What Is Undercut In Welding? How Do You Prevent It?

Are you looking for What Is Undercut In Welding? One of the significant issues in the intricate welding world is undercut. In actuality, this welding flaw is rather typical and affects materials and parts that are put to use regularly.

So, folks are just starting to need a foundational understanding of this undesirable flaw to assist them in dealing with it. This article discusses welding undercut, causes, remedies, and removal methods.

What Is Undercut In Welding?

An unintentional groove that runs along the weld bead is an undercut. At the margin of the weldment, there is a long dip in the base metal. I use the word “trough” since it can contain liquid.

Undercut In Welding

This demonstrates the negative impacts of undercuts. In conclusion, undercuts compromise the joint in several ways. The most apparent effect of an undercut is a lack of material where it is required. This must change. Consider welding a butt joint between two 6mm (0.236″ or 15/64″) plates as an example. The weldment and its surroundings should ideally be 6mm thick.

However, if there is an undercut, the thickness at the weld toe or root will be less than 6mm. The structural integrity of the joint is compromised at these places as a result. These thin portions are typically the first to crack when under load.

An undercut further reduces a joint’s strength because it collects dirt and water. The part prematurely fails mechanically due to the trapped water accelerating corrosion in this vulnerable area. 

How To Prevent Undercutting?

How To Prevent Undercutting

Precise Heat Input

Applying high heat during an operation near the free edges is one of the most significant causes of undercutting during welding. The primary metal or the material from the preceding weld melts as a result. Reduce the welding current to prevent this, which would need a decrease in arc speed. Likewise, when approaching free and thinner edges, pay attention to the welding temperature.

Operating At A Modest Rate

Another factor that causes undercuts is fast welding. When metal is welded too quickly, some base metal melts and cannot be reshaped because of rapid solidification. A depression is made along the margins as a result.

The best welding speed is moderate. The results of extremely slow welding need to be more adequate. Once more, moving too quickly can result in issues like undercutting.

The Correct Electrode Size And Angle

An error-free welding procedure depends heavily on knowing the welding angles. An undercut is likely to result if a welder is heating the free edges at an angle that needs to be corrected.

Remember to apply heat to the edges and regions with thicker components rather than the free edges. Using an electrode that is larger than necessary should also be avoided. An undercut may result if the molten metal’s size exceeds the plate’s thickness.

Appropriate Weaving Method

To control the temperature of a weld puddle, weaving is used. To avoid undercutting on edges, make sure to pause on either side of the weld. In other words, the issue of undercutting may arise when a welder does a welding process using a quick weaving technique.

Hold the duct in the sidewall of the groove if you’re weaving. Another distinguishing factor contributing to the fusion deficit is a messy work surface. An excellent technique to succeed at welding is appropriately and thoroughly cleaning the surface before and during welding.

Selection Of Gas Protection

One of the primary causes of undercuts during welding is selecting the incorrect gas protection: the material’s kind, source derivatives, and thickness corresponding to the appropriate gas composition.

For instance, combining carbon dioxide and inert gases produces high-quality results when welding carbon steel. If necessary, increase the shielding gas flow in the regulator to lessen the likelihood of developing undercuts.

Correct Welding Position

6. Proper Welding Position Welding cuts occasionally result from horizontal and vertical welding. Due to insufficient metal filling along the connecting edges, a poor welding position can result in an undercut. To prevent this, attempt to weld flat.

Use A Multi-Run Welding Method

The easiest way to lessen the number of lower segments, or undercuts, while welding is to use this method. All of the issues above are dealt with via a multi-operation technique. It aids in producing high-quality resources with enhanced mechanical qualities.

Employ The Appropriate Travel Speed

A too-rapid travel speed can result in an undercut. Remember how much weaving is used, pay attention to the welding speed, and try to hold the electrode only a short distance from the vertical plate while performing a horizontal fillet weld to avoid this problem.

Ensure That Your Arc Voltage Is Moderately High And Prolonged

An undercut may happen when the arc voltage is too high or too long. Once more, undercuts result from too much heat in one place.

How To Fix Undercutting Problems?

Placing a stringer bead along the whole length of an undercut will rectify it. If necessary, you can grind it using a grinder to get the proper weld profile. Undercuts less than 0. 5 mm deep typically can be corrected. If they are 10 mm thick but no deeper than 1 mm, they can be left uncorrected in a low-carbon steel plate.

How To Fix Undercutting Problems

What Is Internal Undercutting?

