Lin Feng, Ph.D., Professor of Department of Mechanical Engineering (DME) of Tsinghua University. He is the Council Member of Chinese Mechanical Engineering Society（CMES）, Vice Chairman of Additive Manufacturing and 3D Printing Institute of CMES.Prof. Lin started his research on Rapid Prototyping technique in early 1990, when he was a graduate student in the department of Mechanical Engineering of Tsinghua University and developed the first laminated object manufacturing (LOM) system in China. From 1998 to 2002, he became the post-doctoral fellow and research assistant professor in Drexel University, and began the researches on computer aided tissue engineering. Since 2002, Prof. Lin joined the department of Mechanical Engineering of Tsinghua University and initiated the research and development of electron beam selective melting (EBSM) in China, which possessed active precise powder supply system and the capacity of dual metal gradient structure manufacturing. Recently, he is devoted to improving the function and performance of EBSM process through introducing the multi-scale computational simulation technique into EBSM process and inventing the EB-laser hybrid selective melting processes with an integrated laser in EBSM.

He won the Program for New Century Excellent Talents by Ministry of Education in 2006, the Second Prize of National Science and Technology Progress Award twice in 2015 and 2002, and the Highly Commend Award for Outstanding Paper by the Literati Club of Emerald Publishing in 2001.

Topic title: The exploration on the low stress, low roughness, and low cost powder bed fusion additive manufacturing technology

Abstract:

The powder bed fusion (PBF) technology has been the most common additive manufacturing process, especially for complex metal parts. But it is still subject to several barriers such as the thermal stress, the limited material, the rougher surfaces, the higher cost and the overstock powder. Multiple efforts made in Tsinghua University to overcome the barriers will be presented in this speech.

Since 2004, electron beam (EB) has been adopted in powder bed fusion technology in Tsinghua University. Due to the high power and high energy absorption ratio of electron beam, the electron beam based powder bed fusion (EB-PBF) process has a preheated powder bed with the temperature up to 1000C or even higher, in which the thermal stresses in the workpiece can be controlled to a very low level. By this advantage, the dense crack free parts of several difficult-to-process metals, such as high strength aluminum alloy (Al2024), intermetallics (TiAl alloy), non-weldable superalloys (IN738) and refractory metals (pure tangent) have been successfully fabricated by EB-PBF, which expands the suitable material of PBF technology to the metals with low plasticity, prone to hot/liquid cracking, and very high melt point.

After that, based on the EB-PBF, a novel lower stress additive-subtract hybrid PBF process with the combination of continuous laser and ultrafast pulse laser was invented, called as EB-laser hybrid melting (EB-LHM) process. In EB-LHM, the powder bed is preheated by the EB to a temperature up to 1000C, and selectively melted by the continuous laser to form the cross sections of parts, of which the contour is trimmed and smoothed by the ultrafast laser ablation.

Furthermore, an originative powder bed technique named floated powder bed is proposed recently, in which the powder bed is composed of a powder layer with a constant thickness around 10 mm floating on the metal liquid (such as melted tin). Because no powder is needed to fill the space below the top 10mm powder layer, and hot melted tin can heat the powder bed and the workpiece, the supply of powder and thermal stress in PBD process can be greatly reduced by the floating powder bed.