Papers by Author: Chen Guo

Abstract: The formability of the magnesium alloy sheets is poor at room temperature even though the magnesium alloy sheets are attractive because of their excellent characteristics. Application of pulsating hydroforming is a new and effective method to improve the formability. The effects of the pressure amplitude on the maximum bulging height and minimum wall thickness of the formed parts of AZ31B magnesium alloy sheets are examined using finite element simulations. It is shown that the distribution of maximum bugling height and minimum wall thickness is similar for different pressure amplitude A, and a uniform expansion in bulging region is obtained, the cause of the uniform expansion obtained may be caused by the variation of stress components. The AZ31B sheet has an excellent performance in formability when the pressure amplitude and pulsating frequency are properly selected.

Abstract: The traditional deformation measurement have many limitations, According to actual measurement need, it is requested not only comprehensive, flexible, high-precision, but also can describe the various points displacement within the measurement scope at any time, get the most comprehensive data. In this paper, used speckle methods to carry on deformation accurate and comprehensive measuring. First, compared with traditional methods, showed its many advantages, including: non-contact, high precision, operation simple and flexibility, etc. Then specified the main basic theory of the speckle method, established relevant mathematical models, developed the appropriate measurement and analysis software XJTUDIC, and used the software with the appropriate hardware equipment to test a specific tensile deformation process, and compared the results with using traditional extensometer measurement methods, through calculation got the error is within ± 0.2%. This fully validated the method and corresponding software and hardware were reliable, feasible and excellent.

Abstract: The scheme for cold extrusion process of Seven-speed sleeve is determined according to the experiences and analysis by DEFORM-3D software, the extrusion procedure has been numerical simulation analyzed; The part technology and parameters of die structure has been optimized by orthogonal test. The optimized process parameters are as following: friction factor is 0.10, blank height is 31.4mm, extrusion speed is 200mm/s; The optimized parameters of die structure are as following: 1st step convex fillet is 1.5mm, 1st step concave rounded is 2.0mm, 2nd step convex fillet is 2.0mm, 2nd step concave rounded is 1.0mm, 1st step die-entrance angle is 35°, 2nd step die-entrance angle is 60°.The qualified products are obtained using the optimized process parameters in the production practice.

Abstract: The anisotropic plastic behavior of metallic sheet has a significant influence on spring-back, and is usually modeled by anisotropic yield function in numerical simulation. Material parameters of anisotropic yield function are generally identified either by yield stresses or by r-values, or both of them. For Hill1948 and Yld89 anisotropic yield functions, r-values are still widely used to calibrate their material parameters in spring-back prediction. Here, yield stresses and r-values were respectively used to calibrate them, and the differences of the spring-back simulated by these two identification methods were discussed. To evaluate their accuracy, the simulation results were compared with the spring-back calculated by Yld2000-2d anisotropic yield function. The result shows that when yield stresses were used to identify the material parameters of Hill1948 and Yld89 yield functions, the simulated spring-back was closer to that of Yld2000-2d yield function.

Abstract: The process factors influencing the forming quality of car inner door panel such as stamping direction, binder surface, draw-bead, addendum surface and technical cut are determined based on experience knowledge. Aiming at local fracture problem of test pieces, some key parameters are determined based on experience knowledge, and the strain in thinning area of sheet metal forming is analyzed by numerical simulation. Based on this, process optimization and die modification scheme are put forward. Engineering inspection proved that optimized process and die parameters are reasonable, after increasing die fillet radius and process hole radius, decreasing draw-bead height, qualified products are achieved and fracture flaw is well controlled.

Abstract: Thermal deformation flow stress equation of 1Cr12Ni3Mo2VNbN in the temperature range of 980 °C~1180 °C is established by means of hot simulation test and the regression analysis. The results show that the data obtained accords with hyperbolic sine function and the equation will also enrich the material performance database. The established equation is used in the blade forging production based on numerical simulation technology, and the numerical simulation results show that utilizing flat head billet can solve the problem of filling dissatisfaction at the root of the blade. Adopting water-based graphite lubricant provides better lubrication condition for blade forging. The equipment wear and energy consumption can be reduced by applying initial forging temperature of 1130°C in the blade forging process. The application of thermal deformation flow stress equation and numerical simulation technology can reduce the number of trial production, shorten the process design cycle and improve production efficiency in a large extent.

Abstract: In order to solve the existing problems such as the less-plump corners and wrinkle during the forming process of a double curvature thin-wall part. Material parameter formulas are calculated based on Hill 1948 anisotropic yield criterion and flow rule. The material mechanical property parameters of 2A12 are obtained using uniaxial tensile experiment. Single factor test method is used and LS-DYNA is applied to conduct finite element analysis. So the influence law of holding force, blank shape and blank size imposed on the finite element model are calculated in sequence. On the basis of these laws, that the blanking force, blank dimension and blank shape are decided. Stamping die for the experiment model is designed and made, deformation measurement technology of coordinate grid circle is used to carry out strain analysis. From the comparison result between experiment and simulated data, it can be seen that Hill 1948 yield criterion and flow law can better solve the formability of 2A12 sheet.

Abstract: Many of simulation analysis were carried out under the complex conditions, and in general it will use some viable treatment, so get the reliable results. However, some external force rather complex or can not be directly measured, and some material properties is complex and can not be described by existing parameters, then the direct simulation analysis is not feasible and must have a different effective treatment. This paper narrates the comprehensive simulation analysis of mold cavity and core deformation with complex force by some analysis soft wares, and carries out data processing, data transmission, and gets the final feasible results, it can provide a reference example for the similar situation. Then explores the main issues about the performance of clad metal for simulate analysis, and holds that the relevant performance parameters obtained by experiment and simulation combined are also effective and feasible.

Abstract: We present a scatter point cloud denoising method, which can reduce noise effectively, while preserving mesh features such as sharp edges and corners. The method consists of two stages. Firstly, noisy points normal are filtered iteratively; second, location noises of points are reduced. How to select proper denoising neighbors is a key problem for scatter point cloud denoising operation. The local shape factor which related to the surface feature is proposed. By using the factor, we achieved the shape adaptive angle threshold and adaptive optimal denoising neighbor. Normal space and location space is denoising using improved trilateral filter in adaptive angle threshold. A series of numerical experiment proved the new denoising algorithm in this paper achieved more detail feature and smoother surface.

Abstract: Thermal deformation process of H62 brass is studied, multi-scale simulations of macro-forming property and microstructure distribution are carried out for the hot-extrusion process of double cups part with flange utilizing numerical simulation technology, the process parameters are determined and the microstructure of extruded parts is predicted. The constitutive equation of H62 brass under high temperature deformation is established with isothermal compression test, and the results indicate that the flow stress accords to Arrhenius hyperbolic sine functions. The model of microstructure evolution during hot-deformation is founded and the influence of process parameters on microstructure is revealed. The microstructure prediction on extruded part shows that the simulated results agree well with the experimental results. The high-quality products are obtained using the optimal process parameters.