Axial Metal Flow Research Articles

Theoretical study and prediction of the inner hole reduction and critical mandrel diameter in cross wedge rolling of hollow shaft

The design of mandrel is crucial in the Cross-wedge rolling technology (CWR) of hollow shafts with mandrel. The critical mandrel diameter is a mandrel diameter that the inner hole just contacts the mandrel during the rolling process. The effective mandrel diameter should be between the critical mandrel diameter and the inner diameter of hollow-billet. The prediction of critical mandrel diameter can be finished by predicting the reduction process of inner hole. The reduction process of inner hole is related to metal flow law, we create a new theoretical model to predict the reduction process of inner hole based on the volume consistency and the hypothetical conditions of ring deformation. However, the theoretical model must be solved by numerical method because it is not an explicit analytic expression. For the convenience of engineering application, we also create a semi-empirical model to predict the reduction process of inner hole and the critical mandrel diameter, and verify its accuracy by contrasting the theoretical values with the simulation and experimental values. The prediction model is based on the relationship of radial and axial metal flow that considers the effect of the CWR rollers and hollow-bar parameters. The results show that the critical mandrel diameter increases with increasing the forming angle, and is negatively correlated with the stretching angle, reduction ratio, and initial wall thickness. Finally, the reference range of critical mandrel diameter was calculated and drew to guide the mandrel design. The results show that the prediction model can provide theoretical design reference for mandrel geometry in the hollow shaft CWR practical production.

EBSD Results of Material Flow and Microstructural Changes Around Tool Pin for the Dissimilar Friction Stir Welded AA6082-T6 and AA7075-T651

Frictional stir welding (FSW) generally experiences the forces Mode I axial metal flow and Mode II shear deformation around the rotating pin, along the welding direction to produce high-efficiency joints. The dissimilar FSW of AA6082/7075 joint was fabricated utilizing the process parameters such as rotational speed (R) of 900 rpm, travel speed (S) 90 mm/min, tilt angle (T) 2° and plunge depth (t) 0.9 mm. Subsequently, the zone-wise EBSD and metal flow analyses were carried out and compared with the results of the microstructure and the microhardness. Distinct variations of Mode I and Mode II metal flow and fine grain formation in weld nugget have been shown here.

Numerical and experimental research on cross wedge rolling hollow shafts with a variable inner diameter

The precise forming of inner hole has been a major technical difficulty in the cross wedge rolling (CWR) of hollow shaft. This paper proposes a new process to form hollow shafts with variable inner diameters by using the CWR with mandrel control. The forming characteristics and dimension precision of this process are analyzed by combining finite element modelling (FEM) and forming trials. The hole step of hollow shaft with variable inner diameter is formed in a spiral pattern. The helixes result in many micro-steps in hole step when forming the right-angle inner step. The metal flow lines demonstrated that mandrel step hindered the axial metal flow of inner hole and the metals were accumulated in hole step. The rolling load increases in the process of forming hole step. The mandrel is subjected to axial load when hole contacts the mandrel step. The roundness can be improved by reducing the mandrel diameter in knifing position. The axial accuracy of inner diameter can be classed as three parts: hole expansion, stable rolling, hole shrinkage. The compensated mandrel was designed to improve axial precision of inner diameter. The results showed that the inner hole dimension can be effectively controlled.

Upper bound analysis of axial metal flow inhomogeneity in radial forging process

An axisymmetric upper bound method model is proposed to analyze the inhomogeneity of axial metal flow in the radial forging process from the viewpoint of end profile in the meridian plane of the workpiece. The velocity fields are newly derived using stream function approach so that they can automatically satisfy the volume constancy as well as the velocity boundary conditions on the contact surface between the hammers and the workpiece. The assumed stream function has considered the inhomogeneous deformation mode. As a result, compared to the parallel velocity fields proposed in previous studies, reasonable predictions of radial load can be achieved even though the value of radial reduction is relatively low. Besides, the axial flow inhomogeneity along the radial direction can be described by this model because the axial velocity is no longer independent of the radial position. This model is verified by comparing the predicted forging load with published experimental data. Finally, the influences of axial feed and radial reduction on the end profile in the meridian plane of the workpiece are investigated.

