Fundamental investigation of powder smoking phenomenon during selective electron beam melting

• Applicant: Professorin Dr.-Ing. Carolin Körner, since 1/2023
• Subject Area: Production Automation and Assembly Technology ; Chemical and Thermal Process Engineering ; Metallurgical, Thermal and Thermomechanical Treatment of Materials
• Term: from 2021 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 448758899

• Final Report Year: 2024

Final Report Abstract

The aim of this project was to gain a fundamental understanding of the so-called “smoke” events during electron beam powder bed melting (PBF-EB). During smoke, the interaction of the electron beam with the metal powder leads to an explosive dispersion of the powder bed and thus to the termination of the process. It was shown how the smoke phenomenon develops gradually, with a heating phase followed by local whirling of the powder bed and subsequent avalanche formation. The triggering mechanisms for each phase were examined in detail. Contrary to literature opinion, our results indicate that the local fluidization of the powder bed as an initiating event is not significantly initiated by electrostatic forces. The sudden evaporation of residual gases from the powder upon heating by the electron beam was identified as a key mechanism. The electric charge only comes into its own in the avalanche phase. Powder particles in the atmosphere become electrically charged through direct or indirect interaction with the beam, with the Coulomb forces accelerating individual particles towards the powder bed and thus initiating the avalanche effect. Based on these findings, a model for smoke development was created and a corresponding optimization method for the scanning strategy was successfully tested under extreme conditions. In addition, it was shown how the existence of local disturbances before the actual smoke event can be clearly recognized by analyzing the backscattered electrons. This now opens up the possibility of preventing smoke events through appropriate process control.

Publications

• Actual state-of-the-art of electron beam powder bed fusion. European Journal of Materials, 2(1), 54-116.
  Fu, Zongwen & Körner, Carolin
  
• Electron-optical observation of smoke evolution during electron beam powder bed fusion. Additive Manufacturing, 70, 103578.
  Ye, Jihui; Renner, Jakob; Körner, Carolin & Fu, Zongwen
  
• Correlating outgassing and smoke phenomenon in electron beam powder bed fusion of Ti6Al4V using a residual gas analyzer. Progress in Additive Manufacturing, 10(4), 2191-2203.
  Ye, Jihui; Chen, Tiejue & Körner, Carolin
  
• Revealing the Mechanisms of Smoke during Electron Beam–Powder Bed Fusion by High-Speed Synchrotron Radiography. Journal of Manufacturing and Materials Processing, 8(3), 103.
  Ye, Jihui; Semjatov, Nick; Bidola, Pidassa; Lindwall, Greta & Körner, Carolin