STRUCTURAL ASPECTS OF INNER THREADS MADE BY PLASTIC DEFORMATION

Phenomena that occur during the technological process of inner threading by plastic deformation are multiple (modification of the structure, fibre etc.) and they lead to increase of the qualitative index of parts. Cold plastic deformations are accompanied by elastic deformations of the metal layer; therefore, crystals dislocation and sliding phenomena that occur during processing, by displacements and partial springback of metal, cause a state of residual stresses within the plastic formed layer. The residual stresses are very different and unsymmetrical on the depth of formed layer, but they have the same values and distributions on the part length. Even if the force value can vary within very large limits, the residual stresses keep the same distributions in all cases.