外文文獻翻譯--脈沖電解液流動鈦合金深小孔的電化學鉆削【中文4040字】【中英文WORD】,中文4040字,中英文WORD,外文,文獻,翻譯,脈沖,電解液,流動,鈦合金,小孔,電化學,中文,4040,中英文,WORD Electrochemical Drilling of Deep Small Holes in Titanium Alloys with Pulsating Electrolyte Flow 1. Introduction Deep small holes with considerable aspect ratios, such as cooling holes in turbine blades and vanes, have been widely applied in the aerospace field [1, 2]. These holes are typically made of nickel-based super alloys, titanium alloys, and intermetallic compounds, which are difficult-to-work-with mechanical machining technologies. Nontraditional machining technologies are mostly used, regardless of the mechanical properties of the materials. Laser drilling and electric discharge machining (EDM) produce recast layers on the surface, which must be subsequently removed in applications demanding a specific surface finish. Additionally, with the increase of machining depth, tool wear in EDM worsens and the machining efficiency reduces. Electrochemical drilling (ECD) can achieve high surface quality with an absence of tool wear and metallurgical defects. The inherent characteristics of ECD mean that it can be a major solution for machining deep small holes in difficult-to-cut materials [3, 4]. In industrial applications, acid solutions are developed to avoid the formation of insoluble hydroxides from dissolved metal ions. However, the environmental treatment of acid effluent is expensive. Therefore, many efforts have been made to replace acid solutions with neutral salt solutions [5–7]. In neutral aqueous solutions, the electrolytic products typically cohere into a flocculent structure in deep hole drilling. Delayed sludge removal may block the electrolyte passage, bridge the connection between the electrodes, and induce short circuits. By-product removal in ECD with neutral salt solutions therefore determines the accuracy of control and limits the process capacity. Various approaches have also been proposed to accelerate the electrolytic refreshment. Skoczypiec [8] found that electrode ultrasonic vibrations change the conditions of electrochemical dissolution. The electrolyte flow, as well as electrode polarization, was enhanced by turbulent cavitations. Rajurkar and Zhu [9] applied an orbital motion to the tool cathode, which periodically expanded the side machining gap and made by-product removal easier. Hewidy [10] found that low-frequency vibrations of the tool cathode changed the physical condition in the frontal machining gap and extruded the electrolyte. Guo [11] invented a coaxial method by pumping in fresh electrolyte and extracting by-products at the hole entrance to restrict the submerged region and reduce the waste removal. Figure 1: Schematic diagram of ECD with pulsating flow Li et al. [12] progressively increased the electrolyte pressure in deep hole drilling to maintain a necessary electrolyte velocity for by-product removal. However, this issue has not been satisfactorily solved. Pulsating flow, which creates periodic fluctuations of fluid flow and alters the thickness of the boundary layer, has been verified as effective in multiphase flow [13, 14]. However, there are limited studies on pulsating flow in electrochemical drilling.This work focuses on the improvement of by-product removal in deep hole drilling with pulsating electrolyte flow. Experiments are also carried out to study the effects of pulsation parameters on by-product removal rate, hole performance, and maximum machining depth in drilling of titanium alloys. 2. Principles of ECD with Pulsating Electrolyte Flow Figure 1 shows a schematic diagram of ECD with pulsating electrolyte flow. Different from the typical ECD process with a constant flow, pulsating flow is an unsteady flow characterized by periodic fluctuation of the mass flow rate and pressure. Typical stimulus signals for pressure pulsation are presented in Figure 2. 𝑇 and 𝐴 denote the pulsation period and amplitude, respectively, and 𝑝av is the averaged electrolyte pressure over the pulsation period. In ECD with pulsating electrolyte flow, the workpiece is electrically connected to the positive pole of a pulse power supply and the tube tool is connected to the negative pole.The pulsating electrolyte with a velocity of 10–30 m/s is pumped into the interelectrode gap from the hollow center of the tube tool. When the tool electrode is fed at a constant rate into the workpiece, the material is dissolved, forming the desired hole. The perturbation and turbulence of pulsating flow intensely agitate the electrolyte mixed with insoluble sludge and bubbles. Agitation makes the products disperse more quickly and the distribution more uniform. When the pulsating flow is applied, a periodical low-pressure area is created in the machining gap, which reduces the hold-down pressure caused by the electrolyte on the by-products and enhances the refreshment of the electrolyte. As a result, process stability for deep hole drilling and hole quality can be enhanced. 