Hollow Twist Extrusion: Introduction, Strain Distribution, and Process Parameters Investigation

Twist Extrusion is kind of severe plastic deformation process which enhances the strength of materials by applying a shear plastic strain and consequently grain refinement. The strain distribution is minimum at the center of the die and is maximum at outer surfaces. In this article, the plastic strain distribution will be studied within a hollow section. The billet is solid in previous experimental and numerical studies in the literature, but by adding a new die (mandrel) for extruding the hollow billet, it is possible to twist extrude hollow sections. A finite element model is developed in the ABAQUS finite element software and the effects of process parameters (slope line angle, thickness and friction coefficient) on equivalent plastic strain distribution are investigated. The numerical results show that the equivalent plastic strain will be increased by increasing the slope line angle and decreasing the thickness and more homogeneity in the strain field will be obtained. In addition, increasing the friction coefficient higher than 0.2 can lead to an increase in induced plastic strain. The required force for twist extrusion will be increased by increasing the friction coefficient. Graphical Abstract:

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