ECAP process improvement based on the design of rational inclined punch shapes for the acute-angled Segal 2θ-dies: CFD 2-D description of dead zone reduction

A V Perig,N N Golodenko

doi:10.5194/ms-6-41-2015

Abstract

Abstract. This article is focused on a 2-D fluid dynamics description of punch shape geometry improvement for Equal Channel Angular Extrusion (ECAE) or Equal Channel Angular Pressing (ECAP) of viscous incompressible continuum through acute-angled Segal 2θ-dies with 2θ < 90°. It has been shown both experimentally with physical simulation and theoretically with computational fluid dynamics that for the best efficiency under the stated conditions, the geometric condition required is for the taper angle 2θ0 of the inclined oblique punch to be equal to the 2θ angle between the inlet and outlet channels of the Segal 2θ-die. Experimentally and theoretically determined rational geometric condition for the ECAP punch shape is especially prominent and significant for ECAP through the acute angled Segal 2θ-dies. With the application of Navier-Stokes equations in curl transfer form it has been shown that for the stated conditions, the introduction of an oblique inclined 2θ0-punch results in dead zone area downsizing and macroscopic rotation reduction during ECAP of a viscous incompressible continuum. The derived results can be significant when applied to the improvement of ECAP processing of both metal and polymer materials through Segal 2θ-dies.

Highlights

This article is focused on a 2-D fluid dynamics description of punch shape geometry improvement for Equal Channel Angular Extrusion (ECAE) or Equal Channel Angular Pressing (ECAP) of viscous incompressible continuum through acute-angled Segal 2θ -dies with 2θ < 90◦
In the present work we addressed the 2θ0-punch shape effect on material flow dynamics during ECAP through the numerical solution of the boundary value problem Eqs. (A1)–(A2), (B1), (C1)–(C7) for Navier–Stokes equations in curl transfer form (Figs. 3–10), taking into account the standard rectangular and improved 2θ0-inclined or 2θ0-beveled punch shapes
Both physical (Fig. 1b) and fluid dynamics (Figs. 3a, 4a, 5a, 6a, 7a, 8a, 9a, c, 10) simulations show that the application of a standard rectangular punch with 2θ0 = 90◦ for workpiece ECAP through acute-angled Segal 2θ -dies with 2θ < 90◦ is highly undesirable because of the resulting large material dead zone areas dDb in the neighborhood of the external die angle 2θ =

Summary

Introduction

For the last 20 years a number of research efforts in materials science related fields have been focused on wider development, implementation, commercialization and improvement of new material forming methods known as Severe Plastic Deformation (SPD) schemes (Boulahia et al, 2009; Haghighi et al, 2012; Han et al, 2008; Laptev et al, 2014; Minakowski, 2014; Nagasekhar et al, 2006; Nejadseyfi et al, 2015; Perig et al, 2013a, b, 2015; Perig and Laptev, 2014; Perig, 2014; Rejaeian and Aghaie-Khafri, 2014). The classical SPD processing method is Segal’s Equal Channel Angular Extrusion (ECAE) or Equal Channel Angular Pressing (ECAP) material forming technique (Segal, 2004). ECAE or ECAP realization is based on one or several extrusion passes of a lubricated metal or polymer material through a die with two intersecting channels of equal cross-section (Segal, 2004). Materials’ processing by ECAP results in the accumulation of large shear strains and material structure refinement with physical properties enhancement (Boulahia et al, 2009; Nagasekhar et al, 2006; Nejadseyfi et al, 2015; Segal, 2004). Segal 2θ-dies have neither external nor internal radii at the channel intersection points B; b (Figs. 1–2)

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Discussion

Conclusion