Materials Science Forum Vols. 704-705

Abstract: A single-point load will be applied on the ring in the cold ring rolling process when the ring vibrates violently. This arouses hourglass in finite element simulation of the process using reduced integration element. A one-point quadrature element with hourglass control developed by Hu is used, and the user-defined control parameters are not required. Hourglass energy can be reduced to 3 percent of the internal energy. The element is applied to simulation of a pure radial cold ring rolling with rectangular section. Compared with the experimental results, the simulation results are proved to be accurate. Key-Words: one-point quadrature; Hourglass control; finite element; cold ring rolling

Abstract: With widely use of aluminum alloy in the cares and other industry fields and the like, the aluminum alloy workpieces are becoming the important components, such as load bearing and so on, in which it has been gradually paid attention to the formation and the producing roughcast of shaft forging part of aluminum alloy. the process of across wedge rolling for wrought aluminum alloy has gradually taken notice of improving production rate and saving metal in this field because of its advantages and superiorities. It is very necessary to research and analyze the flow regularity and forming characteristic of aluminum alloy. In this paper, the forming process of cross wedge rolling for wrought aluminum alloy is simulated with Deform 6.0 soft. Thus, it is analyzed that features about cross wedge rolling for aluminum alloy and changeable characteristic of stress in the central axis and changeable regular of effective stress in wedging stage and stretching stage . At the same time, it is researched that the flow characteristic of aluminum alloy from outer layer to central axis. The results as following: in the forming process of cross wedge rolling for aluminum alloy, the central portion of workpiece is applied by two pairs of tensile stress and one pair of compression stress. The flowing velocity of aluminum alloy is gradually reducing from outer layer to center portion along workpiece’s axis. Keywords: Cross Wedge Rolling, Wrought Aluminum alloy, Stress, Numerical simulation

Abstract: T2-copper conductive body is a important part used in high voltage switch, it has poor machining process due to the complex shape. Through Deform numerical simulation, conductive body was formed by open-die forging and closed die forging. In the open-die forging simulation，heat transfer coefficient between blank (880°C) and open-die (200°C) is 11, the surrounding environment temperature is 20°C, friction factor is 0.3. The main open-die forging process parameters is: outer draft angle α=6.5°; inner draft angle β＝10°; bridge width b＝5、8、11mm. punching skin and cylindrical blank. Simulation results show that forging can meet the requirement while properly adjusting mould parameters. The main size of closed-die forging working parts is designed according to the conductive body graph, no draft angle and ring blank of external diameter Φ111mm and inside diameter Φ93mm with the same volume of conductive body. The simulation results shows that forging can be formed using open-die forging, and it is difficult to form product by the process of the closed-die forging for ring blank because of the restriction of solid state metal liquidity, many regions of the filling is not sufficient. Open-die forging and casting blank-closed die forging are both used in actual production. The casting blank-closed die forging is a more reasonable forming process compared with the open-die forging as metal volume of distribution is solved, higher utilization rate of material, more simple process in following work and the like. To make it more suitable for practical production, appropriate adjustments of some parameters was made in the mold design process based on the numerical simulation. Keywords: open-die forging; casting blank–closed die forging; numerical simulation

Abstract: In this paper, the numerical simulation and calculation of injection molding process are taken in the Moldflow software. The BP artificial neural network combining with the orthogonal experiment design method is used to set up the injection molding process agent model, genetic algorithms are applied to realize global optimization, finally, the optimal combination of process parameters of each quality indicators is obtained.

Abstract: Ultra-high strength boron steel is widely used in a new hot stamping technology which is hot formed and die quenched simultaneously in order to obtain stamping parts with 1500MPa tensile strength or higher. Tensile experiments were carried out with ultra-high strength boron steel in a range of temperature 500°C~860°Cand strain rate 0.01/s~1/s with the thermal simulation testing machine Gleeble 3800, and the stress-strain curves were obtained. The influences of the deformation temperature and strain rate on the stress-strain curves were analyzed. The results show that hot behavior at elevated temperature of ultra-high strength boron steel consists of strain hardening and dynamic recovery mechanism, which can be accurately described by the mathematic model. Keywords: Ultra-high strength boron steel, hot stamping, hot flow behavior

