What is Undercut in Welding?

Just like others, do you also think that a welder’s work is only to join two metals together? In addition to joining metals, a welder has to take care of the welds and welded metals. The welder must ensure to have flawless welding without flaws but there could occur undercut. 

What is an undercut in welding? One of the most typical flaws that welders experience is welding undercut. It is the issue that occurs when the gap is made in the base metal component along the welding foot. It results in the metal that has a gap or a hole in the welding.


Let’s go towards its detailed information;

What is undercut in the Welding? 

When a flaw occurs during the welding process of a metal, it is known as an Undercut. It is a gap that develops at the bottom or ground of the fusing during the welding process. 

Undercut can occur from increased electrical use, rapid weaving, wire diameter, inappropriate filler metal, and other factors. As a result, the welding process and metal lose intensity and become thinner. 

It develops when the metal’s cross-sectional width is decreased during the welding process. There is a risk that the defective part will collapse if it is used for the specified use. It might lead to a serious disaster. 

These undercut flaws are similar to the butt-and-fillet welding procedure.

What Causes Undercut? 

Undercutting is caused by using poor techniques of welding. If the supply rates will high then not enough material will be provided to sufficiently filled the craters. They will be formed by the melting of the base material next to the beads. 

MIG Welding 

Undercutting can also happen when the metal part is too melted during welding because of high temperatures. Moreover, welding undercuts are a persistent issue with MIG welding. 

You could get issues with undercuts if the welding cable is too small and the gun is adjusted to a high frequency.

High Temperature 

The major cause of the undercut is an incredibly high arc temperature or excessive power. An undercut will come from an improper welding process, extended arc, improper vibration, inappropriate electrode-to-workpiece alignment, etc. 

Electric Polarity 

The undercut is also an outcome of the arc’s electric polarity during DC welding. It will be increased by vertical, horizontal, upwards, and welding angles. The undercut decreases the parent metal’s cross-section and the material’s load-bearing capacity. In addition, it absorbs heat and becomes a source of fissures at the same time.

Incorrect Gas Supply 

One of the main reasons for undercuts during welding is selecting the incorrect gas barrier. The kind, origin variations, and size of the material are all requirements for the appropriate gas to match. 

For instance, when welding carbon fiber, the combination of carbon dioxide and vapors produces high-quality results. To decrease the chances of undercuts, you can enhance the insulating gas supply in the regulation.


What are the Types of Undercutting? 

There could be two types of undercuts during welding; 


The internal undercut is the term used to describe welds that are done in pipelines and lack filler material at the bead’s base. When the warm wave is implanted, it will result in an overheated root. Similar to undercutting, when the item is properly lighted, the top hole casts a shadow.


The second type of undercut is an external undercut that is also known as a facial undercut. The exterior of the weld joints or fused metals has this type of undercut. The main reason for the undercut is the welder’s inexperience and lack of proficiency. 

When welding at extreme feed rates, the filler material cannot effectively melt. In this way, it will not settle to cover the holes and bring them to an accurate level with the surface of the base material.

How to Prevent the Undercut? 

Weld undercuts can be avoided in numerous ways. A few of these are:

  • You can regulate the welding angle
  • You can decrease in welding current
  • Reducing the intensity of the welding
  • Decreasing the weave’s thickness
  • Selecting the appropriate welding position
  • The base metal should cool
  • You must use a consistent rocking motion when buttwelding
  • Prevent employing electrodes with a greater diameter
  • Limit your welding.
  • When constructing horizontal edges, you must keep the electrode at the distance from the vertical direction.

How I can fix the Undercutting? 

To correct an undercut welding, you don’t have to smooth the undercut or the uneven surface and then begin it again. It is because the issue can’t be resolved by grinding. 

The major reason is that a section that has been undercut lacks filler. So, even if you smooth the area, the issue still needs to be fixed by shaping or fixing the gap.

By lowering the welder’s voltage, quickening the welding, and increasing the cable length, the issue can be successfully fixed. These are the most effective and efficient ways of avoiding undercuts while welding. 

Additionally, you will need to adjust your operating position to reduce the chances of undercutting. Additionally, AC welding rather than DC welding can successfully eliminate undercutting when flank welds are performed.

By following all the above-given methods, you can get rid of the undercut in the welding. 


Here I am after this article that has covered all the information about what is undercut in welding. You will get to know about the causes, fixes, and preventions of the undercuts while welding. 

When there are no holes in the metal connections made by welding, the undercut is produced. Undercutting is caused by the temperature at the welding, which leaves gaps and despair. Additionally, one of the main reasons for undercuts is the use of poor technique. While some undercuts cannot be left, others might be repaired.

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