African Fusion June 2015

GMAW: current progress

(a) 170 A.

Figure 2: Changes of the arc-plasma temperature field and drop shape for the open arc, argon-shielded GMAW process. (a): Welding current of 170 A. (b): Welding current of 250 A. (b) 250 A.

arc [9]. In the low-current case (170 A), globular transfer occurs. As can be seen in Figure 2, the temperature distribution of the MIG arc changes with the detachment of a metal droplet from the wire tip. In contrast at the higher current (250 A), spray transfer occurs. The liquid metal at the wire tip is elongated toward the pool like sharpened pencil. The arc plasma shape appears not to change, and its temperature field is less varied bymoltendropbehaviour. Fluidity, surface tension and viscos- ity of the liquid metal govern the shape and/or size of metal drop at the wire tip. As is well known, the electromagnetic force depends significantly on the current path flowing in the liquid metal. This means that the shape of the arc plasma touchedwith liquidmetal plays an important role on dynamic behaviour of metal transfer. In other words, the metal transfer mode is varied by physical properties such as thermal conductivity and electri- cal conductivity of the arc plasma. Accordingly, the composi- tion of the shielding gas is one of the important variables for controlling metal transfer. With this established, the change in a gas shielded metal arc across a metal transfer cycle can be predicted with aid of numerical simulation. Concluding remarks The essential components of the gas shielded arcwelding pro- cess include theweldingmachine, electrodewire and shielding References 1 H Maruo, Y Hirata, Y Noda: Quarterly Journal of the Japan Welding Society, Vol.2 (1984) No.1. 2 H Maruo, Y Hirata: Quarterly Journal of the Japan Welding Society, Vol.3 (1985) No.2. 3 H Maruo, Y Hirata: Doc.80-436 of Technical Commission on Welding Arc Physics in Japan Welding Society(1980). 4 A Okada, H Yamamoto, W Nishikawa: Doc.80-437 of Techni- cal Commission of Welding Arc Physics of Japan Welding Society(1980). 5 T Ueguri, et al: Doc.80-446 of Technical Commission of Weld- ing Arc Physics of Japan Welding Society(1980). 6 K Hashimoto, Y Hirata: IIW Doc. 212-1300-13(2013)

gas. In addition to universities and national institutes, welding machine makers, consumable makers and gas suppliers have been putting effort into the research and development of de- vices, consumables and newGMAWprocesses in collaboration with various fabricators. Some of these developments have been carried out based on visual observationwith recent high performance digital cameras, along with knowledge derived from numerical results of theoretical model.

7 G Huismann: IIW Doc.212-952-99(1999). 8 K Himmelbauer: IIW Doc.XII-1875-05(2005). 9 Y Ogino, Y Hirata: IIW Doc.212-1324-14(2014).

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June 2015

AFRICAN FUSION