Die Corner Angle Research Articles

Deformation mechanism finite element analysis and die geometry optimization of magnesium alloys by equal channel angular processing

Magnesium alloys are one of the highly promising structural metals. hcp structure makes it less plastic at room temperature, which greatly limits the development of magnesium alloys. The problem of poor plastic deformation of magnesium alloy can be solved by grain refinement methods, and equal channel angle pressing is one of the more effective methods in grain refinement. In this paper, two-dimensional dynamic simulation of equal channel angle pressing of magnesium alloy is carried out by using finite element software DEFORM F2™. The deformation of magnesium alloy with different of die angles and die corner angles was analyzed. The results show that in the main deformation zone, when the die angles are different, the deformation of the workpiece in the horizontal direction is very uniform. However, in the longitudinal direction of the workpiece, the larger the die angle is, the more uniform the workpiece deformation is. The die corner angle has no significant effect on the uniformity of workpiece deformation in the longitudinal direction, but it has an effect on the dead zone area and workpiece warpage. The dead zone area and workpiece warpage increase with the increase of die angle.

Impact design of die parameters on Severe plastic deformation during Equal channel angular pressing: An overview

Equal channel angular pressing causes less uniform deformation than simple shear, even though its not as obvious as with other metal forming procedures. Investigation is done into how internal and external factors affect the deformity inhomogeneity through Equal .channel angular pressing. Finite element analysis of plastic deformity are integrated with die corner angle and the strain harden ability of metallic workpiece. The material characteristics are significantly influenced by the type of plastic shear deformation that occurs through Equal channel angular pressing and this is primarily impacted by the die geometry, the properties of the material and the process factors. Segmenting the workpiece into a front transient zone, end transient zone, outer less sheared zone and the remaining shear deforming zone allowed researchers to examine the uneven strain distribution throughout the workpiece. The deformed geometry for the non-hardening and it was assumed that rate-insensitive materials would be largely homogeneous. In materials that are strain-rate sensitive, gaps between the upper and lower channels developed, whereas strain-hardening materials experienced the corner gap. The strain hardening and implications of strain-rate sensitivity exponent had a considerable impact on the deformation inhomogeneity. Metals having an ultrafine grain microstructure can be created by severe plastic deformation. The FE models were used to affect the process and they all took as inputs the material properties, load variation, Different velocity and boundary conditioned. For the purpose of evaluating the impact of the channel angle on the AA5083 sample, The FE analysis produced the value of strain distribution. When the channel angle was 1200, there was less strain overall, but there was also less concentrated stress in the channel corner area.

Effective Damage Indicator for Aluminum Alloy (AA6082Zr) Processed by ECAE

The present research aims to study the influence of equal channel angular extrusion (ECAE) parameters (die channel angle, die corner angle, and friction coefficient) on cracking and fracture tendency. For this type of analysis, a MATLAB code integrated with finite element Abaqus/Explicit model was developed and used. A parametric study is done to investigate how the damage tendency varies with changes of ECAE parameters. The distribution of the damage factor based on Cockcroft–Latham equation for different channel angles, corner angles, and friction coefficients is depicted. It is observed that the appearance of cracks on the upper surface is more likely to occur than on the lower surface. The reduction in friction coefficient does not guarantee minimum damage tendency. Finally, the optimum parameters for reducing the fracture tendency in ECAE are presented.

Routes Investigation in Equal Channel Multi-angular Pressing Process of UFG Al−3% Mg Alloy Strips

Equal channel angular pressing is one of the most efficient techniques among severe plastic deformation methods that enhances the mechanical properties of polycrystalline metals by refining subjected grains. In this article, equal channel multi-angular pressing was conducted on Al5754 strips. At the first step, finite element analysis was applied to evaluate the possible routes (A and C). The initial analysis showed that the route C was better in strain homogeneity compared with route A. Thus, the route C was considered for further investigations. Then, the effects of the die geometrical parameters on the created equivalent plastic strain (PEEQ) and process force were investigated by FEM. The results showed that the die channel angle (Φ2) was the most effective parameter on both PEEQ and process force, while the die corner angle (ψ1) had the least effect on both objectives.

