The undercut is a welding defect that can occur when too much heat is applied to the weld puddle. This causes the metal at the base of the weld puddle to liquefy and run away, which leaves a hole or undercut in the weld. In this blog post, we will discuss What Is Undercut in Welding and how to prevent it from happening during your projects!
Types of Undercut
Three types of undercut can occur in welding:
- Type I: This is the most common type of undercut and it occurs when too much heat is applied to the weld puddle. This causes the metal at the base of the weld puddle to liquefy and run away, which leaves a hole or undercut in the weld.
- Type II: This type of undercut occurs when there is not enough heat being applied to the weld puddle. This causes the metal at the top of the weld puddle to solidify before the metal at the bottom, which creates an uneven surface and can cause problems with fitup later on.
- Type III: This type of undercut occurs when there is too much heat being applied to the weld puddle and the metal at the base of the weld puddle begins to vaporize. This can create a hole in the weld or cause the weld to be weaker than it should be.
The undercut can also be classified by where it occurs about the weld. There are two types of undercut:
- External Undercut: This type of undercut occurs on the outside of the weld bead and is usually caused by too much heat being applied to the weld puddle.
- Internal Undercut: This type of undercut occurs on the inside of the weld bead and is usually caused by too little heat being applied to the weld puddle.
External Undercut
An external undercut is a form of weld defect that can occur when the welding torch is not held at the correct angle. This results in the molten metal not being able to properly fill the joint, which can cause the weld to be weaker and more likely to fail.
To prevent external undercut, it is important to ensure that the welding torch is always held at the correct angle. If you are unsure of the correct angle, there are many resources available that can help you determine this.
Additionally, it is always a good idea to practice on scrap pieces of metal before attempting to weld on your project piece. This will allow you to get a feel for the correct angle and prevent any mistakes from happening.
Internal Undercut
An internal undercut is a form of weld metal defect that can occur during the welding process. It is characterized by a lack of fusion between the weld metal and the base metal, which results in a decrease in the cross-sectional area of the weld.
This can lead to welding problems such as porosity, poor mechanical properties, and cracking.
An internal undercut can be caused by several factors. To prevent undercut, it is important to use the proper welding techniques and torch angles.
In addition, you should adjust the welding current according to the thickness of the material being welded. If you are unsure about how to prevent undercut, please consult a qualified welder or welding engineer.
What are the main causes of undercutting?
There are three main causes of undercutting: incorrect welding techniques, improper electrode selection, and poor joint design.
- Incorrect welding techniques are the most common cause of undercutting. This usually happens when the welder is inexperienced or not properly trained.
- Improper electrode selection is another common cause of undercutting. This happens when the wrong type of electrode is used for the material being welded.
- Poor joint design is the third most common cause of undercutting. This happens when the joint isn’t designed correctly for the welding process.
Undercutting can also be caused by environmental factors, such as wind or drafts. These factors can cause the arc to wander, which can lead to undercutting.
Wrong Selection of Welding Parameters
The most common cause of welding undercut is incorrect welding techniques. This usually happens when the welder is inexperienced or not properly trained. The main reason for this is that the welder doesn’t know how to select the correct welding parameters.
The wrong selection of welding parameters can lead to several problems, including undercutting. Some of the most common problems are listed below:
- High current: This can cause the arc to be too hot, which can lead to undercutting.
- Greater arc length: This can also cause the arc to be too hot, which can lead to undercutting.
- Wrong electrode selection: This can happen if the wrong type of electrode is used for the material being welded. This can lead to undercutting.
- Poor joint design: This can happen if the joint isn’t designed correctly for the welding process. This can also lead to undercutting.
High Speeds of Electrode Movement
High speeds of electrode movement can also cause undercutting. This happens when the electrode moves too quickly across the weld joint.
This can cause the arc to be too hot, which can lead to undercutting. This usually happens when the welder is inexperienced or not properly trained.
Improper Electrode Material and Size
An electrode that is too small in diameter creates an arc that is more difficult to control.
This can cause the weld to be pushed too hard, which can lead to undercutting. The improper electrode size is one of the most common causes of the undercut.
