Undoubtedly, many professionals have faced one surface welding defect that can destroy the metal and cause all the welding they have done to be in vain. The defect is the undercut. This little but dangerous thing can appear in the metal due to several reasons.
You may not always understand why it happens in the welding process, but you definitely should know how to fix this and remove the undercut in welding.
If you want to know what is the undercut in welding, then you can find everything you need to know in this article.
Contents
- 1 The undercut in weld metal: what is it?
- 2 Welding undercut: ways to prevent it
- 2.1 The right voltage
- 2.2 The travel speed must be slowed down
- 2.3 Set the correct angle of the electrode
- 2.4 Weld on the flat platform with the correct welding position
- 2.5 No improper electrode angle
- 2.6 Correct gas composition
- 2.7 The filler wire must be just for the joint size
- 2.8 The gas lens helps you
- 2.9 The welding arc length must be correct
- 3 The welding undercut: fixing it
- 4 Frequently Asked Questions
- 5 In conclusion: it is better to prevent the undercut than fix it
The undercut in weld metal: what is it?
The welding undercut is a depression or groove in the metal that goes right along all the welded metal. The trough with the little thickness at the weld toe may be long and deep, and in the opposite, in lucky cases, short and at the surface. The undercut in the welding can be very visible and invisible.
The appearance of the undercut in welding means that the metal that is supposed to be part of the fillet welt is not melted completely. As professionals notice, it is most common to happen with stainless steel.
Welding stainless steel is a complicated process, and the undercut in the welding is very possible when you work with stainless steel.
Although, this is only one of the possible causes of the groove appearing in the fillet welt. There are also other welding parameters and situations.
The consequences of the welding undercut may be serious, for example, it may be the failure of the whole weld. Unfortunately, the worse thing is that it can become a beginning of the crack initiation if the surroundings and the conditions promote it. The American Welding Society can advise you on the question of harmless undercuts.
In other words, you definitely have to fix this imperfection before it starts leading to bigger problems. If you do not fix it, it can be dangerous to the metal and the whole construction, and you may have to do the work once again and remake it.
But before getting to ways to remove the welding undercut, we have to define the cause of the problem, and what may be the cause of future welding undercuts. And we also have to find out the types of undercut welds.
The welding undercut: types
There are several main types of undercut in welding: the external undercut, the root undercut (or the internal undercut), and the sidewall undercut. Let’s figure out what each of the types means.
The external undercut is the defect at the junction on a fillet weld of the weld metal.
The internal undercut, or the root undercut, is the defect on the underside of the weld bead.
The sidewall undercut is the defect that is inside the weld joint and by the sides of the weld joint.
The undercut welding in weld bead and other areas: the causes of appearing
As it said, the welding undercut can appear due to several causes that you have to remember to avoid this imperfection in the future. All of them can be the cause of a serious problem with the weld metal and base metal so you definitely have to be aware of them and of the ways to remove them.
The welding technique is bad
Surely, when you look at the welding undercut for the first time, you may think of improper welding straightaway.
And truly, it happens sometimes, especially when the welder is lacking skill.
When the welder is not good enough for the wearing technique or the multi-pass technique, then the welder cannot weld the way to provide the base metal, weld beads, and the weld metal with proper heat distribution, not uneven heat distribution.
When there is improper melting due to the improper fusion of the base metal and the weld material, there the undercut appears.
Working too fast is a sign of bad technique as well. When you are melting the metal, you have to work slowly and carefully, and you have to select the correct welding temperature. When the temperature is too high, it means that the metal is melting quickly, which can definitely get an undercut.
It means that there must be no excessive heat.
The size of the electrode is incorrect
Another cause of the undercut is the incorrect electrode size, which happens quite often. If the electrode that you got is too small, it means that there would be not enough molten metal, which may inevitably lead to an undercut in welding.
If it is the opposite, if the electrode is too big, there would be too much-molten metal, and that also leads you to an undercut.
So, choosing the correct electrode sounds like nothing, but it is important in welding like all other things.
The size of the filler rode is incorrect
The same story is with the size of the filler rod. You have to use the correct size of the filler rod so that there will be no undercut in the welding.
Contaminated and bad gas shielding
Gas shielding is a very important element of melting. Correct and pure from any chemicals and contaminations, it gives the molten metal and the weld puddle protection from any flux and too much oxygen.
If it is a contaminated shielding gas, there will be problems with the porosity of the metal, and the fluidity of the deeper weld pool.
And, therefore, you may get an undercut in welding which can spoil all the work. That is why it is important to take care of getting the proper gas shielding.
The voltage is high
If you apply high voltage in the welding, it leads to too fast melting metal, as well. What does it mean? It means that the metal cannot fill timely, and it means that there may be a groove between the wire electrode and the weld puddle in the wire welding. This is the welding undercut.
Welding undercut: ways to prevent it
Although the welding undercut is a defect that is sometimes hard to fix and repair, the better strategy is to try to prevent it from the beginning. The qualified specialists may face the problem as well as the beginners, but both groups of welders definitely have to know the ways to avert it and reduce the probability of getting the undercut to zero.