Finite Element Analysis of ECAP, TCAP, RUE and CGP Processes

A finite element method was applied to study the various severe plastic deformation processes like, Equal Channel Angular Pressing (ECAP), Tubular Channel Angular Pressing (TCAP), Repetitive Upsetting and Extrusion (RUE) and Constrained Groove Pressing (CGP), considering aluminum AA-390 alloy as specimen material for all these processes. FEA simulation was carried out using AFDEX simulation tool. Effect of the various ECAP process parameters like, die corner angle, channel angle, and the coefficient of friction were analyzed. The die corner angles were divided into 2 equal parts for increasing the effectiveness of ECAP process, thereby increasing the channel number from 2 to 3 and further, their influence on ECAP process was investigated. A 3D simulation of TCAP was carried out for die shapes like triangular and trapezoidal, and variation of the generated stress and strain was plotted. In CGP, four cycle operation was carried out; wherein each cycle is composed of corrugating the specimen and subsequent straightening to original dimension. During RUE process, a maximum effective stress of 683.1 MPa was induced in the specimen after processing it for four complete cycles of RUE process; whereas the maximum strain induced during the same condition was 3.715.

Non-isothermal analysis of die corner gap formation for materials deformed by multi-pass ECAP

In this paper, the upper-bound solutions proposed by Eivani and Karimi Taheri [Comp. Mater. Sci. 42 (2008) 14] to calculate processing force and evaluate die corner angle Ψ formation in terms of tribology and die configurations during cold single pass equal channels angular pressed metals with constant flow stress were extended to work-hardening metals processed by two passes according to route A by using the Swift model combined to von Mises isotropic plasticity criterion. Also, adiabatic heat equation was coupled to solutions to express the final temperature of the workpiece. For that, thermomechanical properties of a hot-dip galvanized interstitial-free (IF) were considered and its behavior under pressing was evaluated to non-hardening and work-hardening conditions in all performed analyses. By including work-hardening in the models and for the critical friction factor of 0.4, theoretical predictions after single pass showed a decreasing of die corner angle and pressing force predictions and increasing of effective plastic strain and end temperature for all friction conditions and tooling geometries evaluated. In addition, after second pass, these responses showed higher values. Finally, with the proposed upper-bound models it was possible to analyze the dependency of angle Ψ, effective plastic strain, pressing load and sample temperature with the instantaneous workpiece height at the entry surface of deformation zone.

Upper-bound analysis of die corner gap formation for strain-hardening materials in ECAP process

In this paper, the upper-bound solutions proposed by Eivani and Karimi Taheri (2008) to calculate processing force and evaluate die corner angle Ψ formation for distinct friction conditions and tooling geometry during single pass equal channels angular pressed perfectly plastic metals at room temperature were extended to work-hardening metals by using the Hollomon model combined to von Mises isotropic plasticity criterion. Also, plane strain finite-element models were developed to validate the proposed extended analytical solutions by comparing the predictions of angle Ψ, effective plastic strains and pressing force. Mechanical properties of an aluminum Al6070 alloy were considered and its behavior under pressing was evaluated to non-hardening and work-hardening conditions in all performed analyses. The theoretical predictions consistently showed that higher values of die corner angle Ψ and smaller predictions of both effective plastic strains and pressing force are obtained when the work-hardening behavior is included in the models independently of either tribology or tooling arrangements. These aspects were confirmed by comparison with the respective finite-element predictions. In addition, with the proposed upper-bound models it was possible to analyze the dependency of angle Ψ, effective plastic strain and pressing load with the instantaneous workpiece height at the entry surface of deformation zone.

