Yuli Liu

A 3D rigid–viscoplastic FEM simulation of the isothermal precision forging of a blade with a damper platform

Abstract A blade with a damper platform, with excellent anti-vibration characteristics and high efficiency, has become one of the most important new types of blade being developed in the aeronautical engine. However, the blade is complicated in shape, and the material used for its manufacture is difficult to deform. Therefore, it is important to undertake research on the blade-oriented precision forging process using three-dimensional finite element method (3D FEM) method numerical simulation for the practice and the development of the process. However, up to now, literature on such research has been scant. In this paper, based on the rigid–viscoplastic principle, three-dimensional finite element simulation is reported for the isothermal precision forging of the blade using the penalty function, and eight-node hexahedral isoparameteric elements for discretizing the deforming workpiece and triangular elements for discretizing the die cavity. The method of contracting from the boundary to the interior, proposed by the authors, is used for remeshing a distorted mesh system, and the method of modifying the position of nodes touching the die according to its original normal, also proposed by the authors, is used to avoid the “dead lock” problem due to the normal uncontinuity of scatted die meshes, to enable the simulation to be successful. Friction is considered for the die–workpiece interface boundary condition, and an arc is considered for the tenon–body joint, and a damper platform–body joint on the blade die cavity, respectively, which make it possible for the simulation to approach the practical forging process of a blade with a damper platform. 3D FEM simulation results have been obtained for the initial and deformed configurations, the deformed meshes of typical cross-sections, the distribution of effective strain at the final stage, load–displacement curves, in this way the deformation law of the forging of a blade with a damper platform being revealed. The achievements of this research serve as a significant guide to the optimization of design for the relevant process and dies. The method used is also of general significance to the forging processes of other type of blades and other complicated massive deformation processes.

Cross-sectional distortion behaviors of thin-walled rectangular tube in rotary-draw bending process

Abstract The cross-sectional distortion usually appears during rotary-draw bending process of thin-walled rectangular tube with small bending radius. To study the cross-sectional distortion of the tube, a three-dimensional finite-element model of the process was developed based on ABAQUS/Explicit code and its reliability was validated by experiment. Then, the cross-sectional distortion behaviors of the tube were investigated. The results show that a zone of larger circumferential stress appears on the tube when bending angle reaches 30°. And in the larger circumferential stress zone, the sagging phenomenon is produced obviously. The maximum cross-sectional distortion is located in the larger circumferential stress zone and the angle between the plane of maximum cross-sectional distortion and the bending reference plane is about 50°. The position of the maximum cross-sectional distortion keeps almost unchanged with the variation of the clearances between dies and tube.

A 3D rigid–viscoplastic FEM simulation of compressor blade isothermal forging

Abstract Based on the rigid–viscoplastic principle, three-dimensional finite element simulation using the penalty function was performed for the isothermal forging of a compressor blade. The key technologies of 3D rigid–viscoplastic FEM simulation are introduced. The workpiece was discretized into eight-node hexahedral isoparameteric elements and the die cavity was discretized into triangular elements. The methods proposed by the authors to remesh the distorted mesh system and to modify a node touching the die have been used. By means of 3D FEM simulation of the compressor blade, the initial and deformed configurations, the deformed meshes of typical cross-sections, the contours of effective strain at the final stage, the vertical load–displacement curve for the upper die, and the horizontal load–displacement curves for the upper and lower dies have been obtained, and so the deformation law of compressor blade forging has been obtained. The research results show that the 3D rigid–viscoplastic FEM simulation system developed in this paper is practical and reliable. In the present simulation, the tenon and the body on the blade die cavity are joined by an arc which coordinates the deformation between the tenon and the body, and friction is considered along the interface between the die and the workpiece. Thus, this simulation approaches practical compressor blade forging. The computational results can also be applied effectively to other types of blade forging processes.

Sensitivity of springback and section deformation to process parameters in rotary draw bending of thin-walled rectangular H96 brass tube

In order to study the effects of the process parameters on springback and section deformation, a sensitivity analysis model was established based on the combination use of the multi-parameter sensitivity analysis method and the springback/section deformation prediction finite element model, and by using this model the sensitivities of the springback and the section deformation to process parameters were analyzed and compared. The results show that the most sensitive process conditions for springback angle are the boost speed and the pressure of pressure die, and the most sensitive process condition for section deformation is the number of cores. When the clamp force, the boost speed and the pressure of pressure die are utilized to control section deformation, the effect of these process parameters on springback should be considered. When the process parameters are mainly used to control springback, the effect of these process parameters on the section deformation should be always considered.