Abstract: Continuous extrusion expansion deforming is an advanced forming process for manufacturing copper bus-bar, die and tool structure is important effect factor of deformation. Based on the characteristics of the forming process, the model of rigid-plastic finite element (FE) on DEFORM^T is established and the numerical simulation of continuous extrusion expansion forming process of the copper bus-bar is carried, The metal flow regularity and the mean-square deviation of velocity (SDV) with the different structure of expansion chamber and port hole and die assembled pattern is analyzed. The result show that when using the drum expansion chamber, the trapezium of port hole without transition surface and the die fitted in reverse, the variance of flow velocity is the minimum and deformation is the most homgeneous, the SDV is 0.62. The simulation results provide a theoretical direction for optimization design of die and tool structure of the continuous extrusion expansion forming. Keywords: copper bus-bar, continuous extrusion expansion deforming, die and tool structure optimization, numerical simulation

Abstract: In this work, On the basis of software ANSYS/LS-DYNA, the strip cold rolling simulation model was established. The process from biting to rolling steady were simulated and investigated for 6-high UCM (6-high middle rolls shift type HC-mill with middle roll bender) cold mill, including the stress, stain state, and velocity field of the workpiece and rolls. The result states that the stability of Biting Process of 6-high cold mill is preferable and the impact of biting process on the roll is acceptable. The simulation regularity corresponds well with the measurements.

Abstract: The hot deformation behavior of a Cr-Ni-Mn-N series stainless steel was studied at temperatures from 850°C to 1175°C with the strain rate ranging from 0.01 s−1 to 10 s−1 using a Gleeble-3500 simulator. The constitutive equation and processing maps were compiled based on a hot compression test to strain of 0.9. The deformation microstructures were observed systematically by optical microscopy. Results show that the efficiency of power dissipation gradually increases with rising temperature and decreasing strain rate. The maps at strains of 0.5 and 0.9 show two distinct domains with one having the peak efficiency of about 28–35% at 1150°C–1175°C and 1–10 s−1 and the other having the peak efficiency of about 33–45% at 1050°C–1150°C and 0.01–0.5 s−1, while complete recrystallization is evident.

Abstract: Rigid-plastic finite element analysis (RPFEA) is an efficient and practical method to calculate rolling parameters in the strip rolling process. To solve the system of simulations equations involved in the RPFEA, a numerous of numerical methods, including the standard Newton-Raphson method, the modified Newton-Raphson method, and etc., have been proposed by different researchers. However, the computational time of the existed numerical methods can not meet the requirement of the online application. By tracking the computational time consumption for the main components in the standard Newton-Raphson method used in finite element analysis, it was found that linear search of damping factor occupies the most of the computational time. Thus, more efforts should be put on the linear search of damping factor to speed up the solving procedure, so that the online application of RPFEA is possible. In this paper, an improved trust-region method is developed to speed up the solving procedure, in which the Hessian matrix is forced to positive definite so as to improve the condition number of matrix. The numerical experiments are carried out to compare the proposed method with the standard Newton-Raphson method based on the practical data collected from a steel company in China. The numerical results demonstrate that the computational time of the proposed method outperforms that of the standard Newton-Raphson method and can meet the requirement of online application. Meanwhile the computational values of rolling force obtained by the proposed method are in good agreement with experimental values, which verifies the validity and stability of the proposed method.

Abstract: The behavior of the flow stress of Al-Fe-V-Si heat-resistant aluminum alloy prepared by spray forming during hot compression deformation was studied. The results show that the true stress-true strain curves of the spray forming Al-Fe-V-Si heat-resistant alloy are characterized by a high true stress occurrence at the early stage of compression, followed by a steady flowing due to recovery and strain softening because of dynamic recrystallization. The flow stress of the alloy decreases with increasing deforming temperature and increases with increasing strain rate. The flow stress of the spray forming Al-Fe-V-Si heat-resistant aluminum alloy during hot compression deforming can be described by constitutive equation in hyperbolic sine function．The deformation activation energy of the alloy during hot deformation by Sellars-Tegart equation is much higher than those of the conventional aluminum alloy. The deformation activation energy decreases with decreasing strain rate at the beginning, then increases with decreasing strain rate. Keywords：Al-Fe-V-Si alloy；heat-resistant aluminum alloy；hot compression deformation；flow stress