Papers by Author: Jian Hua Zhang

Abstract: In this paper, experiments were conducted to investigate the effects of cylindrical electrode and helical electrode on the micro electrical discharge machining (EDM) performances during micro-hole machining of titanium alloy. The results show that the material removal rate (MRR) and the tool wear rate (TWR) increase with open circuit voltage, regardless of electrode shapes. Compared to the cylindrical electrode, helical electrode can result in higher MRR and lower relative tool wear ratio (RTWR). It can be concluded that the helical electrode is more suitable than cylindrical electrode for machining micro parts.

Abstract: Interface bonding property of Mo-fiber reinforced polymer concrete not only depends on its material properties of components but also on microstructure characteristics of fibers including surface state, fiber content, fiber shape, bonding state between fiber and matrix, and so on. Interface bonding mechanism was firstly analyzed in the paper, and finite element simulation was employed to study the influence of fiber surface state, fiber number, bonding state between fiber and resin on interface property respectively. Research results show that the addition of Mo fibers can effectively restrain deformation of matrix, and scrap Mo fibers used as tool electrode material in Wire Electrical Discharge Machining before can improve interface bonding strength better than new smooth Mo fibers. With the increase of fiber number, deformation of the composite is decreasing. When fiber number is identical, maximum deformation of new and scrap Mo fiber-reinforced matrix in complete bonding state is respectively decreased by 12.6% and 14.5% on average compared with in complete debonding state.

Abstract: For the characteristic that the mechanical properties of resin composite are lower than cast iron, steel fibers are used to improve its properties in this paper. A weak interfacial bonding strength between steel fibers and resin indicates that steel fibers’ property cannot perform well in the polymer. In order to improve the interfacial bonding strength, four methods of surface treatment, phosphating, acid pickling, oxidation, and coupling are applied to steel fibers, and the corresponding pull-off tests are carried out to compare with untreated steel fibers. Research results show that the maximum interfacial bonding strength is increased by 45.1% after coupling treatment.

Abstract: Machine tool bed, which supports headstock, tailstock and other functional components, is one of the important structure parts of machine tools. Precision grinding machine tool beds are designed by the authors with artificial granite and cast iron respectively for research. Their three-dimensional models were established via software SOLIDWORKS and then imported into the finite element software (ANSYS) to simulate for the first eight modal frequencies and the corresponding vibration modes. Simulation results show that the first eight order natural frequencies of artificial granite bed are better and the corresponding maximum amplitude of vibration modes are decreased significantly than cast iron bed. The dynamical properties of artificial granite bed are obviously better than grey cast iron bed.

Abstract: Micro EDM is used to machine micro features which are of the same size order as material microstructure of workpiece. Due to the difference of the thermal properties between the crystal grain and grain boundary, the machining performance of micro EDM varies with the crystal grain sizes of workpiece. This paper investigated on the influence of grain size and grain boundary on the machining performance of micro EDM. By drilling micro holes on two pieces of stainless steel 304 (SUS 304) which are different in grain sizes, test results revealed that the characteristics of micro EDM is influenced by grain sizes of workpiece materials significantly.

Abstract: In micro-EDM machining process, the debris of materials is difficult to be removed form the discharging gap. This problem leads the instability of discharge state, and reduces the efficiency of discharge machining. A new method of PZT incentive synchronous compression discharge channel micro-EDM is developed based on the inverse piezoelectric effect of PZT ceramics, driving by a spark discharge and PZT sync pulse power. The composition of the system is described and many experiments have been done and the effects of parameters on electrode wear ratio (EWR) have been analyzed in this paper. The results indicated that increasing the voltage and width of pulse can lower the rate of electrode wear, increase the efficiency of electric-machining, while increasing the frequency of discharge pulse can lead the increasing of EWR.

Abstract: Powder mixed near dry electrical discharge machining (PMND-EDM) is one of the novel EDM processes, which uses gas-liquid-powder mixture as the dielectric medium. The tool wear rate (TWR) in PMND-EDM is researched based on single factor experiments. Effects of process parameters, such as peak current, pulse on time, pulse off time, flow rate, powder concentration, tool rotational speed and air pressure, on TWR are found out. TWR increases with the increase of peak current. TWR decreases with increasing of pulse on time. TWR increases firstly and then decreases while pulse off time increases. Increase of flow rate results in the increase of TWR. With the increase of powder concentration, TWR increases firstly and then decreases. Existence of tool rotation facilities decrease of TWR, however, further increase of rotational speed leads to increase of TWR. Increase of air pressure leads to lower TWR.

Abstract: Resin mineral composite (RMC) reinforced by fibers belongs to a multiphase material, whose mechanical strength depends on its material properties of components and microstructure characteristics of fibers including surface state, shape, and so on. The interface mechanism between fiber and matrix was analyzed. Finite element simulation was employed to discuss the reinforced effect of fiber on resin matrix, and the influence of fiber shape, surface state on interface bonding property respectively. Research results showed that linear fibers with surface dents or fibers shaped like S, U, V, N, W English letters performed well, and had much better reinforced effects on matrix than ordinary linear fibers.

Abstract: To improve the poor mechanical properties of resin mineral composite, molybdenum fibers reinforced technology and mechanism are researched. The micro-surface morphology of new and wire electrical discharge machining used molybdenum fibers are analyzed, and the cohesive reinforce mechanism is deduced respectively. Two-dimensional simplified finite element model of resin mineral composite reinforced by molybdenum fibers is established for the simulation analysis of bond-slip of interface between fiber and resin matrix. Tests on the internal stress distribution of resin mineral composite without fibers and resin mineral composite reinforced by molybdenum fibers are carried out. Research results show that the addition of molybdenum fibers can effectively restrict the deformation of composite, and the randomly distributed pits on the surface of wire electrical discharge machining used molybdenum fibers can enhance the strengthening effect and reduce the cost of composite.

Abstract: Using sol-gel method, a series of nanocrystalline materials La_1-xAE_xCrO₃ (AE=Ca, Sr) were synthesized. Difference between Ca- and Sr-doped lanthanum chromites were investigated by carrying out differential scanning calorimetry (DSC), thermogravimetric analysis (TG), X-ray diffraction (XRD) and high resolution transmission electron microscope (HRTEM). It was found that the synthesis temperature (1-xCa_xCrO₃, and CaCrO₄ as the second phase (x≥0.2) at the room temperature. LSC is composed of single orthorhombic perovskite phase for x=0.1, while the orthorhombic and rhombohedral perovskite phases coexist for x=0.2, and only rhombohedral perovskite phase for x=0.3. Further studies showed that the maximum solubility of Sr was lower than that of Ca in lanthanum chromite.