外文文獻(xiàn)翻譯--脈沖電解液流動(dòng)鈦合金深小孔的電化學(xué)鉆削【中文4040字】【中英文WORD】
外文文獻(xiàn)翻譯--脈沖電解液流動(dòng)鈦合金深小孔的電化學(xué)鉆削【中文4040字】【中英文WORD】,中文4040字,中英文WORD,外文,文獻(xiàn),翻譯,脈沖,電解液,流動(dòng),鈦合金,小孔,電化學(xué),中文,4040,中英文,WORD
脈沖電解液流動(dòng)鈦合金深小孔的電化學(xué)鉆削
1.簡(jiǎn)介
具有相當(dāng)高寬比的深孔，如渦輪葉片和葉片上的冷卻孔已廣泛應(yīng)用于航空航天領(lǐng)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(jī)械加工技術(shù)加工。不管材料的機(jī)械性能如何，大多數(shù)都使用非傳統(tǒng)加工技術(shù)。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(yīng)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(xué)鉆孔（ECD）可以達(dá)到較高的表面質(zhì)量，不會(huì)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(yīng)用中，開(kāi)發(fā)酸溶液以避免溶解的金屬離子形成不溶性氫氧化物。 但是，酸性廢水的環(huán)境處理非常昂貴。 因此，已經(jīng)做出許多努力用中性鹽溶液代替酸溶液[5-7]。 在中性水溶液中，電解產(chǎn)物通常在深孔鉆井中凝聚成絮狀結(jié)構(gòu)。 延遲的污泥去除可能阻塞電解液通道，橋接電極之間的連接并引起短路。 用中性鹽溶液去除ECD中的副產(chǎn)物因此決定了控制的準(zhǔn)確性并限制了處理能力。 也已經(jīng)提出了各種方法來(lái)加速電解更新。
Skoczypiec [8]發(fā)現(xiàn)電極超聲振動(dòng)改變了電化學(xué)溶解的條件。 電解液流動(dòng)以及電極極化由于湍流空化而增強(qiáng)。 Rajurkar和Zhu [9]對(duì)工具陰極施加軌道運(yùn)動(dòng)，這會(huì)周期性地?cái)U(kuò)大側(cè)面加工間隙并使副產(chǎn)物的去除更容易。 Hewidy [10]發(fā)現(xiàn)工具陰極的低頻振動(dòng)改變了正面加工間隙的物理?xiàng)l件并擠出了電解質(zhì)。 Guo [11]發(fā)明了一種同軸方法，通過(guò)在新鮮電解液中泵送并在孔入口處提取副產(chǎn)物來(lái)限制浸沒(méi)區(qū)域并減少?gòu)U物的去除。
圖1：具有脈動(dòng)流動(dòng)的ECD示意圖
Li等人 [12]逐步增加深孔鉆井中的電解液壓力，以保持必要的電解液速度，以除去副產(chǎn)物。 但是，這個(gè)問(wèn)題沒(méi)有得到圓滿解決。
已經(jīng)證實(shí)脈動(dòng)流動(dòng)造成流體流動(dòng)的周期性波動(dòng)并改變邊界層的厚度，這在多相流動(dòng)中已被證實(shí)是有效的[13,14]。 然而，對(duì)于電化學(xué)鉆井中的脈動(dòng)流動(dòng)的研究還很有限。這項(xiàng)工作主要集中在改善伴隨脈動(dòng)電解液流動(dòng)的深孔鉆削中副產(chǎn)物的去除。 還進(jìn)行了實(shí)驗(yàn)以研究脈動(dòng)參數(shù)對(duì)鈦合金鉆削中副產(chǎn)物去除率，孔性能和最大加工深度的影響。
2.脈沖電解質(zhì)流的ECD原理
