Undercut 101: What It Is, Why It Happens, and How to Fix It

As a welder, achieving high-quality welds is essential for ensuring the integrity and reliability of your work. However, one common welding defect that can compromise weld strength and appearance is undercut. In this article, we will explore the concept of undercut in welding, its causes, and effective strategies for prevention.

What is Undercut?

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.

Causes of Undercut:

Understanding the factors that contribute to undercut is crucial for avoiding this welding defect. Some common causes include:

• Excessive Current: When the welding current is too high, the arc melts an excessive amount of the base metal at the edges of the joint, leading to insufficient filler metal deposition.
• Insufficient Filler Metal: Inadequate filler metal can result from using a small electrode size, improper electrode extension, or steep electrode angles. Insufficient filler metal deposition along the edges of the weld bead can contribute to undercut.
• Incorrect Filler Metal Selection: Selecting a filler metal with different melting points or thermal conductivity than the base metal can create temperature gradients within the weld bead, causing mismatch and potential undercut.
• Poor Technique: Inconsistent arc movement, improper weaving, excessive arc length, or slow travel speed can impact the distribution and penetration of the filler metal, increasing the likelihood of undercut.

Preventing Undercut:

To avoid undercut and ensure high-quality welds, follow these best practices:

• Optimize Welding Parameters: Adjust the welding current according to the electrode size, base metal thickness, and joint configuration. Utilize welding charts or calculators to determine the optimal current for your specific welding process.
• Select the Right Filler Metal: Choose a filler metal that matches or is compatible with the base metal in terms of chemical composition, mechanical properties, and thermal characteristics. Additionally, ensure the electrode size is appropriate for the joint design and welding position.
• Control Your Technique: Maintain a consistent arc length, travel speed, and electrode angle throughout the welding process. Adopt proper weaving patterns and avoid excessive weaving width. Strive for a smooth and uniform weld bead that covers both edges of the joint.
• Thorough Inspection: Regularly inspect your welds for signs of undercut and other defects. Employ visual inspection, gauges, or non-destructive testing methods as required. Additionally, remove any slag, spatter, or oxide layers that may conceal undercut.

Solutions for Undercut:

If undercut occurs, consider the following solutions:

• Filling Grooves: Repair grooves formed due to undercut by adding filler metal to the affected areas. Ensure the additional fill matches the welded area as closely as possible.
• Cleaning: Remove any slag, debris, or other particles that may affect the quality of the repair. Use a chisel or appropriate cleaning tools to thoroughly clean the repaired area.

Undercut is a welding defect that can compromise weld integrity and lead to adverse consequences. By understanding the causes of undercut and implementing preventive measures such as optimizing welding parameters, choosing suitable filler metals, controlling welding techniques, and conducting thorough inspections, welders can effectively minimize or eliminate this defect. Prioritizing quality in welding practices will result in reliable and durable welds, ensuring the success of your projects.

At YENA Engineering, we are committed to providing high-quality products and excellent customer support. Contact our qualified and experienced staff to access our wide range of welded products.