Papers by Author: Yu Sheng Shi

Abstract: To satisfy rigid performance specifications of structure light measurement by phase shift method, the algorithm of phase image segmentation and filter based on direction of the gradient factor was introduced in this paper. In this method, phase image was divided into three parts by condition of extreme value and direction of the gradient factor, including continuous area, edge area and regional noise. Only phase data in continuous area was processed by median filter. This method can reduce the point matching computation of 3-D reconstruction, and at the same time can protect the image edge details, so as to reduce the noise data, provide accurate and effective phase data for reconstruction. Results of segmentation verify feasibility and effectiveness of presented method.

Abstract: With main transmission system structural form of main servo motor-worm and worm gear commutation reducer-transmission screw-linkage force increasing mechanism, mathematical model of linkage force increasing mechanism is established to obtain the relationships of the velocity and displacement between nut and slide. Velocity and displacement of feature points of slide on the velocity-displacement curve inputted by user transform into which of nut by binary search algorithm and linear interpolation calculation. The feature points of nut transform into the velocity and displacement arrays of points based on S-curve, and then the arrays of points transfer through UDP protocol to lower computer. After the linear fine interpolation by Siemens Simotion D425 motion controller, slide moves according to the setting velocity-displacement curve. The experimental results show that slide moves smoothly, which meets specific technology requirements. The achievements have been successfully applied to a self-developed 2000KN mechanical linkage servo press in a production line of hot forming technology for more than one year, which extends the technology application scope of traditional mechanical press, and improves product quality.

Abstract: Although pressure compensating emitters (PCE) have many advantages, they are difficult to develop and very costly. Traditional PCE are composed of emitter structures and compensating diaphragms. Their manufacture is very difficult and time-consuming. In this paper, we invented novel PCE with variable flow channels, which are designed as integrated structures with pressure compensating barriers, and manufactured three of them with different structures based on the rapid prototyping/rapid tooling technology. The pressure-flow test showed their behavior indexes were 0.009, 0.008 and 0.011, respectively, indicating this type of novel PCE have remarkable compensating effect.

Abstract: To obtain complex shape alumina ceramic parts, a composite powder of epoxy resin binder E-06 and alumina powder were laser sintered combined with cold isostatic pressing (CIP). Experiments on selective laser sintering (SLS) and CIP were carried out to probe the influencing factors in the processes of forming alumina green parts. When laser power, scan speed, scan spacing and layer thickness were, respectively, 21 w, 1800 mm/s, 100 μm and 150 μm, the density and bending strength of alumina parts were relatively high. Following that, we experimented on different CIP maximum pressure which had different effects on densification of SLS alumina parts, the whole process in CIP was divided into two stages of I and II. Finally, the optimized SLS/CIP alumina parts were degreased and then sintered in 1600 °C for 2 h to produce crack-free alumina parts.

Abstract: To obtain complex shape alumina ceramic parts, a composite powder of epoxy resin binder E-06 and alumina powder are laser sintered combined with cold isostatic pressing(CIP). An orthogonal experiment is carried out to probe the influencing factors of selective laser sintering (SLS) alumina green parts. When preheating temperature, laser power, scan speed, scan spacing and layer thickness are, respectively, 60°C,14 w, 2000 mm/s, 0.10 mm/s and 0.10 mm, the density and bending strength of alumina parts are relatively high. Then, airproof canning prepared for CIP is manufactured in the vacuum environment. Finally, the optimized SLS/CIP alumina parts are degreased and sintered in 1600 °C to produce crack-free alumina parts. The sintered relative density of the parts however is limited to only 57% but the forming integrity during SLS and CIP remains after sintering.

