Thread forming tool with annular ridge

Description

TECHNICAL BACKGROUND OF THE INVENTION

The present invention relates to a thread forming tool comprising an elongated body, having at a first end a connector portion and at a second end a thread forming portion, said thread forming portion comprising at least one annular ridge about the circumference of said body.

It also relates to a method of forming a thread by means of such a thread forming tool.

TECHNICAL FIELD OF THE INVENTION

Such a thread forming tool is known from Hyatt et al. U.S. Pat. No. 5,678,962. It is however disadvantageous, since during milling, chips will be removed from the wall and will disturb the milling operation. Furthermore, the milling speed is relatively low.

SUMMARY OF THE INVENTION

The object of the present invention is to provide an improved thread forming tool.

This object has been achieved by the tool of the initially defined kind, wherein the cross-section of said body at an axial center of said ridge has a non-circular shape.

The object has also been achieved by the method of the initially defined kind, including introducing such a thread forming tool into an opening of a diameter larger than the diameter of said tool, while turning it about its own axis, and performing a circular movement about the circumference of said opening while moving said tool into the opening at a predetermined rate per turn about the circumference of said opening, hereby forming a thread of a predetermined pitch.

Since a relatively small part of the tool contacts the wall, causing less heat release, a longer working life and/or a faster thread forming operation is achieved compared to what is the case regarding the closest prior art tool.

Suitably said cross-section includes at least three lobes. Hereby, thread forming members are achieved.

Preferably, said annular ridge is perpendicular to the axial extension of the elongated body.

Suitably, said annular ridge is provided on at least one flank defining at least one flute for allowing supply of a cooling fluid, said flute dividing said ridge to a discontinuous ridge.

Advantageously, a plurality of parallel annular ridges are provided. Hereby efficient thread forming is achieved.

Preferably, the thread forming tool is made of solid carbide.

DRAWING SUMMARY

In the following, the invention will be described in more detail by reference to the accompanying drawings, in which

FIG. 1 illustrates a thread forming tool provided with one annular ridge,

FIG. 2 illustrates a thread forming tool provided with a plurality of ridges,

FIG. 3 is a cross-section of the thread forming tool shown in FIG. 1 and FIG. 2 along the line III—III, respectively,

FIG. 4 illustrates a thread forming tool provided with four flutes, and

FIG. 5 is a cross-section along the line V—V of the thread forming tool shown in FIG. 4.

DETAILED DESCRIPTION

FIG. 1 shows a thread forming tool 2 having an elongated body 4. At a first end 6, a connector portion 8 is provided and at a second end 10, a thread forming portion 12 is provided. The tool 2 is preferably made of a high speed steel or a solid carbide material.

The connector portion 8 is adapted to be connected to a tool holder of a drilling, milling or tapping machine.

The thread forming portion 12 is provided with a single annular ridge 14.

In FIG. 2, the thread forming portion 12 is provided with a plurality of annular ridges 14, adjacent ridges defining therebetween an annular groove 16. The ridges are thus separated and do not form a helix.

In FIG. 3 is shown a cross-section of the ridge 14 shown in FIGS. 1 and 2, respectively. The ridge has a non-circular diameter. More particular, five lobes 18 are provided for plastically deforming the inner wall of an opening such that a helical thread is shaped. Thus the body has a non-circular shape in a cross-sectional plane P oriented perpendicular to a center longitudinal axis A of the body at an axial center of the ridge.

In FIGS. 4 and 5 are shown the provision of four flutes 20 defined by four flanks 22. In this case, four lobes 18 are provided. The flutes 20 and flanks 22 extend in the longitudinal direction of the body 4 and interrupt the circumferential extension of each ridge 14. Each ridge is thus interrupted four times by the flutes. The flutes are provided for supply of a cooling fluid.

The thread forming tool is preferably made of solid carbide, even though high speed steel may be used.

OPERATION

The thread forming tool is introduced into an opening of a diameter larger than that of the tool itself, while turning it about its own axis. A circular movement is performed about the circumference of the opening, while the tool is moved into the opening at a predetermined rate per turn about the circumference of the opening. A thread of a predetermined pitch is formed by plastic deformation of the inner wall of the opening.

Of course, less than four or more than five lobes may be provided, e.g. three or eight. Furthermore, more or less than four flutes may be provided, depending on the number of lobes chosen.

Of course, also the ridge shown in FIG. 1 may be provided with one or more flutes.