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[Display omitted] • A strengthening-machining integrated ultrasonic peening drilling (UPD) was proposed. • The strengthening mechanism for UPD for Ti-6Al-4V was revealed. • The depth of subsurface plastic deformation is increased by 4 times by UPD. • The residual stress and the micro-hardness were greatly increased by UPD. • Smoother machined surface and narrower dimensional tolerance were obtained by UPD. In aircraft assembly filed, introducing compressive residual stress by cold expansion around the fastening hole is considered as a common method to enhance hole fatigue resistance. However, the conventional cold expansion technology inevitably extends the processing cycle of fastening hole. Therefore, this study proposes a strengthening and machining integrated ultrasonic peening drilling (UPD) to solve this problem by introducing ultrasonic vibration perpendicular to the hole surface during drilling. Both the strengthening principle and dimension accuracy improvement mechanism in UPD were analyzed to better understand the cutting mechanism. The feasibility experiments of UPD of Ti-6Al-4V were conducted to evaluate surface integrity and machining accuracy. The results show that compared to conventional drilling (CD), smoother machined surface and narrower dimensional tolerance were obtained with UPD. Moreover, the subsurface plastic deformation was increased by as high as 4 times with severer deformation degree. Accordingly, the surface residual stress and the depth of circumferential residual stress in the subsurface was increased by 115.7% and 125% respectively. In addition, surface micro-hardness and subsurface hardening layer depth were also significantly increased. The results demonstrated that UPD achieved the integration of strengthening and precision-machining and could be a promising method for finish drilling of aircraft fastening holes. [ABSTRACT FROM AUTHOR]

Ultrasonic assisted milling (UAM) has been demonstrated excellent cutting performance for nickel-based superalloy machining. However, the machining quality improvement achieved by traditional UAM is limited at high cutting speed. Rotary ultrasonic elliptical milling (RUEM) is an unconventional cutting method recently proposed for high quality and efficient machining of difficult-to-cut alloy, breaking the cutting speed limit for UAM. In order to verify the feasibility of this method in thin-walled curved surface machining, the ball end milling cutter was adopted in feasibility experiments of RUEM on Inconel 718 with the evaluation of cutting force, surface integrity and tool wear. The results indicate that compared with conventional milling (CM) without ultrasonic vibration assistance, the cutting force reduction reaches 31.33% in RUEM. The material strength enhancement was obtained in RUEM with the disturbed strengthening phases of Inconel 718. RUEM achieved − 728.65 MPa of surface compressive residual stress and 140 µm depth of compressive residual stress layer beneath the machined surface simultaneously, while CM provided tensile residual stress field near the machined surface. Moreover, the tool flank wear status was significantly improved in RUEM. These results demonstrate that various machinability benefits of Inconel 718 are obtained by RUEM, which is a promising method for nickel-based superalloy thin-walled structure finish machining. [ABSTRACT FROM AUTHOR]

Titanium alloys have been applied in aerospace, biomedical, and chemical industries due to their superior mechanical properties. As a novel machining method, rotary ultrasonic elliptical machining has been successfully introduced into high-speed side milling of Ti–6Al–4V recently. However, the surface integrity in end milling of titanium alloy using this method is still unclear. In this study, a comprehensive experiment on surface integrity in rotary ultrasonic elliptical end milling of Ti–6Al–4V was conducted at various vibration amplitudes and cutting speeds. Results show that regular substantial micro-vibration textures in the form of separated ridges are obtained on the machined surfaces in RUEEM. Surface roughness values rise from Ra 0.160 μm to Ra 0.758 μm with the increasing cutting speed and vibration amplitude. Both the thickness of subsurface deformed layer and the value of surface micro-hardness increase with rising amplitude at low cutting speeds, while the hardening effect gradually weakens as the cutting speed increases to 160 m/min. Besides, the values of surface compressive residual stress gradually decrease with vibration amplitudes at low cutting speeds, while opposite trends show at the high cutting speed (160 m/min). This study can provide a new method for the effective control of the surface integrity for high-speed end milling of titanium alloy. Image 1 • Rotary ultrasonic elliptical machining is introduced to high-speed end milling of Ti6Al4V for the first time. • The effect of vibration on surface integrity in rotary ultrasonic elliptical end milling (RUEEM) of Ti6Al4V is studied. • The effect of cutting speed from 40 m/min to 160 m/min on surface integrity in RUEEM is experimental investigated. [ABSTRACT FROM AUTHOR]