Lihui Lang

Effect of anisotropy and prebulging on hydromechanical deep drawing of mild steel cups

Abstract The hydromechanical deep drawing processes of mild steel cups have been investigated experimentally and numerically. Experiments were carried out with the fixed gap method (with spacers) and the conventional method (without spacers) under different prebulging pressures. The shape variations and the thickness distributions of the workpieces were measured and discussed. The effects of anisotropy and prebulging pressure on the final product quality are discussed. The processes were analyzed by the explicit finite element code DYNA3D with the Barlat–Lian’s three-parameter material model. The numerical results are compared with those obtained in the experiments.

Analysis of key parameters in sheet hydroforming combined with stretching forming and deep drawing

Abstract Sheet hydroforming has proven to be an effective method for manufacturing complicated parts. To explore sheet deformation under complex strain conditions, the forming process of a conical cup was studied on the basis of the proposed hydromechanical deep drawing with uniform pressure on to the blank. The failure types including fracture and wrinkling were analysed in detail. The process windows for the pressure in the die cavity were drawn out using the different roughness of the punch surface in local areas. The forming process of the conical cup was explored using pure aluminium and soft steel. Effects of the key process parameters including the punch surface roughness and the pressure variation on the finally formed parts were investigated in both experiment and simulation. It was shown that the results from the simulation were in reasonable agreement with those from the experiment.

Pre-bulging effect during sheet hydroforming process of aluminum alloy box with unequal height and flat bottom

Pre-bulging effect on the sheet hydroforming process of irregular box with unequal height and flat bottom was investigated by means of numerical simulation and experiment. The influences of pre-bulging height and pre-bulging pressure on the forming were discussed respectively. The pressure loading path was optimized. The results show that pre-bulging has important influences on the forming results. Too high pre-bulging height causes the crack and obvious crease at the punch nose near the lowest corner. Too low pre-bulging height causes fracture at the punch nose of the highest corner. Pre-bulging pressure has a smaller effect on the fracture at the punch nose of the highest corner when the pre-bulging height is reasonable. But over high pre-bulging pressure causes crack and obvious crease at the punch nose near the lowest corner. Failure can be avoided by using reasonable pre-bulging height and pre-bulging pressure.

Experimental and numerical investigation into useful wrinkling during aluminium alloy internal high-pressure forming

Abstract Internal high-pressure forming is a process for manufacturing lightweight components, especially automotive parts, with advantages of lower cost and weight reduction, better structural integrity and increased strength and stiffness over the conventional stamping process. One of the typical failure modes, including wrinkling, buckling and splitting, will occur through an unreasonable combination of the control parameters: the internal pressure and the axial punch feeding. In most previous papers, wrinkling is considered to be a failure mode. However, not all wrinkles are defects. The collection of materials in an expanding area by the formation of wrinkles is an alternative method for obtaining a preformed shape in the hydroforming die. In this case, the key point is to obtain ‘useful’ wrinkles instead of ‘bad’ wrinkles. In this paper, an investigation will be conducted on how to control the shape of the wrinkle waves and its effect on the thickness distribution after hydroforming by using finite element simulation. LS-DYNA finite element software is used in this paper. An experiment has been carried out and the results obtained from experiment and simulation are in good agreement.

Investigation into Sheet Hydroforming Based on Hydromechanical Deep Drawing with Uniform Pressure on the Blank

Abstract Sheet hydroforming has gained increasing interest in the automotive and aerospace industries because of its many advantages such as a higher forming limitation, good quality of the formed parts, the capability of forming complicated parts, etc. Based on the proposed hydromechanical deep drawing (HDD) with uniform pressure on the blank, some characteristics of sheet hydroforming, including the drawing ratio improvement, the quality of the formed parts, the thickness distributions of the formed parts and the process window, are investigated in detail. The effect of the process parameters on the features and ways to improve the sheet formability are discussed both in experiment and simulation. With consideration of the forming limit diagram (FLD), the forming process was studied in simulation. The results from a simulation were in reasonable agreement with those from an experiment.

