A Study of the Application of Low Frequency Oscillations to Multi-Tool Drawing Processes

Abstract

Within the last decade a number of researchers have investigated the effects of applying vibrations to the tooling when forming metals. Sane of these investigations indicate that vibrations may modify the state of stress in the body of the de forming metal and/or change the fricional boundary conditions between the tools and the workpiece. The first part of this thesis describes and discusses the research so far conducted in this field of metalworking, and attempts to isolate the areas of possible benefit to industrial practice. The remainder of this thesis describes the progress, and presents and discusses the results of a two-part investigation into the application of low frequency ‘axial vibrations (O to 100 Hz) to the tandem wire and fixed plug tube drawing processes. The investigation was conducted on a 2000 lbf horizontal bull block, the tools being oscillated by two electrohydraulic vibrators, Mild steel wire and medium carbon steel tube were selected for the workpieces, and sodium stearate, as the lubricant. Results show that when wire is drawn through two dies in tandem which are oscillated axially and in anti-phase; or when tube is drawn through the annular gap between a die and a fixed plug which are oscillated axially in antiphase: (a) The workpiece moves relative to the tools for a short period on every cycle. (b) During the remainder of the cycle the drawn product is elastically off-loaded and loaded by the motion Of the tooling, (c) The workpiece moves alternately over each tool. (d) The peak load in the drawn product is reduced by oscillations, since the product never experiences the force necessary for movement relative to both tools simultaneously. (e) There is no indication of a reduction in yield stress or frictional coefficient produced by the application of oscillations, (f) The reduction in peak drawing force is most marked for high frequencies and amplitudes, and low drawing speeds. A theoretical analysis was conducted for single die oscillatory wire drawing to establish the basic mechanics of the process. This analysis was extended to cover the tandem wire drawing process which produced predictions of the upper and lower limits of the peak drawing force reductions. Experimental data was found to fall within these predicted limits. The results of the investigation are discussed and suggestions for further work are presented