The primary sort of uppercutting discussed in this article is external uppercutting. In a butt joint weld close to the base metal, internal undercutting, also known as root undercut, frequently happens. They appear directly adjacent to the weld’s root.

Internal uppercuts can develop when welding pipes close to the interior and next to a slight edge. A weld may contain another form of internal undercutting. It is a groove left at the top of a root weld, close to the sidewall.

Weld beads placed in the weld location are used to fix internal uppercuts. These beads may create weld inclusions. Internal welding prevention strategies are comparable to traditional uppercut prevention strategies. To avoid internal uppercuts, pay close attention to the roots.

Tips To Prevent Undercut In Welding 

Here are some guidelines you can use to avoid undercutting when welding:

  1. Use the Proper Current: Consider reducing the current if you notice long, recurring undercuts. To achieve optimal fusion, this lessens overheating.
  2. Use the Proper Voltage: Locate the voltage knob’s “sweet spot,” which results in a bead profile with no undercuts, a clean finish, and no irregularities.
  3. Never Weld Hastily: Move the stick slowly to allow enough time for mixing and prevent early solidification.
  4. Utilize Suitable Fillers: Consult a chart or an expert welder when selecting filler material.
  5. Maintain a Proper Work Angle: Maintain your angle so that filler is deposited evenly in the weld pool. This can be determined by examining the differences between the bead’s two sides.
  6. Choose the Proper Electrode Size: An appropriate electrode delivers energy consistently and fills your groove.
  7. Consider the Situation While Shielding: Choose wisely depending on the desired weld and ensure the gas mix suits the task.
  8. Using a Consistent Hand, Weave: Consider weaving with a tiny delay at the edges to guarantee good fusion where it is most crucial.
  9. Keep a Steady Arc: Your arc length is inaccurate if there is excessive splatter or resistance to your movement. Using these indicators, adjust it and keep it that way throughout the welding process.
  10. Retain the desired fillet grooves, smooth them out, and clean them expertly to prepare the edge properly. 

What Much Of Undercut Is Acceptable?

During your quality checks, if undercuts are seen, you must determine whether they are acceptable. There are two approaches to this problem. If you need to follow precise quality control guidelines, you can decide based on visual inspections, joint type and thickness, and material strength. Welders often consider anything less than 0.5 mm (.02 in.) safe.

The second formal method refers to the American Welding Society’s (“AWS”) accepted standards. Any undercut below 1/32″ is safe, even if it extends the entire weld length, according to AWS D1.1 Code. You must watch throughout the examination if it rises above this. The maximum is 1/16″. Any undercut that is even the tiniest bit deeper than 1/16″ causes the part to be rejected.

The criteria become a little more complicated between this 1/32″ and 1/16″ range. The quality inspector must determine the total length of undercuts within this range. This comprises both lengthy single undercuts and sporadic minor undercuts. Their overall length in a 12″ portion cannot be longer than 2″.


To be concluded, What Is Undercut In Welding? When there are no gaps in the metal connections made by welding, the undercut is produced. Undercutting is mainly caused by the overspread of heat at the weld, which leaves gaps and depressions. Moreover, one of the main reasons for undercuts is poor technique.

This event weakened the source, which could lead to fracture later. There are numerous justifications for undercutting. While some undercuts can be left alone, others need to be repaired. Do you want to share any techniques you have? Tell us in the comments section below.

Frequently Asked Questions

What is the primary reason for weld undercut?

There are several causes for undercutting: excessive heat caused by high voltage and current levels. When the travel speed is too high, the electrode leaves the weld pool too soon. If edges are not adequately cleaned or prepped, debris or grit tends to restrict heat transfer, which can result in undercutting.

Will undercut make a weld weaker?

An undercut may weaken the structural integrity of the joint. These thin portions are typically the first to crack when under load. By encasing water and debris, an undercut can further lessen the strength of a joint. Water that has been captured speeds up corrosion in this already vulnerable area.

How is the welding undercut corrected?

Undercuts are frequently lengthy and thin. Therefore a common way to fill them is using stringer or bead weaving. Another choice is to use an angle grinder to altogether remove the defect. The joint must be thick enough to survive the strength loss for this method to be effective.

What causes weld undercut?

It results from high welding current and welding speed. This problem is one of the main errors that will adversely affect the installation since it will cause a notch effect in dynamic loads. Undercuts typically happen parallel to the seam of the weld.

What distinguishes an undercut from an overlap?

Undercut A groove near the weld toe or weld root that is melted into the base metal and is not filled with weld metal. Overlapping is the weld metal extending past the weld toe or root.

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