Papers by Author: Fan Jun Meng

Abstract: A robotic additive manufacturing system of GMAW constrained by electromagnetism has been developed recently. In this paper, the work principle, functions and composition of this system are introduced. A metal part to be manufactured should be constructured three-dimension CAD model firstly, then the delamination process of three-dimension model is carried out. Furthermore, the forming path planning of additive manufacturing is performed and finally the part is fabricated layer-by-layer in virtue of GMAW process. The additive manufacturing system consists of the robot system, GMAW power, a device producing magnetic field, a linear laser system monitoring precision of the forming part, a digital measuring device monitoring forming temperature,central control system and software modules that support various functions. The functions of the additive manufacturing system comprise CAD model construction of parts, discretization of three-dimension model, forming path planning and GMAW deposition forming layer-by-layer, and etc. It is indicated that the exploitation of the additive manufacturing system will provide an effective way for the manufacturing of metal parts.

Abstract: A GMAW additive manufacturing process is performed with H08Mn2Si wire to fabricate a cube forming part. A optical microscope was used to observe the cross section aspect of forming part and the structure mechanism has been analysed. The results demonstrate that the forming part structure presents a characteristic that macrostructure is uniform and microstructure changes circularly. The circularly heating pattern of GMAW surfacing forming results in circular microstructure change and preheating of formed bead to subsequent bead and postheating of subsequent bead to formed bead are primary reason. Electromagnetic stirring effect of longitudinal dc magnetic field to molten pool can break dendritic crystal and refine crystal grain, which is in favor of enhancing forming part performance.

Abstract: Weld bead stability has an important effect on the quality of prototyped products .In the paper, hierarchy analytical theory, combined with the experiment, is employed to determine the weld bead stability synthesis evaluation weight coefficient of surface quality, weld reinforcement and weld width of weld bead. The membership degree tables of surface quality, weld reinforcement and weld width are created by using fuzzy theory. Thus a evaluation method of bead stability is established and applied to evaluate practical bead stability. It is approved that the calculation value accords with the actual result, which proves the evaluation method of bead stability is effective.

Abstract: Nanocrystalline surface layer was fabricated on a quenched and tempered Cr-Si alloy steel by using Surface mechanical treatment. The microstructure features of various sections in the surface layer were characterized by using transmission electron microscopy (TEM). By analyzing the microstructural characteristic at different depths in the treated surface, the effect of the initial microstructures on grain refinement process of quenched and tempered steel was investigated. Experimental evidence showed the initial subgrains with small angle boundary and lower dislocation density were firstly developed into Lamellar-type dislocation cells (DCs) with dense dislocation walls (DDWs). Some initial subboundaries were moved to DDWs by dislocation activities. The width of lamellar-type DCs was 2-3 times of that of initial lathy subgrains. The size of the DCs and subgrains formed in the interim of refinement process was not uniformity. On the top surface the cementite granules were decomposed or fragmented to hyperfine particles, and the size of the grains tended to uniformity. Experimental analysis indicated the configuration of microstructure was affect by the initial microstructure in the initial stage and the interim of the grain refinement process. Surface nanocrystallization of Cr-Si steel can be attributed to dislocation activities.

Abstract: The nanostructured surface layers were fabricated on a hardened and tempered chrome-silicon alloy steel and a normalized medium carbon steel by mean of Supersonic Fine Particles Bombarding (SFPB). The microstructure features in the treated surface layer were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations. Experimental results show the nanostructured surface layer is fabricated on both samples after SFPB treatment. The microstructure of the top surface is characterized by uniformly distributed nano-scale grains with equiaxed shape and random crystallographic orientations. The mean size of equiaxed nanocrystallites on the top surface layer is approximately 15-20nm for the SFPB treated medium carbon steel and Chrome-silicon alloy steel. During severe deformation the grain refinement in ferrite and cementite phases is observed, the cementite phases are exposed to breaking and dissolution due to mechanical alloying resulting in the formation of a supersaturated solid solution of carbon in α-Fe matrix. In the ferrite phase, the grains are refined by the process of dislocation actives and forming cell structures separated by dense dislocation walls (DDWs), as well as evolution of dislocation to subboundaries and grain boundaries.

Abstract: A remanufacturing system based on robot MAG surfacing has been developed recently. In this paper, the work principle, functions and composition of this system are introduced. A worn metal part to be remanufactured should be preprocessed firstly, and the defective model of the part gained by reversing engineering technology is compared with normal model of the metal part, then the prototyping path layout is carried out combined with MAG welding process, finally the remanufacturing prototyping is implemented. The remanufacturing system is composed of robotic system (as executing machine), 3D laser scanner (as reversing scanning device), digital pulse MAG welding power source (as prototyping equipment), desk computer (as central control unit) and software modules that support various functions. The functions of the remanufacturing system comprise calibration of system, part reversing measurement, data processing, defective model reconstruction, welding remanufacturing prototyping path layout and etc. It is indicated that the exploitation of the remanufacturing system will provide an effective way for the remanufacturing of metal defective parts.