What is Undercut in Welding? The Causes & Fixes & Prevention

What is Undercut in Welding? The Causes & Fixes & Prevention

Unfortunately, welding mistakes can occur, and one of the most common errors is an undercut.

In this article, we will discuss what undercut in welding is, its causes and fixes, and how to prevent it.

We will also provide a few tips on how to improve your welding skills and techniques.

By the end of this article, you should have a good understanding of what undercut in welding is and how to avoid it.

What Is an Undercut in Welding

An undercut in welding is a type of defect that occurs when the weld bead has penetrated too deeply into the base material.

It is caused by incorrect welding parameters, such as too high of a welding current, or incorrect welding technique.

An undercut can weaken the weld joint and reduce its overall strength and integrity.

Undercuts occur when the weld pool penetrates too deeply into the base material.

This can cause a step or ridge along the edge of the weld which is known as an undercut.

Welding parameters, such as current, voltage, travel speed, and arc length, can affect the depth of penetration, and incorrect settings can result in an undercut.

Additionally, incorrect welding technique can result in an undercut, as poor manipulation of the torch can cause too deep a penetration.

Undercuts can weaken the weld joint and reduce its overall strength and integrity.

The depth and size of the undercut are important factors in determining the severity of the defect.

If the undercut is very deep, it can cause the weld to be prone to cracking.

Additionally, the undercut can reduce the amount of surface area for the weld joint, resulting in a weaker bond.

In order to avoid undercuts, welders should ensure that the correct welding parameters are used, and that they are manipulating the torch correctly.

Additionally, welders should regularly inspect their welds to ensure that they are free of defects.

If an undercut is discovered, the weld should be reworked to ensure that it is free of defects.

Types Of Undercut

Undercut is a common defect in welding that occurs when the weld fails to fully penetrate the base metal.

It can result from improper welding techniques, high welding current, or incorrect joint design. Understanding the different types of undercut can help welders prevent and repair them.

  • Arc Undercut: Arc undercut is the most common type of undercut, occurring when the weld does not completely penetrate the base metal. This results in an edge of the weld that is lower than the surface of the base metal. Arc undercut can happen when the welding current is too high or the arc length is too long.
  • Angular Undercut: Angular undercut occurs when the weld metal does not completely penetrate the joint and the weld metal has a sharp edge. It is usually caused by incorrect joint design or incorrect welding current.
  • Uneven Undercut: Uneven undercut occurs when the weld metal is not distributed evenly along the weld joint. It can be caused by irregular weld penetration, incorrect joint preparation, or incorrect welding current.
  • Thermal Undercut: Thermal undercut occurs when the heat from the welding process has caused the weld metal to melt away from the base metal. This can be caused by incorrect joint preparation, incorrect welding current, or incorrect welding technique.

By understanding the different types of undercut and their causes, welders can better prevent them. Proper joint preparation, welding techniques, and welding current are essential for producing quality welds.

What Causes Undercuts in Welding:

  • Poor Fit-up: Poorly prepared joints can create an undercut due to the welders being unable to fill the joint correctly. This can be caused by gaps in the joint, misalignment of the pieces, or incorrect bevels.
  • High Heat Input: Excessive heat input can create an undercut due to the weld metal melting and the base metal not being able to flow into the molten weld pool. This often happens when the welding amperage or voltage is too high.
  • Incorrect Travel Speed: Welders who weld too quickly may not be able to completely fill the joint, resulting in an undercut.
  • Incorrect Electrode: Using an incorrect electrode can cause an undercut due to its inability to provide the necessary heat input and penetration.
  • Incorrect Welding Technique: If the wrong welding technique is used, the heat input may not be sufficient to completely fill the joint, resulting in an undercut.
  • Inadequate Gas Coverage: Using an inadequate gas coverage, such as shielding gas, can cause an undercut due to the lack of protection from the environment. This can cause the weld metal to oxidize, which can lead to an undercut.
  • Contamination: Contamination from oil, grease, paint, or rust can cause an undercut due to its inability to properly bond with the base metal. This can lead to a weaker joint and an undercut.

10 Tips To Prevent Undercut In Welding 

  1. Ensure Proper Preparation: Before welding, be sure to clean the joint area of any dirt, scale, rust, or other contaminants. This is key to achieving a successful weld and preventing undercut.
  2. Use the Appropriate Filler Metal: Always use the recommended filler metal for the base material being welded. Using the wrong filler metal can lead to undercut and other issues.
  3. Adjust Your Welding Machine Settings: Setting your machine to the correct parameters is essential for a successful weld. If the settings are too high, you’ll be prone to undercut.
  4. Ensure Proper Travel Speed: Travel speed plays a huge role in preventing undercut. Too slow and the molten weld pool will be deep, which can cause undercut. Too fast and the weld will be weak.
  5. Use the Correct Shielding Gas: Shielding gases are essential for protecting the weld pool from atmospheric contamination. Using the wrong gases can lead to undercut.
  6. Use the Right Torch Angle: When welding, the torch angle should be such that the filler metal is being deposited at the center of the weld pool.
  7. Use the Correct Stick-Out: Stick-out is the length of the electrode that is extending beyond the contact tip. Too short of a stick-out can lead to undercut.
  8. Ensure Proper Joint Fit-Up: Proper fit-up is essential for a good weld and for preventing undercut. Make sure the joint is clean and free of gaps and other defects.
  9. Use the Right Welding Technique: Using the correct technique and technique variations is important for preventing undercut. Make sure you’re using the correct technique for the job.
  10. Experiment with Different Parameters: Experimenting with different parameters can help you find the optimal settings for your application. This can help you achieve a strong and undercut-free weld.