3. System for ECD with Pulsating Electrolyte Flow A specific system for drilling deep holes, equipped with pulsating electrolyte flow, is shown in Figure 3. This machining system consists of an electrochemical drilling machine, a pulsating pressure generator, an electrolyte circulatory system, a tool cathode guiding apparatus, and a power supply. The self-developed drilling machine can achieve precise feed in the 𝑋-𝑌-𝑍-axis. In trial tests of this system, it is found that the tube electrode was forced to vibrate with the pulsating flow. In this case, the tube electrode acts like a cantilever beam and the vibration amplitude of the electrode tip was amplified with the increase of the pulsating frequency. The vibration Advances in Mechanical Engineering generated by pulsating flow would be harmful to the machining. So, a guiding apparatus is designed to restrict the tool’s vibration and enhance the hole profile cylindricity in the feeding direction. The pulsating flow is generated by a servo-controlled module, which is connected in series in the electrolyte circulatory system. This servo system is composed of an energy accumulator, a servo valve, a controller chip, a filter, and a power unit, as shown in Figure 4. The core component of this module is a Get-type electrohydraulic servo valve (RT6615E, Radk-Tech, China), which can quickly respond to a broadband stimulus signal ranging from 0 to 100 Hz. The outflow of this valve varies with the position of the valve core, which is controlled by the stimulus signals. A real-time full feedback control system was established to set the stimulus signals and acquire the electrolyte pressure. 4. Experimental Results and Discussions 4.1. Selection of Stimulus Signals. Experiments were conducted to check the dynamic responses of the pulsating pressure servo system to typical stimulus signals, which are shown in Figure 2. Real-time electrolyte pressure at the outlet of the servo system was recorded and is presented in Figure 5. When the stimulus signals were at a frequency of 40 Hz, the electrolyte pressure consistently varied with the fluctuation of the signals. When sinusoidal and triangular waves were encouraged, the details of the original signals were maintained. However, distortions were observed when sawtooth waves and rectangular waves were driven. This servo system operates through mechanical actions of the servo valve core. Mechanical systems have inherent characteristics of coupling delay and filtering of high-frequency harmonics, which cause signal losses or jumping signals, such as sawtooth and rectangular waves. Hence, sinusoidal waves, which approximate to the fundamental wave, were selected to drive the pulsating electrolyte flow in the following experiments. 4.2. Effects of Pulsating Flow on Product Removal. Samples of Ti6Al4V with a thickness of 20 mm were electrochemically drilled with different electrolyte flow conditions to study the effects of pulsating flow on by-product removal. In this experimental set, we applied a voltage of 26 V and an electrode feed rate of 0.6 mm/min. The other machining parameters are listed in Table 1. Immediately after the experiments and before cleaning, the samples were observed using a 3D video microscope (DVM5000, Leica, Germany). The entrance characteristics of the deep drilled holes are presented in Figure 6. The hole shown in Figure 6(b) was machined with a constant electrolyte pressure of 0.4 MPa. Massive white electrolytic products were observed on the hole’s inside surface.The holes in Figures 6(c) to 6(f) were drilled with a pulsating electrolyte at amplitude of 0.2 MPa. The pulsating frequencies were 2, 5, 8, and 10 Hz, respectively. It is obvious that when pulsating flow is applied, the residual products are mostly decreased. Figure 4: Servo system for pulsating pressure. When titanium and its alloys are dissolved, ions are diffused into the electrolyte and form TiO2, which is insoluble and easily coheres into a flocculent structure. Furthermore, TiO2 is hydrophilic and adhesive and may adhere to the hole inside surface and block the electrolyte passage. These characteristics are harmful to further material dissolution and to process stability. From the results presented in Figure 6, it can be concluded that pulsating electrolyte flow is effective in reducing residual by-products on the machined surface and accelerating their removal. 