Abstract: Pre-alloyed Ti6Al4V powder produced by plasma rotating electrode process (PREP) was consolidated by hot isostatic pressing (HIP) under the parameters of 930°C/100MPa/3h. The microstructure is analyzed using scanning electron microscopy (SEM). The tensile property is measured at room temperature, the fracture surface morphology of the tensile specimens was investigated using SEM as well. The results show that the dense body has homogeneous microstructure and fine grain size. The average values of ultimate tensile strength (UTS), yield strength (YS) and elongation (EL) are 1119 MPa, 1043 MPa and 18% respectively. The fracture of specimen presents ductile fracture.

Abstract: Movement behavior of AISI 316L stainless steel powder under hot isostatic pressing (HIP) were investigated using finite element analysis (FEA). The analysis, which was based on the porous metal yield criterion, was carried out in the FEA program. Density distributions, deformations and displacements of compact were discussed. The evolution of displacement for some typical positions in the compact was also studied in this paper. The calculation results show that thermal expansion plays an important role at the early stage of HIP. There are large displacements for powder compact during the ramp stage and the early holding stage in the HIP cycle. Correspondingly, the improvement of densification increases significantly. Simulation results for the shape change and average density of a sample were also compared with experiment.

Abstract: Selective laser melting (SLMing) is a new advanced material processing technology which is used in fabricating parts with complex shape. Hot isostatic pressing (HIPing) is a manufacture technology which forms parts by imposing high heat and pressure on metal powders or semi-manufactured parts. Considering the advantages of both the technologies, they can be combined to produce higher-quality parts free from the limitation of the shape of parts. AISI316L stainless steel is widely used in manufacturing varies of complex metal parts. In this research, three AISI316L stainless steel samples with different relative densities were acquired by controlling the fabricating parameters in SLM. The SEM and optical microscopy analysis were employed to characterize the relative density, microstructure, deformation by comparing the differences between SLM samples and SLM-HIPped samples. In addition, the influence of HIP process on microstructures of samples in different laser fabricating parameters was investigated by analyzing the mechanisms of SLM and HIP. The results show that HIP can close vacuum crack and pore, consequently, the relative density of SLM samples increases after HIP, making the property of the samples improved and microstructure better-distributed. Moreover, the increment of relative density under the same HIP condition is also discussed.

Abstract: Selective laser melting (SLM) is an advanced manufacturing technology, which is flexible in building three-dimensional (3D) metallic parts. In this work, SLM experiment of a multicomponent Ni-based composite powder, which consisted of Ni, Cr, Fe, and Al powders, was conducted with favorable forming ability. The SEM, EDX, and XRD analysis were used to characterize the surface morphology, microstructure, and phase structure of as-formed Ni-based alloy. The XRD analysis showed that the as-received phase structure was Ni based solid solution. The SEM analysis of surface morphology revealed that metal agglomerates or balls were very easily formed in SLM surface, between which some pore channels existed. The surface condition and porosity could be improved by increasing laser energy input, because of a higher molten temperature and accordingly better flowing and flatting characteristics. The SEM analysis of microstructure showed that the crystalline grains were in cellular and columnar shape. Moreover, the grains were very fine with average dimensions about 5μm, due to the rapid cooling rate with rapid laser beam moving. The EDX analysis illustrated that the element contents of starting powder were uniformly distributed in as-prepared sample. A case investigation into SLM of this composite powder to form an impeller was also performed.

Abstract: Selective Laser Melting (SLM) can produce high-performance metal parts with complex structures. However, it’s difficult to control the processing parameters, because many factors involves. From the perspective of the molten pool, the study focuses on the effects of processing parameters, including scanning speed, laser power, scanning space, layer thickness, and scanning strategies, on the surface quality, the balling effect, the density of SLM parts, by conducting experiments of single track, single layer and block forming. The results show that the quality of the molten pool is affected by laser power and scanning speed. Scanning drove in the strategy of “jumping and turning”，a smooth surface and a less balling effect will be obtained. The thicker the powder layer is, the lower density will be obtained. The optimal parameters from series of experiments are: laser power of 98W; scanning speed of 90mm/s; scanning space of 0.07mm; layer thickness of 0.1mm; and scanning strategy of “jumping and turning”.