Qing Song Wei

Investigation and development of large-scale equipment and high performance materials for powder bed laser fusion additive manufacturing

The current available selective laser sintering (SLS) and selective laser melting (SLM) systems have relatively small effective building volumes, which do not offer capability to integrally manufacture a large dimension component. Therefore, our research team in Huazhong University of Science and Technology, China, has broken through some key techniques such as the large powder bed preheating system and multi-laser scanning technique, and then successfully developed a series of large-scale SLS systems with effective building volumes up to 1400×1400×500 mm3, and an SLM system with an effective building volume of 500×250×400 mm3. These large-scale SLS/SLM systems will not only offer new capability to make large complex prototypes and products, but also provide higher volume production capability to make numerous small parts rapidly and cost-effectively. In addition, several high performance materials have been developed for the large-scale SLS/SLM systems.

Fabricate Mould Insert with Conformal Cooling Channel Using Selective Laser Melting

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.

Study on Direct Hot Isostatic Pressing Technology for Superalloy Inconel 625

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.

Manufacturing AISI316L Components via Selective Laser Melting Coupled with Hot Isostatic Pressing

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.

Effects of the Processing Parameters on the Forming Quality of Stainless Steel Parts by Selective Laser Melting

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”.

Effects of the Processing Parameters on Porosity of Selective Laser Sintered Aliphatic Polycarbonate

Selective Laser Sintering (SLS) has been successfully and broadly applied in biomedical engineering to fabricated biomedical part. And the porosity and microstructure of part can be controlled by main sintered parameters. This research focused aliphatic Polycarbonate (PC) sintered with SLS. According to the orthogonal experiment, the effect of laser power energy and interaction between main sintered parameters on porosity has been studied. Then the micro structure and mechanical properties of specimens sintered with the best optimal parameters have been analyzed.

Numerical Investigation into Movement Behavior of Metal Powder during Hot Isostatic Pressing

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.

Near Net Shape Forming Process of a Titanium Alloy Component Using Hot Isostatic Pressing with Graphite Mould

Ti6Al4V component has been formed by hot isostatic pressing (HIPping) using internal graphite mould with Ni isolation layer. The shape of the graphite had no deformation after HIPping. The Ni isolation layer with a thickness of approximately 5μm on graphite before HIPping was diffused into the dense Ti6Al4V component surface and formed a uniform, compact and crack free layer with a thickness of approximately 100μm after HIPping. The Ni diffusion layer is not damaged after removing the graphite mould by unpolluted sandblasting. The interface topography and the elements diffusion have been assessed and it is found that the non-machined surface of Ti6Al4V component was improved by using graphite mould than those used mild steel. The roughness of non-machined surface after removing the graphite mould by sandblasting is Ra=1.6μm, and the roughness of non-machined surface after removing the mild steel by acid pickling is Ra=10.8μm. It is concluded that graphite mould could be used for the HIPping process to produce complex-shaped components.

Rapid Development of Novel Integrated Pressure Compensating Emitters

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.

Microstructure and Properties of Ti6Al4V Alloy Prepared by Hot Isostatic Pressing

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.