Papers by Author: L.J. Wang

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: 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.