The major property of formed threads, in the case of steels, is the high strain hardening, which results from the plastic flow under very severe friction conditions at the interface with the tap, and leads to a strongly deformed layer at the thread surface. The lubricating effect of the tapping fluid is a preponderant operational parameter. It considerably influences the increase in hardness and in thickness in the deformed layer and it also influences on the tool damage and wear. Nevertheless, the strain hardening is responsible for an increase in formed thread strength under static force, compared to those obtained by cut tapping. Residual stresses in the deformed layer are compressive due to the predominance of their mechanical origin, which would increase fatigue strength. The second dominant property of formed threads is the geometrical quality which is much better compared to those obtained by cutting. Moreover, the tightening torque is unchanged by using form tapping, which facilitates the change of the cut tapping to the form tapping. Form tapping performance has been established on process aspects as well as on thread characteristics, and this process would be an alternative to cut tapping.
Precision and surface integrity of threads obtained by form tapping
2005
4 Seiten, 10 Bilder, 1 Tabelle, 8 Quellen
Aufsatz (Konferenz)
Englisch
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