Combined effect of drawing and stretching in axisymmetrical sheet forming

Abstract

In this paper, axisymmetrical forming of sheet materials is conceived as a mixture of pure stretch forming and pure deep drawing. A parameter χ is defined subsequently to describe the combined effect of thinning of the blank due to stretching and thickening due to inward flow of the flange. The efficacy of process parameters in sheet forming is better understood with the use of this parameter than with others such as the Erichsen number and the limiting drawing ratio. To increase the maximum polar height, it is desirable to increase the amount of stretching in the forming process, but excessive stretching can cause premature failure of the blank. That stretching may become more severe with the use of a higher blank holding load, a larger punch nose radius, a smaller die shoulder radius, and a larger drawing ratio should throw some light on the design ofdie sets.