Research on the effect of flow stress calculation on aluminum alloy sheet deformation behavior based on warm bulging test

Confirmation of material properties is an important research area for determining metals deformation behavior. In order to research the effect of flow stress calculation on aluminum alloy sheet deformation behavior, warm sheet bulging test was carried out to obtain bulging height - pressure curves with different bulging heights and diameters in this study. Based on the bulging parts profile data measured by three coordinate measuring machine, the least square circle fitting radius were fitted. Existing theoretical models for radius of curvature and thickness were compared and best models were selected to obtain more accurate stress — strain curves by calculating the bulging flow stress. Combination model was used to calculate the bulging height — pressure curves obtained by bulging test and the stress-strain curves with different temperatures and pressure rates were obtained. A monotonous increasing function was resulted which is of great significance in the area of formability and deformation behavior of warm sheet hydroforming.

Modified MK model combined with ductile fracture criterion and its application in warm hydroforming

Abstract A modified MK model combined with ductile fracture criterion (DFC-MK model) is proposed to compute the forming limit diagrams (FLDs) of 5A06-O aluminum alloy sheet at different temperatures. The material constant ( C ) of ductile fracture criterion and initial thickness imperfection parameter ( f 0 ) at various temperatures are determined by using a new computing method based on wide sheet bending test. The FLDs at 20 and 200 °C are calculated through the DFC-MK model. The DFC-MK model, which includes the influence of through-thickness normal stress, is written into the subroutine VUMAT embedded in Abaqus/Explicit. The cylindrical cup hydroforming tests are carried out to verify the model. The results show that compared with experimental observations, the predicted FLDs based on DFC-MK model are more accurate than the conventional MK model; the errors between the simulations and experiments in warm hydroforming are 8.23% at 20 °C and 9.24% at 200 °C, which verify the effectiveness of the proposed model.

Optimized constitutive equation of material property based on inverse modeling for aluminum alloy hydroforming simulation

Abstract By using aluminum alloys, the properties of the material in sheet hydroforming were obtained based on the identification of parameters for constitutive models by inverse modeling in which the friction coefficients were also considered in 2D and 3D simulations. With consideration of identified simulation parameters by inverse modeling, some key process parameters including tool dimensions and pre-bulging on the forming processes in sheet hydroforming were investigated and optimized. Based on the optimized parameters, the sheet hydroforming process can be analyzed more accurately to improve the robust design. It proves that the results from simulation based on the identified parameters are in good agreement with those from experiments.

Research on aluminum alloy sheet thermoplastic deformation behavior based upon warm bulging test

The rate of fluid pressure variation is a crucial factor to indicate the forming speed and the pressure rate is applied to be one factor that can influence the deformation of material in warm sheet hydroforming. In this study, warm bulging test was conducted to obtain bulging pressure-height curves with different temperatures and pressure rates. Fitting the bulging pressure-equivalent strain curves obtained using bulging test with surface fitting method, the fitted equation of bulging pressure on equivalent strain and pressure rate was achieved, and the fitting result shows a good accordance with experimental and calculated values. Then, the relation between pressure rate and strain rate was obtained. The results of warm bulging test indicated that the deformation behavior of metal material is sensitive to pressure rate, which is of great significance for warm sheet hydroforming.

Cost Optimization Method of Large-scale Prestressed Wire Winded Framework on Multiple-island Genetic Algorithm

Abstract Prestressed wire winded framework (PWWF) is an advanced structure and the most expensive part in the large-scale equipment. The traditional design of PWWF is complicated, highly iterative and cost uncontrolable, because PWWF is a variable stiffness multi-agent structure, with non-linear loading and deformation coordination. In this paper, cost optimization method of large-scale PWWF by multiple-island genetic algorithm (MIGA) is presented. Optimization design flow and optimization model are proposed based on variable-tension wire winding theory. An example of the PWWF cost optimization of isostatic equipment with axial load 6 000 kN is given. The optimization cost is reduced by 21.6% compared with traditional design. It has also been verified by the finite-element analysis and successfully applied to an actual PWWF design of isostatic press. The results show that this method is efficient and reliable. This method can also provide a guide for optimal design for ultra-large dimension muti-frame structure of 546 MN and 907 MN isostatic press equipment.