Helical Extrusion Process of General Polygonal Section Shapes through Curved Dies

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Practically, the helical products used as a mechanical part to satisfy the needs of mechanical strength and artistic appearance. In addition, during recent 5 years it used to produce an ultra-fine grain metal structure. However, there are very little works regarding this type of extrusion so far. This work proposed a new formulation for helical deformation zone to produce general helical polygonal shapes through a streamlined die that are usually made by hot extrusion through taper die. The general die surface was represented analytically. The velocity and strain rate fields are derived depending on the volume constancy and the velocity boundary conditions. The upper bound forming pressure was obtained for various frictional conditions, area reduction, helix angle, and die length. The results show that the axis of the product does not rotate through the helical extrusion. The peak value of the strain rate is located close to the die outlet and decreases as the helix angle increases. The optimum die length becomes high as the helix angle increases. The forming pressure increases with increasing helix angle, area reduction, factor of friction, while decreases when the number of sides increases. The theoretical results were verified with previous work of zero twist and showed completely compatible. A finite element solution was done using hardening material model to verify the analytical results and metal flow and to examine the strain and stress fields in the product.