Arc Welding Defects Explained

Arc welding is a process used to join metal parts using an electric arc. During this process, various defects can occur if the parameters are not set correctly. Understanding these defects and their causes is crucial for ensuring weld quality.

Identifying Defects from Incorrect Current

The question asks about the specific defect that arises when the welding current used is higher than recommended during arc welding. Let's examine the common welding defects:

• Overlap: This defect occurs when the weld metal does not properly fuse with the base metal at the edges (toes) of the weld. It typically happens due to insufficient heat input (low current) or moving the electrode too quickly.
• Undercut: This is a groove or reduction in thickness in the base metal next to the weld toes or root. It essentially removes base metal, weakening the joint.
• Blow holes: These are cavities or pores within the weld metal, often caused by trapped gases (like hydrogen) during solidification.
• Slag inclusion: This defect happens when non-metallic slag material is trapped within the solidified weld metal. It usually results from improper cleaning between weld passes or poor slag control.

Why High Current Causes Undercut

Using a current that is too high for the specific welding conditions provides excessive heat and energy. This intense heat causes:

• Excessive Melting: The base metal melts excessively, creating a larger pool of molten metal.
• Washing Action: The force of the arc and the fluid dynamics of the large molten pool can wash away or displace the base metal at the edges of the weld joint.

This washing action creates a noticeable groove or depression along the edge where the weld meets the base metal, which is precisely the definition of an undercut defect.

Comparing High Current Effects

While other issues like blow holes or slag inclusions can occur in arc welding, they are generally not directly caused by excessively high current. Blow holes are typically gas-related, and slag inclusions stem from poor cleaning or flux issues. Overlap is usually associated with low current or high travel speed, the opposite of the condition described.

Therefore, when higher than recommended current is used in arc welding, the resulting defect is most commonly undercut.