What is Undercut in Welding?- Causes, Effects, and Prevention

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.

Welding Undercut

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

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:

  1. Excessive welding current.
  2. Arc voltage is too high.
  3. Excessive travel speed which does not allow enough filler metal to be added.
  4. Erratic feeding of the electrode wire.
  5. Excessive weaving speed.
  6. Incorrect electrode angles, especially on vertical and horizontal welds.

Preventing Undercut:

Undercut can be prevented by:

  1. Use proper welding current for electrode size and welding position.
  2. Reducing the welding voltage.
  3. Use a proper electrode angle.
  4. Using a travel speed slow enough so that the weld metal can completely fill all of the melted-out areas of the base metal.
  5. Select the right filler metal.
  6. 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.

Final Thoughts

Undercutting in welding is a severe defect that results in a loss of productivity and quality. It also significantly compromises the weld’s safety. Nevertheless, it is a common problem among welding professionals. Without regular practice, the weld quality could considerably be reduced.

By now, you already know that it can be managed to minimal levels by simply observing the best practices of welding. If you follow the above remedies, an undercut will be the least of your worries as you weld. Treat each project as a learning experience, identify new cost-effective, and efficient welding techniques with reduced or no chances of an undercut and soon enough you will become a better welder!