An Analysis of Redundant Deformations in Rotary Piercing

Abstract

In rotary piercing, as in most other metal-working processes, there occur redundant deformations, i.e. deformations which are not essential to the required change of shape of the workpiece. Since these deformations are responsible for unnecessary additional straining of the material and can impose limitations on the range of applications of the process, it is important to establish their nature and the way in which they vary with piercer conditions. Means can then be devised of reducing them and hence reducing the severity of the process. This investigation, based on work carried out on a specially designed experimental mill and using wax as model material, was concerned with three types of deformation, viz. circumferential shear, longitudinal shear, and shear due to twist. The incidence and pattern of these deformations for two-roll barrel piercers, both with freely rotating and with driven plugs, are analysed and the probable reasons for their occurrence are given. Methods of calculation of redundancy in the system are derived which enable all redundant deformations in rotary piercing to be compared with each other and, if necessary, with redundant deformations in other processes. General conclusions concerning the pattern and flow for various conditions of rotary piercing are set out and discussed.