Abstract
During metal additive manufacturing, the porosity of the as-built part deteriorates the mechanical property and even hinders the further application of metal additive manufacturing. Particularly, the mechanisms of keyhole pores associated with the keyhole fluctuation are not fully understood. To reveal the mechanisms of the keyhole pores formation, we adopt a multiphysics thermal-fluid flow model incorporating heat transfer, liquid flow, metal evaporation, Marangoni effect, and Darcy’s law to simulate the keyhole pore formation process, and the results are validated with the in situ X-ray images. The simulation results present the instant bubble formation due to the keyhole instability and motion of the instant bubble pinning on the solidification front. Furthermore, comparing the keyhole pore formation under different laser scanning speeds shows that the keyhole pore is sensitive to the manufacturing parameters. Additionally, the simulation under a low ambient pressure shows the feasibility of improving the keyhole stability to reduce and even avoid the formation of keyhole pores.
Highlights
Metal additive manufacturing (AM) is well known for its ability to fabricate complex-shaped parts without special tooling[1] and functionally graded parts[2], shorten the development cycle of products[3], and save the cost of the material[4]
The porosity of the as-built part, one kind of defect, decreases the ultimate strength directly and is a fatal flaw to the fatigue and fracture strength of the part[6,7,8]. The presence of such defects does not meet the standards required in industry and prevents the adoption of AM technology in these industries
The laser parameters and ambient pressures in the simulation cases are listed in Supplementary Table 1, which are the same as the experiments[19] except the Case 5
Summary
Metal additive manufacturing (AM) is well known for its ability to fabricate complex-shaped parts without special tooling[1] and functionally graded parts[2], shorten the development cycle of products[3], and save the cost of the material[4]. A multiphysics thermalfluid flow model[24] incorporating heat transfer, molten pool flow, Marangoni effect, recoil pressure by metal evaporation, Darcy’s law, and laser ray-tracing is adopted to simulate the keyhole fluctuation and keyhole pore formation process.
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