Abstract: In a method for monitoring laser beam welding, a sequential signal representing a laser oscillating wave form is received, light of a predetermined wavelength in the light emitted from the weld zone is received, and the two signals thus received are processed to determine the minimum intensity of the light of the predetermined wavelength and thereby accurately deduce welding beam input and penetration of welding. An apparatus used in practicing the monitoring method includes a monitoring optical fiber for receiving and transmitting the light emitted from a weld being made on a workpiece, an interference filter for selectively passing light of a predetermined wavelength, and a processing device for determining an intensity of the light of the predetermined wavelength.

Abstract: A narrow gap arc welding process comprises steps of defining a narrow gap between a pair of members to be welded arranged so as to face each other at a predetermined distance, feeding a consumable electrode into a guide cylinder which is movable along the narrow gap, and generating electric arc between the tip of the consumable electrode and the members to be welded to unite them with each other, wherein the consumable electrode, while being deformed plastically to have a wave-like pattern with a pitch of about 10 to 30 mm and a molding width of about 2 to 5 mm depending on welding conditions, is fed into the narrow gap with the direction of the molding width being in line with the direction of the width of the narrow gap and the direction of the tip of the consumable electrode being changed so as to point out one after the other facing edge of the members to be welded alternately at a high frequency. Also, an apparatus for practicing the process is described.