Numerical Simulation and Experimental Investigation of Grain Refinement Behavior in Equal Channel Angular Pressing/Extrusion Process

The ultra-fine grained (UFG) materials have been widely investigated due to their mechanical properties such as super high strength and super high plasticity. The finite element simulation schemes are planned for the deformation mechanism of ECAP pressing. It will greatly affect the extrusion process when processing parameter changed such as die geometrical parameters and friction condition. It is considerable to determinate the range of die channel angle and die corner angle during ECAP process, and a moderate die corner angle is usually chosen. The friction condition of the ECAP should be lubricated as good as possible in the pressing on the basis of optimal die geometrical conditions. The ECAP process is a non-uniform shear deformation process in the cross-section of the workpiece for first-pass pressing. There have low angle grain boundaries along the cross-section of the grain microstructures. For the multi-pass pressing, although the pressing pass numbers are same, the processing routes were of important significance on the grain sizes and grain distribution and grain boundaries (GBs) orientations of workpieces. The formation mechanism of nanostructure was given for the ECAP through studying the deformation behavior and dislocation’s evolution. The dislocation is one of the main defects in the processed materials, but the form of the dislocations and its density are difference for different processing route. The processed workpiece with high surface quality, refined grain microstructure and optimization grain boundaries were obtained with optimal processing parameters and routes.

Equal channel angular pressing die to extrude a variety of materials

In order to design an equal channel angular pressing (ECAP) die that can be used to process a variety of materials, it is crucial to understand the effect of die design and material parameters on the deformation behaviour, strain distribution and load requirement. In this regard numerical modeling has been carried out to understand the effect of three important parameters: Die corner angle ( ψ), friction and constitutive relationship of materials [ σ = f( ε, έ, T)]. Though these parameters have been studied and reported earlier, current study has produced some significant new results and has helped to arrive at an optimized die design which can be used to process a variety of engineering materials. Physical modeling experiments using plasticine and tin have been used to validate the numerical modeling results and to gain further insight in to the process. The results obtained are presented and discussed.

Die design for homogeneous plastic deformation during equal channel angular pressing

It is well known that deformation during equal channel angular pressing (ECAP) is not as perfectly homogeneous as simple shear, although the inhomogeneity is not as distinct as the other metal forming processes. The sources of this inhomogeneity are (i) external conditions such as die geometries, loading modes, temperature, ram speed and die frictions and (ii) internal conditions such as material's strain hardenability and strain rate sensitivity. In spite of a lot of recent research results, factors and mechanisms of the inhomogeneous deformation were not elucidated systematically. In this paper, the effects of external and internal factors on the deformation inhomogeneity during ECAP are investigated. The finite element analyses of plastic deformation are employed for this purpose in conjunction with die corner angle and strain hardenability of metallic workpieces. Optimum die corner angles with strain hardening exponent are presented.

The development of hardness homogeneity in aluminum and an aluminum alloy processed by ECAP

Equal-channel angular pressing (ECAP) is an effective fabrication process for obtaining ultrafine-grained materials. This paper examines the development of homogeneity in materials processed by ECAP with emphasis on samples of pure aluminum and an Al-6061 alloy processed by ECAP for up to 8 passes at room temperature. The Vickers microhardness was recorded on the polished cross-sectional planes of each as-pressed billet and the results are plotted in the form of contour maps to provide a pictorial depiction of the hardness distributions throughout the cross-sections. The factors influencing the homogeneity are examined, including the die corner angle within the ECAP die and the number of imposed passes. It is shown that good homogeneity may be achieved through ECAP processing when the number of passes in ECAP is reasonably high.

The Effect of Cold Equal Channel Angular Process on Texture of Magnesium Alloy (AZ31)

In the present study, we have attempted to refine a microstructure of conventional AZ31 magnesium alloy using a new combination process including hot extrusion followed by a cold equal channel angular pressing (ECAP). ECAP die was specially designed with an inner die corner angle of 135 degree, the fillet angle of 45 degree and dimensional thermo-coupled elastro-plastic material model in order to understand the change of stress and strain of the deformed material after a cold ECAP. ECAP for the AZ31 alloy, which was extruded in the extrusion ratio 20 to 1 and heat-treated at 623K, was successfully carried out at room temperature. The uniform shear band obtained from experiment was well matched with the zone of effective strain more than 0.533 estimated from calculation. On the basis of the results, it is suggested that the room temperature ECAP makes microstructure to be refined and the basal plane to be rotated slightly from extrusion direction to axis direction. Compressive yield strength of AZ31 alloy can be enhanced up to twice in applying ECAP process. Hall-Petch relations do not fit to the experimental data This can be ascribed to the texture effect. Room temperature ECAP process is very promising in improving mechanical properties of AZ31 alloy in terms of grain refinement and texture control.

