PSI - Issue 46

Gaurav Singh et al. / Procedia Structural Integrity 46 (2023) 149–154

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Gaurav Singh et al. / Structural Integrity Procedia 00 (2021) 000–000

efficient way to strengthen the hexagonal close packed materials such as Zirconium, Magnesium, Titanium alloys by imposing low strain on each pass (Mao et al., 2021). It is challenging to design process conditions due to complex processes such as rotational and feeding movement of the material in the rotary swaging process. Many parameters include feed rate, die angle, dies geometry, amount of reduction, friction coefficient, and hammer speed involved during swaging. Die angle is one of the important parameters as it affects the residual stress. The presence of residual stress can significantly affect the mechanical properties of materials. Seong et al. (2007,2009) investigated the dimensional deviation and surface roughness of the swaged tube by varying the feed rates and percentage reduction. It was shown in their work that higher surface roughness and more dimensional deviation were observed for a higher feed rate (more than 2 m/min). Moumi et al. (2014) studied the material flow during the rotary swaging process using finite element analysis. The behavior of the neutral plane (location and geometry) has varied with the friction coefficient. Wang et al. (2015) studied mandrel influence on titanium tubes using the rotary swaging process. The introduction of the mandrel has improved the hardness, surface roughness of titanium tubes. Ishkina et al. (2019) studied the influence of process fluctuations (feed rates, die geometry, feed per stroke) on residual stress evolution in the rotary swaging process. These process parameters affect more on the surface residual stress as compared to centre residual stresses. Liu et al. (2019) have investigated the influence of friction coefficient on material flow of steel processed by rotary swaging. The friction coefficient controls total plastic deformation and material flow during the swaging process. Ishkina et al. (2021) studied the influence of die angle and calibration zone during swaging of steel. They found that increasing the die angle caused an increase in tensile residual stress at the outer surface and decreased compressive residual stresses at the centre of the specimen. Groche et al. (2021) simulated the residual stress distribution during the rotary swaging process and validated it with experimental data. The results showed that with a smaller degree of deformation, high compressive residual stresses are found in the near-surface region of the materials. These differences in outcomes are due to the properties of materials and processing parameters. Liu et al. (2021) investigated the material flow in swaged steel using a 2D axis-symmetric FE model. It is essential to optimize the die angle for achieving lower compressive residual stresses. Therefore, the present work is focused on simulating the effect of different die geometries on residual stress-induced into Zr-4 alloy during swaging. 2. Rotary Swaging simulation 2.1 Rotary Swaging Rotary swaging (RS) is an incremental forming process utilized to reduce cross sections of bar, tubes, wires, and other cylindrical workpieces, schematically shown in Fig. 1(a). Set of dies (generally two to eight) perform short, high-frequency (from 6800 to 12,000 times per minute) and simultaneous radial movements and apply a compressive force onto the enclosed workpiece. RS is deemed a plasticity enhancement process because of the 2-axial compression and uniaxial tension stress applied to the swaged material, which can effectively refine the grains and improve the mechanical properties of metallic materials. The advantages of the rotary swaging process are low tooling costs, better surface finish, and more precise dimensional tolerance, saving materials, reducing lead time, and improving product quality (Singh et al., 2020). The workpiece can be classified into three zones inside the dies: the sinking zone, the forging zone, and the sizing zone (Fig. 1b). Similarly, the dies can be classified into three zones: reduction, calibration, and exit zones. The outer part at the sinking zone suffers from triaxial compressive stress as it is in direct contact with the die, and therefore, the deformation of this part is more severe. The outer part at the sizing zone suffers from axial tensile stress due to axial elongation. The axial elongation of the workpiece and the necking predicted in the simulation are caused by the axial tensile stress by the deformation occurring in the sizing zone (Singh et al., 2020). 2.2 Die Design Die design is an important aspect of the Swaging process. Various features of the test specimen are directly dependent on the design parameters of the dies. There are multiple ways to alter the design parameters and study their impact on the overall mechanical properties of the produced sample. In the present study, die angle and its die diameter are considered as two primary parameters and observed its impact on the overall structure of the sample.