The University of Massachusetts Amherst
University of Massachusetts Amherst

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MIE Seminar Series: "TPMS-based mechanical metamaterial fabricated by micro laser powder bed fusion process"


Friday, February 18, 2022 - 8:00am


Professor Song Xu, The Chinese University of Hong Kong




Micro laser powder bed fusion (μLPBF) technology offers great potentials to additive manufacturing research community, as it enables fabrication of complex components with greater accuracy, better properties and new capabilities. By comprehensively comparing the μLPBF with conventional LPBF, it is found that better surface finish, finer microstructure, more desirable mechanical properties and smaller part distortion can be obtained by μLPBF. Moreover, due to higher volume energy density than the conventional LPBF process, μLPBF is capable to fabricate highly reflective materials, such as pure copper, while maintaining low laser power, high resolution and good material properties. A new integrated digital design and manufacturing method to solve the scalability and efficiency challenges of μLPBF is also presented here. It seamlessly integrates implicit solid modelling for design and direct slicing for manufacturing without any intermediate steps related to STL meshes. The presented method enables printing multiscale triply periodic minimal surface (TPMS) structures, which otherwise cannot be handled by conventional LPBF system. Furthermore, as TPMS structures show great potential in lightweight applications, SS316L TPMS sheet structures with small shell thickness and different cell orientations were fabricated by our μLPBF machine. Experimental and numerical study on their compressive responses show that Primitive TPMS has the highest anisotropy of compression response, while Diamond TPMS presents the highest strength and weaker anisotropy. This indicates TPMS has great potential in formulating a new class of mechanical metamaterial which is isotropic and lightweight. Therefore, to reduce the anisotropy of the uniform thickness TPMS sheet structures, we propose a family of variable thickness TPMS structures with isotropic stiffness, which are auto-designed by a strain energy - based optimization algorithm. The optimization results show that all the selected types of TPMS lattices can be made to achieve isotropic stiffness by varying the shell thickness, among which N14 and OCTO can maintain over 90% of the H-S upper bound of bulk modulus, which is confirmed by our experiments.

Dr X Song obtained his Doctorate degree from University of Oxford in the area of material engineering. After working two years as postdoc for Rolls Royce University Technology Center (RR-UTC) Oxford on residual stress analysis in selective laser melting and linear friction welding processes, he joined SIMTech, A*STAR as scientist from 2012 (promoted to senior scientist in 2019), working on micro metal processing, including micro forming and micro selective laser melting. He joined Chinese University of Hong Kong in 2019 as Assistant Professor, conducting research and teaching on micro selective laser melting and design for additive manufacturing. He has more than 100 papers published in academic journals and 3 book chapters on the topic of material deformation and manufacturing processes, and currently serving as editor of the academic journal <Materials and Design> and editorial board member of <Materials Today Communications>.. He has helped many companies to improve their manufacturing processes as the lead investigator, and many of his designs and processes have been adopted and currently in active use in the industry. 

Time: Feb 18, 202, 8am-9am EST.