Papers by Author: Xu Yue Wang

Abstract: A laminated plate with excellent mechanical properties is commonly used for a bulkhead part in which the interface structure of diffusion bonded is detrimental to the bending quality. In this study, 304 stainless steel and Q235 carbon steel were cladded by laser cladding technique. Microstructure, yield strength, elements diffusion, hardness and tensile fracture morphology of the clad metals were evaluated. The bond interface of the cladded metals demonstrated a wavy morphology in this work. Tensile test results shows that yield strength reaches 400-410MPa and tensile strength reaches 405-419MPa. They are higher than the standard value 235MPa and 370MPa, respectively. In wavy interface region, transition layer of metallurgical bond was formed as a result of mutual diffusion of Fe, Cr and Ni. The hardness is increased in the substrate and cladding plate near the bond interface. The mechanical properties of the low-carbon steels is increased by laser cladding with austenitic stainless steel, which are far beyond the national standard and other bending methods.

Abstract: A new EDM method of small hole is presented in which critical size of EDM drilling can be reduced less than that of limit of primitive EDM system by current dividing. The drilling characters of small hole EDM by means of current dividing based on a principle of discharging-area equalization were studied and discussed. The experimental results show that drilling speed and discharging gap decrease a little, and electrodes wear increases slightly. There is a drilling consistency in EDM ability between single and double electrodes under discharging-area equalization, and new method helps to improve the drilling precision. The research outcomes provide a deeper understanding for a small hole EDM.

Abstract: A theoretical analysis was carried out to investigate the characteristics of plasma arc injected transverse to a transverse-alternating magnetic field. Two mathematical models were developed to describe both the oscillating amplitude of the plasma arc root and the heat flux density distribution of plasma arc on the workpiece surface. The characteristic of plasma arc under the external transverse-alternating magnetic field imposed perpendicular to the plasma current was discussed. The effect of processing parameters, such as working gas flux, arc current, magnetic flux density and the standoff from the nozzle to the workpiece, on the oscillation and heat flux distribution of plasma arc were also analyzed. The results show that it is feasible to adjust the shape and heat flux density of the plasma arc by the transverse alternating magnetic field, which expands the region of plasma arc thermal treatment and uniforms the heat flux density upon the workpiece. Furthermore, the oscillating amplitude of plasma arc decreases, and the heat flux density gradient upon the workpiece increases with decrease of the magnetic flux density. Under the same magnetic flux density, more gas flux and more arc current cause the oscillating amplitude to decrease. The researches have provided a deeper understanding of adjusting of plasma arc characteristics.

Abstract: Flexible forming of metal sheet using plasma arc is a new technique which forms parts by thermal stress without moulds and external force. To improve the surface quality of formed parts, a magnetic-driving plasma arc (MDPA) was applied in monitoring the distribution of heat flux. A mathematical model was developed to study the variations of temperature fields and deformation fields with MDPA and merely with plasma arc, which was validated by the forming experiments. The results indicated that the swing amplitude of MDPA increased linearly when the exciting current Ie < 1.2 A, and the distribution of heat flux with MDPA was more uniform than that merely with plasma arc in the heating zone, which avoided the possible partial melting and ablation of metal sheet. Moreover, the “U-shape” occurred with MDPA, and the material accumulation with MDPA was smaller than that merely with plasma arc on the surface of metal sheet.

Abstract: A method is presented based on geometric-curvature characteristics in which a scanning path planning for laser bending of a straight tube into a curve tube in a two- and three-dimensional space. In a two-dimensional (plane) bending, the steel tube is divided into several segments according to the extreme point and inflection point of the desired shape of the tube, taking the extreme point as the initial place of the path planning, using different scanning space for every segment in order to identify the scanning paths. For a tube bending in a three-dimensional space, a projection decomposition method is used, where the three-dimensional is decomposed into two two-dimensions, and respective scanning path planning and process parameters are thus acquired. By combining the data in the two-dimensional planes, the three-dimensional scanning path plan was obtained. Finally, an experimental verification is carried out to bend straight tubes into a two-dimensional sinusoidal and a three-dimensional helical coil-shaped tube. The results show that the proposed method of scanning path planning is effective and feasible.

