Papers by Author: Wen Ji Xu

Abstract: Gears’ accuracy has important influences on its working performance and life. Electrochemical mechanical finishing (ECMF) was applied to finish cylindrical gears. The influence of the generative type of ECMF was studied theoretically and experimentally on the shape of gear teeth, and on the dimensional accuracy between teeth, and that in the tooth thickness direction. The results indicate that the generative type of ECMF can improve the accuracy between teeth, as well, the dimensional accuracy of gear tooth and that in the thickness direction may be also improved.

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: 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: All countries of the world carry forward progress in engineering education reform actively to meet the keen demand of innovative engineering talents which results from the global industry development, the source from which the global engineering excellence research project stems. Firstly, this paper reviews the origin and prophase research results of exemplary engineering innovators (EEI) research project. Secondly, this paper provides a systematic and comprehensive introduction to the industry-oriented EEI cultivation mode for bachelor’s degree engineering practiced in Mechanical Design & Manufacturing and its Automation of Dalian University of Technology based on an analysis of the cultivation actuality of EEI. Finally, this paper puts forward advices to form EEI cultivation mode with Chinese characteristics.

Abstract: Dry electrostatic cooling (DESC) assisted machining is one of the green machining technologies that uses ionized air flow as lubricating and cooling medium in the machining process. The influence of discharge parameters on the efficiency of ion transport and ozone concentration in the DESC is experimentally researched. The results show that the efficiency of ion transport increases with the rising of the discharge current and air pressure, but decreases with the rising of the distance from the nozzle and the nozzle diameter. The tungsten electrode is used to obtain high ozone concentration with the nozzle diameter of 2-4mm, air pressure of 0.2-0.4MPa, and the distance from the nozzle within 0.5mm. Experimental research on the DESC assisted machining for hardened steel GCr15 shows that cutting force decreases by 7%-28%, tool wear reduces by 30-50%, and tool life is 1.5-3.3 times more than dry cutting. Better results are achieved when increasing the cutting speed.

Abstract: The image collecting devices, which consist of optical lens, neutral density filter, narrow-band interference filter, CCD and the other equipments are set up to collect the images of plasma arc column with and without external transverse alternating magnetic field (ETAMF). On the basis of de-noising and enhancing morphological characteristics to the collected images, the characteristics of plasma arc with and without ETAMF are analyzed comparatively. The results show that the application of ETAMF is capable to get oscillation of plasma arc, and change its location, shape and heat flux density distribution, which can get efficiently control in the width of heated area and flatten heat flux density of workpiece surface.

Abstract: A theoretical analysis was carried out to investigate the characteristics of atmospheric pressure plasma arc injected transverse to a transverse alternating magnetic field and a mathematical model was developed to describe the heat flux density distribution of the plasma arc. The effect of processing parameters, such as flow rate of working gas, arc current, magnetic flux density and the standoff from the nozzle to the workpiece, on the heat flux density distribution of plasma arc were also analyzed. The results show that it is feasible to adjust the heat flux density of the plasma arc by the transverse alternating magnetic field, which can expand the region of plasma arc thermal treatment and flatten the heat flux density upon the workpiece. With the magnetic flux density enhancing, the heat flux density gradient upon the workpiece decreases. Under the same magnetic flux density, the more gas flow rate and arc current, the more heat flux density peak increase. Contrarily, more distance from nozzle outlet to workpiece descends the heat flux density peak.