Papers by Author: Di Chen Li

Abstract: The paper presents an integral core/shell fabrication of ceramic casting mould for hollow turbine blades by combining SL (Stereolithography) with gelcasting. This method could guarantee the positional accuracy between ceramic cores and shell, thus achieving the rapid fabrication of complex turbine blade castings. The paper focuses on the design of resin mould for gelcasting, the preparation of ceramic slurry, the pyrolysis of resin prototype and the sintering of ceramic green body. The feasibility and effectiveness of above mentioned method were verified through successful manufacturing of hollow turbine blades with double-walled structure.

Abstract: Multi-track laser cladding is necessary in the forming of parts. The overlap between neighbor tracks plays an important role, which determines the quality and surface smoothness of the clad layer. In this paper, numerical simulation of the multi-track laser cladding process is studied. The heat source of laser spot is applied by updating the profile of clad region and the location of the moving laser spot. The clad profile of overlapped track was obtained, from which the surface roughness was analyzed by the variation of overlap ratio. Meanwhile, experiments were carried out to evaluate the effect of overlap ratio. The simulated and the experimental results are in good agreement; both show that there is an optimal overlap ratio to achieve best surface roughness.

Abstract: The parameters obtained in the study of single layer of laser cladding forming are not suitable for the forming of actual structures. The cooling condition varies with the height of clad layers, which result in instability and then failure of cladding. Therefore, the stability of laser cladding forming is of significance. In this paper, melt pool depth is used as a criteria for stability. And the effect of processing parameters such as laser power and laser velocity on melt pool depth, are investigated by numerical simulation method. The results unveil that there is a transition zone from the beginning to stable stage during laser cladding forming. In the transition zone, laser power should be decreased or laser velocity should be increased to maintain the constant melt pool depth and to ensure the former clad layer would not be remelt. The optimized processing parameters are obtained for stable processing for a thin flat wall and a cylindrical wall, which successfully guide the manufacturing of the real structures.

Abstract: The traditional method to manufacture the medical implant or prosthesis is based on sculpting and on the tissue site,or takes impressions of the entire face about human. The accuracy and efficiency of medical implant or prosthesis produced by conventional method is heavily relied on the skill and experience of both designer and manufacturer. In this paper, an integrated method of medical implant manufacture is approached. This integrated strategy was to establish a system that allows fabrication of facial prosthesis from digital information, and integrates the rapid prototyping with modeling technology of complex three-dimensional geometry from high-resolution non-invasive imaging, reverse engineering and computer aided design. The research results have shown that the integrated method can produce more exact-fit medical implant, that is, the physical model of the implant is more exactly fitted on the skull model. The advantages of this method are that the surgeon can plan and rehearse the surgery in advance, and a less invasive surgical procedure, and less time-consuming reconstructive, and an adequate esthetic can result.

Abstract: We used ethylene glycol as pore-forming agent to prepare porous carbon with interconnected pores derived from phenol–formaldehyde resin. The mixture of resins and glycol was by polymerization and pyrolysis monolithic material of porous carbon with interconnected mesopores and a narrow pore size range. The average pore size of the porous carbon obtained was 28.2 nm. The nitrogen adsorption isotherm for the porous carbon exhibited type IV isotherm, which corresponded to mesoporous adsorption. The method could endow porous carbon with BET surface area and pore volume about 500 m2/g and 0.607 cm3/g, respectively. The mesopores in porous carbon formed as a result of phase separation of resin-rich phase and glycol-rich phase at polymerization and remove of glycol-rich at subsequent pyrolysis.

Abstract: Reaction bonded silicon carbide (RB-SiC) was fabricated by phenol resin, starch, solidified agent and silicon powder through the following steps: first, carbonizing at high temperature for 7-9h, infiltrating silicon at 1450-1600oC for 0.5-2h, and then removing excessive silicon at 1700oC for 0.5h. Scanning electron microscopy and X-ray diffraction were employed to characterize and analyze the microstructures and phase composition of the preforms and the final RB-SiC products. In addition, the effect of carbonization temperature, the amount of starch and solidified agent on strength and apparent porosity of final RB-SiC were also discussed. The results showed that the carbonization process of phenol resin can be divided into three steps: at temperatures from 400oC to 600oC, the structure of polymer changes less; at temperatures from 600oC to 1000oC, the fundamental chain of polymer is destroyed, and inverts to glass-like carbon; at temperatures from 1000oC to 1200oC, with the increasing of carbonization temperature, the structure of glass-like carbon changes into the structure of disorder graphite. And the increased micro-pores could be obtained by adding starch.

Abstract: Self-hardening calcium phosphate cement (CPC) could not be used to repair a large segmental defect in a load-bearing bone because of its brittleness and weak shock resistance as well as ultra-minute pores. Recent studies incorporated fibers into CPC to improve its strength. A novel approach by rapid prototyping and rapid tool technique (RP/RT) was used in this paper to fabricate fibre-reinforced CPC composite artificial bone. The subsequent mechanical experiments demonstrated that the compressive strength of the CPC-fiber artificial bone was 24MPa, which was significantly higher than 6MPa for CPC control without fiber. And in-vivo experiment about canine radius repair proved that the implanted CPC-fiber artificial bone enabled to provide short-time reinforced mechanical strength, while the degraded fibers created new macropores for new tissue ingrowth. In summary, the CPC-fiber artificial bone may facilitate bone ingrowth and its four times increase in strength may help extend the use of CPC to larger bone repairs in moderately stress-bearing locations.