What is Undercut in Welding

Welding is never a simple task as it sounds. Probably the first time you tried welding, you ended up with a deformed weld. This can be because you have a weak point in your weld making it less durable. This deformity is what is called undercutting. Undercutting diminishes your weld quality. 

Undercutting in welding is a situation where the weld reduces the cross-sectional thickness of your base material. This results in an overall reduction of the strength of your weld and workpieces. Even the most experienced welders fall victim to undercutting, so it’s not just novices.

Undercutting leads to loss of money and productivity. This article will examine everything you need to know about undercutting including causes and how to prevent it. 

How to Identify an Undercut in welding?

You need to remember two things.

1. Undercut always forms in the base metal
2. Always runs parallel to the weld metal

What Causes Undercutting in Welding?

If you have frequent undercutting problems, maybe your welding technique is wrong. Probably you are overheating your metal. Common causes of undercutting include:

Using Larger Electrodes

When the electrodes are too large, it creates undercutting as it melts the metal part of your parent metal apart from joining the edges.  

High Travel Speed

This makes the weld appear peaked because of the extremely fast degree solidification. The surface tension forces draw your molten metal directly along the weld bead edges and piles it up at the center.

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This also affects the base material where an undercut groove is formed. The melted base material is first drawn into your weld and is not allowed to properly wet back because of the rapid solidification.  

Higher ARC Voltage

As much as raising your arc voltage can do away with undercutting, it can reappear if you raise the arc voltage too high. Mostly, it happens in spray welding.

In this instance, the arc gets too long increasing the amount of molten base material. The heat transfer of this long arc to your weld zone is poor, causing the outer regions to cool down quickly and prevent proper wetting. The arc length should be short to prevent undercutting, to increase penetration depth and your weld strength.   

Higher Welding Current

Undercut forms when your welding current is too high because the arc force, penetration, and heat are too intense blowing away the base plate under that arc. This results in the outermost area of your base metal being melted and solidifying too fast. This prevents proper wetting of the puddle because of the surface tension and puddle turbulence. Always remain in the proper current ranges as specified for the wire size.  

Being in a Wrong Welding Position

It often happens when you weld a horizontal area but are holding your electrode subconsciously over the vertical metal causing significant undercutting because of the insufficient filler metal in the joint area. 

Incorrect Electrode Angle

Incorrect electrode angle results in more heat to your thinner edges subsequently causing undercutting. Correcting the angle ensures you have heat to the thicker areas ensuring you have strong welds in that area. 

Wrong Use of your Electrode

Inefficient manipulation of your electrode leaves excessive molten metal on the weld area causing undercutting. 

Contaminated Shielding Gas

The base metal may need a unique combination of shielding gas according to the type of metal and thickness. The wrong combination leads to undercutting of the weld area. The shielding gas in an accurate ratio forms a protective layer preventing atmospheric contamination. 

Improper Filler Metal

When the filler metal is too hot or improper, you can have an undercut weld just like a contaminated shielding gas. The temperature gradient across your weld area results in undercutting.

Welding metals require sufficient filler metal supply across the joining position. Not doing it properly causes undercutting because the filler metal is crucial to getting perfect welds. 

How To Prevent Undercut in Welding?

Weld at Medium Speed

Fast welding is the most common cause of undercutting. The base metal becomes molten metal and fails to solidify properly to its initial shape because of rapid solidification. Quick solidification creates depressions along the weld area. Medium welding speed yields positive outcomes.  

Use the Right Heat Input

Excessive high heat close to the weld edges melts the main metal. Check your welding current to ensure it’s low enough to maintain moderate arc speed. Always check the welding temperature when approaching thinner and free weld edges. 

Check the Weaving Technique

Weaving regulates the weld puddle heat and prevents undercutting, so pause each weld site to avoid fast weaving. Carefully hold the duct at the sidewall of your groove and avoid working on dirty base metal surfaces to avoid fusion deficiency. Thoroughly clean the weld surface before welding and after. 

Observe Proper Electrode Angle and Size

Know the appropriate welding angles to avoid errors as undercutting happens when you add heat to free edges at wrong angles. Refrain from using larger electrodes than necessary.  

Use Proper Welding Position

Be more careful when welding vertically or horizontally to ensure you are in the proper welding position. This prevents insufficient metal fillings on your connecting edges causing undercutting. Weld flat to prevent undercutting, although it depends on your welding project. 

