What Is A Undercut In Welding?

Welding is an essential process in many industries, from construction and automobile manufacturing to aerospace and shipbuilding. With proper techniques and procedures, welders can create strong, reliable structures. However, welders need to be aware of a potential problem that can weaken the weld, called an undercut.

This article will provide a detailed overview of what an undercut is in welding and how it can be prevented. Welding is responsible for 500,000 jobs in the US alone, and there are nearly 34,000 welding-related businesses in the US.

Moreover, there are nearly 2 million welding machines in active use in the US. It is essential that welders understand how to avoid problems like undercut in order to ensure safety and reliability in their projects.

Keep reading to find out more about undercuts in welding!

What is an Undercut in Welding?

Undercut in welding is an indentation that is made in the weld pool along the edges of a welded joint.

It is caused due to insufficient filler metal or weld metal that has been deposited in the joint. Undercut appears as a groove or notch in the weld root and should be avoided as it weakens the weld integrity.

Causes of an undercut in welding

When it comes to weld joints, undercut is one of the common imperfections that can occur due to a number of reasons.

As mentioned earlier, insufficient filler metal or weld metal can be one the leading causes. Below are few of the other causes of undercut:

  • Using incorrect gas flow settings and pressures.
  • Using wrong electrode and wire feed speeds.

  • Improper welding position.
  • Using incorrect voltages for the metal type being welded.

  • Improper welding techniques.
  • Using wrong welding currents, for example alternating current.

Effects of an undercut in welding

The effects of an undercut in the weld joint can be very severe, ranging from complete loss of strength to fatigue failure and even fracturing of the weld joint at the undercut structure. In addition, it increases welding cost as the welding job will have to be performed again or the undercut will have to be repaired. Thus, it is important to avoid undercut in the weld joint, and if there is one, it should be repaired in order to provide the required weld strength of the job.

Preventing an undercut in welding

Undercuts are difficult to catch before welding as it usually becomes visible after the welding process is completed. However, there are certain steps that can be taken to minimize the chances of undercuts during the welding process.
  • Using the appropriate welding technique, including proper gas flow settings, pressures, welding positions, etc.
  • Using the right electrodes, wires and feed speeds.
  • Maintaining the right welding current, like direct current.
  • Ensuring adequate control over the welding machine speed and voltage.


Undercut in welding is an indentation that appears on the weld pool along the edges of the welded joint due to lack of filler metal. It can negatively affect the integrity of the weld joint and should be avoided. The most common causes of undercuts during welding process can be prevented easily by following the recommended techniques for the specific metal being welded. Citation URL: https://www. thefabricator. com/article/arcwelding/what-is-an-undercut-in-weldinghttps://www. millerwelds. com/resources/article-library/three-root-causes-of-weld-defectshttps://azweldingsupply. com/prevent-weld-undercuts/

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