Application of a Cold ECAP to Magnesium Alloy (AZ31) by a Combination of Extrusion Process

It is well known that magnesium alloys have difficulties in room temperature formability because of their HCP structure. As a basic approach to enhance a cold formability, a new combination process including an extrusion followed by a cold equal channel angular pressing (ECAP) was attempted. ECAP die has an inner die corner angle of 135 degree, the fillet angle of 45 degree and thickness of 5mm. A finite element analysis with a three-dimensional thermo-coupled elasto-plastic model was also carried out to understand the change of stress and strain during ECAP. Experiments showed that the AZ31 alloy, which is extruded at a ratio of 20 and is heat-treated at 350°C, was successful in a cold ECAP. From the simulated results, it was found that the effective strain gradually decreased from the inner die side (0.533) to the outer die side. This was confirmed by the analytical analysis via von Mises criterion. Furthermore, it also matched well with the experiments, which showed a uniform shear deformation band. It was also interesting to note that compressive yield strength was drastically increased, which is caused by the occurrence of numerous twins spread across the materials during a cold ECAP.

Evaluation of Strain Rate During Equal-channel Angular Pressing

Strain rate is an important factor in plastic deformation because it determines the constitutive behavior of rate sensitive materials, e.g., dislocation density and flow stress evolution, deformation heat generation, etc. In the present study, the strain rate of workpiece materials during equal-channel angular pressing (ECAP) was evaluated by a geometric approach. The results were compared to those of the finite element analyses of a model ideally plastic material with various mesh sizes. The derived equation for strain rate is in reasonably good agreement with the results of the finite element method. The effects of the die geometry (a channel angle and a corner angle) were investigated. The strain rate during ECAP increases with punch speed and decreases with die channel angle, die corner angle, and the width of the workpiece. The relation obtained can be used for analytical calculations of the deformation, thermal, and microstructural evolution behavior of materials during ECAP. In particular, the size of the deforming zone and the effect of the finite element size are discussed.

Finite element analysis of equal channel angular pressing using a round corner die

The properties of the materials are strongly dependent on the shear plastic deformation behavior during equal channel angular pressing (ECAP), which is controlled mainly by die geometry, material properties, and process conditions. In this study, the plastic deformation behaviour of the materials during the ECAP process with a round die corner angle (90°) and a frictionless condition was investigated using the commercial two-dimensional rigid-plastic finite element code (DEFORM2D). The ECAP process for these conditions was explained using the five steps based on the calculated load curve (fast increase, slow increase, fast increase, steady and finally decreasing stages). The inhomogeneous strain distribution within the workpiece was analyzed by subdividing the workpiece into a front transient zone, an end transient zone, an outer less sheared zone, and the remaining shear deforming zone. Due to the faster flow of the outer part compared with the inner part within the main deforming zone, the lesser shear zone in the outer part of the workpiece occurs. If the lesser deformation zone is ignored, the effective strain by the theoretical equation is in good agreement with the FEM results.

On the die corner gap formation in equal channel angular pressing

A die internal corner gap is usually found during equal channel angular pressing (ECAP) of materials. Finite element analysis using the DEFORM2D code is carried out in order to investigate the corner gap formation between the die and workpiece during the plane strain ECAP process. The comparison of the deformation and the corner gap formation behaviour between the strain hardening material and the quasi-perfect plastic material was made. The mechanism of the corner gap formation is described in conjunction with the strain hardening behaviour and local flow velocity of the workpiece in the deforming zone. The adjustment of the corner angle from the die corner angle to the arc curvature of the workpiece is necessary for a better prediction of the strain during ECAP.