It is possible, and it is easy. Read the information below and consider it.
The right voltage
We start with the easiest things. The correct voltage prevents the metal from melding too fast and, therefore, prevents the undercut. It requires from you only to be attentive and careful. You have to set the correct voltage and set higher amperage before you start melting the metal, so that you don’t fault.
The travel speed must be slowed down
The correct travel speed is another way to get the perfect welding and no undercuts. When the travel speed is low, you have fewer possibilities to get wrong at some place which may easily lead to an undercut.
High travel speed may result in carelessness and mistakes in welding. The metal may melt too fast, and there may be an inevitable groove.
Set the correct angle of the electrode
The electrode angle is an important part of welding. The performance of the work also depends on it. So, you have to set the angle of the electrode that’s got to be from thirty to forty-five degrees right to the horizontal surface.
This is the optimal angle that was proven many times. You get to follow this strong recommendation to prevent the appearance of the welding undercut in the future.
Improper electrode angle is a problem to fix and prevent.
Weld on the flat platform with the correct welding position
The platform which you use for welding is better to select beforehand. And it is better to ensure that the surface of the platform is perfectly even and flat. It’ll provide you with work of the best weld quality without any defects. But if you select a platform that is not flat, that has defects itself, it gets to raise the chances of the welding undercut appearing.
That is why the place where you work is not less important than any other factor that influences the quality of the work.
No improper electrode angle
As you could get from the previous part of the article, the angle of the electrode may define the quality of the work, as well. You now know what the correct angle of the electrode is.
And now, you also need to remember and never forget that if you select another angle of the electrode that is not from thirty to forty-five degrees, you may not prevent the welding undercut. Be attentive and careful when you work with the metal. Otherwise, there may be a groove between the filler material and the molten metal.
Correct gas composition
Shielding gas is a good protection for the melting metal and the weld puddle that prevents oxygen and other gasses and chemicals from getting inside and spoils the purity of the weld metal.
Select the proper shielding gas and ensure that it brings no harm to the metal you are going to weld beforehand. You are also better to verify all the standard welding manuals. It may also help you in welding and preventing the undercut.
The filler wire must be just for the joint size
When the size of the filler wire fits the size of the joint, it ensures the work you are doing will be done perfectly. The filler wire has to be of the correct size because its job is to melt and prevent the metal from getting out at another metal piece.
If the filler size is incorrect, you may get a weld undercut in the welding and other welding defects. So, it is better to get a correct match of the filler wire and the joint beforehand.
The gas lens helps you
The gas lens can help you to get the perfect and smooth flow of melted metal with the proper high pressure. If you use the gas lens, then the metal gets to be protected from the undercuts on its surface.
The welding arc length must be correct
The arc length must be of proper measurement, otherwise you may get a defect on the mold metal. What you should set, is the arc length that matches their filler material and electrodes, and no more. The correct arc length may help you as well. Just do not apply excessive arc length.
The welding undercut: fixing it
There is a way to fix the defect on the metal, but it requires resources, time, and effort that you could have avoided. Read the instructions, but you are better to learn the ways of avoiding getting the undercut in the welding.
So, to fix the welding undercut, you got to start by finding this undercut weld on the metal surface.
When you have detected the defect, you can do several things that can help you.
You got to select which one suits you best and follow it.
The first way is to try to use the weaving technique or stringing. If the undercut is narrow, you get to choose the stringing method. If the undercut weld is wide, you get to select the weaving method.
The second way is welding the area where the undercut is again. By the way, this time, you have to add filler metal wire of a bigger amount under the weld area, to ensure that all possible gaps will be filled with the melting metal, and there is nothing like an undercut.
Try out these methods and you will see that it is possible and not that hard to fix such a problem in welding.
Frequently Asked Questions
What causes undercut in welds?
Several factors make the undercut appear. Firstly, it is the poor welding technique of the welder, which is working too fast with the welding bead and other components and with too high temperatures of the welding torch. Secondly, the size of the electrode is incorrect.
The size of the filler metal wire that does not match the size of the joint is also critical. Wrong voltage, weld bead, fast welding speed, and bad gas shielding can lead to the welding undercut as well.
What is meant by the term undercut in welding?
To put it simply, it is the groove or just a gap in the welding material between two connected parts of the metal, for example, the base metal and the weld metal.
How do I know if my weld is undercut?
You may see that there is a gap between two parts of the material that are not filled with the melted metal. It is critical and you fix it and prevent it from appearing in the future.
In conclusion: it is better to prevent the undercut than fix it
As you can understand now what is undercut in welding, you are aware that there are more ways to prevent the appearance of the undercut than the ways to fix it. The undercut is a defect that can lead to serious problems if you choose to overlook it and forget about it during the welding process.
All you have to do is to be careful, slow, and attentive while working with metal. This may save you time, effort, and resources in the future.
Learn More: Welding Undercut – Types & Tips To Prevent