Another common cause of undercut is using the wrong type of electrode material. Electrode materials are classified by their welding current range. Using an electrode with a lower current range than what is specified for the application can also cause undercut.
Holding the Electrode at a Wrong Angle
The most common cause of welding undercut is holding the electrode at the wrong angle.
When you weld, you should always hold the electrode perpendicular to the workpiece. If you hold it at an angle, the heat from the arc will be concentrated on a small area. This can melt through the metal too quickly and create an undercut.
To prevent this from happening, practice welding on scrap metal before you start your project. This will help you get a feel for how to hold the electrode correctly. You should also use a low setting on your welder until you get comfortable with it.
Incompatible Shielding Gas
The gas you use to shield your weld from the atmosphere can also cause undercut. If you use an incompatible gas or one that has been contaminated, it can create a chemical reaction with the metal that causes undercut. To prevent this, always make sure you’re using the correct shielding gas for your welding process and that it’s clean and dry.
Quality of Surface of Parent Material
One of the main reasons for undercut in welding is the lack of edge preparation.
The surface of the parent material must be clean, free from rust, paint, oil, grease, etc. In addition, it is important to remove any mill scale or other foreign matter that may be present on the surface.
If the surface of the parent material is not prepared properly, it can cause problems with the weld bead and lead to undercutting.
Incorrect Proportion of the Filler Material
Another reason for undercut can be found in the quality of the filler metal used. If the filler metal is not of good quality, it can cause problems with adhesion and lead to undercutting.
In addition, if the wrong type of filler metal is used for a particular application, it can also cause problems. For example, using a filler metal that is too soft can lead to an undercut.
How to Prevent Undercutting
One of the best ways to prevent undercut in welding is by using a smaller electrode. This will help to create a smaller and more focused arc, which will reduce the amount of heat that is applied to the base metal.
Another way to prevent undercut is by increasing the travel speed of the electrode. This will help to spread the heat out over a larger area and reduce the chance of creating an undercut.
Finally, you can try welding with a lower current setting. This will help to control the heat better and reduce the chance of creating an undercut. If you are having trouble preventing undercut, then you may need to switch to a different type of welding process or electrode material.
Accurate Heat Input
An undercut is a condition that can occur during welding if the heat input is not properly controlled.
It appears as a groove or channel melted into the base metal along with the weld bead and can weaken the joint or cause cracking.
While it’s not always possible to eliminate undercut, there are steps you can take to minimize its occurrence.
One of the most important things you can do is to ensure accurate heat input. This means using the correct welding procedure and setting your welder to the proper parameters. If you’re unsure about how to set your welder, consult the owner’s manual or ask an experienced welder for help.
Working at a Medium Speed
The best way to avoid undercut is by welding at a medium speed. This allows the puddle to remain in place without cooling too quickly.
If you weld too slowly, the heat will cause the metal to warp and distort. If you weld too quickly, the puddle will cool before it has a chance to fully fuse with the base metal.
By welding at a medium speed, you’ll be able to strike a balance between these two extremes.
Using short strokes
Another way to prevent undercut is by using short strokes. This helps to control the puddle and prevents it from cooling too quickly. It also helps to minimize the amount of heat that’s transferred to the base metal. Short strokes also help to reduce warping and distortion.
Correct Electrode Angle and Size
The electrode angle is critical to prevent undercut. A 90-degree electrode is the most common and provides the best weld bead profile and penetration for most applications. The electrode should also be the correct size for the metal thickness you are welding. If the electrode is too small, it will not have enough heat to penetrate the metal and create a strong weld joint.
Undercut occurs when the molten weld metal cools and shrinks faster than the base metal, causing it to pull away from the edge of the base metal. This leaves a groove or notch on the edge of the weld that can weaken it.
Undercut can also cause porosity in the weld, which can lead to leaks or other problems.
Correct Weaving Technique
The correct weaving technique is important to prevent undercut. When welding, you should always use a back and forth motion. This will help to ensure that the weld is not too deep and does not penetrate through the metal. If you are using a MIG welder, you should also keep the gun at a consistent angle.
If you are welding on thin metal, it is especially important to use the correct technique.
