Define "incomplete fusion".

Incomplete fusion is defined as a defect characterized by the failure of the weld metal to properly fuse with the base metal. This condition typically arises when the welding process does not generate enough heat or when the parent materials are not adequately prepared or positioned to allow for proper bonding. When incomplete fusion occurs, there are areas in the weld where the weld metal does not adhere to the base metal, leading to weak points that can compromise the integrity and strength of the weld joint.

Understanding this concept is crucial for welders and fabricators, as it emphasizes the importance of proper welding techniques, material preparation, and heat application to ensure strong, reliable welds. Incomplete fusion can lead to significant structural failures in welded components, making it essential to recognize and address this defect during the welding process.