圖1顯示了具有脈動(dòng)電解液流的ECD的示意圖。與恒定流量的典型ECD過(guò)程不同，脈動(dòng)流量是一種非定常流量，其特征在于質(zhì)量流量和壓力的周期性波動(dòng)。壓力脈動(dòng)的典型刺激信號(hào)如圖2所示。𝑇和respectively分別表示脈動(dòng)周期和振幅，𝑝av表示脈動(dòng)周期內(nèi)的平均電解質(zhì)壓力。在脈動(dòng)電解液流動(dòng)的ECD中，工件電連接到脈沖電源的正極，管工具連接到負(fù)極。速度為10-30m / s的脈動(dòng)電解液被泵入電極內(nèi)與管工具中空部分的間隙。當(dāng)工具電極以恒定速率進(jìn)入工件時(shí)，材料被溶解，形成所需的孔。脈動(dòng)流的擾動(dòng)和湍流劇烈攪動(dòng)混有不溶性污泥和氣泡的電解質(zhì)。攪拌使產(chǎn)品分散得更快，分布更均勻。當(dāng)施加脈動(dòng)流時(shí)，在加工間隙中產(chǎn)生周期性的低壓區(qū)域，這降低了由電解質(zhì)對(duì)副產(chǎn)物引起的壓緊壓力并且增強(qiáng)了電解液的更新。因此，可以提高深孔鉆孔和鉆孔質(zhì)量的加工穩(wěn)定性。
圖2：壓力脈動(dòng)的典型刺激信號(hào)。
3.用脈沖電解液流動(dòng)的ECD系統(tǒng)
圖3中示出了用于鉆深孔的特定系統(tǒng)，其配備有脈動(dòng)電解液流。該加工系統(tǒng)由電化學(xué)鉆孔機(jī)，脈動(dòng)壓力發(fā)生器，電解液循環(huán)系統(tǒng)，工具陰極導(dǎo)向裝置和電源。自主研發(fā)的鉆孔機(jī)可實(shí)現(xiàn)𝑋-𝑌-𝑍軸的精確進(jìn)給。在這個(gè)系統(tǒng)的試驗(yàn)測(cè)試中，發(fā)現(xiàn)管電極被迫與脈動(dòng)流一起振動(dòng)。在這種情況下，管電極像懸臂梁一樣起作用，并且電極尖端的振動(dòng)幅度隨著脈動(dòng)頻率的增加而放大。脈動(dòng)流動(dòng)產(chǎn)生的機(jī)械工程振動(dòng)進(jìn)展會(huì)對(duì)加工造成危害。因此，設(shè)計(jì)了一種導(dǎo)向裝置，以限制工具的振動(dòng)并提高進(jìn)給方向上的孔輪廓圓柱度。
脈動(dòng)流由伺服控制模塊產(chǎn)生，該模塊在電解液循環(huán)系統(tǒng)中串聯(lián)連接。如圖4所示，該伺服系統(tǒng)由一個(gè)蓄能器，一個(gè)伺服閥，一個(gè)控制器芯片，一個(gè)濾波器和一個(gè)動(dòng)力單元組成。該模塊的核心部件是Get型電動(dòng)液壓伺服閥（RT6615E，Radk中國(guó)），它可以快速響應(yīng)從0到100 Hz范圍內(nèi)的寬帶激勵(lì)信號(hào)。該閥的流出量隨著閥芯的位置而變化，閥芯的位置由刺激信號(hào)控制。建立實(shí)時(shí)全反饋控制系統(tǒng)來(lái)設(shè)置激勵(lì)信號(hào)并獲取電解質(zhì)壓力。
4.實(shí)驗(yàn)結(jié)果和討論
4.1 刺激信號(hào)的選擇
進(jìn)行實(shí)驗(yàn)以檢查脈動(dòng)壓力伺服系統(tǒng)對(duì)典型刺激信號(hào)的動(dòng)態(tài)響應(yīng)，如圖2所示。伺服系統(tǒng)出口處的實(shí)時(shí)電解質(zhì)壓力記錄在圖5中。當(dāng)刺激信號(hào)頻率為40Hz，電解質(zhì)壓力隨信號(hào)波動(dòng)而一致地變化。當(dāng)鼓勵(lì)正弦和三角波時(shí)，保持原始信號(hào)的細(xì)節(jié)。然而，當(dāng)鋸齒波和矩形波被驅(qū)動(dòng)時(shí)觀察到失真。該伺服系統(tǒng)通過(guò)伺服閥芯的機(jī)械動(dòng)作進(jìn)行操作。機(jī)械系統(tǒng)具有耦合延遲和高頻諧波濾波的固有特性，這些高頻諧波會(huì)導(dǎo)致信號(hào)損失或跳躍信號(hào)，例如鋸齒波和矩形波。因此，選擇近似于基波的正弦波以在下面的實(shí)驗(yàn)中驅(qū)動(dòng)脈動(dòng)電解液流動(dòng)。