4.3. Parametric Effects of Pulsating Flow on Hole Performance. In this section, parametric experiments were carried out to study the effects of pulsation frequency and amplitude on deep hole drilling. Figure 7 shows the variations of the machining gap with pulsation parameters. It shows that when the pulsation frequency and amplitude increase, the machining gap firstly increases and then decreases, while the range of the machining gap firstly decreases and then increases. (a) Machining gap varied with 𝑓, 𝐴 = 0.2 MPa (b) Machining gap varied with 𝐴, 𝑓=5 Hz Figure 7: Effects of pulsation parameters on deep hole drilling. In ECD, the electrolyte at the front machining gap creates a hold-down pressure on the cohered flocculent by-products. This effect makes the removal of the by-products difficult, and some of them adhere to the hole inside wall. When pulsating flow is applied, a periodical low-pressure area is created in the machining gap, which reduces the hold-down pressure due to the electrolyte. With increasing pulsation frequency and amplitude, the by-product removal rate increases. The electrolyte conductivity in the machining gap is then much closer to the conductivity of fresh electrolyte at the inlet, and the conductivity distribution is also uniform [15]. Therefore, the machining gap increases and the gap range decreases. However, when the frequency is greater than 5 Hz, the response time of this machining system is delayed by the slender tube electrode and the inertia of the electrolyte liquid. Moreover, the experimental results also indicated that when the pulsating frequency increases, the electrode tip will vibrate and the machining process is unstable and short circuits took place frequently. It is due to the fact that the specified guiding apparatus is limited to restrict the tool’s vibration as the pulsating frequency increases, especially when the electrode is fed long beyond the guiding apparatus. All these adversely affect the machining gap deviation. When the pulsation amplitude is larger than 0.3 MPa and the time is at 3/4 period, the electrolyte pressure at the inlet is nearly zero. Zero pressure difference exists between the electrolyte inlet and outlet and by-product removal driven by the electrolyte flow stops. As the tool feeds into the hole, this phenomenon becomes worse, which adversely affects the hole characteristics. From the results, an optimal group of pulsating flow parameters is selected. When the pulsating flow is 5 Hz in frequency, 0.2 MPa in amplitude, and 0.5 MPa in average pressure, a minimum machining gap deviation of 25 𝜇m is obtained. 4.4. Effects of Applied Voltage on Deep Hole Drilling. Figure 8 shows the effects of applied voltage on deep hole drilling with constant flow and with pulsating flow, respectively. The constant pressure is 0.5 MPa, while the pulsating flow is 5 Hz in frequency, 0.2 MPa in amplitude, and 0.5 MPa in average pressure. The voltage varies between 22 and 25 V. The electrode feed rate is 0.6 mm/min. Figure 8(a) shows the effects of applied voltage on the machining gap and the maximum machining depth. Figure 8(b) shows the effects on the machining gap range. In both of these two flow conditions, with increasing applied voltage, the averaged machining gap, the machining gap range, and the maximum machining depth all increase. When the voltage is increased, the current density increases and the material removal volume per unit time increases, which means a larger machining gap. Comparing the results obtained with the same voltage, it can be concluded that the machining gap drilled with pulsating flow is nearly the same as that with constant flow, while the machining gap range decreases; that is, the machining accuracy is improved. Furthermore, the maximum machining depth with pulsating flow is obviously superior to that with constant flow. When the voltage is 22 V, the hole drilled with the constant flow has a 0.159 mm gap and a 0.016 mm gap range, while the hole drilled with the pulsating flow has a 0.161 mm gap and a 0.013 mm gap range. The machined depth with pulsating flow is 12.5 mm, which is about 20% deeper than that with constant flow (10.4 mm). When the voltage is 24 V, the maximum machined depth with pulsating flow is 20 mm, which is 30% deeper than that with constant flow (15.3 mm). 4.5. Effects of Electrode Feed Rate on Deep Hole Drilling. Figure 9 shows the effects of electrode feed rate on deep hole drilling with constant flow and with pulsating flow, respectively. The constant pressure is 0.5 MPa. The pulsating flow is 5 Hz in frequency, 0.2 MPa in amplitude, and 0.5 MPa in averaged pressure. The electrode feed rate varies between 0.6, 0.8, and 1.0 mm/min. The applied voltage is 24 V. Figure 9(a) shows the effects of electrode feed rate on the machining gap and the maximum machining depth. Figure 9(b) shows the effects on the machining gap range. In both of these two flow conditions, with increasing electrode feed rate, the averaged machining gap, the machining gap range, and the maximum machining depth all decrease. When the electrode feed rate is increased, the time in which the current attacks the workpiece per unit length decreases and the material removal volume decreases, which means a smaller machining gap. Comparing results for the same electrode feed rate, the maximum machining depth with pulsating flow is obviously superior to that with constant flow. When the feed rate is 0.6 mm/min, the machined depth with pulsating flow is 20 mm, which is about 30% deeper than that with constant flow (15.5 mm). 