Residual Strain in Surface Textures Generated by Ultrasonic Vibration Cutting in Thrust Direction

This study clarifies the relationship between cutting conditions and residual strain in ultrasonic vibration cutting (UVC) performed in the thrust direction. Focus is placed on the working relief angle θw -defined as the difference between the tool relief angle and the tangent of the tool motion trajectory- as a key indicator of geometric interference between the tool relief face and the machined surface. Experimental results revealed that subsurface hardness increased with increasing θw. When the difference in θw was approximately 1°, similar hardness values were obtained regardless of cutting speed. Under interference-free conditions, the hardness remained comparable to that produced by ordinary cutting. Finite element analysis further showed that the plastically strained region enlarged with increasing θw, consistent with the observed hardness distribution. Moreover, stress fluctuation analysis during the ultrasonic cycle showed that geometric interference induced localized surface compression by the tool relief face, thereby generating compressive stresses. Tool-wear measurements indicated that wear width under low-interference conditions was similar to that in ordinary cutting, while under high-interference conditions it increased 1.4 times; however, both levels remained within practical limits. These results show that controlling interference and θw enables selective regulation of the occurrence and magnitude of residual stresses.