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Abstract Extrusion processes are quite extended in the manufacturing of long products for a wide range of industrial applications. There are different approaches of extrusion processes, depending on either the final shape of the product to obtain or the maximum loading capacity of the equipment to be used. This work presents a comparative study of extrusion processes (solid and cup extrusion), considering both direct and indirect forming conditions and showing the most interesting differences between them. 36022
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The comparison is realized by Finite Element simulation of the processes, using the code DEFORM F2. The material is a low carbon steel (AISI-1010) and the same extrusion ratio and ram displacement are considered in all cases. By comparing the required forces it can be concluded that required loads are higher in cup extrusion processes than in solid extrusion ones. Regarding the friction load, the maximum contribution due to the die-billet contact in cup extrusion is much higher than in the case of solid extrusion. On the contrary, the maximum friction load contribution due to the container wall is much higher in the case of solid extrusion than in cup extrusion. © 2015 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of DAAAM International Vienna. Keywords: extrusion; friction; direct; indirect; FEM 1. Introduction Extrusion processes are one of most extended processes used in the manufacturing of long products for a wide range of industrial applications. There are different approaches of extrusion processes, depending on factors such as the final shape of the product to obtain or the maximum loading capacity of the equipment to be used [1]. Extrusion processes can also be pided into direct/forward and indirect/backward/reverse ones; in direct © 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).Peer-review under responsibility of DAAAM International Vienna 75 A. García-Domínguez et al. / Procedia Engineering 100 ( 2015 ) 74 – 83 extrusion, the directions of work piece and tool movement are identical, whereas in indirect extrusion, both movements are opposite to each other so the metal is forced to flow through the extrusion die in a direction opposite to the motion of the ram [2]. Friction is one of the most significant parameters to be considered in direct extrusion, as the workpiece surface is moving along the container, so the contribution to the required energy can be extremely high; however, recently some studies are also focused on friction influence in inverse extrusion [3] and extrusion of non-rounded products [4]. Friction reduction in metal forming processes such as extrusion ones contributes to a more efficient performance of manufacturing processes [5]. In the last decades, different tests to determine friction coefficients under cold forming conditions have been developed on the basis of extrusion processes [6-8]; especially when other methods, such as the ring compression test [9, 10], are not suitable for metal forming processes where the surface expansion is high. Some examples are the double-cup extrusion test [11], the boss and rib test [12] or the combined forward rod-backward extrusion [13], among others. For quasi-stationary conditions at extrusion processes, required forces can be calculated as the sum of ideal forming force, friction force at the container, friction force at the die wall and shear force.
Most of these studies have been implemented considering the Finite Element Method (FEM), as one of the most widespread computation tools in manufacturing engineering [14] and specifically in metal forming [15, 16]. By Finite Element Analysis (FEA) attention can also be paid to the improvement of die design [17]. In some other studies such as the one from Gouveia et al. [18], specific guidelines for FE simulation of cold forward extrusion are given. This work presents a comparative study of solid and cup extrusions of low carbon steel (AISI-1010), considering both direct and indirect forming conditions, showing in detail the most interesting differences between them. The comparison is realized by FE simulation of the processes, using the code DEFORM F2. Nomenclature A0 initial transverse section of the billet Af final transverse section of the billet D0 initial diameter of the billet Fc extrusion load due to friction at the container-billet interface Fdie extrusion load due to friction at the die-billet interface Fdh extrusion load due to homogeneous deformation Fex total extrusion load Ff extrusion load due to friction Fs extrusion load due to shear L remaining billet length a Johnson model empirical constant b Johnson model empirical constant rx extrusion ratio Hx extrusion deformation ߪത average flow stress 2. Methodology This work analyses four different extrusion processes using a numerical simulation tool, concretely the code DEFORM F2. FEA is very useful in the study of manufacturing processes based on plastic deformation of materials such as metal forming processes. DEFORM F2 is a code especially developed to perform two dimensional analysis of metal forming processes. It is a simulation software that shares the FEM solver with DEFORM-2D.