4.6. Drilling of Deep Hole in Titanium Alloy. From the results presented in Section 4, it can be concluded that using a parameter group with a high voltage and a low electrode feed rate contributes to enhancing the maximum machining depth. In addition, pulsating flow is effective in enhancing the maximum machining depth and the homogeneity of the deep hole diameter. With the optimized parameters of 5 Hz frequency, 0.2 MPa amplitude, 0.5 MPa average pressure, 25 V applied voltage, and 0.6 mm/min electrode feed rate, a deep hole of 20 mm in depth and 1.97 mm in average diameter was machined in titanium alloys, as shown in Figure 10. 5. Conclusions This paper proposed a method of electrochemical drilling with pulsating electrolyte flow, and the effects of pulsating flow on deep hole drilling were experimentally investigated. The conclusions can be summarized as follows. (1) Pulsating flow varying with the sinusoidal rule is effective in accelerating by-product removal and in reducing the adhesion of flocculent products to the hole inside wall. (2) The correct increase of pulsation frequency and amplitude could enhance by-product removal and the homogeneity of the machining gap, but an excessive increase is harmful to the process stability. (3) Pulsating flow is superior to constant flow in enhancing both maximum machining depth and machining accuracy Conflict of Interests The authors declare that there is no conflict of interests regarding the publication of this paper. Acknowledgments The authors acknowledge the financial support provided by the National Natural Science Foundation of China (51175258) and the Jiang Su Natural Science Foundation (BK20131361). References [1] R. S. Bunker, “A review of shaped hole turbine film-cooling technology,” Journal of Heat Transfer, vol. 127, no. 4, pp. 441–453, 2005. [2] M. Sen and H. S. Shan, “A review of electrochemical macro- to micro-hole drilling processes,” International Journal of Machine Tools and Manufacture, vol. 45, no. 2, pp. 137–152, 2005. [3] K. P. Rajurkar, D. Zhu, J. A. McGeough, J. Kozak, and A. de Silva, “New developments in electro-chemical machining,” CIRP Annals: Manufacturing Technology, vol. 48, no. 2, pp. 567– 579, 1999. [4] X. Fang, N. Qu, H. Li, and D. Zhu, “Enhancement of insulation coating durability in electrochemical drilling,” International Journal of Advanced Manufacturing Technology, vol. 68, no. 9– 12, pp. 2005–2013, 2013. [5] W.Wang, D. Zhu, N. S. Qu, S. F. Huang, and X. L. Fang, “Electrochemical drilling with vacuum extraction of electrolyte,” Journal of Materials Processing Technology, vol. 210, no. 2, pp. 238–244, 2010. [6] M. S. Hewidy, S. J. Ebeid, K. P. Rajurkar, and M. F. El-Safti, “Electrochemical machining under orbital motion conditions,” Journal of Materials Processing Technology, vol. 109, no. 3, pp. 339–346, 2001. [7] W. Wang, D. Zhu, N. Qu, S. Huang, and X. Fang, “Electrochemical drilling inclined holes using wedged electrodes,” International Journal of Advanced Manufacturing Technology, vol. 47, no. 9–12, pp. 1129–1136, 2010. [8] S. Skoczypiec, “Research on ultrasonically assisted electrochemical machining process,” International Journal of Advanced Manufacturing Technology, vol. 52, no. 5–8, pp. 565–574, 2011. [9] K. P. Rajurkar and D. Zhu, “Improvement of electrochemical machining accuracy by using orbital electrode movement,” CIRP Annals: Manufacturing Technology, vol. 48, no. 1, pp. 139– 142, 1999. [10] M. S. Hewidy, S. J. Ebeid, T. A. El-Taweel, and A. H. Youssef, “Modelling the performance of ECM assisted by low frequency vibrations,” Journal of Materials Processing Technology, vol. 189, no. 1–3, pp. 466–472, 2007. [11] J. C. Guo, Study on Micro electrochemical machining using coaxial for gushing and sucking method [M.S. thesis], National Yunlin University of Science & Technology, 2007, (Chinese). [12] Z. Li, D. Wei, and S. C. Di, “Research on electrochemical machining small hole in variable pressure field using tubular electrode,” Electromachining & Mould, no. 5, pp. 30–32, 2011 (Chinese). [13] X. Fang, N. Qu, Y. Zhang, Z. Xu, and D. Zhu, “Effects of pulsating electrolyte flow in electrochemical machining,” Journal of Materials Processing Technology, vol. 214, no. 1, pp. 36–43, 2014. [14] E. M. Benavides, “Heat transfer enhancement by using pulsating flows,” Journal of Applied Physics, vol. 105, no. 9, Article ID 094907, 2009. [15] N. S. Qu, X. L. Fang, Y. D. Zhang, and D. Zhu, “Enhancement of surface roughness in electrochemical machining of Ti6Al4V by pulsating electrolyte,” International Journal of Advanced Manufacturing Technology, vol. 69, no. 9–12, pp. 2703–2709, 2013 脈沖電解液流動鈦合金深小孔的電化學鉆削 1.簡介 具有相當高寬比的深孔，如渦輪葉片和葉片上的冷卻孔已廣泛應用于航空航天領域[1,2]。這些孔通常由鎳基超合金，鈦合金和金屬間化合物制成，這些材料難以用機械加工技術加工。不管材料的機械性能如何，大多數(shù)都使用非傳統(tǒng)加工技術。激光鉆孔和放電加工（EDM）在表面上產(chǎn)生重鑄層，必須隨后在需要特定表面拋光的應用中去除重鑄層。此外，隨著加工深度的增加，電火花加工中的刀具磨損惡化，加工效率降低。電化學鉆孔（ECD）可以達到較高的表面質量，不會出現(xiàn)刀具磨損和冶金缺陷。 ECD的固有特性意味著它可以成為在難切削材料中加工深孔的主要解決方案[3,4]。 在工業(yè)應用中，開發(fā)酸