Browsing by Author "Lee, Weng Hoh"

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    Characterization of Microstructure and Mechanical Properties of Direct Metal Laser Sintered 15–5 PH1 Stainless Steel Powders and Components
    (Springer, 2016) Zhang, Jing; Zhang, Yi; Guo, Xingye; Lee, Weng Hoh; Hu, Bin; Lu, Zhe; Jung, Yeon-Gil; Lee, Je-Hyun; Department of Mechanical Engineering, School of Engineering and Technology
    15–5 PH1 stainless steel powder is one of the common materials used for the DMLS process. In this study, both the powder and parts fabricated via DMLS have been characterized. The microstructure and elemental composition have been examined. The microhardness and surface roughness have also been measured. The results show that most powder particle are in spherical with a particle size of 5 ~ 60 μm. Chemical compositions of the powder compare well with the literature data. The thickness of rough surface is about 1 μm. The measured Rockwell hardness is HRC 42.9±0.3, which is also in good agreement with literature.
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    Discrete Element Modeling of Powder Dispensing and Laser Heating in Direct Laser Metal Sintering Process
    (Office of the Vice Chancellor for Research, 2016-04-08) Lee, Weng Hoh; Zhang, Yi; Zhang, Jing
    ABSTRACT The growth of reliable methods to improve part created from additive manufacturing technologies greatly depend on the quantitative understanding of the mechanical properties and the microstructural behavior of the powder particles during the 3D printing procedure. To obtain a greater understanding of this process, a particle- based discrete element modeling (DEM) has incredible potential benefits in the field of manufacturing for reducing cost and control specific structures and materials of the parts created from this process. In this research, we developed a numerical tool and use it to study the powder characterization of the powder deposition process in the Direct Metal Laser Sintering (DLMS) machine. Our simulations include the modelling of particle insertion, particle spreading, and temperature distribution due to laser beam sintering process. The DEM simulation results show that the particle distribution of the powder bed after powder dispersing process. Temperature distribution after laser heating is also given.
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    Implementation of Conformal Cooling & Topology Optimization in 3D Printed Stainless Steel Porous Structure Injection Molds
    (2016) Jahan, Suchana A.; Wu, Tong; Zhang, Yi; El-Mounayri, Hazim; Tovar, Andres; Zhang, Jing; Acheson, Douglas; Nalim, M. Razi; Guo, Xingye; Lee, Weng Hoh
    This work presents implementation of numerical analysis and topology optimization techniques for redesigning traditional injection molding tools. Traditional injection molding tools have straight cooling channels, drilled into a solid body of the core and cavity. The cooling time constitutes a large portion of the total production cycle that needs to be reduced as much as possible in order to bring in a significant improvement in the overall business of injection molding industry. Incorporating conformal cooling channels in the traditional dies is a highly competent solution to lower the cooling time as well as improve the plastic part quality. In this paper, the thermal and mechanical behavior of cavity and core with conformal cooling channels are analyzed to find an optimum design for molding tools. The proposed design with conformal cooling channels provides a better alternative than traditional die designs with straight channels. This design is further optimized using thermo-mechanical topology optimization based on a multiscale approach for generating sound porous structures. The implemented topology optimization results in a light-weight yet highly effective die cavity and core. The reduction in weight achieved through the design of dies with porous structures is meant to facilitate the adoption of additive manufacturing for die making by the tooling industry.
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    A Multi-Scale Multi-Physics Modeling Framework of Laser Powder Bed Fusion Additive Manufacturing Process
    (Elsevier, 2018-05) Zhang, Jing; Zhang, Yi; Lee, Weng Hoh; Wu, Linmin; Sagar, Sugrim; Meng, Lingbin; Choi, Hyun-Hee; Jung, Yeon-Gil; Mechanical Engineering, School of Engineering and Technology
    A longstanding challenge is to optimize additive manufacturing (AM) process in order to reduce AM component failure due to excessive distortion and cracking. To address this challenge, a multi-scale physics-based modeling framework is presented to understand the interrelationship between AM processing parameters and resulting properties. In particular, a multi-scale approach, spanning from atomic, particle, to component levels, is employed. The simulations of sintered material show that sintered particles have lower mechanical strengths than the bulk metal because of their porous structures. Higher heating rate leads to a higher mechanical strength due to accelerated sintering rates. The average temperature in the powder bed increases with higher laser power. The predicted distortion due to residual stress in the AM fabricated component is in good agreement with experimental measurements. In summary, the model framework provides a design tool to optimize the metal powder based additive manufacturing process.