Which welding process is most susceptible to lack of fusion?

• A. MMA
• B. TIG
• C. CO2 (metal active gas)
• D. Submerged arc

Answer: (C)

The welding process that is most susceptible to lack of fusion is associated with CO2 (metal active gas) welding. Lack of fusion occurs when the weld metal does not properly bond with the base metal or with the previous weld layer, which can lead to weak joints and is a critical defect in welds.

In CO2 welding, which relies on a shielding gas of carbon dioxide, the process may face challenges related to the heat input and the characteristics of the filler material. The rapid cooling that occurs in this method can result in insufficient melting and therefore insufficient bonding, particularly if the parameters such as travel speed and voltage are not well controlled. Additionally, if the surface of the base metal is not adequately clean, or if the gap between the base metals is too large, the risk of lack of fusion increases further.

While other processes like MMA (Manual Metal Arc), TIG (Tungsten Inert Gas), and submerged arc welding can also experience lack of fusion under certain conditions, CO2 welding is particularly sensitive due to its inherent process characteristics. In MMA, for instance, the ability to manually control the electrode means welders can often compensate to reduce this risk. In TIG welding, the precise control of heat and filler metal allows for better fusion. Similarly