Burn-through is one of the most frustrating welding defects, especially when working with thin materials. It can weaken joints, waste material, and slow down production. Understanding why burn-through happens and how to prevent and repair it is essential for producing strong, reliable welds—particularly in precision or structural applications.
What Is Burn-Through in Welding?
Burn-through in welding occurs when excessive heat melts completely through the base metal, creating a hole or cavity in the weld joint. This defect is most common when welding thin materials, but it can also occur in thicker metals if heat input is not properly controlled.
Burn-through compromises the structural integrity of the weld and is typically unacceptable under most welding codes and quality standards. It may appear as visible holes, sagging molten metal, or excessive penetration beyond the weld root.
Common Reasons Burn-Through Occurs
Several factors contribute to burn-through during welding:
- Excessive heat input
Using amperage or voltage settings that are too high causes the base metal to melt faster than the filler metal can compensate. - Slow travel speed
Dwelling too long in one area allows heat to accumulate, increasing the likelihood of melting through the material. - Thin base material
Thin metals have limited heat capacity and are more prone to burn-through, especially without proper backing support. - Improper joint preparation
Large root gaps, poor fit-up, or sharp edges can concentrate heat and make the joint vulnerable to burn-through. - Lack of backing or support
Without a backing bar or backing material, molten metal may have nothing to support it, leading to collapse at the weld root.
How to Control Heat and Prevent Burn-Through?
Preventing burn-through requires controlling heat input and adjusting technique to match material conditions.
- Lower welding parameters
Reduce amperage, voltage, or wire feed speed while maintaining stable arc characteristics. - Increase travel speed
Move steadily and avoid pausing in one spot, especially on thin metal sections. - Use pulsed or intermittent welding
Pulsed current or stitch welding helps manage heat input by allowing brief cooling periods between weld segments. - Employ backing materials
Copper backing bars or chill blocks absorb excess heat and provide support for the molten weld pool. - Select proper filler and process
Smaller-diameter filler wires and processes such as TIG welding allow better heat control on thin materials.
Repair Methods and Practical Tips
When burn-through occurs, proper repair is crucial to restore joint integrity.
- Clean and prepare the area
Remove slag, oxidation, and damaged material around the hole before attempting repairs. - Build up the area gradually
Use low heat and short welds to bridge the opening, allowing the weld pool to cool between passes. - Use backing for repairs
Placing a copper plate behind the hole helps support molten metal and prevents further burn-through. - Adjust technique after repair
Evaluate welding parameters and technique to prevent recurring burn-through during subsequent welds. - Practice on scrap material
Before continuing production welding, test adjusted settings on scrap metal of the same thickness.
Conclusion
Burn-through in welding is a common defect that often results from excessive heat and poor control, particularly when working with thin materials. By understanding its causes, managing heat input, and applying effective prevention and repair techniques, welders can significantly reduce burn-through and produce cleaner, stronger welds. Careful setup, consistent technique, and proper inspection are the keys to achieving high-quality weld results.
