The carrying energy of a harmonic scalpel determines biological tissue coagulation quality, and is related to the clamping force between the blade of a harmonic scalpel and the biological tissue. The objective of this study is to investigate the effect of clamping force on the carrying energy ability of a harmonic scalpel. First, the carrying energy model of a harmonic scalpel transducer is developed, which is regarded as a mass-spring-damper oscillator. Then, the characteristic parameters at various clamping forces are determined by a least-square parameter identification method, which represent the carrying energy ability of harmonic scalpel. Furthermore, the carrying energy ability relative to clamping force is evaluated by coagulating biological tissue in vitro. The results show that mass, force resistance and stiffness of mass-spring-damper oscillator increase with increasing clamping force, which reflects the increase of the harmonic scalpel carrying energy ability. This trends plateaus with the continuous increase of clamping force. Correspondingly, the coagulation depth of biological tissue increases with the increase of clamping force, and an optimal clamping force exists. The results of the histological investigations are in good agreement with carrying energy under different clamping force conditions.
Ultrasonic vibration has received widespread attention for its dramatic effect on grain refinement and microstructure modification during casting, additive manufacturing, cold rolling, and cutting, changes which can significantly improve the mechanical and physical properties of components. As a novel ultrasonic vibration cutting method, rotary ultrasonic elliptical milling (RUEM) has been introduced to mill the alloy Ti-6Al-4V. However, the effects of ultrasonic elliptical vibration on the microstructures of machined surfaces in end milling of Ti-6Al-4V are still unclear. A comprehensive study on the surface characteristics and sub-surface microstructure in RUEM of Ti-6Al-4V was conducted. The results show that the uniform textures, in the form of ridges mapped on the machined surface in RUEM, varied with the cutting speed. Compared with conventional milling, microchip debris adhesion on the machined surface was significantly reduced by using RUEM. Moreover, intense plastic deformation in the sub-surface was obtained, and nanocrystalline layers, with grain dimensions of 10 nm to 100 nm, were fabricated on the processed surfaces of RUEM. Additionally, the improvement in sub-surface microstructure increased the surface micro-hardness from 21.22% to 33.84%. This study allows an in-depth understanding of sub-surface deformation and surface nanocrystallization in RUEM of Ti–6Al–4V.
Imposing the compressive residual stress field around a fastening hole serves as a universal method to enhance the hole fatigue strength in the aircraft assembly filed. Ultrasonic peening drilling (UPD) is a recently proposed hybrid hole making process, which can achieve an integration of strengthening and precision-machining with a one-shot drilling operation. Due to the ironing effect of the tool relief surface, UPD can introduce large compressive residual stress filed in hole subsurface. In order to reveal the strengthening mechanism of UPD, this paper analyzed the characteristics of dynamic relief angle and its corresponding effect on surface integrity in UPD. The experiments were conducted to verify the effect of tool relief angle on surface integrity and fatigue behavior of Ti-6Al-4V hole in UPD. The results indicate that the specimen features smaller surface roughness, higher micro-hardness, plastic deformation degree and circumferential compress residual stress under smaller tool nominal relief angle and higher vibration amplitude. The maximum thickness multiple of plastic deformation layer achieved by UPD is 6.25 times when vibration amplitude increases from 0 μm to 5 μm at 7°, in which the surface circumferential compressive residual stress reaches -982.6 MPa. The fatigue life increases along with the decrease of tool nominal relief angle or the increase of vibration amplitude, and the fatigue source site in UPD shifts from the surface to the subsurface comparing with that without vibration assistance. The results demonstrates that a better strengthening effect can be obtained by reasonably controlling the tool relief angle in the process of UPD.
Titanium alloy (Ti) has been widely used in aerospace industry due to excellent mechanical properties and the demands of Ti parts with a high length-to-diameter ratio and a large diameter are increasing. However, deep hole drilling of large-diameter Ti holes is usually both time-consuming and cost-consuming due to a series of problems such as unfavorable chip removal, helical structure on the hole surface, poor hole precision and severe tool wear. This paper reports on the cutting mechanism and experimental results of low-frequency vibration-assisted single-lip drilling (LFVASLD) of large-diameter Ti holes (Ø17mm) for the first time. In this paper, a novel rotary low-frequency vibration device was developed and the vibration generation mechanism was analyzed. Thereafter, the material removal mechanism of LFVASLD was established. Then, the comparative experiments between LFVASLD and conventional single-lip drilling (CSLD) of Ti were conducted. The experimental results show that, compared with CSLD, LFVASLD can significantly prolong the drilling depth by 9 times due to reduced tool wear and alleviate helical structure on the hole surface due to the separated cutting mode. Furthermore, the influence of drilling parameters in LFVASLD on hole quality were also investigated. It is concluded that, the LFVASLD method is suitable for deep hole drilling of large-diameter titanium alloy and the developed rotary low-frequency vibration device can be used as a machine tool accessory to significantly improve the processing capacity in the industrial practice.
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