Experimental study on the metal transfer control by using pulsed Ar addition in CO₂ arc welding process: studies on pulsed gas MAG welding

ABSTRACT

CO₂ gas-shielded arc welding, which is widely used in the industrial world, has been recognized as an efficient and economical GMA welding process. However, its characteristic repelled transfer produces a large amount of spatter which results in costly cleanup and, thus, practical methods to overcome this weakness have been highly demanded. In the series of this study, ‘Pulsed Gas MAG’ welding was proposed as a new approach to reducing spatter, in which Ar gas pulses were periodically injected into CO₂ shielding gas so that gas composition of arc atmosphere was largely modified in a very short period of time and a metal droplet formed at the electrode tip during CO₂ atmosphere was released before repelled transfer had occurred. In this report, the influence of parameters of Ar gas injections, such as frequencies, average gas flow rates and gas injection periods, on the metal transfer was investigated. It was found that synchronous metal transfer stimulated by pulsed Ar gas injections was achieved at any frequencies from 35 to 65 Hz under the conditions of gas injection periods longer than 4 ms and of Ar gas volumes larger than approximately 1mL/pulse. This is because Ar gas injections below these critical levels resulted in lack of time for arc shape changes and metal drop detachment. From these experimental results, a model to explain the metal transfer phenomena was developed. The amount of spatter was reduced to the levels as low as that of the conventional MAG welding with 80 %Ar +20 %CO₂ shielding gas mix and penetration profiles were round shape like those obtained in CO₂ arc welding.

KEYWORDS:

• CO₂ gas-shielded arc welding
• metal active gas welding
• control of metal transfer
• spatter
• shielding gas