Undercutting has always been a serious concern in welding, especially in the steel welding industry.
In recent times, series of efforts have been made to curtail this problem. Undercutting in welding is a weld defect usually characterized by a groove formation at the weld toe, this occurs when the free edges of the weld metal or base metal are overheated.
The major cause of undercuts in welding is when the operator (welder) uses a high welding current or welds with fast travel speed. At the same time, the use of incorrect shielding gas, incorrect welding angle, wrong welding technique, and position are some of the primary causes of this welding flaw.
In this article, we shall be discussing the 7 possible ways to prevent the undercutting welding problem.
What is Undercutting in Welding
Undercutting is a crater or groove that occurs near the toe of the weld. Undercutting in welding occurs when the weld metal failed to fill-in the grooved area.
The result of which is a weak weld that is prone to cracking along the toes. In that case, the edge of the weld assumes a U-shape. Undercutting in welding may occur as a result of high travel speed, poor welding techniques, excessive heat, and too high amperage.
Causes of Undercutting in Welding
Undercutting appears as a groove in the weld metal along the edges of the weld. This kind of welding defect is mostly common in lap fillet welds, and can also be encountered in butt and fillet joints.
It’s mostly caused by using improper welding parameters; usually the arc voltage and travel speed.
Excessive heating as well as using the wrong welding technique may both lead to undercutting on a weld joint. Below are some of the major causes of undercut welding:
1. High travel speed
When the travel speed is very high, the weld bead will appear very peaked. This is because of its extreme fast degree solidification.
What happens here is that the forces of surface tension draws the molten metal directly along the edges of the weld bead and pilled it up at the center. this same way, the metal portions of the base material are also affected.
The Undercut groove is formed where the melted base material is drawn into the weld and not allowed to wet-back properly because of its rapid solidification. But decreasing the arc travel-speed gradually reduces the size of the undercut and slowly eliminates it.
Where only small undercut is present, raising the voltage or using a leading torch angle can eliminate the undercuts, making the weld bead flatter and improving the wetting as well.
2. Too High arc Voltage
While raising the arc voltage could help eliminate undercut, raising it to excessive levels may cause the undercut to reappear again.
This occasionally occurs in spray arc welding. By the time the arc becomes very long, it as well becomes very wide, leading to an increase in the amount of the base metal being melted. In such a case, the heat transfer of a long arc to the weld zone is comparably poor.
This cause the outermost areas to quickly cool down, preventing proper wetting. Note: The Arc length should always be kept short, not only to prevent undercutting but also to increase the penetration depth and weld strength.
3. Too high welding current
Too high welding current can lead to the formation of undercut on a weld. This is because the arc force, heat, and penetration will be so intense that the base plate under the arc could be blown away.
When this occurs, the outermost area of the base metal is melted and solidifies fastly. In such a case, puddle turbulence and surface tension avoid the puddle from wetting properly.
Therefore, to prevent this from happening, it is always required for the welder to remain within the current ranges specified for each wire size.
How to Prevent Undercutting in Welding
Undercutting in welding has always been a serious problem, especially in the steel welding industries.
A number of efforts have been made recently to resolve this welding problem. Some of which include reducing the welding current, voltage, and reducing the travel speed to the appropriate rate that allows the molten metal to fill in the joint completely.
Also, using a weaving technique; where the welder pauses slenderly at each side of the weld bead helps to prevent this type of a weld defect.
Below are the 7 important measures for preventing the problem of undercutting in welding.
1. Appropriate heat input
Extremely high heat settings is one of the leading causes of undercut grooves in welding. The major disadvantage of high heat settings is that it could lead to the overheating and melting of previous weld metal. To avoid this from happening, the welder must carefully reduce the weld heat by regulating the current whenever he’s approaching thinner and free edges.
2. Correct Electrode Angle
It’s generally known that welding angles play a crucial role in producing flaws-free welds. If the welder uses an incorrect angle which transfers more heat to the free edges more than the required, the weld is likely to be prone to undercut. Therefore, one is advised to use the correct angles in order to transfer the appropriate heat to the free edges.
3. Correct selection of Gas shielding
In the case of MAG process, the wrong choice of gas shielding can also lead to undercutting. Therefore, the welder must ensure the correct gas composition according to the requirement of the metal type and thickness. The use of inert gas (especially argon) in conjunction with Carbon dioxide (CO2) usually delivers quality results in carbon steel welding.
4. Moderate Travel speed
Welding with high travel speed is also one of the major causes of weld undercutting. What happens while welding with high travel speed is that some portion of the parent material is drawn into the molten metal and never came back because of its extremely fast solidification rate, leaving a depression along the edges. In order to avoid this, one is advised to weld with an average travel speed, neither too fast nor too slow. This is because too high travel speed causes undercutting, whereas slow travel speed does not always give a satisfactory result.
5. Suitable welding position
Sometimes weld undercuts may arise when the welder makes a fillet weld in a horizontal-vertical position. The Undercut is formed as a result of inadequate metal filling along the edges of the joint being welded. In order to prevent this from happening, it’s recommended to weld in a flat position.
6. Appropriate welding technique
Also, the problem of undercuts can arise when the welder makes a weld run with excessive weaving style. It’s recommended to maintain the width of weaving according to the size of the electrode. I.e. The size of the weaving should not exceed the acceptable limit, if not, the weld may be liable to undercut grooves. To prevent this, the welder must ensure that the size of weaving is maintained within its acceptable limits.
7. The use of multi-run technique
One of the best methods to adopt in order to minimize the level of undercuts in welding is to employ the multi-run technique. This technique supports all of the above-mentioned preventions and can also help achieve satisfactory results with improved mechanical properties.