What Is Undercutting In Welding?

Undercutting is an often-overlooked welding issue that can lead to various weaknesses or faults in the weld. The US Department of Labor’s Bureau of Labor Statistics estimates that welding-related accidents are responsible for nearly 10,000 serious injuries each year.

Understanding what undercutting is and how to prevent it can help protect against accident and injury. Undercutting is a type of inefficiency in the welding process that occurs when oxygen from the welding space is not completely consumed and then penetrates the heat affected zone of the material, resulting in a shallow steel groove just below the weld bead. This can weaken the weld, making it more susceptible to cracking, delamination, and low fatigue resistance.

What is Undercutting in Welding?

Undercutting in Welding is when the weld does not properly fill the joint designated for welding, prevents proper heat transfer, and produces a defective weld. It is commonly seen in fusion welding processes, specifically when Tungsten Inert Gas (TIG) welding and Shielded Metal Arc Welding (SMAW) type of welding is used.

In this article, we will discuss the causes and effects of undercutting, prevention, and prevention methods.

Causes of Undercutting

Undercutting is mainly caused by an improper electrode angle, too long of arc length, incorrect amperage, and wrong rod size.

  • Incorrect electrode angle: The distance between the electrode and the workpiece is too short, which will cause an incomplete weld puddle to form. It may also cause the arc to pierce through the weld and travel to the base metal.
  • Too long of arc length: If the arc length is too long, it can cause the electrode to not fully penetrate the puddle, resulting in undercut.

  • Incorrect amperage: Heat input can be too high, causing the weld to become brittle, and in some cases, the weld could penetrate too deep, also resulting in undercut.
  • Wrong rod size: Incorrect rod size can result in the electrode not able to properly fill the joint.

Effects of Undercutting

Undercutting can weaken the weld, reducing its overall strength and reducing its ability to hold metal pieces together. This can lead to breakage and cracking, as less metal is available to take stress and strain from the surrounding joints. It can also affect the metal structure of the metal, making it more brittle and prone to corrosion.

Prevention of Undercutting

Undercutting can be prevented by following the correct welding practices:
  • Ensure the correct electrode angle: The electrode angle is important for creating a full weld puddle.
  • Use the correct arc length: Too long of an arc length increases the heat input and can also cause undercutting.

  • Use the correct amperage and rod size: Amperage and rod size play an important role in helping to create a good weld.
  • Use a jig or guide: A jig or guide can help to hold the electrode at the right angle, and prevent it from moving.


Undercutting in welding is a common problem that can reduce the strength of the weld and weaken the metal structure of the joint. It is important to ensure proper welding practices and use the correct electrode angle, arc length, amperage, and rod size. Additionally, having a jig or guide can help to maintain the correct angle of the electrode and also help to prevent undercutting. Citation URL:https://www-stuartconnections-com. ezproxy. lib. ou. edu/blog/what-is-undercutting-in-welding https://www. weldingtipsandtricks. com/undercut. html https://welding-advisers. com/undercutting-welding. html

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