Final answer:
A tie-in is where the welder starts to add to an existing weld bead. Welding uses various fuel sources like gas, electricity, and laser and has been used for centuries in fabrication work.
Step-by-step explanation:
A tie-in is where the welder begins to add to an already existing weld bead. During the welding process, this is an essential step to ensure that new welding material successfully bonds with the previously welded area, creating a strong, continuous joint. Welding has been an important technique for combining metal materials, which has evolved to use various fuel sources such as gas, electricity, and laser.
Forge welding is one of the oldest welding methods, and it has been used by blacksmiths for joining iron and steel for thousands of years. While the specific term used in the question refers to a term commonly used among welders, understanding its significance is important for maintaining the integrity of the welded structure.