Materials Science Forum Vols. 505-507

Abstract: In this paper, the geometry influence of reflectors for infrared rapid surface heating on micro-injection molding was studied. A three-dimension ray tracing combined with transient thermal simulation was used to evaluate the thermal condition of injection mold surface. Several kinds of reflectors were applied to study the heating ability of the infrared rapid surface heating system. A commercially available optical analysis program, TracePro, was used to simulate the infrared emission to the center of mold surface. Thermal module of a structure analysis software, ANSYS, was used to study the absorption and heat transfer of the infrared heating on the mold surface. Then, Taguchi method was adopted to find the close to optimal reflector for rapid surface heating of micro-injection molding.

Abstract: For multiple-axis stages, it is required to operate the axes simultaneously, such that the resulting trajectory of platform follows a given contour. For most stage systems, friction acts as the major disturbance which degrades the precision of system motion and its effect should be compensated. In this paper, contouring control of a two-dimensional stage system subjected to friction is investigated. A systematic contour controller design based on task coordinate frame is proposed and its effectiveness is studied through theoretical analysis and numerical simulations.

Abstract: The repression of wrinkling during sheet metal forming has been a significant issue in recent years. In order to provide a reliable and efficient tool to predict the critical blank holding force to prevent wrinkles, an axi-symmetric analytical model for flange wrinkling is introduced here. Using a conventional theory of the critical condition, the critical blank-holding force and wave numbers are numerically predicted. Comparison between the numerical and experimental results shows excellent agreement for various blank dimensions and materials.

Abstract: In this paper, a 3D slab method model has been developed. Two differential equations governing the longitudinal and transverse force equilibriums coupled with the Von Mises yield criterion have been solved to obtain the rolling pressure distribution. The strip speed is calculated according to the volume constancy. The Coulomb friction law with different frictional coefficient and speeds were applied to the longitudinal and transverse direction. Coupled with the roll stack deformation model and thermal model, the developed 3D slab method model was used to predict the strip profile and edge drop. The effects of bending force, reduction and transverse friction on the strip profile and edge drop have been discussed in this paper. The calculated result predicted by the 3D slab method is in very good agreement with measured results. The results have shown that the large bending force, small reduction and small friction will improve the strip profile and reduce the edge drop.

Abstract: The variation of the friction in the roll bite is of great importance in cold strip rolling. The main interest of the paper is to model the friction coefficient in the roll bite during cold rolling. The deformation resistance of the rolled products and friction coefficient in the roll bite were determined simultaneously by minimizing the error of the measured and calculated rolling forces based on nonlinear least squares optimization algorithm. The neural network was introduced to further improve the accuracy of friction coefficient calculation in cold strip rolling. The results already obtained shows that friction decreases with roll wear, and the lower the rolling speed, the higher is the friction.

Abstract: An oxide scale layer is formed on the steel strip surface due to the high temperature (850-1100 °C) of the strip in hot rolling. The oxide scale layer may not be continuous because of the defects such as void existing in the layer before the strip enters the roll bite. The non-zero cracks may therefore be formed on the oxide scale layer, especially, when the oxide scale layer is relatively thick. These cracks may become narrower (even become closed) or wider (even form steel substrate extrusion) after hot rolling deformation. The development of the crack depends on the materials flow in the hot rolling process. The shape of the profile of the oxide scale layer has a significant effect on the materials flow in hot rolling process so it is important to investigate the effect of the oxide scale profile on the propagation of the crack. In this paper, the authors used the FEM method to simulate the crack propagation in oxide scale under hot rolling conditions for different profile parameters of the oxide scale layer. Simulation results indicate that the larger is the initial profiles surface roughness, the larger the crack width remained after rolling. With a rough profile and large initial crack width, the steel substrate extrusion may be formed.

Abstract: A convolute cut-edge design is performed using FEM (Finite Element Method) for a single step cup drawing operation in order to produce an earless cup profile. Mini-die drawing based on a circular blank shape is initially carried out in order to verify the earing prediction of the Yld2004 anisotropic model (Barlat et al. [1]) for a body stock material. Realistic cup geometry is then employed to design a non-circular convolute edge shape. An iterative procedure based on finite element method is initially used to design a convolute shape for an earless target cup height. A constant strain method is suggested to obtain a new convolute prediction for the next iteration from the current solution. It is proven that Yld2004 model is accurate to predict the anisotropy of the material.

Abstract: An upper bound solution for axisymmetric upsetting of two-layer cylinder made of rigid perfectly plastic materials is provided. An important feature of the solution is that the kinematically admissible velocity field, in addition to the necessary requirements of the upper bound theorem, satisfies the frictional boundary condition in stresses, the maximum friction law. The latter is archived by introducing a singular velocity field such that the equivalent strain rate approaches infinity at the friction surface. The dependence of the upper bound limit load on geometric parameters and the ratio of the yield stresses of the two materials is analyzed. The solution can be used in industrial applications for evaluating the load required to deform two-layer cylinders.

Abstract: In this paper, an upper bound approach of rotating compression forming of ring is established. Using the upper bound approach, the effects of friction factor, reduction, aspect ratio etc upon compression force, radius of neutral surface, internal radius, spiral lead etc are investigated systematically. The experiment of rotating compression forming of ring made of aluminum alloy A6061 was carried out. Comparisons between the analytical results and the experiment are used to verify the validity of present upper bound approach. The analytical results are in good agreement with the experiment.

Abstract: In twin-roll strip casting process, the casting speed has a significant influence on the metal flow and temperature distribution in the molten pool, which will affect the stability of this process and the quality of the produced products. Based on a 3D coupled thermal-flow analysis, a combination of the experimental results for twin-roll strip casting of stainless steel, heat equilibrium calculation and simulation results was conducted, and the boundary conditions of the heat exchange between the rolls and molten pool has been treated effectively. The effect of the casting speed on the flow and temperature in the molten pool was given. Simulation result is in agreement with the measured value.