Materials Science Forum Vols. 575-578

Abstract: On the base of analyzing material constitutive model, chip-tool contact friction, and chip separation and fracture, a finite element model (FEM) was built to study the high-speed machining process of alloy cast-iron. The shaping process of serrated chip in high-speed milling alloy cast-iron was simulated and analyzed in detail. It was shown that machining parameters affect the serrated chip forming greatly. The model can be used to optimize machining parameters, prolong tool life and improve machining surface quality.

Abstract: The quenchable boron steel is a novel type of ultra high strength steel used for automotive parts so as to reduce the weight of the whole automobile. The hot stamping processing experiments for bending parts were studied. The influence of the hot stamping processing parameters, such as the heating temperature, the heat holding time and the cooling water flow velocity, on the mechanics properties and microstructure of the hot stamping parts is obtained. And then the optimal ranges of these parameters are determined, which provides a basis for the control of the hot stamping process applied in complicated shape parts’ production.

Abstract: The taper-rolling model, the elastic-plastic constitutive equations with limited deformation conditions, and FEM model for the cold rolling process of spiral blade are established. The FEM software SUPERFORM based on elastic-plastic theory is adopted to simulate the spiral blade forming process for the first time. The influence of different parameters (feeding height H, adjusting parameter of the working pressure 1 S , translation slip S2 , elastic angle θ , workpiece material and friction coefficient) on the shape of spiral blade are simulated and analyzed systematically. And the law of the forming of spiral blade is concluded. The simulation results indicate that workpiece is very regular and there is in good agreement between simulation and practical results. The results obtained by simulation provide a foundation for optimizing production and adjusting parameters of taper-rolling.

Abstract: Equal channel angular pressing (ECAP) is one of the most promising processes to fabricate ultra-fine grained materials. The material deformation is affected by die geometry, material behavior, friction and back pressure. The optimum back pressure for 1100Al during ECAP was studied. The effect of back pressure on deformation behavior, effective strain and deformation load were analyzed by using finite element software. The results show that the corner gap between the billet and the die in the external part of the deformation zone decreases and even disappears with the increase of back pressure, which can produce more uniform and larger strain in the billet. The deformation load enhances with the increase of back pressure. From the simulation results, it can be found out that the optimum back pressure for 1100Al pressed in the die of Φ=90° is about 30MPa.

Abstract: This paper puts forward a negative clearance fine-blanking theory and its technique process, and introduces the technical processing of fine-blanking which can be used on ordinary punching machines. In this paper, computer simulation and the experimental study of negative clearance fine-blanking process are carried out. Thus the parameters of the force of blanking, the value of negative clearance are determined. The effect of fine-blanking quality was obtained, and the perfect rate of the blanking fracture achieves 90%. By comparing negative clearance precise blanking with conventional blanking, the following conclusions are drawn: 1. Blanking quality of negative clearance blanking is increased by 57% than that of conventional blanking. 2. The down surface of the work-pieces obtained by the conventional blanking processing have 0.2 - 0.5 mm longitudinal burrs, while the work-pieces obtained by the negative clearance blanking have no burrs. Thus the processing of clear away the burrs could be spared. And the manpower, the material, energy and the equipment investment are saved. The researching result provides theoretic reference and the experimental data for the engineering practice. It has instructive significance and reference value to engineering manufacturing.

Abstract: The objective of this research work is to design optimally dies and the blank sheet for manufacturing of the back panel of a PDP TV. The influence of design parameters of the dies and the blank sheet on the formation of wrinkling in the upper trimming area of the stamped part has been quantitatively investigated through three-dimensional elasto-plastic finite element analysis. The corner radius of the upper trimming area of the die and the blank gap, which is the distance from the outer line of the blank holder to that of the blank, have been chosen as design parameters to remove wrinkling associated with a stamping part in a upper trimming area. From the results of the analyses, it has been shown that a product without wrinkles and skid lines can be manufactured when the corner radius is 8 mm and the blank gap is 60 mm. Several stamping tests have been performed using the manufactured die set and the blank sheet according to the proposed optimum design. From the results of the stamping tests, it has been shown that a back panel of the PDP TV can be successfully manufactured using the proposed optimum design condition.

Abstract: High pressure valve always takes several dozens to several hundreds MPa pressure and which was difficulty to form because of its complex internal structure. In this paper, three-dimensional numerical simulation was carried out to investigate metal flow behavior during the three-way valve extrusion process. The block shape materials were formed to shell shape three-way components by the level and vertical direction uniform temperature simultaneous extrusion. The simulation results show that the metal flows were influenced by both loading sequence and time of the moving die of two directions. The loading process worked out through dynamic simulation can guide the actual processing.

Abstract: Technology and die design are very important in the development of forging products due to its great influence on the quality, cost and manufacturing efficiency of the final products as well as the life of the forging die. In the environment of the severe competition, how to improve the quality of forging technology and die design, to reduce the product cost and ultimately to enhance competitiveness of the forging factory are the problems that forging technology and die designer have to solve. In order to improve the quality of forging technology and die design, a design optimization method based on approximate model (response surface model) and FEM technique for hot forging process is proposed in this paper. During design optimization process, finite element analysis is incorporated to calculate the objective function and check the design alternatives. Design of experiment (DOE) method is used to collect sample points and calculate the polynomial coefficients of response surface model, and approximate model is used to calculate the optimum search direction. Finally, a case study is conducted for a gear workpiece hot forging process. The objective function is the degree of uniformity of equivalent-strain, which can be defined as mean square deviation of the equivalent-strain in each element and the average equivalent-strain of all elements, and the design parameters are the initial H0/D0 ratio of billet and the key dimensions of the die. Then the design optimization mathematical model is established. The result shows that the objective function value is dropped from 0.7914 and converges at 0.4843 within 17 iterations, the optimal design parameters are obtained.

Abstract: Dynamic superplasticity of aluminium alloys is considered from positions of the theory of nonequilibrium phase transitions. Evolution of the open nonequilibrium system by which temperature-rates process in materials is modelled, is investigated within the framework of worked out defining relations with attraction of thermodynamic functions of the response. It is shown, that to peak of superplasticity there corresponds a maximum of a specific thermal capacity. The entropy production in optimum thermomechanical conditions of superplasticity aspires to a minimum which corresponds to formation of qualitative ultrafine-grained structure. With use of the Focker-Plank equation mechanisms of deformation characteristic for superplasticity and boundary conditions are analyzed. It is shown, that at superplasticity the main is the mechanism grain-boundary sliding, and in metastable conditions are added diffusionary processes. Influence of the specified processes in conditions of superplasticity becomes prevailing.

Abstract: Heavy axial forgings made by conventional methods have obvious fibrous tissue in the axial direction, leading to the anisotropy of mechanical properties. The forging method with horizontal V-shaped anvils (HVA) is introduced to control fibrous tissue flow direction, to improve the anisotropy of mechanical properties of axial forgings. The forging method is superior to the common flat anvils (FA) forging method in inner stress states, metal tissue, overall properties and geometrical shapes of forgings. Qualitative physical simulation and pilot production for the HVA forging method are conducted, verifying the fact that the HVA forging method is an effective process to control the mechanical properties of axial forgings. The HVA forging method may reduce the anisotropy of the mechanical properties of axial forgings and increase their uniformity by 5~50%.