A system and method for directing an incoming telephone call. Engaging portions for holding a right terminal fitting and a left terminal fitting assembled are provided on both upper and lower surfaces of terminal main bodies. In the modification step, the graphene film is placed in a vacuum environment and radiated by an electron beam to obtain a graphene material. A welding installation for carrying out the welding method achieves optimal welding results using the smallest possible number of settings by setting a displacement frequency of the welding rod as a welding parameter using a control organ.