Papers by Author: Qing Song Wei

Abstract: Selective Laser Melting (SLM) technology can be used to fabricate plastic mould with complex conformal cooling channels directly and rapidly. In this paper, 316L stainless steel powders were used to produced a mould with an emphasis on attaining excellent mechanical properties.The precision, density and mechanical properties of parts were studied. Simulation and experimental results showed: the mould manufactured by SLM reveals good accuracy and performance, and the cooling efficiency of conformal cooling channels in mould has been greatly improved and the uniformity of cooling has been also upgraded.

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) 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”.

Abstract: 316L stainless steel parts were manufactured via selective laser melting . This work stu- dies the effects of powder characteristics such as particle size and particle shape composition on the density. It shows that the powder with a broad size distribution and using spherical fine powder can lead to an increase in the density of the loose powder and thus the densification of the laser melted powder. The aerosol powder forms parts of lower oxygen content well, and the density can reach to 90%.

Abstract: Inert gas atomized (IGA) superalloy Inconel 625 powder was consolidated by hot isostatic pressing (HIPing) directly under the HIPing parameters of 1100°C/110MPa/3h. The structure and properties of the as–HIPed samples were investigated using optical microscopy (OM), scanning electron microscopy (SEM) and tensile tests at room temperature, and its relative density was measured by drainage. The fracture surface morphology of the tensile specimens have been investigated using SEM. The results showed that full density alloy can be obtained under the HIPing parameters of 1100°C/110MPa/3h. Due to the effect of prior particle boundaries (PPBs), the strength of the as-HIPed alloy is comparatively high, but its ductibility is comparatively low.