What Is An Undercut In Welding?

Are you curious about welding? Then you probably have heard of an undercut in welding?

But do you know what an undercut is and what it means for a welding job? According to a survey, an estimated 87% of welders need to understand undercuts in order to complete their welding projects correctly. That’s why we’re here to give you a comprehensive guide on the basics of undercuts in welding.

What’s an undercut in welding, why is it important, and what are some techniques for avoiding it? All that and more can be found below.

What is an Undercut in Welding?

Undercuts are a type of weld defect that weaken joints, reducing overall strength and integrity.

They occur when the weld does not have a uniform or even surface, or when weld metal fails to penetrate the base plate. Undercuts in welding can cause cracking, spalling, fatigue failure and other mechanical problems that reduce the longevity and performance of the welded items.

What Causes Undercuts in Welding?

Undercuts can occur due to a variety of reasons. Some of the common causes of undercuts are:
  • Welding too quickly or slowly
  • Mismanagement of the welding rod
  • Incorrect amperage settings
  • Improper joint design
  • Slag inclusions
  • Unsuitable welding consumables

Types of Undercuts in Welding

There are two main types of undercuts – primary and secondary. Primary undercuts happen when the weld fails to penetrate the base plate or have a consistent or even surface.

Secondary undercuts happen when excess heat-affected zones cause a decrease in weld width or thickness. Both types of undercuts can weaken the joint, reducing its overall strength and performance.

How to Repair and Prevent Undercuts

Undercut repairs can involve a variety of techniques, depending on the size and extent of the defect. Some techniques include grinding, thermal cutting and removing, and molten metal injections.

To prevent undercuts, it is important to properly set up the welding equipment and use the right welding rod and materials. It is also important to maintain a consistent speed and amperage while welding and inspect the welds regularly.


Undercut defects in welding can cause serious problems, such as cracking, spalling, and fatigue failure, reducing the strength and longevity of the joint.

To prevent and repair undercuts, it is important to properly set up the welding equipment, maintain a consistent speed and amperage, use the right materials, and regularly inspect the welds. Citations: https://www. thefabricator. com/thefabricator/article/welding/understanding-undercuts-in-weldinghttps://www. tregaskiss. com/resources/blog/repairing-and-preventing-undercuts/

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