Multiple stages of smoking phenomenon in electron beam powder bed fusion process

Abstract

Smoking is a unique phenomenon in the electron beam powder bed fusion (EB-PBF) process. The far-field effect and fast expansion features of smoking often cause the destruction of the powder bed, resulting in part failure or even equipment damage, which seriously restricts the application and development of EB-PBF. However, the generation and development of the “powder cloud” during the smoking process are yet open research questions. This study proposed and established optical & electronic monitoring systems to observe the process of smoking and collect electronic signals to reveal the mechanism behind smoking. Simulation at a small scale where the powder motion of each powder at the affected zone in the powder bed is described by the discrete element method was conducted to simulate the effect of the inertial force and electrostatic force. Observations demonstrated that the smoking process consists of multiple stages. The powder bed showed different motion characteristics and generated different electronic signal patterns at different stages. Numerical simulations revealed that the electrostatic force is the main driving force and confirmed the promoting effect of charged particles striking the powder bed on smoking expansion. The current study provided interpretations of the mechanism as well as a potential solution for real-time monitoring and smoking prevention.