What Are The Causes of An Undercut Weld?

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An undercut weld is a defect that can occur when welding steel. It can be caused by a number of factors, including incorrect welding technique, incorrect filler metal choice, and poor fit-up.

Welds can be made from either solid or gas-based materials, and it’s important for them to have the proper quality in order not only to ensure productivity but also worker safety. Microscopic cracks known as micro-cracks will begin developing at any point during production if not remedied quickly enough so they become more advanced than what is expected – which leads us back again towards structural failure is inevitable because there are no strong points of resistance left against external forces once all yield boundaries have been transgressed

Undercut Weld

The groove that forms under the weld is known as “undercutting.” It occurs when there’s not enough metal to fill in this area and so you end up with a laminated toe. 

This makes your welding more likely than not have cracks along its length because while it doesn’t affect structural integrity, any stress put on one side will travel through all three layers like they were nothing – which isn’t really good for anything!

Undercuts weaken the joint in several ways. For example, an undercut causes a groove running along with weld beads that look like this one — called “the welfare bowl” by some welding experts because it’s so deep and wide.

The result is material removal from areas where you need it most: around fasteners or other structural members which will eventually fail due to tension, loads applied simultaneously across their whole bases.

Undercutting can be a costly and dangerous problem for welders. It leads to decreased productivity, speed reduction on the job site which could lead to an accident with serious consequences including injury or death!

There are several ways that you as an operator might want to eliminate this issue in order to get back working quickly:  

  1. Keep more than one set (or close)of assistants during production. 
  2. Wear protective equipment like gloves & eyewear at all times.
  3. Make sure your torch has been properly adjusted before starting any project.
  4. Use consumables wisely 5 substitutes include metal sheets.

Undercut Types

The external undercut is typical of toe welds, which are often seen as byproducts when working with fillet joints.

The visible groove on these types can be problematic during welding because it creates an imperfection that may not go away completely unless you’re willing to sacrifice some strength for aesthetics!

Internal undercut forms on the bottom side of a butt joint. These are often seen as one is working their way up towards more complex shapes, and they provide an easy method for creating flat bottoms that can’t be done easily any other way!

undercut weld

Causes of Undercut Weld

Current Too High

The current is too high, and it will cause the parent metal to melt. The molten gallons that result from this excessive heat then drain into your welded area where undercut joints are more likely than not due in part to how fast they cool down after being created! When there is a very high voltage between two electrodes, the metal may melt into large beads that move from side to side. 

This low fusion reaction results in an increased number of undercut welds because it takes longer for all parts to combine and form one solid mass instead of many separate lumps or particles stuck together with filler material at their center.

Long Arc Length

To avoid undercutting, try to maintain a shorter arc length. The improper selection of gas shields can also lead to an undercut happening quickly if you weld with high current and long strokes. One common cause for this problem is rust; make sure there isn’t any before trying again!

Unaligned Electrodes

Another possibility would be that your electrodes aren’t aligned correctly – check them against each other as well as the protective gloves (and clothing) which should have been provided by whoever delivered them. Welding skills are important when it comes to welding because if the welder is not experienced enough then they may cause undercuts by making welding speeds too high which would lead to vertically inconsistent melting of metal in an area due to its uneven distribution heat-wise.

Incorrect Filler Material

Inconsistent melting is caused by the use of incorrect filler material, which leads to inconsistent production and formation. This results in an undercut on the top side where there should be no metal loss at all!

Welding Surfaces with Debris

To avoid undercuts while welding, it’s important to keep your workspace clean and free of any excess materials. Both paint chips or rust flakes can get caught between the electrodes which will lead you into trouble when attempting an arc-weld through them!

Improperly Mixed Gas

Shielding gas is the medium between your cutting tool and workpiece that prevents contamination by transferring air away from both. If it’s not properly mixed, you may end up with an undercut because of interference on metal properties- leading to dirty cuts!

Incorrect Hold

Undercuts are a major issue for welders. When holding the electrode vertically, it is difficult to distribute filler material evenly without spilling any over certain areas of your welder’s surface which can lead to an improper build-up and thus create undercutting at higher heat settings on certain marry types of metals such as aluminum or magnesium alloys because they hold more conductive than others do (e..g., copper).

Prevention Of Undercuts Weld

Undercut weld can be prevented by understanding the causes of under-cutting. 

By knowing how to recognize and prevent this welding defect, you will greatly reduce your chances of creating an unwanted cut in any material being welded with a gas or electric machine!

Multi-pass welding is a great way to reduce the occurrence of undercut by helping prevent relaxation. 

This process requires two different passes, with one weld placed on top after each heating element has cooled slightly before adding more material and completing your second pass through all areas that were not covered in the first go-around – this helps stabilizes fusion properties so there’s less risk for cracks or breaks! 


It is possible to get an undercut weld from a number of different causes. The most common cause for this type of weld, however, is when the materials used are not compatible with each other and they cannot be properly fused together by heat or pressure alone. 

If you want to avoid this issue altogether, make sure that your material choice will work well with the welding process. 

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