New Die Design Configuration for Grain Refinement by Hollow Twist Extrusion (HTE) Process

The severe plastic deformation (SPD) processes used for applying an extensive shear plastic strain in the material and consequently grain refinement and increase in the strength of materials. The strain distribution is very important and more homogenous plastic strain is desired in SPD process modifications. In this article, four different die configurations will be investigated during the hollow twist extrusion (HTE) process and the plastic strain distribution will be compared within a hollow section. The die configurations are similar slope line angle of inner and outer dies (SD), opposite slope line angle between the inner and outer dies (OD), outer die with twist zone and flat inner die (FI) and inner die with twist zone and flat outer die (FO). The Von-Mises stress, plastic strain, and material deformation are studied by using a finite element model which was developed in the ABAQUS finite element software. The results show that the FI and FO die configuration produce higher plastic strains than SD die configuration, but the strain homogeneity is not satisfactory. The plastic strain is higher and more homogenous for OD die configuration in comparison to the other die configurations. The required force for twist extrusion of the billet is almost equal for FI and FO die configuration (similar to 216 kN) and increases to about 256 kN for SD die configuration (16% increase). The required force for OD die configuration increased once more to 370 kN (44.5% increase). The element distortion along the two defined paths determined the material flow during the HTE process. The flat die retards the material flow for FI and FO die configurations. A significantly material flow will happen for OD die configuration. The element distortion leads to better material mixing in OD die configuration and consequently higher magnitude and more homogenous plastic strain distribution and higher grain refinement will be obtained. Graphic

Automated summary

The study investigates the influence of four different die configurations on the plastic strain distribution during the hollow twist extrusion (HTE) process, showing that the die configuration with opposite slope line angles between inner and outer dies has the highest and most homogeneous plastic strain distribution.