The laser metal deposition process is characterised by the occurrence of mutually influencing phenomena. Particularly important for understanding particle deposition are the phenomena originated by the three-way interaction of the laser beam, the powder stream and the substrate, which in previous models have been consistently oversimplified or neglected. This work presents a numerical model useful for studying powder stream formation, powder heating and mass addition into the melt pool, as well as various interactions that occur during processing. Experimental work is performed to validate powder stream formation and heating, and particle addition to melt pool. Good agreement is found with the modelled results. It is revealed from this work that the role of the substrate is more significant than previously thought and that considering the beam-stream-substrate interrelations allows simulations closer to real processing conditions to be performed.
Laser cutting is a key technology for the medical devices industry, providing the flexibility, and precision for the processing of sheets, and tubes with high quality features. In this study, extensive experimentation was used to evaluate the effect of fiber laser micro-cutting parameters over average surface roughness (Ra) and back wall dross (Dbw) in AISI 316L stainless steel miniature tubes. A factorial design analysis was carried out to investigate the laser process parameters: pulse frequency, pulse width, peak power, cutting speed, and gas pressure. A real laser beam radius of 32.1 μm was fixed in all experiments. Through the appropriate combination of process parameters (i.e., high level of pulse overlapping factor, and pulse energy below 32 mJ) it was possible to achieve less than 1 μm in surface roughness at the edge of the laser-cut tube, and less than 3.5% dross deposits at the back wall of the miniature tube.
The laser metal deposition process continues to receive attention from researchers and industry due to its unique capabilities in applications such as surface coating or rapid manufacture. The development of numerical models has proven useful for improving the process. However, most models have focused on analyzing individual stages of the deposition process and have required the introduction of a number of assumptions at their limits. This paper describes a complete CFD model that, starting from particles in the deposition head, simulates all interactions that govern the dynamics of a deposition melt pool. Individual phenomena that are included in the gasphase stage of the model include the ricocheting of particles within the head, the flow of powder particles, their interaction with the laser and powder catchment/bouncing. Phenomena in the liquid phase (melt pool) stage of the model include particle enthalpy effects, buoyancy, temperature-dependant material properties and Marangoni forces. The model is demonstrated using the actual geometry and gas flows found in a typical coaxial nozzle. The method, using a single technique to capture all phenomena, allows simulation of the melt pool dynamics from input parameters in a single model.
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