Tokihiko Kataoka

Development of a low-spatter CO2 arc welding process with a high-frequency pulse current

In CO2 arc welding of solid wire, metal transfer phenomena and spatter generation are investigated with rectangular pulse current, and a low spatter CO2 arc welding process with high frequency pulse current is developed. The optimal conditions of high frequency pulse CO2 arc welding are in the range of peak current: 450–550 A and pulse frequency: 450–750 Hz. These high frequency pulse currents have the effect of droplet oscillation due to resonance between applied pulse frequency and the natural frequency of the droplet. The droplet is transferred consistently every 9–11 pulses and the average interval of metal transfer is about 16 ms which is reduced to half that of conventional CO2 arc welding. This average droplet weight is 34 mg, showing a large reduction in comparison with that of the conventional method. As a result, total spatter weight is reduced by 70% in comparison with the conventional method, and especially, large spatters more than 0.5 mm in diameter are reduced from 1.5 to 0.2 g/min.

Influence of minor elements in electrode wire on spattering phenomena in CO2 gas shielded arc welding

The CO2 gas shielded arc welding method was developed in the 1950s and through the improvements in welding power and consumables it has now developed to become the mainstream arc welding method. However, because a large amount of spatter is generated during CO2 gas shielded arc welding, even now the improvement in the procedures of welding execution in terms of spatter generation is still a task to deal with. Studies into the effect of welding wire composition on the welding arc phenomenon have already been reported4,1,2 and they have shown that, in CO2 gas shielded arc welding, the reduction of C content and the increase of Ti content in the welding wire induce the restriction of short-circuiting and the reduction of spatter as a result2 . However, it cannot yet be said that the degree of spatter reduction has been sufficient. The authors also achieved a reduction of spatter generation by developing the high frequency pulsed CO2 gas shielded arc welding method 3, but, even with this welding method, to reduce the generation of spatter sufficiently it is essential to optimise the composition of the welding wire. Therefore, in this paper on the reduction of spatter in CO2 gas shielded arc welding, an investigation was made of changes in arc mode and spatter generation by adding Ti, REM (rare earth metal), Ca and K to the welding wire.

Effect of REM addition of wire on CO2 gas shielded arc phenomenon

Carbon dioxide (CO2) gas shielded arc welding is the main arc welding method, but it generates a large amount of spatter during welding. The root cause of spatter lies in the fact that the droplet undergoes repeated irregular shaking. To solve this problem, spatter generation modes were clarified and the effects of polarity and rare earth metal (REM) addition of the wire on CO2 gas shielded arc welding were investigated. As a result, when welding is performed with an electrode negative (DCEN) polarity using REM added wire, it was found that a conical arc plasma is formed, and the droplet which is transferred from the wire tip to the molten pool is fine and continuous, in what is termed ‘spray transfer’. Thus, spatter generation was reduced to 10% of amount of the conventional CO2 gas shielded arc welding (from 0.058 to 0.005g/s).