2017 Volume 58 Issue 672 Pages 47-52
Welding is widely used for constructing many structures. Residual stress is generated near the bead. Tensile residual stress degrades the strength of a structure. The authors have proposed a method of reducing residual stress using vibration during welding and applied it during the welding of thin plates. Residual stress is reduced more when a larger amplitude of the vibration is used. In this paper, repair welding of the mold is considered, and the surface of a thick plate is welded. Two ultrasonic vibrations are used to realize large amplitude and the reduction of residual stress is examined. Residual stress is reduced more than when using one ultrasonic vibration. Next, experimental results are examined by a simulation method. An analytical model that takes plastic deformation into consideration is proposed because the yield stress immediately after welding is very low. It is demonstrated that residual stress is reduced more when two ultrasonic vibrations are used. Finally, the advantage of the method using two ultrasonic vibrations is examined statistically. The reduction probability of residual stress is obtained. The reduction probability of the method using two ultrasonic vibrations is very high. By the t-test, it is demonstrated that the method using two ultrasonic vibrations is more effective than that using one ultrasonic vibration for the reduction of residual stress.