Fig. 8: Comparison between experimental data and modelling results of bubble migration in the melt pool.
From: Pore evolution mechanisms during directed energy deposition additive manufacturing
a A radiograph showing melt pool with impacting powder. b For the forced case, the temperature field obtained by modelling with the same parameters as the X-ray imaging experiments, velocity and temperature perturbations given to the surface to simulate powder hitting effects, and (c) corresponding velocity and trace of a bubble inside the melt pool. The up-down migration of a bubble under forced oscillation on the surface, caused by the formation of circulation cells compared with the large Marangoni circulation shown in Fig. 6c, d. Modelling and experiment results are shown in blue and black lines, respectively. d Temperature field considering impacting powder at t, (e) formation of smaller cells at t + 0.2 ms. And (f) corresponding velocity and trace of a bubble inside the melt pool. The modelling and experimental curves are connected in black and blue lines, respectively. Direct simulation of random powder bombardment where sudden velocity increase is induced in the impact region, which causes irregular bubble migration such as the up-down migration and local circulation. Modelling and experiment results are shown in blue and black lines, respectively. For the forced case, the (circular) surface wave period is set as 0.6 ms, surface wave number is 5 in the pool lateral direction. For the direct bombardment case, the impacting velocity is 4 m s−1, the powder diameter is 90 µm, the impacting interval is 0.5 ms and the powder temperature is 1800 K for simplicity. These values for modelling are determined by the X-ray imaging experimental video. T in the colour bar in (b) and (d) represents temperature in K. The velocity unit in (b, d, e) is m s−1. Scale bars in (a, b, d, e) are 300 μm.
