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Thread tools \ Technical introduction – thread forming

Core hole drilling when thread forming

Process:
In contrast to tapping, where sections are cut out of the material, thread forming is a non-cutting, pressure forming procedure.
Advantages:
ƒ No chip formation
ƒ Up to 30% higher surface quality than with thread cutting
ƒ Up to 40% higher processing speed than with thread cutting
ƒ Threads in through holes and blind holes can be produced with the same tool
ƒ Wide range of materials processable
ƒ Cutting of thread eliminated
ƒ Thread pitch and thread angle errors as with cut threads eliminated
ƒ Shaped threads have higher strength owing to non-continuous cut
Requirements: For all shapeable materials with elongation >10 %.
It is also necessary to drill core holes when thread Pre-drill diameter too large: By optimising the pre-drill diameter, a significantly
forming, in order to create a shaped thread. The ƒ Thread not fully formed higher service life can be achieved, not only in
core hole must have a defined diameter within a series production generally, but also with materials
certain tolerance range. Countersinking is also ƒ Moulding recess too big which are difficult to machine such as stainless
essential. When thread forming, however, the ƒ Profile height too low steel. This graphic illustrates the relationship:
core hole is significantly more accurate than when
tapping.
Optimal pre-drill diameter: ① Minimum dimension
Example: ƒ Thread fully formed ② Nominal dimension
Thread M10 x 1.5 is 9.30 mm. ƒ Small moulding recess ③ Maximum dimension
Tolerance = max. hole 9.38 mm - min. hole = ƒ Ideal profile height ④ Service life
9.26 mm = 0.12 mm. ⑤ Torque
When tapping, the tolerance for the same thread
is 0.3 mm. Pre-drill diameter too small:
ƒ Thread over-formed
It is important that the drilling is conducted with ƒ No moulding recess
very accurate drills. The best results are achieved
with solid carbide tools. The following graphics ƒ Profile height too high 4
illustrate the relationship between the various core
hole diameters and their impact on the formed
thread.
5

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h For more detailed information and explanations, refer to the technical manual.

Source: Hahn+Kolb Werkzeuge GmbH
Technical data subject to change. www.iconridge.com 229
Availability subject to country specific rules and regulations.