AWS Certified Welding Inspector — FundamentalsWelding ProcessesMedium
A welding inspector is performing a visual inspection of a Friction Stir Weld (FSW) on a 6 mm thick aluminum plate. The inspector observes a continuous, shallow groove or indentation along the weld centerline, often accompanied by some surface tearing. This defect is commonly known as a:
- ATunnel defect
- BFlash defect
- CWormhole
- DKissing bond
Show answer & explanationAnswer & explanation
Correct answer: A. Tunnel defect
A tunnel defect (or 'wormhole') in FSW is a subsurface defect that often manifests as a continuous, shallow groove on the surface, sometimes with tearing. It's caused by insufficient material flow during the welding process, leading to a void or channel within the weld nugget, often due to incorrect tool pin profile, rotational speed, or travel speed.
Why the other options are wrong
- B. Flash defect refers to excessive material extrusion from the weld sides, not a groove or indentation along the centerline.
- C. Wormhole is another term for a tunnel defect, which is the correct answer. The question describes this defect.
- D. A kissing bond is a lack of fusion at the root, not typically a surface groove or indentation.
FSW Tunnel Defect
A tunnel defect (or wormhole) in Friction Stir Welding is an internal void or channel, often appearing as a continuous surface groove, caused by insufficient material flow around the stirring pin.
- Caused by inadequate material flow or consolidation.
- Often linked to incorrect tool geometry, rotational speed, or travel speed.
- Reduces weld strength and fatigue life.
- Can be detected by radiography or ultrasonic testing.
- Surface manifestation: groove, indentation, or tearing along centerline.
Memory trick: Stirring too slow, a tunnel will show.