Welding is an important process in manufacturing, construction, and various industries, it gives a strong and durable joint between metal parts. Just like any other fabrication process, welding also faces some challenges, and one of them is undercut. This article covers welding undercut and its causes, solutions, and removal techniques.
What Is Undercut?
In welding, undercut refers to the groove or depression that forms along the edge of the weld bead, where the base metal has melted but has not been adequately filled by the filler metal. This results in a weakened joint that is prone to cracking, corrosion, or failure, particularly under cyclic loading conditions.
Undercut is the result of the arc force removing metal from a joint face which is not replaced by weld metal. Undercut occurs along the toe of the weld bead. It can result from excessive
current.
It is a common problem with GMA welding when insufficient oxygen is used to stabilize the arc. Incorrect welding techniques, such as incorrect electrode angle or excessive weave, can also cause undercut.
To prevent undercutting, you can weld in the flat position by using multiple instead of single passes, changing the shield gas, and improving manipulative techniques to fill the removed base metal along the toe of the weld bead.
Causes of Undercut:
Undercut is caused by one or more of the following:
- Excessive welding current.
- Arc voltage is too high.
- Excessive travel speed which does not allow enough filler metal to be added.
- Erratic feeding of the electrode wire.
- Excessive weaving speed.
- Incorrect electrode angles, especially on vertical and horizontal welds.
Preventing Undercut:
Undercut can be prevented by:
- Use proper welding current for electrode size and welding position.
- Reducing the welding voltage.
- Use a proper electrode angle.
- Using a travel speed slow enough so that the weld metal can completely fill all of the melted-out areas of the base metal.
- Select the right filler metal.
- Cleaning the nozzle, inside of the contact tube, or removing the jammed electrode wire.
Undercut of the sidewalls of a welding groove will in no way affect the completed weld if it is removed before the next bead is deposited in that location. A well-rounded chipping tool or grinding wheel will be required to remove the undercut.
If the undercut is slight, however, it is possible for the welder to estimate how deeply the weld will penetrate and fill the undercut with the next pass.
Undercut is sometimes repaired by grinding and blending or welding. Grinding should be performed with a pencil-type grinder. and the grinding marks should be transverse to the length of the weld with a 250 micro-inch finish or better.
FAQs
What is a cause for undercut that occurs during the welding process?
Incorrect Angle of the Electrode: Holding the electrode at an incorrect angle can cause the arc to focus too much heat on one side of the weld, melting the base metal without depositing enough filler material.
What is the difference between undercut and underfill?
Undercut and underfill are two distinct issues: An undercut is a common welding defect that refers to the groove or depression along the edge of the weld, which can weaken the weld and lead to cracks. Underfill occurs when there’s insufficient weld material, causing incomplete fusion and reduced strength.
How to prevent underfill in welding?
1. Reducing your arc length and current.
2. Reducing the welding speed.
3. Ensuring you have the correct electrode angle and size.
4. Using an optimal weaving technique, allowing enough dwell time at edges.
How much undercut is allowed?
The maximum depth of undercut shall be no greater than 10% of the material thickness which has the undercut, the length of the undercut shall not exceed 10% of weld length provided the weld seam meets minimum size. b. Maximum width of an undercut shall not exceed twice the depth.
Why am I getting undercut on my welds?
Undercut is most commonly caused by improper welding technique and not adhering to welding parameters. Undercut is almost inevitable when a welder is welding too hot, too fast, and with an incorrectly sized electrode.
How to stop undercut welding?
1. The appropriate voltage value must be selected.
2. The height of the arc is high. The arc distance can be reduced.
3. Incorrect torch or electrode angle.
4. Consumables with lower diameters should be selected.
5. The welding speed may be too low.