Abstract
Laser engineering net-shaping (LENS), based on directed energy deposition (DED), is one of the popular AM technologies for producing fully dense complex metal structural components directly from laser metal deposition without using dies or tooling and hence greatly reduces the lead-time and production cost. However, many factors, such as powder-related and laser-related manufacturing parameters, will affect the final quality of components produced by LENS process, especially the powder flow distribution and thermal history at the substrate. The powder concentration normally determines the density and strength of deposited components; while the thermal behaviours of melt pool mainly determines the cooling rate, residual stress and consequent cracks in deposited components. Trial and errors method is obviously too expensive to afford for diverse applications of different metal materials and various manufacturing input parameters. Numerical simulation of the LENS process will be an effective means to identify reasonable manufacturing parameter sets for producing high quality crack-free components. In this paper, the laser metal powder deposition process of LENS is reported. The gas-powder flow distribution below the deposition nozzle is obtained via CFD simulation. The thermal behaviours of substrate and as-deposited layer/track during the LENS process are investigated by using FEM analysis. Temperature field distributions caused by the moving laser beam and the resultant melt pool on the substrate, are simulated and compared. The research offers a more accurate and practical thermal behaviour model for LENS process, which could be applied to further investigation of the interactions between laser, melt pool and powder particles; it will be particularly useful for manufacturing key components which has more demanding requirement on the components’ functional performance.
Highlights
Laser engineering net-shaping (LENS), based on a kind of directed energy deposition (DED), is one of the popular AM technologies for producing complex metal structural components production
The range of deposited component size, imperfect surface quality and high cost of metal powder limited LENS applications. Many factors, such as the laser-related and powder-related input manufacturing parameters will affect the final quality of components produced by LENS process, especially the thermal history of laser metal-powder
The gas-powder flow distribution below the deposition nozzle is obtained via CFD simulation
Summary
Laser engineering net-shaping (LENS), based on a kind of directed energy deposition (DED), is one of the popular AM technologies for producing complex metal structural components production. As seen in Fig., there are at least 4 sub-processes to model and simulate for the whole LENS process: (1) powder dynamics; (2) melt pool temperature field formation; (3) solidified track with microstructure evolution; (4) machining (if needed). Linking variables, such as particle mass concentration (PMC), velocity, temperature field of melt pool, cooling rate and residual stress, are transferred in-between different sub-processes for the holistic analysis. As for the melt pool formation, the moving temperature field on the substrate caused by moving laser heat source is critical to determine the cooling rate, residual stress and consequent cracks in deposited components. To study the influence of gas-powder flow and thermal behaviour during LENS process on the deposited components and its mechanical properties, accurate modelling, analysis and optimisation of these corresponding sub-processes are indispensable
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