Backward tracing simulation of precision forging process for blade based on 3D FEM

In order to obtain the desired final shape, the blade precision forging requires a reasonable preformed billet which can be obtained from a given final shape by using backward tracing scheme based on FEM. The key technologies of backward tracing scheme based on 3D rigid-viscoplastic FEM were explored, and some valid algorithms or methods were proposed. A velocity field was generated by combining the direct iterative method with Newton-Raphson iterative method, and then the initial velocity field of backward tracing simulation was achieved by reversing the direction of the velocity field. A new method, namely the tracking-fitting-revising method, was proposed and can be used to determinate the criterion of separating a node from die in the backward tracing simulation. The ceasing criterion of the backward tracing simulation is that all the boundary nodes are detached from dies. Based on the above key technologies, the 3D backward tracing simulation system for the blade precision forging was developed, and its feasibility and reliability were verified by forward loading simulation.

Influence of the shape and position of the preform in the precision forging of a compressor blade

Abstract The influence of the shape and the initial position of the preform in precision forging of a compressor blade has been studied by 3D rigid–viscoplastic finite element method (FEM) in this paper. The results show the following: (1) a short and thick preform results in necking at the arc transition zone between the tenon and the blade body, and at the zone near the tip of the blade during deformation; (2) a long and slender preform produces bending in the middle of the blade body during deformation; (3) if a long and slender preform is bent in advance, an advisable product without flash can be obtained; (4) a reasonable initial position of the preform deviates to the thinner side of the blade die cavity; (5) this research is beneficial for the practice of the precision forging process of a compressor blade and it has a general significance for other types of blade.

Physical modeling of the forging of a blade with a damper platform using plasticine

In order to inspect and analyze the deformation in the forging of a blade with a damper platform, a method of locally making a layer-built billet has been proposed, and physical modeling of the forging of a blade with a damper platform using plasticine has been carried out based on this method. By physical modeling of the forging of a blade with a damper platform, some basic flowing laws in the forging of a blade with the damper platform have been obtained. The simple and valid accomplishment of experiment shows that this method of a making billet is reasonable and practicable, and it can be popularized to the physical modeling of other components.

Numerical Simulation on Influence of Clearance and Friction on Wrinkling in Bending of Aluminum Alloy Rectangular Tubes

The clearance and friction have large influence on wrinkling in rotary draw bending process of thin-walled rectangular tube. In this paper, a three-dimension Al FEM model of rotary draw bending of thin-walled rectangular tube is built under the ABAQUS/ Explicit environment. Based on the model, simulation and analysis of rotary draw bending for aluminum alloy 3A21 thin-walled rectangular tube have been carried out. The results show that the height of wrinkling wave decreases obviously with the decrease of the clearance between mandrel and tube or with the increase of the friction coefficient between wiper die and tube; however, the effect of friction coefficient on wrinkling becomes weaker while increasing the clearance between mandrel and tube. The achievements of this study provide a guideline for determining the process parameters for thin-walled rectangular tube in rotary draw bending process.

Experimental study on cross-section distortion of thin-walled rectangular 3A21 aluminium alloy tube by rotary draw bending

The cross-section distortion is inevitably produced in rotary draw bending process of thin-walled rectangular 3A21 aluminium alloy tube, which severely affects the forming quality of the tube. To predict and control cross-section distortion, the experiments with different process parameters are carried out. It is indicated that the effects of bending angle, core number and clearance between the pressure die and tube on the cross-section distortion are significant, but the effects of clearance between wiper die and tube and the boost velocity of the pressure die can be neglected. The maximum cross-section distortion is produced in the section of the angle 50°, and the position does not change with the variation of the process parameters. The results are of significance in the determination of the process parameters for the rotary draw bending process of rectangular tube.

Superplastic deformation of duralumin LY12CZ under an electric field

Abstract The general superplastic deformation of many alloys had been studied exhaustively. Recently, the superplastic deformation of some alloys has been achieved by the application of an electric field to the process. Conrad and his colleagues have obtained the change of the flow stress and the strain-rate exponent during the superplastic deformation of 7475 Al alloy subjected to an external dc electric field. However, it is not clear how the electric field will affect the elongation and the growth of cavities quantitatively, and whether the type of cavities will change because of the existence of the external electric field. In this paper, the optimum process parameters for the super plastic deformation of duralumin LY12CZ, without any pre-treatment, subjected to an external dc electric field have been obtained, LY12CZ (corresponding to ASTM 2024) being used widely in the aeronautic-astronautic industry. Furthermore, the effect of the electric field on the superplasticity and the superplastic-deformation conditions has been investigated. The experimental results show that the application of the electric field: (i) decreases the flow stress by 10–25% and the degree of cavitation at the onset of the fracture by 11% approximately; (ii) reduces the rate of strain-hardening; and (iii) increases the strain-rate sensitivity exponent by 26–38%. It is important to note that: (iv) the elongation of the superplastic deformation of LY12CZ under the electric field increases by 14–45% as compared with that without the electric field; (v) the equivalent strain at the onset of the rapid growth of the cavities increases by 25% with the application of the electric field; and (vi) spherical cavities exist in the specimens after the tensile test when applying the electric field, as opposed to the V-type cavities for the general superplastic deformation of LY12CZ. From these investigations, the optimum process parameters for the superplastic deformation of LY12CZ under an electric field are as follows: the deformation temperature is 471°C and the initial strain rate is 0.333 × 10−3 s−1.