Papers by Author: Hai Tao Zhang

Abstract: With the developing control and configuration pattern of modern manufacturing system, the complexity of manufacturing system is enlarged and the operating environment is filled with uncertainty. Under the influence of many uncertain factors, reducing delivery time, due-date performance and low inventory become the important goals of production enterprise. This paper presents a bio-inspired manufacturing system control model, combining the knowledge of manufacturing system, biological control and control system. The relationship between response time and production rate of manufacturing system with different capacity is analyzed, production capacity controller is designed using PI and PD, and the control strategy differences of production rate deviation and overshoot is also discussed. Finally, an optimized design for the parameters of a two-layer work-in-process (WIP) inventory controller is analyzed, with the reference to the neuroendocrine regulatory mechanism. The simulation analysis shows that in bio-inspired manufacturing system made of organic manufacturing cells, the shorter the response time of production capacity is, the faster its production rate responses. With the combination of two-layer WIP inventory controller and traditional PID production capacity controller, the production system is more responsive and the production offset and overshoot are small when the unexpected external demand changes of manufacturing system occur.

Abstract: In this paper, Low frequency electromagnetic field and air knife are applied simultaneously to produce large-size AA 7055 aluminum alloy ingots during DC casting. Moreover, the effects of low frequency electromagnetic field and air knife on macro-physical fields during DC casting as well as microstructure and crack in the ingots are studied and analyzed by the numerical and experimental methods. Comparison of the calculated results indicates that applying electromagnetic field can modify the flow direction and increase the velocity of melt flow and homogenize the distribution of temperature in the sump, and applying air knife can homogenize the distribution of temperature and decrease the stress and strain in the solidified ingots. Further, the microstructure of the billet is refined remarkably and the crack is eliminated by applying electromagnetic field and air knife during DC casting because of modification of the macro-physical fields

Abstract: The effect of electromagnetic field and iron content on the solidification structure of copper-iron alloys had been investigated in this paper. The results show that the addition of iron to copper causes considerable grain refinement, and the refinement increases with the iron content. Applying electromagnetic field during the solidification of Cu-Fe alloys can further refine grain of hepoperitectic alloys, but has no obvious effect on the grain size of heperperitectic alloys. Primary γ-Fe dendrites are gradually broken and scattered uniformly throughout the matrix under the influence of electromagnetic field. When the current intensity is 200A, the primary γ-Fe appears as fine petal shape distributed uniformly over the matrix.

Abstract: The effect of electromagnetic field on the solidification structure of C90500 tin bronze (Cu-10%Sn-2%Zn in mass%) had been investigated in this paper. The results show that applying electromagnetic field during the solidification of C90500 tin bronze can refine macrostructure and δ phase, promote columnar-to-equiaxed transition, inhibit inverse segregation of Sn, and make the dendrite degenerate. The width of eutectoid structure (α-Cu+δ) becomes smaller, and the morphology of eutectoid δ changes from coarse acicular and massive shape to fine dotlike shape. The above mentioned effects become more obvious with the increasing of current intensity.

Abstract: Al-4.5%Cu ingots were prepared by a process of low frequency electromagnetic casting (LFEC) and conventional direct chill (DC) casting, respectively. The effects of low frequency electromagnetic field on the microsegregation were investigated from eutectic analysis and electro probe microanalysis (EPMA). It was found that the amount of the nonequilibrium eutectic and the dimension of the nonequilibrium eutectic were decreasing markedly. In contrast, the solute content in the α-Al phase increased to a certain extent in the presence of the low frequency electromagnetic field, and it increased with the incerasing electromagnetic.

Abstract: A method for manufacturing composite ingot of 3004/4045 aluminum alloy using direct-chill (DC) casting was introduced. The casting process, the temperature distribution near the composite interface and the macro- and microstructures were investigated. The results show that composite interface is well-bonded, planar and clean with little evidence of porosity, which belongs to a kind of metallurgical bonding. Also semi-solid layer with a certain thickness is formed under the effect of cooling plate, which can ensure the realization of casting process of composite ingot.

Abstract: In the present study, the influencing factors such as the intensity and the direction of gradient magnetic fields, the magnetic susceptibilities of non-magnetic metals on the structures are studied theoretically and experimentally. In the theoretical analyses, the influences of high gradient magnetic fields on nucleation and structures are investigated. In the experimental research, high gradient magnetic fields are imposed on paramagnetic material Al and diamagnetic one Sn during their solidification processes. Then the macro- and microstructures of these samples are examined and the influences of magnetic susceptibilities of metals, the intensity and the direction of high magnetic fields are analyzed in details. It is found that solidified structures could be refined when the magnetization force and gravity were in the same directions, while the solidified structures could be coarsened and the coarse dendrites grew along the direction of the imposed magnetic fields when the directions of these two forces were opposite. Those phenomena could be explained from the views of reduced gravity and elevated gravity effects caused by magnetization force and the convection suppression effect caused by high magnetic fields. The results indicate that high magnetic fields can be applied to control the solidified structures of metals and then improve the quality and the properties of materials for different purposes.

Abstract: Low frequency electromagnetic casting is a new developed technology that appears in the recent years. In this paper, a comprehensive mathematical model has been developed to describe the interaction of the multiple physics fields during LFEC (low frequency electromagnetic casting) process. The model is based on a combination of the commercial finite element package ANSYS and the commercial finite volume package FLUENT, with the former for calculation of the electromagnetic field and the latter for calculation of the magnetic driven fluid flow, heat transfer and solidification. Moreover, the model has been verified against the temperature measurements obtained from one 7XXX aluminum alloy billet of 200mm in diameter, during the LFEC casting processes, respectively. There was a good agreement between the calculated results and the measured results. Further, the effects of electromagnetic frequency on fluid flow, temperature field and solidification during LFEC process have investigated numerically by using the mathematic model. The choosing criterion of the electromagnetic frequency during LFEC process has been used in order to obtain the best structure of the billets by analyzing the effects of fluid flow and temperature field on the solidification process in the presence of electromagnetic field.

Abstract: A comprehensive mathematical model has been developed to describe the interaction of the multiple physics fields during the conventional DC casting and LFEC (low frequency electromagnetic casting) process. The model is based on a combination of the commercial finite element package ANSYS and the commercial finite volume package FLUENT, with the former for the calculation of the electromagnetic field and the latter for the calculation of the magnetic driven fluid flow, heat transfer and solidification. Moreover, the model has been verified against the temperature measurements obtained from two 7XXX aluminum alloy billets of 200mm diameter, cast during the conventional DC casting and the LFEC casting processes. In addition, a measurement of the sump shape of the billets were carried out by using addition melting metal of Al-30%Cu alloy into the billets during casting process. There was a good agreement between the calculated results and the measured results. Further, comparison of the calculated results during the LFEC process with that during the conventional DC casting process indicated that velocity patterns, temperature profiles and the sump depth are strongly modified by the application of a low frequency electromagnetic field during the DC casting.