The extrusion force and the mean strain rate during the extrusion of strain rate sensitive materials

The force required to extrude a strain rate sensitive material under conditions of homogeneous deformation is calculated by the uniform work method. The force is shown to be a strong function of the rate sensitivity of the material. A new definition of the mean strain rate during extrusion is proposed, which is particularly appropriate to rate sensitive materials. For extrusion ratios of 40 to 160 and a power law strain rate sensitivity of 0.2, the present method leads to extrusion pressures 30 to 60 pct higher than when no account is taken of the rate sensitivity of the flow stress in the die zone. In an appendix, a design for a constant true strain rate (CTSR) die is described, which permits experiments to be carried out without the necessity for rate sensitivity corrections.