Whether you’re a beginner, a professional, or just have a curious mind, I’m sure you’ve heard of undercut welding. But what is an undercut in welding?
The undercut is one of the most common weld defects and is caused by an improper or incomplete preheat.
Undercuts affect the quality of the weld. As a result, it’s crucial for both welders and those who inspect and evaluate their work to understand this defect.
In this article, I’m going to tell you what an undercut is, why it happens, and how to prevent it.
What Is An Undercut in Welding?
An undercut is when a weld’s heat causes the base metal to become molten and flow away from the weld, leaving a depression in the base metal. This leaves you with a gap between your base material and the weld. It’s not always desirable, but sometimes it is necessary.
This allows room for cracks to form and prevent the weld from reaching its full strength. An undercut occurs when the filler wire is laid too low in the joint or if it is laid at an angle too low to make a complete fillet with the base metal.
The biggest cause of undercuts is human error; operators who aren’t paying attention, who don’t know what they’re doing, or who don’t know the proper techniques may cause undercuts unintentionally, but they can also be caused by poor equipment maintenance and poor quality materials.
I recommend that if you want to go for an undercut purpose during welding for any positive outcome, then do it with some technique; otherwise, my suggestion is that avoid doing it.
Difference Between External & Internal Undercut
An undercut is a form of weld defect that occurs when the weld metal does not completely fill the joint. Undercuts can be external or internal.
External undercuts occur when the weld metal extends beyond the edges of the joint, while internal undercuts occur when the weld metal does not fully penetrate into the joint.
External undercuts are more common than internal undercuts, but both present problems for a welder and cause weak welds that can lead to cracking and failure.
What Causes Undercut in Welding?
Undercut is a phenomenon that occurs when the molten metal of a weld cools, hardens, and shrinks back from the surface of the base material.
It’s one of the most common flaws in welding, but if you know what causes undercut and how to prevent it, you can avoid this problem in your own welding projects. I will show you the following possible undercut causes:
1. Long Arc Length:
Long arc lengths can cause undercut by causing the arc to be too big for the weld metal, which means that the weld metal doesn’t have enough time to melt before passing through the molten pool at the end of the weld. This results in a gap between the end of your weld and your base metal.
2. Weaving Technique:
The weaving technique can cause undercut in welding because it leaves gaps between passes on either side of where you are working with your electrode holder (e.g., when moving up or down over an area).
These gaps allow coolant to escape and prevent proper heat input into the joint being created by your arc and electrode holder movement across it, therefore causing undercuts or incomplete fusion between those areas as well as other issues such as porosity (hollow spots).
No doubt, alot of welders use weaving techniques for different projects. But I recommend only applying this if you have enough ideas about this.
3. Edge Preparation Issues:
In this case, the edge of the weld shows signs of porosity and/or slag inclusions. This happens when the base metal or electrode is not prepared properly before welding.
It can also occur when there is a gas flow problem, which can cause the hot metal to pool up at the top of the groove.
4. Improper Shielding Gas:
Gas shielding is used to protect against oxidation and other forms of corrosion while welding.
Some types of metals require specific kinds of shielding gases in order to prevent this from happening, but other types can be used interchangeably with each other without any problems whatsoever.
Unfortunately, some welders don’t know which materials work best with certain gases, so they just use whatever they have on hand instead, and this can cause undercut problems!
5. Improper Arc Voltage:
Arc voltage that’s too high can cause undercut because it generates heat at a higher rate than the metal can dissipate it. The result is that the weld bead becomes too hot and pulls away from the base metal before it has time to fuse together.
This can also cause porosity in the weld bead, which means air pockets and weak spots in your final product. In extreme cases, this kind of undercutting will even cause the weld to crack or break off entirely.
6. Electrode Angle:
The angle at which your electrode meets the base metal is a big factor in whether or not you’ll get undercut.
If you’re using an angle grinder or other hand-held power tool, I suggest making sure that the tip of your electrode is perpendicular (90 degrees) to your work surface when you start welding; this will ensure that all parts of your project are equally strong and durable.
If your electrode isn’t at 90 degrees, then some parts won’t fuse together as well as others, and those are exactly where cracks will start forming!
7. Wrong Electrode Material & Size:
The wrong electrode size or material can lead to undercutting because it limits the heat transfer from the arc into the base metal.
In addition, if you use an electrode that doesn’t transfer enough heat into the base metal, then there won’t be enough energy present for fusion.
8. Travel Speed & Current Issues:
Travel speed and current are directly related. Higher travel speeds require higher currents to generate enough heat energy for adequate penetration.
