Which of the following describes a process that does not require an external power source?

The process that describes not requiring an external power source is oxy-fuel welding. This method primarily relies on the combustion of oxygen and a fuel gas, such as acetylene, to produce a flame. The cutting or welding action occurs as a result of the heat generated by this flame, allowing the metal to reach its melting point for either welding or cutting purposes.

In oxy-fuel welding, the equipment is self-contained, and it does not depend on electricity or any external electrical sources to function. This capability makes it especially useful in various locations and conditions, including outdoor settings where electric power may not be readily available.

The other processes mentioned typically involve external energy sources. For example, arc welding relies on an electric arc produced between an electrode and the workpiece, manual welding processes might still incorporate external power sources depending on the specific technique used, and electric welding is inherently dependent on an electrical supply to create heat for melting metal. Hence, oxy-fuel welding stands out as the only process in this context that operates independently of external electric power.