Dr. Wentao Yan from Tsinghua University & Northwestern University, invited by Prof. Yongxing Shen, gave us a talk on Mar.17th, 2017.

Time & Date: 10: 00 a.m. -11:00 a.m., Mar.17th, 2017 (Friday)

Location: 2nd floor conference room, JI Building

Title: Multi-scale multi-physics modeling of metallic powder-bed-based additive manufacturing processes

Abstract

Metallic Additive Manufacturing technologies have proven to be very promising in recent years, which is believed to lead a new technological revolution. However, the manufacturing process, which consists of multiple complex physical phenomena over a broad range of time and length scales, poses a significant challenge for experimental observations and measurement. In this talk, a multi-scale multi-physics modeling framework is proposed to simulate the typical metallic powder-based Additive Manufacturing process, which mainly consists of three models ranging from micro-scale to meso-scale to macro-scale.

The micro-scale electron-atom interaction model using the Monte Carlo method, is aimed to deriving a new heat source model for the electron beam, by tracking the collision and energy transition between electrons and atoms. The heat source model, named as "double-Gaussian" heat source model, is material-dependent and experimental set-up specific, which is able to guide the process design and provide insight into uncertainty in experiments.

The meso-scale powder evolution model, which incorporates multiple physical phenomena and takes into a variety of influencing factors, is capable of reproducing the complex melt-flow-solidify process of individual powder particles. The formation mechanisms of the single track defects, including balling effect and single track irregularities, are systematically investigated, which reveals the dominance of surface tension. The melting processes along various scan paths in multiple powder layers are revealed in 3D simulations to investigate the influence of successive tracks and layers, which is the first report. Thanks to the multi-layer multi-track simulations, the formation mechanism of surface roughness is discussed.

The macro-scale heat transfer model, in which the loosely packed powder bed is simplified as an effective continuum material, is a powerful tool to rapidly reproduce the experimental fabrication process. To make the model simplifications more physically-informed, the effective thermal conductivity of powder bed, the effective thermal conductivity due to molten pool flow and the effective energy absorptivity, are calculated by the meso-scale simulations.

Bio

Wentao Yan, received his bachelor degree with the awards such as Outstanding Dissertation and Outstanding Graduate at 2012, and recently finished his PhD thesis defense (co-advised by Professor Feng Lin and Professor Wing Kam Liu), both at the Department of Mechanical Engineering, Tsinghua University. He was a joint PhD student at Northwestern University from October, 2014 to December, 2016. His PhD study is focused on multi-scale multi-physics modeling of metallic additive manufacturing processes. He first-authored several journal and conference papers, and gave invited talks at Peking University, Beihang University etc. He is also the co-inventor of four Chinese patents and one international patent.