Abstract: Laser cladding of micro-fluidic channels mold was performed using Nd:YAG laser and synchronous powder feeder. Influences of laser power and powder feed rate on clad layer geometrical dimensions and qualities were investigated. Results show that powder feed rate 1.5-2.5 g/min used obtains micro clad layers which meet geometrical dimensions’ requirement of micro-fluidic channels mold and combination of parameters laser power 400 W and powder feed rate 2.0 g/min achieves micro clad layer with better clad quality. Scanning paths of micro-fluidic channels mold was planned through CAD-CAM software. Using optimum parameters combination, multilayer laser cladding experiment was carried out and a sample of micro-fluidic channels mold was fabricated with expectative structure and hardness. A little milling and polishing makes the sample meet technical requirements, 0.2mm in height and 0.3mm in width. Fabricating a mold takes 15-20 min totally.

Abstract: To reduce stair-step effect when layered forming samples using 2.5D slices, a geometric model with variable thickness slices was developed. Experiments were performed with varying of powder feed rate. Relationships between geometrical precision of samples formed by laser clad forming (LCF) and a variable of powder feed rate were investigated. While the variation of powder feed rate with a calculated step was approximately continuous, clad layers with height increasing approximately linearly along clad length were achieved. Clad height increased from 0.05 to 0.39 mm with powder feed rate varying from 0.5 to 2.5 g/min. Scanning paths were planned by simulating forming process of the ramp through Matlab program. Using the scanning path, a relatively smooth ramp thin wall of 316L stainless steel was formed with a slope angle 3.37° by the experimental validation.

Abstract: In this paper, surface topography characteristics of electrochemical mechanical finishing (ECMF) for steel was investigated. The scanning electron microscopy (SEM) was used to observe the surface topography. And the microcosmic geometry parameters were measured by Talysurf SLI2000. Compared with original surface, the surface topography characteristics of the workpiece machined by ECMF have been analyzed with altitude density function (ADF) and auto correlation function (ACF). The results show that there exist periodicity component in surface profile before and after finishing. The auto correlation curves of ECMF surface have a smaller average period compared with grinding surface. The low-frequency component and the mean ripple peak distance of original surface profile are obviously decreased. Furthermore, the ripples and peak density are increased, and the surface roughness Ra is decreased from 0.231μm to 0.023μm. The results indicate that surface quality, material ratio of the profile and wear resistance machined by ECMF are improved obviously.

Abstract: The drilling burr is taken as the research object. A mathematical model of electrochemical deburring (ECD) is established and the effects of main influencing factors, such as inter-electrode gap, applied voltage and deburring time, on burr height have been analyzed. The results show that the deburring time increases with the increase of initial burr height, inter-electrode gap, with the decrease of volume of electrochemical equivalent of the workpiece material, conductivity of electrolyte and applied voltage. The deburring time for various burr heights can be predicted by the mathematical model. The calculated results obtained from the mathematical model are approximately consistent with the experimental results. The results show that initial burr height h0=0.722mm is removed, and the fillet radius R=0.211mm is obtained.

Abstract: Based on a principle of laser drilling size and the roundness copied with respect of laser spatial mode, heat absorbing rate for laser drilling of YG8 is presented in theory and application. The mathematical models are then developed. The relationship of heat absorbing rate compared to the original absorbing rate is thus derived that is A = T +A0. It shows that heat absorbing rate to laser beam increases linearly with drilling temperature. The research outcome is used to optimize preheating process in which the novel method improves laser drilling precision from 0.03mm of primitive laser system to 0.01mm under the condition of heat absorbing.