Liping Lei

Finite element analysis and design in stainless steel sheet forming and its experimental comparison

Abstract Bending and drawing processes are analyzed in stainless steel sheet forming using solid element and finite-strain formulation by the Finite Element Code MARC. In bending deformation, the springback increases through augmentations of the clearance between punch and workpiece. Divergences between theoretical and experimental results occur due to the simplification of the contact condition at the die–workpiece interface. For the square cup deep drawing process which includes bending and drawing deformation modes, the lubrication conditions are critical factors for producing sound products. All the results derived from the FEM analysis show reasonable agreement with the experimental data.

Bursting failure prediction in tube hydroforming processes by using rigid–plastic FEM combined with ductile fracture criterion

Abstract The most common failure in tube hydroforming is the bursting failure due to excessive thinning of large deformation. To evaluate the forming limit of hydroforming processes, the Oyanes ductile fracture integral I was introduced and calculated from the histories of stress and strain according to every element by using the rigid–plastic finite element method. The region of fracture initiation and the forming limit for three hydroforming processes, such as a tee extrusion, an automobile rear axle housing, and a lower arm under different forming conditions are predicted in this study. Also it is shown that the material parameters used in the ductile failure can be obtained from the experimental forming limit diagram. From the results, the prediction of the bursting failure and the plastic deformation for the three hydroforming examples demonstrates to be reasonable so that this approach can be extended to a wide range of practical tube hydroforming processes.

Three-dimensional rigid–plastic finite element simulation for the two-roll cross-wedge rolling process

Abstract In this paper, the process of cross-wedge rolling (CWR) has been simulated and analyzed by the 3D rigid–plastic finite element method. Considering the characteristic of CWR, the static implicit FEM program DEFORM-3D is selected. To simulate all forming stages in the CWR process, dynamic adaptive remeshing technology for tetrahedral solid elements was applied. The stress distributions in the cross-section of the forming workpiece are analyzed to interpret fracture or rarefaction at the center of workpiece. The authors have also analyzed the time–torque curve and the laws of load changing.

Prediction of the forming limit in hydroforming processes using the finite element method and a ductile fracture criterion

Abstract Using the finite element method, Oyane’s ductile fracture integral I was calculated from the histories of stress and strain according to every element and then the forming limit of the hydroforming process was evaluated. The fracture initiation site and the forming limit for two typical hydroforming processes, a bumper rail and a subframe, under different forming conditions are predicted in this study. For these products, the ductile fracture integral I is not only affected by the process parameters, but also by the shape of the pre-forming blank. Due to no axial feeding at the end of the blank, the possibility of cracking in hydroforming of these products is influenced by the friction condition more strongly than for the axial feeding of products such as a the tee extrusion. All the simulation results show reasonable plastic deformation and the applications of the method could be extended to a wide range of hydroforming processes.

Manufacture of an automobile lower arm by hydroforming

Abstract An automobile lower arm has been fabricated in a prototype form by hydroforming with the aids of numerical analysis and experiments. For the numerical process design, a program called HydroFORM-3D developed here on the basis of a rigid–plastic model, has been applied to the lower arm hydroforming. The friction calculation between die and workpiece has been dealt with carefully by introducing a new scheme in three-dimensional surface integration. To accomplish successful hydroforming process design, thorough investigation on the proper combination of process parameters such as internal hydraulic pressure, axial feeding and tool geometry has been performed. Results obtained from numerical simulation for a lower arm in the hydroforming process are compared with a series of experiments. The comparison shows that the numerical analysis successfully provides the manufacturing information on the lower arm hydroforming, and it predicts the geometrical deformation and the thinning.

Analysis and design of hydroforming processes by the rigid–plastic finite element method

Abstract A three-dimensional finite element program, HydroForm-3D, based on the rigid–plastic model for the analysis and design of hydroforming process was developed. Several typical hydroforming processes such as tee extrusion, cross-extrusion, the hydroforming process combined with the pre-bent process and subframe are analyzed by using this numerical program. The hydraulic pressure force is applied to the normal direction of the tube workpiece by integrating the pressure with respect to each element’s surface area. The predicted simulation results provide information on the actual design. This numerical approach to the hydroforming process will be useful to the development and application for a wide range of automobile structural components.

Analysis and design of hydroforming process for automobile rear axle housing by FEM

Abstract An FEM program, HydroFORM-3D, for the analysis and design of tube hydroforming processes, has been developed by modifying and adding some subroutines to the previous rigid-plastic finite element program, and then applied to the hydroforming process for an automobile rear axle housing. This paper includes the theoretical background of the program development. Through a numerical simulation, an optimum process is proposed to meet the practical requirements, which shows the efficiency of the numerical simulation. Two types of hydroforming dies are analyzed by numerical simulation. The sliding-type die has the drawback of a possibility of buckling, whereas the fixed-type die causes bursting failure. The thickness distribution of the final product is affected not only by the types of die, but also by the loading paths. The potential failure site for rear axle housing predicted by the numerical simulation is consistent with the experimental results. The values of maximum axial compression force for the first and second hydroforming processes are also in good agreement with experimental data. To manufacture a sound automobile rear axle housing without failure, it is better to use the sliding-type die and it is also critical to maintain a suitable hydraulic pressure level.

Preform design in hydroforming of automobile lower arm by FEM

Abstract By using a three-dimensional finite element program HydroFORM-3D based on a rigid–plastic model, the hydroforming process for automobile lower arm is analyzed in this study. The goal of the study is to accomplish proper design and control of processes for producing hydroformed lower arm component most soundly. Prior to hydroforming, the tube must be bent to the approximate centerline of the finished part to enable the tube to be placed in the die cavity. After then, a preforming operation is carried out to the pre-bent tube. Finally, the hydroforming operation is performed to the preformed tube to get the final production. The influences of forming conditions, such as the loading path of the hydraulic pressure and the axial feeding, on the hydroforming process is discussed.

Experimental investigation on local mechanical response of superelastic NiTi shape memory alloy

In this paper, primary attention is paid to the local mechanical response of NiTi shape memory alloy (SMA) under uniaxial tension. With the help of in situ digital image correlation, sets of experiments are conducted to measure the local strain field at various thermomechanical conditions. Two types of mechanical responses of NiTi SMA are identified. The residual strain localization phenomena are observed, which can be attributed to the localized phase transformation (PT) and we affirm that most of the irreversibility is accumulated simultaneously during PT. It is found that temperature and PT play important roles in inducing delocalization of the reverse transformation. We conclude that forward transformation has more influence on the transition of mechanical response in NiTi SMA than reverse transformation in terms of the critical transition temperature for inducing delocalized reverse transformation.

Comparative analysis between stress-and strain-based forming limit diagrams for aluminum alloy sheet 1060

The forming limit diagram (FLD) and forming limit stress diagram (FLSD) of aluminium alloy 1060 under linear and nonlinear strain paths are investigated. The calculation of FLSD is based on experimental FLD using the method proposed by Stoughton. Different from the FLD that varies with the strain path, the FLSD is not sensitive to the strain path. Therefore, FLSD is convenient as a forming limit criterion for multi-stage sheet forming. The influences of the materials yield criteria on FLSD are also discussed by comparison of the Hills 48, Hills 79 and Hosford non-quadratic criterion. The impacts of material hardening laws (Voce and Swift models) on translation of FLD and FLSD are analyzed. The Voce hardening law and the Hosford yield criterion are appropriate for the FLSD calculation of the aluminium alloy 1060. The stress calculation program and display interfaces of FLD and FLSD are developed on MATLAB, where the strain data can be input from experiment measurement or FEM calculations.