Die design and experiments for shaped extrusion under cold and hot condition

https://doi.org/10.1016/j.jmatprotec.2007.01.033Get rights and content

Abstract

The paper presents designing, fabrication and experiments for shaped extrusion of aluminum alloy (Al 2024) and lead alloy (70Pb30Sn). Flat and conical dies of H, T, L, elliptical and two-hole sections have been designed on the basis of upper bound technique by the authors for cold and hot extrusion. Hot extrusion has been performed in the temperature range 300–500 °C. Experimental investigation have been conducted for average extrusion pressure in cold case for lead alloy (70Pb30Sn) billets and in hot case for commercial grade aluminum (Al 2024) billets respectively. Extrusion pressure in the both cases has been compared with the theoretical work by the author for cold extrusion and for hot extrusion of aluminum alloy, result have been compared with a finite element based commercial package HyperXtrude. Theoretical results obtained by the upper bound technique and the HyperXtrude compares well with the experiments.

Introduction

An extrusion die through a proper die arrangement plays an important role to extrude complicated shapes. Different dies have been used for cold and hot extrusion of solid as well as hollow sections. The aim of die design has been to withstand a long die life with better mechanical and metallurgical properties for extruded products without defect. A good die design involves: design of optimal die length with proper bearing length and surface finish, selection of die profile, die arrangement, run speed and proper heat treatments, etc.

An extensive literature exists on optimal die profile and design based on power minimization criteria using the slip line field technique, the upper bound technique and the finite element method. Gunasekera and Hoshino1 [1], Yang et al. [2], Balaji et al. [3], Joun and Hwang [4]; Reddy [5] and Kumar et al. [6] are some of them. Several attempts have been made to analyse cold as well as hot extrusion problems. Some of the cold cases are due to Gatto and Giarda [7], Boer and Webster [8], Lee et al. [9], Yang et al. [10], [11], [12], Gunasekera and Hoshino [1], Shim et al. [12], Joun and Hwang [13], [4], Onuh [14] and most recently by Kumar et al. [15], [16]. A variety of sections both simple and complicated including many with re-entrant sections are cold extruded economically with high-dimensional accuracy. There has been a considerable interest in the investigation by Fragomeni [17] on the effects of die profile geometry and extrusion parameters for structure of flow patterns, extrusion pressure and mechanical properties of the product.

Many authors have shown that streamlined dies are superior to straight converging dies for reducing extrusion pressure in cold as well as hot conditions. Kumar et al. [15], [16] proposed a feature-based upper-bound analysis with strain hardening suitable for die design of non re-entry and re-entry cold extrudable shapes. In case of hot extrusion, some of the recent attempts are due to Altan et al. [18], Sheu and Lee [19], Hao and Li [20], Zienkiewicz et al. [21], Smelsor [22] and Reddy et al. [23]. Recently commercial software HyperXtrude [24], DEFORM-3D and FLUENT are being used for hot extrusion die design extensively. HyperXtrude [24] is hp-adaptive finite element program to analyze fluid flow and heat transfer problems commonly encountered in plastics and metal processing industry where materials undergo plastic deformation and flow is described by incompressible Navier–Stokes equations. HyperXtrude saves design and analysis engineer's time from performing several mesh generation and analysis cycles that are common with conventional numerical tools.

In the present work an attempt has been made to design and fabricate solid extrusion dies along with backers for H, L, T, two-hole and elliptical sections and to analyze extrusion under cold and hot conditions for the commercial grade aluminum (Al 2024) and the lead alloy (70Pb30Sn), respectively. Load versus ram displacement obtained from the experiment has been compared to verify with the theoretical work Kumar et al. [15], [16] for cold extrusion of lead alloy. Commercially available FE software HyperXtrude [24] has been used to verify the hot extrusion case of the aluminum alloy.

Section snippets

Design and manufacturing of extrusion die

Geometry and profile of an extrusion die constitute very important aspect of die design and determines the extent of redundant work done during the deformation. It cannot be totally avoided in extrusion process rather it can be minimized by choosing a proper die profile that minimize the extrusion pressure. Optimal die profile has been expressed as a function of several parameters as a polynomial with multiplying constants. The present work is mainly related to design of dies for solid sections

Experiments and validation

Experiments on the fabricated set-up by Bishwajit [28] have been performed using H, L, T, two-hole and elliptical dies manufactured in the Section 2. Average extrusion pressures for all the section is determined experimentally and load versus ram displacement curve have been drawn. A comparison of the extrusion pressure for cold extrusion of lead alloy is made with theoretical work obtained by the upper bound analysis Kumar et al. [15], [16]. HyperXtrude [24] has been used to analyze the hot

Conclusion

The experimental result for complicated shape extrusion confirms the proposed validity of the die design to be safe and satisfactory. Products have been found with better surface finish without any defect such as surface crack, central burst etc. It is also observed that as the complexity of section increases, extrusion power also increases and it compares well with the theoretical work for cold extrusion of lead alloy (70Pb30Sn) and with aluminum (Al2024). The study indicates that upper bound

Acknowledgements

The financial support from Department of Science and Technology (INDIA) [Grant No. III.5(109}/2001-SERC(Engg) Dated 19.02.2002] is gratefully acknowledged. Authors wish to express there thanks to Dr. A.K. Jha of Mechanical Engineering Department I.T.- B.H.U. Varanasi (INDIA) for his help and support.

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