Geometrical texture and surface integrity in helical milling and ultrasonic vibration helical milling of Ti-6Al-4V alloy

Abstract

Abstract Surface integrity of hole-making for Ti-6Al-4 V alloy is very important due to its application in aviation industry. Geometrical and mechanical behaviors of machined holes by helical milling (HM) and ultrasonic vibration helical milling (UVHM) were investigated. The textures of machined holes by the two processes were analyzed and the distances of adjacent textures were calculated according to the movement of peripheral edges. Due to the different surface geometrical textures, the hole-diameter error and surface roughness in UVHM are smaller than those of HM. A plastic deformation layer with thickness of 4–6 μm was observed by the distorted β phase in the cross-section of hole-surface in UVHM by SEM results. Compared with HM process, UVHM generates larger hardness at the subsurface of machined holes (20–200 μm) due to the material deformation caused by ultrasonic vibration. Compared with HM, the compressive residual stress of hole surface was increased larger than 63.5% by UVHM. The compressive stresses in UVHM are larger than 150 MPa at the depth less than 10 μm, which is consistent with the microstructure evolution caused by mechanical deformation.