Design and Fabrication of Equal Channel Angular Extrusion Process Analysis for Non-Ferrous Materials

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Chapter 2.3 Finite Element Analysis of Equal Channel Angular Extrusion Process:
Kim et al (2000) studied about the die corner gap formation in equal channel angular extrusion. The finite element analysis DEFORM 2D code was used to investigate the corner gap formation between die and workpiece during plain strain ECAP process. The comparison of the deformation and die corner gap formation behavior between strain hardening material and quasi perfect plastic material was made. The result found, the larger gap formation was formed in the material with higher strain hardening rate because the softer outside part of the workpiece in the deforming region flows faster in the strain hardening material. The corner gap formation reduced the strain in the outside region of the workpiece, increased the strain in the inside region and decreased the average strain. The strain distribution of the workpiece with larger die corner gap becomes more inhomogeneous. Li et al (2004) analyzed the formation of the plastic deformation zone (PDZ) and evolution of the working load along with the ram displacement in a single pass of equal channel angular extrusion (ECAE) with an intersection angle of 90°. This study explored systematically coupled with the effects of material response, outer corner angle (? = 0°, 45°, or 90°), and friction on ECAE deformation. Effective strain calculations are compared with various analytical models and it is directly an account for the PDZ tends to perform better. Nagsekhar et al (2004) studied about the optimal tool angle for equal channel angular extrusion of strain hardening materials by finite element method. This deformation technique was imported the large amount of plastic strain in to the bulk material through the application of uniform simple shear. This process can be carried out by finite element code ABAQUS/explicit. This analysis was used to analyze the deformation behavior of extruded materials and strain homogeneity was studied for different tool angles. By considered, the influence of realistic parameters like, strain hardening behavior and frictional contact between the die and sample. The result found, the optimal strain homogeneity in the sample with lower dead zone deformation, without involving any effects, can be achieved with channel angle of 900 and outer corner angle of 10°.
Nagasekhar et al (2005) investigated about the stress and strain histories in equal channel angular extrusion/pressing. In this analysis several plastic strains were induced in the material through multiple equal channel extrusion. It can produce bulk ultrafine grains and it was suitable for structural applications. In this study to design an optimized ECAE die, the stress-strain histories, and punch force requirements are very important. This work was carried out by the finite element analysis code was ABAQUS/Explicit for a range of different channel angles. The result found, the peak punch force decreased gradually with the increase in channel angle. Son et al (2006) studied about the finite element investigations of friction condition in equal channel angular extrusion. This study was mainly focused on the investigation of contact phenomenon at the interface between dies and the work piece. In this, the material flow and forming load were main requirement. In this used methodology was numerical simulation of an ECAE with a CP-TiGr-1 cylindrical specimen were carried out by applying the mixed finite element formulation with tetrahedral elements under non isothermal condition. Compression test was used to determination of material data. The result found from the analysis, the forming loads varied very sensitively depending on the friction conditions. Luri et al (2006) studied about the new configuration for equal channel angular extrusion dies. This process was used to impart severe plastic deformations to processed the material and improving the properties of the materials and reducing the grain size. In the present study discuss the configuration of new die proposed for ECAE process. This new configuration of die has more advantage compare to conventional die. The new die was obtaining higher plastic strain in each passage than conventional die. The optimization of die geometry was important using finite element methodology. This analysis was determined how the variations are effected on die geometry. The result found, both finite element method and analytical methods will allow us to affirm that by using this new die configuration it is possible to achieve higher deformation values per ECAE passage.
