Thread former

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The thread former is a screw-like tool for the non-cutting production of internal threads .

Process description

The thread former is used in a similar way to the tap, i.e. it is used in a rotating machine tool . It consists of a cylindrical shaft with a continuous thread on the work surface. In contrast to the tap, this does not have to be interrupted by cutting edges, but can have lubrication grooves that also interrupt the profile. However, the shank does not have any flutes to hold machined material like a classic tap.

The production of an internal thread with a thread former is carried out as with the tap by screwing the tool into a drill hole with a suitable diameter. In contrast to tapping, however, the thread is not created by cutting out material from the drill hole, but by deforming it. The edges of the thread former press the material to the side and form a ridge that, after several turns, takes on the shape of the grooves.

commitment

The thread former can be used to machine cold-formable materials, i.e. most metals . In many materials, thread forming, due to work hardening and texturing, achieves a higher pull-out strength of the thread than would be achieved with cut threads. Thread formers must also be used when no chips are allowed, e.g. B. because a workpiece is difficult to clean.

Advantages of the procedure are:

• No chips
• No interrupted material fiber course
• Longer service life than with the tap
• Higher processing speed
• Smoother material surface after processing
• High precision possible.

Disadvantages of the procedure are:

• Higher demands on the drill hole tolerances
• Use as a hand tool is difficult
• Higher heat generation than when cutting
• Many materials cannot be shaped

Thread formers are often used for bores that have been produced using flow drilling .

variants

In reality, self- tapping tapping screws are often screws that form a thread . There are also thread-forming or thread-rolling screws for metric threads . These are able to generate a metric thread in the counterpart by displacement, if a corresponding drill hole exists. The thread-rolling screws often have a special profile that z. B. based on a deformed cylinder as a basic shape to reduce the sliding friction when forming the thread. The prerequisite for use is that the material to be displaced has a lower strength class than that of the screw. The use of such screws saves at least two work steps compared to conventional thread production with core hole drilling and threaded hole.