An upper bound solution of axial metal flow in cold radial forging process of rods

Abstract In process design of radial forging, the prediction of axial metal flow, which has an effect on the forging efficiency, is very important. In this paper, based on a kinematically admissible velocity field, an axisymmetric model of radial forging of rods by an upper bound method (UBM) is proposed. Because the deforming process in a stroke is non-steady, it is divided into finite small steps so that the deformation in a step can be assumed as homogeneous steady flow. In addition, front-pull and back-push forces are taken into account. The amounts of metal flowing forward and backward can be predicted reasonably. The UBM model is validated by comparing the predicted forging load with published experimental data, and by comparing the predicted neutral plane position and axial metal flow with that of finite element simulation. Then the influences of friction factor, axial feed per stroke, reduction in cross-section area, inlet angle of hammer, front-pull and back-push forces on the percentage of forward material flow are investigated.

Effect of Thread Helix Angle on the Axial Metal Flow of Cross Wedge Rolling Thread Shaft

When rolling thread shaft in cross wedge rolling, forming quality of thread is affected by many process parameters such as the thread helix angle, which is a special and complex parameter. However, there is few study of the effect of the thread helix angle on thread shaft forming. In this paper how thread helix angle affects axial metal flow was analyzed from the perspective of rolling force and the forming process of thread shaft was simulated with different helix angles by the deform-3D software. Through the measurement of the point coordinates, the effect of the helix angle on the axial metal flow of rolled pieces was analyzed. Finally, the conclusion was obtained that helix angle causes the asymmetry of axial metal flow with small difference values for asymmetry and the axial metal flow of rolled pieces increases as the helix angle increases. The rolling thread segment can be ensured in the middle of rolled pieces by moving the blank a suitable distance in the reverse direction of the axial flow direction.

Numerical Analysis of Feed Rate Influence on Hollow Hub Shape during Rolling Extrusion Process

This paper presents the results of numerical calculations of rolling extrusion process of a hollow hub. Due to the necessity of flanges manufacturing at both sides of the product, in the analyzed process of rolling extrusion, as additional tool limiting axial metal flow a rear bumper was implemented [1,. Numerical calculations of the hub forming process were conducted basing on finite element method, applying software Deform3D v.X in conditions of three dimensional state of strain. The obtained small shape faults, in the form of characteristic triangulation and small changes of the hub walls thickness, show that it is possible to conduct the further research works of experimental character, with the application of modernized aggregate for the rolling extrusion process PO-2.

Effect of Drive Roll Rotation Speed on Ring Rolling Process

Based on the platform ABAQUS, 3-D FEA model for ring rolling has been constructed to investigate the effect of drive roll rotation speed on the metal flow in the ring rolling process. It can be seen clearly that the axial metal flow in the outside diameter of the rolled ring increases with the increasing of drive roll rotation speed and with the decreasing of the feeding magnitude per revolution , which causes the increasing of fishtail coefficient FT and maximum spread coefficient and in turn makes the quality deterioration of end-plane in the rolled ring. The rolling force and rolling torque necessary to execute the rolling process are reduced when the drive roll rotation speed is elevated, which results in the lower requirement for the characteristic of force and energy in the rolling machine. Besides that, average equivalent plastic strain PEEQ also increases, which indicates the enhancement of plastic deformation and is beneficial to the improvement of the mechanical property of the formed ring. But one point that we should pay attention is that uneven deformation and possibility of the inner defects in the rolled ring might be increased with the increasing of the drive roll rotation speed.

Determination of experimental axial and sideways metal flow in open die forging

For the sake of automation in open die forging; some preliminary experimental calculations such as measurement and calculation of metal flow in lateral and axial directions, and manipulation of the workpiece are evaluated. For a small batch production sequence, first a suitable workpiece manipulator is designed and manufactured accommodating all material displacement and movements, and solutions are presented to calculate the amount of material displaced from under flat tools in the axial and lateral directions. Comparisons between experimental flow measurements and calculations with theoretical results showed good agreement.