Welding Arc stability

Arc stability is an essential issue in the welding operation. in the sense of a stable arc, it must be uniform and steady

It produces a good weld bead and a defect-free weld nugget if it is stable.

An unstable arc can introduce many welding imperfections such as porosity, blowhole, slag entrapment, and lack of fusion, etc.
Several factors are responsible for the stability of the welding arc. Some common factors are discussed below.

Power source:

Appropriate matching of the welding arc and power source characteristics can control the welding arc variation.such as this can prevent the arc from extinguishing when the arc voltage is slightly variable.

For this purpose, a number of power sources are used to meet the requirements of various arc welding processes. A power source AC., DC. or both can give. It may also have the characteristic of providing constant current or voltage. In relation to the input.

Movement  of electrode:

Mixing thorium or zirconium metal in welding electrodes to control electrode movement can maintain arc stability to some extent. By this, the electrode (cathode) and thermal ionization in the arc column produce a continuous and reasonable emission of electrons.

Other factors:

• Electrodeposition
•  Arc current
• Arc length 
• Presence of dirt, oil, grease on the surface of the base metal.

Possible welding imperfection due to unstable welding arc:

porosity: 

Porosity is the group of cavities in the weld metal that results due to freezing of gas from the weld pool as it freezes. There can be many reasons for this defect such as:

•  Absorption of atmospheric gases like (oxygen, nitrogen, and hydrogen) in the molten weld pool.
•  The improper coating on the electrode.
• Long arc length
• Improper Current 
•  Lack of welding technique.

Blowhole:

When entrapped gas pocket formed a single large cavity called Blowholes.

slag entrapment:

Slag inclusion is a type of slag entrapment between weld layers or between the base metal and weld metal, especially in the multilayer welding process, but sometimes it can come in single pass welding also. Slag inclusion occurs in which the slag material is used like SMAW, SAW.

Lack of fusion:

Lack of fusion occurs, when the weld metal fails to fuse boundaries of the base metal or sidewall of the base metal,

Lack of fusion can come in the sidewall of the base metal or between inter pass and root area respectively called Lack of sidewall fusion, Lack of inter run fusion, and Lack of root fusion. The root cause of this defect is an unstable arc due to improper cleaning, Low welding current, fast arc travel speed, short arc length, and lack of preheating in thicker metals.