If your travel speed is too high, especially with low current levels (less than 5 amps), then there won’t be enough heat generated for proper penetration into the base metal.
This will also result in undercutting since there won’t be enough energy present for fusion!
How to Avoid Undercut in Welding?
Undercutting is one of the most common welding defects. It occurs when the weld is not as strong as it should be and causes problems with the strength of the weld.
Undercut is caused by too much heat, which causes the wire to burn through or vaporize. This can happen when you do not have enough amperage or voltage, when you are using too long of a filler rod, or are welding too fast.
There are several other ways to avoid undercut, including:
1. Use Proper Shielding Gas:
If you are welding with an electrical arc, you will need to use the proper shielding gas. The most common types of shielding gases used in the welding industry include argon, helium, and carbon dioxide.
Argon is the preferred option for many welders because it does not react with molten metal, which can cause splatter or slag.
However, if you are using a gasless flux-cored wire that does not require shielding gas as part of its setup process, then helium may be your best option.
2. Utilize Proper Technique:
The key to preventing undercut is to utilize proper technique when welding. If you are using a shielded metal arc welder (SMAW) or flux-cored arc welding (FCAW), then I recommend trying to keep your arc length as short as possible while moving at a slow speed and applying even pressure on the gun trigger to maintain consistent amperage throughout the entire weld seam.
If you are using gas tungsten arc welding (GTAW), then focus on keeping your torch angle consistent throughout each pass so that there is no variation in current flow through the weld puddle.
3. Go for the Right Voltage:
The voltage setting on your welder will affect how much heat is generated during the welding process. A high voltage setting will produce more heat and thus more chance for undercuts (and other defects).
On the other hand, if you use too low of a voltage setting, then you won’t get enough heat to melt through all of your materials and create a strong weld joint.
4. Use Correct Current:
Another way to avoid undercut is by using the correct, current requirements. This means that if you have an arc length of 1 inch, then your current requirement should be around 40 amps or more.
If it’s less than 40 amps, then there is a chance that your weld may end up being undercut because there isn’t enough heat being generated by the arc, so it ends up cooling down too quickly before it melts through everything properly which causes an incomplete fusion between two pieces of metal together (this can result in poor quality).
5. Use the Right Electrode:
Always use a high-quality electrode that is well-suited for the material being welded.
Make sure you have the right size electrode for the joint you are welding. The size of the electrode should be no less than 1/8” (3mm) larger than the base metal thickness and no more than 1/4” (6mm) larger than the base metal thickness.
6. Edge Preparation:
Proper edge preparation is also important to help prevent undercuts from occurring. You should be sure not to leave any sharp edges on the metal where it’s being welded because these can cause internal stresses that will cause cracking during cooling from the heat of welding.
7. Proper Weld Angle:
The angle at which you make your weld will affect how well it holds up over time. If you have too much angle on your welds or if they are very shallow, then there will be an increased risk of cracking or breaking off during use.
I recommend that you make sure that your welds have an appropriate angle so that they can withstand any type of strain without breaking apart while still being able to withstand pressure from above as well as below!
8. Weld with Patience:
Welding is a slow process, especially when you’re trying to avoid undercut in welding. It’s important to take your time and make sure everything goes smoothly so that you don’t end up with any weak spots in your finished product!
Wrapping Up!
This article has been about undercut in welding. In this article, the basic meaning of undercut was first explained, and then some examples were given.
It is hoped that with this knowledge, readers will undoubtedly be able to understand what is an undercut in welding.
I have shared the undercut possible causes & remedies to overcome this issue during welding projects. Do not forget this article’s guidelines.
FAQs:
What is the difference between undercut and overlap?
In welding, the difference between undercut and overlap is that the cut edge of an undercut weld has been completely finished by grinding or filing. An overlap weld is one where the contour of the base metal is completed in a single pass.
Why is an undercut needed?
Undercut is a technique that can be used to create thicker weld deposits. Welders use this technique when the part being welded has a large amount of undercut or pinch, which causes the molten metal to flow away from the puddle and leave voids in the weld joint.
What is spatter in welding?
Spatter is the welding beads (or splatter) that fall off the face of the weld. The combination of heat, pressure, and arc force creates a spatter. Spatter can be thought of as tiny balls of molten metal that adhere to the surface or underside of a weld bead, planar joint, or seam.
What is the defect of the undercut?
Undercut refers to material that is not properly covered by the adjoining area or any surface which has been under-cut during welding.
