However, they have the conventional depth and configuration for the particular type of thread to be formed at all locations spaced from the fade out section between the point 27 and the point 28. Consequently, the end of the thread formed on the fastener blends to root diameter as best illustrated in FIGS. 4 and 5.

Located between the base line 26 and the lateral face 23 is a ridge 29 which functions to form the groove 17 and rib 13. In the illustrated embodiment the ridge 29 is tapered from substantially zero width at the start end 30a of the die as best illustrated in section 1a and FIG. 2. The width of the ridge 29 progressively increases in width toward the finished end 30b of the die as illustrated by comparing FIGS. 1b and 1c with FIG. 1a. At the location of the section 1c the ridge is at its maximum width which continues to the finished end of the die at 31. Preferably the side of the ridge provides a surface 32 at an angle of about 60.degree. with respect to the working face which extends from the top of the ridge 29 downwardly to a tapered bottom surface 33 parallel to the working face 21.

As best illustrated in FIG. 1 the surface 32 extends at a slight angle with respect to the long axis of the die until the point approximately at 34 is reached. Between the point 34 and the finished end of the die the surface 32 is parallel to the lengthwise axis of the die. Also the bottom surface 33 has a maximum width at the beginning end of the die and tapers to zero at the point 34.

As the blank being rolled engages the die the ridge 29 penetrates the blank material to the same depth as the thread forming grooves. As the blank rolls along the die the surface 32 causes a continuing axial force which moves the material of the blank axially of the blank to form the ridge 13. Therefore, substantially all of the material displaced from the groove 17 formed by the ridge 29 is moved into the rib 13 and there is no tendency for a second ridge to be developed at the ends of the threads themselves. It is recognized that this axial force may produce some limited elongation of the blank. However, for blanks formed of conventional materials the displacement of blank material into the ridge occurs with little axial stretching of the blank itself.

In instances in which the washer or clip has a sufficiently large diameter, it is preferable to extend the surface 32 all the way to the intersection of such surface with the plane of the lateral face 23 and it is not necessary to form the tapered bottom surface 33. On the other hand when the clip 16 is of a small diameter or is an elongated terminal type device, the structure best illustrated in FIGS. 2 is preferred since it insures that the washer is held up against the head as the blank is rolled by the dies.

The illustrated die functions to produce a clean uniform thread to the end 12 where the thread blends down into the root diameter of the blank and the material displaced during formation of the groove is moved axially of the blank to form the ridge 13. In practice it has been found that with the present invention a sufficiently large ridge 13 is formed to properly lock a washer or clip member 16 properly adjacent to the head 10 without jamming and that if desired, such ridge can be formed to have a diameter even larger than the major diameter of the threads. Further, the axial displacement produces a more sharply defined rib than devices which do not produce continued axial displacement as rolling progresses. In the illustrated fastener the ridge 13 has a maximum diameter substantially equal to the major diameter of the thread.

It should be understood that the present invention is not limited to flat dies of the type illustrated but that it is also applicable to rotary dies and arcuate dies. Also, it should be understood that although this invention is illustrated in conjunction with the manufacture of fasteners assembled with washers, clips or the like, that it is also applicable to the manufacture of fasteners which have ribs or shoulders for other purposes.

Although a preferred embodiment of this invention is illustrated it is to be understood that various modifications and rearrangements may be resorted to without departing from the scope of the invention disclosed and claimed.