Hydrostatic Ironing—Analysis and Experiments

Abstract

The classical ironing process by which walls of cups (or cans, etc.) are thinned is hereby replaced by a new fluid-pressure assisted process. This “hydrostatic ironing process” has the advantage of providing, under some restrictions, an unlimited amount of wall-thickness reduction. The analysis offered here is intended to explain why and how this can be achieved and to provide guidelines for designing such a process. Essentially, the analysis relates the governing variables of the process (geometrical variables, material variables, operating speed, and various friction parameters) with the applied fluid pressure via lower and upper bounds solutions. Based on these solutions, the technological advantages (and limitations) of this process are shown. Some generality is obtained by allowing the material to behave, not only as ideally perfect, but also as visco-plastic (to simulate warm temperature conditions) and as a power-law hardening material. The dynamic response to high speeds is predicted, showing that operating at high speeds is not recommended if the fluid pressure source is limited in its power. The two bounds of the solution, presented here, are relatively close to each other and coincide at small die angles. They provide, subsequently, a useful engineering tool for predetermining the operating fluid pressure for a given situation. The solutions match satisfactorily preliminary tests generated by a semi-industrial hydrostatic ironing machine with fluid pressure drive of 600 MPa. Presently, the process proves its capabilities by ironing wall-thickness of steel cups to 60 percent of its initial thickness, at relatively slow speeds (few centimeters per second).