What Is An Acceptable Amount Of Undercut?

An acceptable amount of undercut in welding depends on the application and the welding process being used. Undercut is a groove that is melted into the base metal at the toe of a weld, and it can be a sign of inadequate fusion or excessive welding current. In general, undercut should be kept to a minimum and should not exceed 0.5mm (0.020″) in size on structural welds.

For aesthetic and cosmetic welding applications, undercut should be kept to an absolute minimum and should not exceed 0.3mm (0.012″). This is to ensure the finished weld looks uniform and aesthetically pleasing.

When welding with steel and other metals, the goal is to keep the weld bead as narrow as possible and the undercut to a minimum.

In some cases, a small amount of undercut can provide benefits in terms of strength and fatigue resistance.

However, too much undercut can lead to reduced joint strength and can also create a risk of cracking or failure. 

When welding aluminum, undercut should also be kept to a minimum.

Excessive undercut can lead to weld cracking and hydrogen embrittlement.

The best way to minimize undercut when welding aluminum is to use a low amperage and a fast travel speed.

In conclusion, an acceptable amount of undercut depends on the application and the welding process.

Generally speaking, undercut should be kept to a minimum and should not exceed 0.5mm (0.020″) in size on structural welds and 0.3mm (0.012″) in size on aesthetic and cosmetic welds.

Removing Undercuts From A Bad Weld

  1. Begin by turning off the welding power supply. Ensure that all tools and materials are removed from the work area.
  2. Put on safety glasses and gloves to protect yourself from sparks and heat.
  3. Use a grinder to remove the undercut from the weld. Be sure to grind in the direction of the weld bead and maintain a consistent motion.
  4. Once the undercut has been removed, inspect the area with a magnifying glass to identify any weak points or irregularities.
  5. If necessary, use a grinding wheel to smooth any rough areas.
  6. Apply welding rod to the area to fill in any gaps or weak spots.
  7. Turn on the welding power supply and use a low heat setting to complete the weld.
  8. After the weld is complete, use a grinder to clean up any excess weld material.
  9. Inspect the weld to ensure that it meets the desired standards.
  10. If necessary, use a grinding wheel to smooth the surface of the weld.
  11. Put on safety glasses and gloves to protect yourself from sparks and heat.
  12. Use a grinder to remove any slag or impurities from the weld.
  13. Once the slag is removed, inspect the weld with a magnifying glass to make sure that it is free of any imperfections or weak points.
  14. If necessary, use a grinding wheel to smooth any rough areas.
  15. Put on safety glasses and gloves to protect yourself from sparks and heat.
  16. Apply welding rod to the weld to fill in any weak spots or gaps.
  17. Turn on the welding power supply and use a low heat setting to complete the weld.
  18. After the weld is complete, use a grinder to clean up any excess weld material.
  19. Inspect the weld to ensure that it meets the desired standards.
  20. If necessary, use a grinding wheel to smooth the surface of the weld.

Frequently Asked Questions (FAQs:)

What's the main cause of undercuts in welding?

The main cause of undercuts in welding is incorrect welding parameters. Incorrect welding parameters can lead to excessive heat input in the weld area, which can cause the metal to melt beyond the desired area. This can cause the metal to shrink away from the weld joint, resulting in an undercut.

What is meant by the term undercut in welding?

The term “undercut” in welding refers to the formation of a groove along the edges of a weld bead. This groove is formed due to the melting of the base metal around the edge of the weld and is used to create a stronger joint. Undercutting can be caused by a variety of factors, such as insufficient heat or excessive penetration.

How do you fix an undercut on a weld?

Fixing an undercut on a weld involves grinding away the undercut, ensuring the weld is clean and free of any contaminants, and then rewelding the area.

To avoid an undercut in the future, use proper welding techniques and parameters, such as a lower current setting, slower travel speed, and a welding technique that allows for better penetration.

What causes undercut in MIG welding?

Undercut in MIG welding is caused by a combination of several factors, including the current, travel speed, and the type of wire being used.

High current can cause the weld to penetrate too deeply, leading to an undercut.

If the travel speed is too slow, the weld pool may become too large, resulting in an undercut.

Finally, using a wire with a larger diameter can also lead to an undercut.

What causes undercut in TIG welding

Undercut in TIG welding is caused by an improper weld bead width, an incorrect welding current setting, or welding in the wrong direction.

It can also be caused by an incorrect arc length, inadequate joint preparation, or an incorrect tungsten electrode size.

What causes undercut in stick welding

Undercut in stick welding is caused by insufficient heat input into the weld zone.

This can be caused by a number of factors, such as improper current settings, improper electrode angle, or a too-high travel speed.

The electrode must be held at the correct angle and a consistent travel speed must be maintained to ensure adequate heat input.

Additionally, proper current settings must be adjusted for the electrode size, material, and joint thickness.

Conclusion

Undercut in welding is an unacceptable defect that can be caused by a variety of factors.

However, it is possible to prevent undercut by following the correct welding parameters and procedures.

Proper welding technique, correct welding amperage, and proper welding rod selection can help to prevent undercut.

In addition, it is important to properly maintain the welding equipment and use the correct shielding gas to reduce undercut.

By understanding the causes and fixes of undercut, welders can ensure that their welds are free of defects and meet the highest quality standards.

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