Applied Mechanics and Materials Vols. 16-19

Abstract: Defects of pieces rolled by cross wedge rolling (CWR) have great effect on its practical applications. With reference to the center-pressure method used often in the forging, the effects of non-uniform temperature field on defects were studied by using the three-roll CWR tests under different cooling conditions and the coupled thermo-mechanical finite element models. The porous can be reduced or even eliminated when the billets were rolled with a controlled non-uniform temperature filed. The optimal temperature gradient was determined by FEM, which can be used in practical applications.

Abstract: The precision forming technology developed rapidly during passing two decades, however technologies of precision plastic forming the parts with deeper hole are far behind developed countries. The warm backward extrusion-ironing forming technology was presented for precision forming of non-circular hole joint in this paper. The forming process and parameter variable trend were simulated by finite element method, which the software MSC.Marc was applied. The forming die was designed and the forming experiment was finished. The products were deserved with good quality and performance. The feasibility of the forming technology is proved by experimental results and numerical simulation.

Abstract: Based on the back propagation multi-layer forward feed neural network, the neural network model is built for the dielectric sensitive structural parameters between the equivalent permittivity and the equivalent permeability, which is used to analyze the basic left-hand materials(LHMS) structural. The experimental results show that the analysis time is 145.535648 seconds and the training mean error is 0.000113426 while adopting the scaled conjugate gradient method. The results are coincident with these ones by the full wave method, satisfying the engineering demand, reducing the faults caused by thickness resonance in the traditional numerical analysis method, realizing the coexistence between the high analysis precision and the high efficiency of the left-hand materials.

Abstract: Chip velocity is a crucial parameter in metal cutting. The continuous variation of chip velocity in primary shear zone can not be obtained from conventional shear plane model. Therefore a general streamline model was used to investigate the distribution of chip velocity field in metal cutting. This paper also verified the continuity of plastic flow in metal cutting by tracing the variation of particle area. The velocity of chip material was calculated from the mathematical expression of streamline model. The velocity results were compared with conventional shear plane model.

Abstract: The Metal Laser Sintering (MLS) process has been developed over the last decade to produce 3D parts from CAD files using metal powders. A considerable amount of research has been conducted into the melting and solidifying process of metal powders, mainly to predict the temperature distribution in a single metal powder layer or a few layers. The temperature and thermal residual stress distribution in real parts built using MLS has rarely been reported. Finite element simulations of temperature distributions in metal powders and parts requires huge computing resources, this is the main obstacle to successfully predicting temperature and thermal stress distributions in MLS parts. However, from the numerical results in this paper, the periodic nature of temperature distributions in parts around the laser spot can be used to simplify the numerical simulation process to achieve the prediction of temperature and thermal stresses distributions in parts built by MLS.

Abstract: The dynamic performance of the grinding wheel system is one of the key factors to affect the super-high speed grinding process The excessive centrifugal stress acted on the wheel body can make the wheel rupture due to the super-high rotary speed of the wheel. And the alternating centrifugal force caused by the wheel imbalance can not only make the spindle and bearings vibration and failure, but also lower the machining precision and the wheel life, as well as make against the safety. In this paper, the centrifugal stress of the high speed grinding wheel and its effect on machining process were analyzed by means of finite element analysis and simulation. The alternating centrifugal force and its effect on the wheel spindle system were investigated. Furthermore, the balance precision of super high speed grinding wheel and system was discussed for achieving the high precision, safety and efficiency machining process.

Abstract: The medium-thick sheet metal extrusion has been a typical bulk forming feature used in the sheet metal forming industry while there isn’t enough know-how available. Therefore, the sheet metal extrusion process was simulated in this study by using an arbitrary Lagrangian-Eulerian (ALE) finite element method implemented in MSC. Marc. Firstly, the simulation results are compared with experimental data from a reference to verify the usefulness of the simulation. Then, based on the simulation results, some phenomenological characteristics of the sheet metal extrusion process, such as the material flow, shrinkage cavity and the effect of area reduction on the forming force, are present. The work presented in this paper might be used for as design fundamental of the sheet metal extrusion process.

Abstract: On the basis of their similarities with forward rod extrusion, three analytical force computation models are introduced for the forming force prediction of sheet metal extrusion. By comparing with finite element solutions, it has been found that the forming forces obtained by these models deviate at more or less 30% from the numerical solutions under different area reductions. These deviations are due to the neglect of friction or shear force terms in the models. Therefore, a new model, one that fully considers the contributions of extrusion force, shear force, and friction terms to the forming force, is proposed. With tremendous numerical computations, the relationships between forming force and area reduction, sheet metal thickness, and penetration depth, among others are analyzed. Thereafter, the factors in the proposed model are determined. Additionally, a corresponding experiment work has been designed to validate the proposed model. Compared with the experimental results, the predicted results show a relative error of less than 15% under different extrusion ratios, which is acceptable in the industry.

Abstract: The fine blanking process with a stepped-edge punch was researched by finite element method (FEM) and experiment investigation. Finite element analysis showed that the hydrostatic stress of the blank around the edges changes a little during fine blanking process using a stepped-edge punch with negative clearance. The burnish zone of sheared surface increases with the increase of the relative negative clearance. The reasonable forming parameters were presented by a lot of experiment investigations. Parts of three kinds of materials, Q235 steel, copper and industrial aluminum, were formed using fine blanking process with a stepped-edge punch. Full burnish zone were obsearved for all the parts.

Abstract: To explore geometrical shape, stress distribution, strain distribution and wall thickness of product in the process of polycarbonate hot gas bulge forming, numerical simulation of 4mm PC double curvature and large-area workpiece with the chord 1050mm has been conducted by the finite element software DYNAFORM. The results indicate that the deformation of large-area workpiece starts from blank holder to sheet center, and the maximum latitudinal stress and longitudinal stress is located in the center of PC sheet. The maximum reducing rate is approximate to 6.4%. The experimental results fit well with the numerical simulation.