Abstract: In a laser welding method of varying a waveform and a frequency of a laser output in a controlled manner so as to prevent occurrence of weld defects, a time change in light emission strength of a plasma or plume generated from a laser welded portion is detected, a laser output variation condition is set so that the time change in the light emission strength is in response to the variation in the laser output during laser welding. In a laser welding method of varying the waveform and frequency of a laser output suitably so as to prevent the occurrence of the weld defects, a new laser welding method can optimize a laser output variation condition more simply and securely.

Abstract: In a laser welding method, the invasion of atmosphere gas into a molten metal and the occurrence of welding defects are prevented by coating a material having a high affinity for the atmosphere gas on the back surface of a work and therefore it is possible for a large output laser to easily weld a thick plate by employing a simple method.

Abstract: In a laser welding method, occurrence of weld defects is effectively prevented, and a high-quality weld joint is provided, and in addition, a wide range of material processes including a laser-using de p-penetration welding technique can be implemented. In keyhole welding using a laser performing output pulse modulation, the welding is conducted in accordance with a frequency conforming to a natural frequency of a metal molten pool.

Abstract: In a laser welding method, occurrence of weld defects is effectively prevented, and a high-quality weld joint is provided; and in addition, a wide range of material processes including a laser-using de p-penetration welding technique can be implemented.

Abstract: The present invention is to provide a novel laser welding method, capable of preventing formation of a welding defect, and achieving a deep penetration by a low heat input so as to enable formation of a welding structure with a high strength and a high toughness even in the case of welding by a high power laser. A welding operation is executed with a periodical fluctuation adjustment so as to have a base output of 50% or more with respect to a peak output.