What process is used for automatic welding without filler metal additions?

The process referred to for automatic welding without the addition of filler metal is flash butt welding. This welding method is characterized by its ability to join two pieces of metal together by melting the surfaces at the point of contact, without requiring additional filler material. The process involves generating heat through electrical resistance, typically by clamping the metal pieces together and passing a high current through them. As the temperature rises, the materials near the joint are heated to a molten state, and once sufficient heat is achieved, the two pieces are pressed together, resulting in a welded joint.

Flash butt welding is commonly used in applications such as steel rail and pipeline fabrication, where a strong, heat-affected joint is essential. The automatic aspect of the process adds efficiency and consistency, making it suitable for mass production environments.

The other welding methods mentioned, such as the GTAW (Gas Tungsten Arc Welding) and the oxy-fuel welding, do involve filler material and are not classified as processes that permanently join metals without additives. Therefore, flash butt welding is distinctly recognized for its unique capability to function without filler metal in an automated capacity, which solidifies why it is the correct choice.