Welding is widely used for construction of many structures. Since welding is the processing method applying heat, residual stress is generated near a welding part. Residual stress has a bad influence on strength of material. A practical method of reducing welding residual stress for a short time, adding vibration was proposed. In the previous method one vibration was used. In this paper, while welding, two ultrasonic vibrations with different frequencies are added. Residual stress is reduced when two ultrasonic vibrations are added.
