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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]

As a superior hole manufacturing process, rotary ultrasonic elliptical machining (RUEM) has been successfully employed for drilling carbon fiber reinforced plastics (CFRPs) recently. The delamination of CFRP during drilling is generally considered as the most undesirable form of damage and the most challenging failure mode. In order to reduce the delamination in this novel process, it is important to understand the formation and suppression mechanisms during RUEM of CFRP. In this study, the delamination formation in both core drilling (CD) and RUEM was observed and analyzed. The variation trend of delamination factor with feed speed as well as cutting speed was obtained. The experimental results show that, compared with CD, RUEM method can effectively reduce hole exit delamination by 5.4%–19.3% between 1/2 plies and 0.7%–8.4% between 2/3 plies at the feed rates from 50 to 100 μm/rev. Moreover, the delamination suppression mechanism in RUEM was fully analyzed and verified. In a word, in the industry practice, RUEM can be considered as a competitive and promising technique to drill CFRP compared to other delamination suppression techniques. [ABSTRACT FROM AUTHOR]

Small-diameter CFRP holes have a number of applications such as aerospace structures, circuit boards and rehabilitation medical equipments. High quality hole-making technology for the small-diameter CFRP holes is urgently needed due to various mechanical damages in twist drilling and chip removal clog in core drilling. In order to improve the hole quality, rotary ultrasonic helical machining (RUHM) was developed for machining small-diameter CFRP holes in this paper. The trajectory of cutting edge in RUHM was modelled and the intermittent cutting mode in RUHM was analyzed. Afterwards, the comparison experiments were conducted between RUHM and conventional grinding (CG). The results shows that compared to CG, both thrust force and transverse force were remarkably reduced in RUHM with a maximum decrement of 71.3% and 61.5%, respectively. Meanwhile, both the hole edge quality and surface integrity were significantly improved in RUHM. Compared to CG, delamination factor at hole exit was reduced by 12.8–25.7% and surface roughness for hole inner surface was reduced by 51.9%–53.2% for Ra value in RUHM. Moreover, the mechanisms of cutting force reduction, delamination formation and suppression, and surface roughness improvement in RUHM were also analyzed. The results suggest that RUHM is a promising processing strategy for machining small-diameter CFRP holes. [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]