Applied Mechanics and Materials Vols. 217-219

Abstract: The overall distribution of mechanical properties of A357 aluminum alloy connection beam casting after solidification and T6 heat treatment was researched in this paper, through the mechanics performance test, metallographic microstructure observation, SEM and EDS scanning analysis of the fracture surface, the ensemble mechanical properties of connection beam casting was characterized. The results show that owing to the low cooling rate nearby the arc thick-walled department and the trasition region between the thick and thin-walled of the connection beam casting, leading to the morphology of the crystalline grains and silicon particles in this vicinity are thick. Some casting defects such as oxide inclusions located in the lateral stud district were caused by the strong erosion of high temperature melting liquid during the pouring process, resulting in the mechanical properties decreased significantly, casting defects were not eliminated in the T6 heat treatment process. Due to both the high cooling rate and the smooth pouring process among the thin-wall, forward stud and square box region of A357 aluminum connection beam casting, after the solid solution and limitation strengthening of T6 heat treatment, resulting in the overall mechanical properties were higher than other areas. The tensile strength has reached 360.96MPa, also with the yield strength and elongation respectively attained 297.95MPa and 8.82 %.

Abstract: In order to reduce cyclic variation in rotational speed of generated gears or shaper cutter induced by additional rotation during shaping, tooth-leap shaping method for helical gears was proposed. Based on fundamentals of helical gears shaping kinematics, principle of tooth-leap shaping for helical gears was introduced. Furthermore, mathematic models of tooth-leap shaping motions for helical gears are established. Finally, several examples are calculated, results show that cyclic variation in rotational speed of generated helical gear can be reduced largely by tooth-leap shaping method comparing with conventional shaping method. Consequently this method will make shaping motions of helical gears more smooth and improve the machining accuracy of helical gears.

Abstract: In the tube hydroforming process, the friction behavior between the tube blank and the die is very complex. As a result, it is very difficult to build a precise friction model in accordance with the actual working conditions by fully taking into account the various factors. In this paper, the friction behaviors between the tube blank and the die in the guided, transition and expansion zones have been studied with the help of numerical simulation and experimental tests. The influences of the different friction conditions in the three zones as well as the uneven friction behavior in the expansion zone on the thickness distribution of tube wall and the characteristics of material flow have been analyzed and experimental tests have been carried out for the verification. The conclusions have provided theoretical references for the process planning, selection of lubrication and tooling design in the actual production process of tube hydroforming.

Abstract: The equipment for measuring electron beam (EB) focus in electron beam produced by the effect of extremum temperature of powder molten pool caused by the interactive effect of electron beam with metal powder is described. The principle of operation of apparatus and examples of EB characteristics are presented. During electron beam processing, the mechanical analysis of metal powder molten pool temperature following focusing current are studied. As a result, the transferring point of critical energy density described by the peak of metal powder pool temperature can be obtained. Based on the temperature characteristics of critical energy density, the measuring concept of dynamic focal spot of electron beam is put forward in the paper. The method of measuring dynamic focal spot of electron beam will provide a new possibility for 3D scanning prototyping through changing focus position of EB.

Abstract: The LPDC process parameters of A356 thin-walled aluminum alloy were designed based on numerical simulation by precisely setting the thermal boundary conditions. By applying the designed process parameters, a sound casting with 300mm in length, 100mm in width and 1.5mm in thickness was successfully prepared. The results indicate the numerical simulation technology is an effective tool for designing casting process and reducing the manufacturing cost.

Abstract: Optical freeform surfaces have a strict request on surface quality, but the vibration of tool , which is often ignored in previous studies, have a great influence on surface topography in micro-milling. This paper constructs a micro-milling motion model concerned with tool vibration, and the impact of tool vibration on feed-interval scallop in micro-milling is analyzed. The results show that tool vibration always lead to an increment of surface roughness; and vibration amplitude and feed per tooth are the major factors that have an effect on feed-interval scallop form and surface quality.

Abstract: In the contrast study of establishing the frictional models in finite element (FE) simulations of high-speed machining Ti6Al4V in this work, FE predictions from the simulation are greatly influenced by frictional coefficient μ, which shows the predicted force at the speed of 166m/min is much closer to the experimentally measured one when μ=0.2. In order to investigate the tool wear in high-speed cutting to prolong the tool life and reduce the tool cost, the influences of the tool geometric parameters including the rake angle γo, clearance angle αo and cutting edge radius rε on the chip formation, on the cutting forces and on the cutting temperatures are numerically simulated under the given cutting conditions, then the general rule of the selection of γo, αo and rε is presented accordingly. In the meantime, the average cutting forces and temperatures are obtained under different simulation conditions, which are the basis of further study on the relationship between the tool geometric parameters and cutting forces together with temperatures to obtain the proper tool geometric parameters for simultaneously controlling both cutting forces and temperatures to their proper values in high-speed machining in practice.

Abstract: Using periodic density functional theory within the generalized-gradient approximation to electron exchange and correlation, we have studied S adsorption four-fold hollow site on Fe(100) in different hydrostatic pressure. We find that the adsorption height decreases with hydrostatic pressure increasing is non-monotonic. The adsorption energy decreases with an increase with pressure is monotonic and we have obtained density of states is almost unchanged, the adsorption energy change is mainly caused by lattice deformation in the hydrostatic pressure, and the adsorption energies increase linearly with pressure.

Abstract: For the composite powders with different NdFeB powder content , the effects of processing parameters including injection temperature, injection pressure, holding pressure and injection velocity on the sizes and properties of injection molded bonded NdFeB magnet were investigated, and the reasons of effects were also analyzed. The results show that changes in injection parameters can influence the size, density, mechanical properties and magnetic properties of bonded NdFeB magnets, and has strong influence regularity. The injection temperature and injection pressure have the greatest impact on the performance. On the basis of research, the injection molding bonded NdFeB magnet with high performance is obtained with magnetic properties Br=0.539T, Hcb=345.37kA/m, Hci=681.02kA/m, (BH)max=47.37kJ/m3 and density 5.07g/cm3 respectively.

Abstract: The step size tolerance for the two-sided forming base complex parts is ±0.1mm, and sharp corners of and roots are required for the 12 vertical facades and edges. Therefore，it is difficult to guarantee the products quality by conventional extrusion. In this paper, the new calculation methods about scaling rates were adopted to control the size of the mould, and computer simulations were carried out for analyzing the forming processes for the extrusion. This method can meet the requirements of the product, improve the performance and material utilization rate, which might replace the machining methods used conventionally.