This is because thin metal can be easily damaged if the weld is too deep. When welding on thin metal, you should start by making a small pool of molten metal. Once this pool is created, you can then begin to weld in a back and forth motion.
Gas Protection Selection
The gas that you use for welding is also important. When welding, you should always use an inert gas. This will help to protect the metal from oxidation. The most common gases used for welding are argon and helium.
If you are welding on stainless steel or aluminum, you may need to use a different gas. For these metals, you can use a mixture of argon and carbon dioxide. This gas will help to prevent the formation of oxide on the metal.
While many factors can cause undercut, using the correct technique and gas protection is the best way to prevent it. By taking these steps, you can ensure that your welds are strong and have a good appearance. If you do experience undercut, there are ways to repair it. However, it is always best to prevent it from happening in the first place.
Correct Welding Position
To avoid undercut when welding, it is important to use the correct position and technique. The most common cause of undercut is welding in the vertical or overhead position.
This is because the heat from the arc tends to concentrate at the top of the weld bead, causing the metal to melt too fast and resulting in an undercut.
The best way to prevent undercut is to use a slightly larger electrode than necessary and welding in the flat or horizontal position whenever possible.
Use a Multi-Run Welding Technique
One way to prevent undercut is to use a multi-run welding technique. This means making multiple passes over the weld area, rather than just one pass. By making multiple passes, you can build up the weld gradually and avoid creating too much heat at once. This will help to prevent the metal from warping and causing undercut.
Use the Right Travel Speed
One of the biggest mistakes welders make is traveling too fast. When you travel too fast, you don’t give the puddle time to freeze and this can cause undercut.
The rule of thumb is to travel at a speed that allows you to see the size of the puddle. If you can’t see the puddle, you’re going too fast.
If you find that you are having trouble controlling your puddle, try using a welding gas with a higher argon content. This will help shield your arc and give you more control.
Another way to help control your puddle is to use a smaller electrode. This will give you more control and help you avoid undercut.
Internal undercuts and how to fix them
Internal undercuts are one of the most common welding defects. They occur when the weld metal does not fill the entire width of the joint, leaving a small groove on the inside edge of the weld. This can happen for several reasons, including incorrect electrode angle, improper torch position, or poor technique.
There are a few ways to fix an internal undercut:
- Use a smaller electrode
- Increase travel speed
- Reduce current
- Change wire feed direction
- Add filler metal
With any of these techniques, it’s important to practice first on some scrap pieces before trying to fix the issue on your final project. Otherwise, you could end up making the problem worse!
If you follow these tips, you should be able to avoid undercut in welding. Just remember to take your time, use the right gas, use a small electrode, and find the right travel angle. With a little practice, you’ll be welding like a pro in no time!
What Is the Acceptable Amount of Undercut?
The amount of undercut on a weld is typically specified by the welding engineer or designer. It is important to note that the amount of undercut specified is usually based on aesthetic or functional requirements rather than structural considerations.
In most cases, the acceptable amount of undercut is between 0.005 and 0.020 inches (0.13 and 0.51 mm).
Does an undercut weaken a weld?
The short answer is yes; an undercut can weaken a weld. The reason why has to do with the way that welding works. When two pieces of metal are joined together by welding, the heat from the welding process melts the metal at the joint. This creates a pool of molten metal that cools and solidifies, joining the two pieces together.
If there is an undercut present at the joint, it weakens the weld because it creates a void in the molten metal pool.
This void leaves less material to join the two pieces of metal together, making the weld weaker overall.
Additionally, an undercut can also cause problems with corrosion and fatigue cracking in a weld joint.
Conclusion
Undercutting can be a serious problem in welding, as it can weaken the weld and cause it to fail. It is important to be aware of the causes of undercutting and how to prevent it.
Undercut can be a problem for both novice and experienced welders alike. But by using the proper welding techniques and paying attention to your welds, you can avoid this defect and produce high-quality welds!
Do you have any tips for preventing undercut? Share them in the comments below! If you found this blog post helpful, be sure to share it with your friends!
Please stay tuned for next week’s blog post where we will discuss another welding topic! If you have any suggestions for future blog posts, please let me know in the comments section below. Thank you for reading and until next time! Happy welding! 🙂
