Welding definitionThe act of joining two pieces of metal together through fusion. An oxyacetylene torch or oxacetylene welding applies high heat to the metal to fuse them together (in arc welding an electrical method is used). Often along the joint a filler rod is melted (called brazing). Fusion welding is the term used when a person directly welds two pieces of metal by joining the molten edges. Joints last longer and are stronger done this way, because it is done under higher temperatures than soldering.