This paper describes the measurement of net punching force required for plastic deformation of aluminum sheet in folding work.
For the object of measuring the net punching force was used an octagonal ring road cell, which was proposed by Loewen and Cook as a tool dynamometer in orthogonal cutting process.
The net punching force was obtained being resolved into vertical and horizontal componemts by means of the above apparatus.
The material mainly used in the experiment was annealed aluminum sheet; and annealed mild steel and stainless steel were also used for comparison.
The results were obtained under a wide range of experimental conditions with respect to punching force-stroke diagram and shape of bent side and bending angle of the product.
Both vertical and horizontal punching forces reached their maximum values at a very early stage of deformation process. The maximum values depended upon the sheet material and working conditions; they were lower when the material was softer.
Shape accuracy of the bent product was improved by axial tensile force, but the criterion of this force was not analytical obtained.
An expression showing one component of this force, which means the frictional force between the punch and sheet material, was given. Its numerical values were calculated by this expression from measured values of punching forces and bending angles.