Materials Science Forum Vols. 575-578

Abstract: Long distance transmission pipeline is one of promising transportation methods developed in recent years. It is safe, economical, convenient and prompt. It is mainly used in transmitting gas, liquid, and other dispersed material. Oil and natural gas is especially suitable to be transmitted by high pressure large diameter longitudinal submerged arc welded (LSAW) pipelines. Mechanical expanding is one of the most important processes in the production of large diameter LSAW steel pipe for long distance transmission pipeline. Firstly, the LSAW steel pipe mechanical expanding is modeled. Two FEM models are established to simulate the mechanical expanding process at the cross section and longitudinal section of the LSAW steel pipe respectively. Secondly, the deformation characteristics of the LSAW steel pipe are simulated while mechanical expanding processes. Finally, main mechanical expanding process parameters and their influence on the quality of finished LSAW pipe are analyzed in detail according to the FEM simulation. The results presented by the analyses are very consistent with the experiment, and can be used to direct the production of LSAW steel pipe.

Abstract: Flat receptacle, which is used in extruding the large aluminum profiles, is in harsh work conditions. Due to the irregularity of inner hole of flat receptacle, inconsistent resistance of shrinking fitting affects the inner hole within which nonuniform deformation occurs. If the nonuniformity exceeds the specified dimension accuracy, tiresome work including mould repairing and structure optimization has to be done. ANSYS is used to simulate the flat receptacle. It is shown that the maximum stress appears in the arc area of inner hole. Therefore, we present one new method using the preloaded layer with changeable shrinkage to replace the preloaded layer with uniform shrinkage. Considering the processing and assembling factors, we adopt the elliptical outer layer and circular inner layer as the new structure. Then the optimizations of flat receptacle with uniform and changeable shrinkage are implemented using the optimizing module, receptively. The optimized results show the maximum equivalent stress in the corner of inner-hole decreases about 5.47% if adopting the changeable shrinkage. The numerical simulation results show that the feasibility of changeable shrinkage and elliptical preloaded layer.

Abstract: High speed wire-rod rolling is a typical large deformation process which includes geometry, material and boundary condition non-linearity, thus it belongs to a highly nonlinear problem. The finite element models of the billet and the rollers in the intermediate rolling region had been established based on actual sizes by using 3-D thermo-mechanical coupling FEM and advanced contact analysis technology. The deformation field, stress, strain, temperature field and rolling force of the billet were calculated and analyzed in the rolling passes precisely. The distribution and change characteristics of temperature had been discussed especially. The results of the simulation are reliable and precise, which are useful for practical manufacture and the optimization of process-parameters.

Abstract: The maximum mean stress gradient direction in typical plane strain and axisymmetrical plastic deformation problems was calculated by numerical method to investigate relationships between material flow direction and related local stress field. Good agreement was found between the movement direction in the deforming bodies and the maximum mean stress gradient direction of the related local mean stress field. This agreement was also found in typical 3-D problems by numerical simulation and visualization.

Abstract: A solid geometry model of porthole die is built up by CAD . Pointing to some problems in the extruding process, such as the die fraying and the low quality of the welding during the extruding process, and the interrelated parameters, the main forming process of 7005 aluminum alloy gear pump by porthole die is simulated by using numerical analysis software DEFORM-3D with regard to heat-stress fields. Based on the results of numerical simulation, this paper gives some improvements and suggestions for optimizing the forming process.

Abstract: Recently, physical simulation has played a more and more important role in modeling hot forming process. However, difficulty still existed in simulating real hot forming process using physical simulation results directly for obvious difference in deformation history between physical simulation condition and real hot forming process. In this work, difference between physical simulation and real hot forming process was discussed and a mathmatical approach was proposed to model real hot forming process using physical simulation results. The main consideration of the method was to put physical simulation results into differential forms in order to take count in the contribution of deformation history (temperature and strain rate) at each incremental step. For the application of the approach, modeling of material flow stress, dynamical recrystallization including critical condition and recrystallziaton fraction, damage evolution and fracture criteria during real hot forming process were presented as examples, although experimental support was still needed for validation and further application.

Abstract: A special elasto-plastic dynamic finite element code named RingForm has been developed to analyze cold ring rolling process. Central difference method was introduced to solve the dynamic explicit finite element equations. Strain state was estimated by the value of yield function of the last and the present time step. To reduce the accumulative error caused by elasto-plastic constitutive relations, the radial return algorithm was employed. In comparison with the experimental results, the cold ring rolling process of a ring with rectangular section has been simulated to verify the accuracy and stability of the system solver.

Abstract: The cold closed-die forging process of the gear is a kind of new technique of the precise forming of gear in recent years. In this paper, the cold closed-die forging process of differential satellite gear in car was analyzed through numerical simulation method. Forming mold was designed with Pro/E Wildfire2.0 which included four components : upper punch, lower punch, tooth shape upper die and lower die for Normal Cone. The three-dimensional models of satellite bevel gear mould were built and imported into numerical simulation software DEFORM-3D. Because the gear has the uniform circumferential features, in order to save time and improve the accuracy, only one tooth was simulated, and the full simulation outcome of 10 teeth was mirrored from this one. Through the numerical simulation analysis of DEFORM-3D, the instantaneous deformation and stress filed were gained. Forming defects were forecasted and the cold closed-die forging rule for satellite gear used in car was obtained which can provide effective references for no-flash cold forging process of planet bevel gear and the mold design.

Abstract: A novel hybrid method is proposed in the paper, which is an assistant tool for product designers to estimate springback in sheet metal forming process at the preliminary design stage. In the hybrid method, the forming results are obtained firstly by an inverse finite element approach (IA) with a membrance element. The thickness strain and stress can be calculated according to the approximate curvature radius of the discrete meshes. Then, a rotation-free shell element is employed, with only three displacements at the corner nodes of the element, to calculate the springback. To verify the accuracy and efficiency of the hybrid method, the numerical results of the hybrid method on two benchmark tests are compared with experimental results.

Abstract: In the H-beam rolling process, the deformations and temperature field of workpiece significantly influence the mechanical properties due to the change of product microstructure. Prediction of them is important for the groove design and passes sequences. To get the deformation behavior and the temperature field of workpiece, commercial FEM program LS-DYNA has been used to analyze the whole process of H-beam rolling. The approach is based on 3D thermal mechanical coupled finite element method. The rolling process is divided into several units for calculation. The mesh of workpiece is rebuilt in the simulation for reducing the influence of element distortion. The result shows that, the temperature at the wed to flange position maintains the highest during the whole rolling process, while area of the web the lowest. After the rolling, temperature difference is above 150K between the web’s surface and flange’s inside surface, approximate 130K on the flange’s outside surface and 200K in the cross section. The simulation results show good agreement with the measured temperature data.