Use the Right Shielding Gas Combination

The right shielding gas composition is based on base material thickness, type, and source derivatives. For example, carbon-steel welding does well with a combination of carbon dioxide and inert gases. Increase the flow of shielding gas in the regulator to eliminate undercuts. 

Use the Right Travel Speed

Keep track of your weave and watch your weld speed. Don’t hold the electrode close to your vertical plate when making horizontal fillet welds. 

Use Multi-run Weld Technique

This is crucial to reducing undercutting and lowering segments when welding. Use a multi-run technique to generate great resources. The technique helps you achieve satisfactory results and improves your mechanical properties. 

What is Underfill in Welding?

An underfill is when your weld metal surface is below the adjacent base metal surface. In simple terms, an underfill is undersized welding. You can see it by visually inspecting the weld surface. Most underfills are caused by high heat input and high welding travel speeds. 

Why is Undercut Bad in Welding?

An undercut is bad in welding because it’s an imperfection that negatively affects the weld strength and durability. Mostly it’s caused by using improper welding processes or techniques. Undercut causes a reduction of the base material thickness giving you poor quality welds. 

An external undercut happens on the outside section of the weld seen as a groove alongside the weld edge. It’s never a good sign because it weakens your weld and makes the weld prone to cracking on the edges of your weld. 

How to Repair Undercut in Welding?

Welding needs dedication and proper training to achieve perfection. However, even experts make mistakes and the primary task of the welder is to give a perfect weld with no defects like undercuts. Undercutting is a mistake most welders make. 

Fixing an undercut reduces your welding speed, is costly, and lowers productivity, but it’s necessary. The best repair is to prevent undercuts by strictly following the preventive tips mentioned earlier. 

Undercuts that are 0.5mm deep or even lower don’t need repairs, simply avoid them. However, undercuts that are 10mm needs repairing. To repair an external undercut place a stringer bead along the length of the undercut. Alternatively, you can use your grinder to grind the external undercut to get the desired weld profile. 

Repair an internal undercut using weld beads by placing them within that weld area.  The weld beads form inclusions fixing the flaws in your weld. Mastering the skill needs practice and some dedication and always observe preventive measures to avoid undercutting. 

Lack of Fusion in Welding

The primary aim of arc welding is to achieve fusion between two separate metal pieces. Lack of fusion is when you have incompletely fused spots in your welds causing a discontinuity in the welds. This happens during welding and most welders hardly notice it. 

Lack of fusion is difficult to detect through visual inspection. The only way to detect it is by bend testing the weld joint when there is a fracture when a low load is applied. 

Lack of fusion defect runs along with the individual beads or weld interface. What causes it? Lack of fusion is mainly caused by insufficient energy input in your weld area. Also, when the parent metal in your made beads or weld groove is not heated to the required melting temperature for it to mix to form a uniform weld. 

In short, the lack of fusion is not because of the filler material but primarily because of the improper weld preparation and unsuitable welding technique. A good welder melts the parent metal using an arc before mixing it with the filler material to make a weld. Use proper procedures to avoid lack of fusion. The defect only occurs in one dimension, the direction of welding progression. 

Other causes include using a higher arc voltage and improper positioning of the burner. Using long arcs with two wires causes a lack of fusion besides a wide weld face. This means that your two arcs give arc energy distributed over a larger area while the energy density is small. Therefore, the supplied energy is inadequate and can’t melt your parent metal. You can improve weld quality by: 

Using Correct ARC Voltage

Lack of fusion happens because of insufficient heat at the point of contact. To prevent it, simply adjust the current and voltage to increase the heat level traveling to the weld points.  

Line up the Edges Correctly

Properly place the base material at the edges and ensure the surface has no contaminants or debris that can prevent fusion. Contaminants cause imperfect final products. 

Bead Alignment

Properly position all beads at the welding point to ensure the welder melts them to get a complete seal and avoid a lack of fusion. Imperfect bead alignment causes gaps or slots. 

Final Thoughts

The undercut is a serious welding defect that can be prevented if you follow sufficient precautions. The comprehensive guide above helps you understand what causes undercutting and how to prevent undercuts. Take the remedial steps to get quality welds. Our main objective here is to offer you detailed information and the best welding tips to make your welding experience and task professional and more convenient. Stay with us to learn more.