Zairi et al (2006) studied about the influence of the initial yield strain magnitude on the material flow in equal channel angular extrusion process. In this analysis using methodology was finite element method. This process was to simulate the material nonlinearity characteristics such as strain hardening, plastic strain ratio, and strain softening and die geometry on the deformation behavior of a sample were simulated. The result found from this analysis was, the plastic strain heterogeneity and sample bending were increases with initial yield strain. The maximum processing load was decreased. Nagasekar et al (2007) studied about the deformation behavior and strain homogeneity in equal channel angular extrusion. In this process, finite element code ABAQUS was used. In ECAE process several plastic deformation techniques were widely used for fabrication of bulk nano structured materials, powder materials and tubular materials. The deformed materials microstructure and mechanical properties were strongly depended on the amount of strain induced and strain homogeneity. Strain homogeneity and deformation behavior was most important to design an ECEA die. The result found, the effective strain variation across the width at the centre of the sample showed that strain homogeneity was greater. Cheng et al (2008) studied about the investigation of equal channel angular extrusion process of billet with internal defects. In this mainly focused on the shear plastic deformation behavior of a material during ECAE process. This process was governed primarily by the material properties, process conditions and die geometry. The used methodology was commercial DEFORM-2D (two-dimensional). This finite element code was focus on the plastic deformation behavior of material with internal defective voids. These simulations were investigated, the damage factor distributions, stress-strain distributions around the defective voids, and the void dimensions. The result found, the effective stress distribution is clearly greater in the void region of the billet in the inner and outer of the channel. The mesh element distribution was significantly increasing in the 2-turn ECAE. Jun et al (2008) studied about the die structure optimization of equal channel angular extrusion for AZ31 magnesium alloy based on finite element method. In this analysis DEFORM-3D finite element code was used. The die was designed in three dimensional geometric models with different angles and with or without inner round fillets in the bottom. Important process parameters were calculated using above finite element code. The process parameters were stress-strain data of compression test, temperature of die and billet, and friction coefficient on deformation process were discussed. The result found, the equivalent strains are increased by comparing the 3D FEM results with theoretical calculations because of thermal and friction conditions. The lubrication condition is important to plastic deformation. The deformation homogeneity caused by fillets of the outer corner is larger. Eivani et al (2008) studied about the dead metal zone formation on strain and extrusion force during equal channel angular extrusion. The deformation of material during ECAE was analyzed using upper bound model. The ECAE considered the effect of die angle and friction between the samples and die walls on the geometry of dead metal zone formation. The result found, the friction coefficient between the material and die wall was more. When increasing the die angle, the critical value for friction coefficients increased that means formation of dead metal zone formation was less. The larger deformation zone develops with increasing the friction coefficient and decreasing the die angle. The total strain not only dependent on the die angle but also depend on friction coefficient.
Patil et al (2008) studied about the influence of friction in equal channel angular pressing. The friction between die and work piece has most influence on the on the extrusion pressure and flow in the process. This analysis was carried out using the ABAQUS software. The three dimensional finite element analysis was using for different values of coefficient of friction to understand the influence on material flow, pressure and strain homogeneity in equal channel pressing. The result found this analysis was, if the friction was increased the corner gap decreased due to back pressure. The inhomogeneity in strain distribution decreases with increase in friction until the backpressure is just sufficient to fill the corner gap. Patil et al (2010) studied about the influence of outer corner radius in equal channel angular pressing. In this study the plastic deformation and strain distribution was necessary for understanding the relationships between strain homogeneity and die geometry. In this study, the three dimensional simulation of ECAP process was carried out for six outer corner radii with channel angle of 1050. The result found from above analysis was, the outer corner has a significant influence on the strain distribution in the body of work piece. The strain inhomogeneity was found to be high for both sharp and large outer corner dies. The average strain was decreased towards the head of the work-piece for all cases. Egrahimi (2010) studied about the investigation of strain behavior in the modified equal channel angular pressing die by 3D finite element code. ECAP process modification and die shape modification were carried out. The modification was the process to be continues for several passes, resulting a high homogeneity of strain distribution by using route C and the second modification was to obtain high magnitude of effective strain and high uniform strain distribution during ECAP process. In this analysis the simple and modified die was used to press the aluminum up to four passes. The result of the analysis was, the in-homogeneity of strain distribution was decreased in the modified ECAP die due to increasing the number of passes.