[ 30 p. 1-8 (2012)] / ** *** Numerical Analysis of Metal Transfer Phenomena - critical condition between globular and spray transfer mode - by KADOTA Keiji and HIRATA Yoshinori Metal transfer modes in GMA welding process are different from welding variables: current, voltage, shielding gas, electrode wire and etc. Essentially they are influenced by physical properties of molten metal and electro-magnetic force. Then we numerically investigated the timechange of liquid transfer process using calculation model developed. The numerical result agreed very well with experimental result of water drop transfer from cylindrical nozzle. Numerical analysis shows that liquid transfer modes depend on the pressure balance at the tip of drop. When the dynamic pressure induced by liquid flow is lower than capillary pressure due to surface tension, globular transfer occurs. In contrast, when the dynamic pressure of liquid flow is higher, spray transfer occurs. In the case that the electrical current flows in the liquid, electromagnetic force significantly influences on the transfer mode and the drop detachment. As for liquid flow-out from the nozzle of 1.2 mm in diameter, calculated results with use of physical properties of molten mild steel show that electro-magnetic force induced by higher current than 250 A changes the transfer mode from globular to spray. Whereas in real GMAW with pure argon gas shielding the transfer mode changes at around 230 A. The behavior of drop detachment is varied by both spatial distribution and time-change of the electro-magnetic force. Key Words: Metal transfer phenomena, Globular transfer, Spray transfer, Surface tension, Viscosity, Electro-magnetic force 1. GMA GMA GMA * 23 9 2724 1 10 20 ** Student Member, Graduate School of Engineering, Osaka University *** Member, Graduate School of Engineering, Osaka University 1985 Cram 1) 1989 2 3) 1995 Haidar Lowke 4) 5) GMA
2 2. 2.1 GMA Fig. 2.1 1 2 3 4 5 6 7 2.2 Kothe VOF Volume-of-Fluid method 6 7) VOF F (1) F=1 F=0 F VOF (2) (3) VOF F = 1 in the liquid phase 0 < F < 1 in the boundary region (1) F = 0 in the gaseous phase (2) b = l F g (1 F) (3) F v [m/s] b l g v = 0 (4) (5) P [Pa] [Pa] g [m/s 2 ] F [N/m 3 ] SMAC (5) F VOF CSF 8) VOF CSF CSF F st [N/m 3 ] (6) [N/m] [m -1 ] F em [N/m 3 ] F em = J B (7) J [A/m 2 ] B [T] J = V (8) B = 0 J (9) [S/m] 0 4 10-7 H/m
30 2012 1 3 3. 3.1 Table 1 GMA 1.2 mm Table 2 Fig. 1 ab - Fig. 2 (a) 0.21 m/s 3mm Table 1 Physical properties of water. Table 2 Boundary conditions for calculation of water drop transfer. 0.35 m/sfig. 2 (b) GMA 3.2 Fig. 3 1.2 mm Fig. 4 (a) 0.21 m/s 3mm 79 ms 71 ms (a) Average flow velocity = 0.21m/s (b) Average flow velocity = 0.35m/s Fig. 1 Schematic of electrically conductive liquid transfer model. Fig. 2 Numerical simulation of water drop transfer from glass nozzle of 1.2 mm in diameter.
4 Table 3 Physical properties of molten mild steel. Table 4 Boundary conditions for calculation of metal transfer. Fig. 3 Schematic diagram of experimental apparatus of water drop transfer. 4. Fig. 4 (a) Average flow velocity = 0.21 m/s (b) Average flow velocity = 0.35 m/s High speed pictures showing water drop detachment and transfer from glass nozzle of 1.2 mm in diameter. GMA Table 3 Table 4 3 4.1 1.5 0.35 m/s Fig. 4 (b) 3 1 / Fig. 2 (a) Fig. 2 (b) Fig. 5,
30 2012 1 5 Fig. 5 Influence of surface tension and flow speed on metal transfer mode without electric current. (a) Surface tension ( = 1.0 10-6 m 2 /s) (b) Kinematic viscosity ( = 0.5 N/m) Fig. 7 Influence of surface tension and viscosity on the drop volume. (Flow speed = 0.177 m/s) G-S (11) Fig. 6 Schematic of simplified model for prediction of the critical condition of globular to spray transition. Fig. 6 P st P' st (10) v f [m/s] [kg/m 3] [N/m] D [m] [Pa s] v' [m/s] (10) 1 2 1 2 3 (10) Fig. 5 (11) / (11) (11) 5 Fig. 7 (a)
6 (10) (12) Fig. 8 Dependence of current and flow speed on transfer mode with cylindrical current path. I [A] P em P' em 3 9) (12) v' 0 (13) Fig. 9 Schematic of simplified model for prediction of the critical current of globular to spray transition. (b) 4.2 Fig. 8 Table 3 Fig. 8 200 A 250 A 200 A 0.6 m/s 250 A 0.01 m/s () Fig. 9 Fig. 8 (13) / (13) 0.6 m/s 220 A 1.2 mm 230 A 10) 200 250 A Fig. 10 15
30 2012 1 7 (a) Cylindrical shape Fig. 10 (b) Conical shape (Spread angle = 15 ) Influence of conductive region shape on liquid transfer mode. (Current = 300A, Flow speed = 0.177 m/s) Fig. 12 Peak current and pulse width required for detachment of liquid drop. (Current path with cylindrical shape) 2.5 ms Fig. 12 5. Fig. 11 Time-change of liquid transfer with pulsed current. (Current path with cylindrical shape) Fig. 11 1ms 400 A 600 A 800 A 400 A 1ms 600 A 2.5 ms 800 A 2ms GMA 1 GMA 2
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