Problem/issue being addressed: Laser powder bed fusion (LPBF) technology fabricates parts layer by layer via a focused laser beam to fuse the loose powder along the pre-designed path, is promising in aerospace, automotive and medical for its customization and free of geometric limitations that can’t be realized by the traditional technologies. A keyhole pore forms when gas is trapped by the cavity. In LPBF, when the melt pool transforms form conduction mode to keyhole mode, which is beneficial for low laser-absorptivity material, it is likely to generate a keyhole pore. Therefore, conducting in-depth research on the formation mechanism of keyhole pore is needed.
Importance: AM is a collection of emerging manufacturing techniques, e.g. Laser powder bed (LPB), laser metal deposition (LMD), electron beam powder bed (EBPD), and has the potential to make greater breakthrough than conventional methods. AM offer many advantages, e.g. of making complex components with relatively low cost. A fundamental understanding of the laser-metal powder interaction is critical to improving the quality and efficiency in the laser AM process. Our research provides a strategy to reduce or remove the pore in laser powder bed fusion, which is extremely important for the mass production of additive manufacturing technology.
Overall objectives: a three-dimensional thermal-mechanical-fluid coupled model is established via finite volume method, considering the heat transfer, fluid flow, recoil pressure as well as solidification drag model, and reproduces the formation processes of three representative pores. The proposed model is validated by the in-situ X-ray imaging results and reveals the fluid flow, keyhole fluctuation, three types of pores formation process and mechanism under a range of high-speed welding and powder bed fusion conditions. The goal of this research is to provide a comprehensive understanding of keyhole induced-porosities in laser powder bed fusion of aluminium and suggests the strategy towards pore-free laser fusion.
Conclusions: Through the research of the action, we clearly clarify the mechanism for pore formation in laser additive manufacturing and suggests the method to avoid the pore. Our work is beneficial to improving the quality of AM and promote its application in many fields, e.g. aerospace, transportation, automobile, and so on.
