What best describes how a welded joint is formed?

• A. Fusion by mechanical fastening.
• B. Cold welding without heat.
• C. Melted filler metal only.
• D. Fusion of the workpieces by heating to above their melting point, often with filler metal.

Answer: (D)

Welding forms a joint by melting the base metals at the joint and letting them fuse as they cool. The heat source raises the workpieces above their melting temperature, and filler metal may be added to fill gaps or modify properties, but isn’t required in all welds. This metallurgical bonding is what sets welding apart from methods that join with mechanical fasteners or with heat that only melts filler metal. When only the filler metal melts, that describes brazing or soldering, not welding. So the best description is the fusion of the workpieces by heating to above their melting point, often with filler metal.