4.2。 脈動(dòng)流對(duì)產(chǎn)品去除的影響
用不同的電解液流動(dòng)條件電化學(xué)鉆出厚度為20mm的Ti6Al4V樣品以研究脈動(dòng)流動(dòng)對(duì)副產(chǎn)物去除的影響。 在這個(gè)實(shí)驗(yàn)裝置中，我們施加了26V的電壓和0.6mm / min的電極饋送速率。 其他加工參數(shù)列于表1中。實(shí)驗(yàn)結(jié)束后和清潔前，立即使用3D視頻顯微鏡（DVM5000，Leica，德國(guó)）觀察樣品。 深鉆孔的入口特征如圖6所示。圖6（b）所示的孔是用0.4MPa的恒定電解質(zhì)壓力加工的。 在孔的內(nèi)表面上觀察到大量的白色電解質(zhì)產(chǎn)物。圖6（c）至6（f）中的孔用脈沖電解質(zhì)以0.2MPa的幅度鉆孔。 脈動(dòng)頻率分別為2,5,8和10Hz。 很明顯，當(dāng)施加脈動(dòng)流時(shí)，殘留產(chǎn)物大部分減少。
圖4：脈動(dòng)壓力的伺服系統(tǒng)
當(dāng)鈦及其合金溶解時(shí)，離子擴(kuò)散到電解質(zhì)中并形成不溶且容易凝聚成絮狀結(jié)構(gòu)的TiO 2。 此外，TiO2是親水性和粘合性的，并且可能粘附到孔內(nèi)表面并堵塞電解液通道。 這些特性對(duì)進(jìn)一步的材料溶解和加工穩(wěn)定性有害。 從圖6所示的結(jié)果可以得出結(jié)論，脈動(dòng)電解液流動(dòng)對(duì)于減少加工表面上的殘留副產(chǎn)物并加速它們的去除是有效的。
4.3 脈動(dòng)流對(duì)孔性能的參數(shù)影響
在本節(jié)中，進(jìn)行參數(shù)實(shí)驗(yàn)來(lái)研究脈動(dòng)頻率和振幅對(duì)深孔鉆削的影響。 圖7顯示了具有脈動(dòng)參數(shù)的加工間隙的變化。 結(jié)果表明，當(dāng)脈動(dòng)頻率和振幅增大時(shí)，加工間隙先增大后減小，而加工間隙范圍先減小后增大。
（a）加工間隙隨著𝑓，𝐴= 0.2 MPa而變化 （b）加工間隙隨著𝐴，𝑓= 5 Hz而變化
圖7：脈動(dòng)參數(shù)對(duì)深孔鉆探的影響。
在ECD中，正面加工間隙處的電解液對(duì)粘附的絮狀副產(chǎn)物產(chǎn)生壓制壓力。這種效果使得副產(chǎn)品的去除變得困難，并且它們中的一些粘附到墻內(nèi)的孔。當(dāng)施加脈動(dòng)流時(shí)，在加工間隙中產(chǎn)生周期性的低壓區(qū)域，這降低了由于電解質(zhì)造成的壓緊壓力。隨著脈動(dòng)頻率和振幅的增加，副產(chǎn)物去除率增加。加工間隙中的電解質(zhì)電導(dǎo)率接近于入口處新鮮電解質(zhì)的電導(dǎo)率，并且電導(dǎo)率分布也是均勻的[15]。因此，加工間隙增加，間隙范圍減小。然而，當(dāng)頻率大于5Hz時(shí)，該加工系統(tǒng)的響應(yīng)時(shí)間被細(xì)長(zhǎng)管電極和電解質(zhì)液體的慣性延遲。此外，實(shí)驗(yàn)結(jié)果還表明，當(dāng)脈動(dòng)頻率增加時(shí)，電極頭會(huì)振動(dòng)，加工過(guò)程不穩(wěn)定，頻繁發(fā)生短路。這是由于這樣的事實(shí)，即特定的引導(dǎo)裝置被限制為當(dāng)脈動(dòng)頻率增加時(shí)限制工具的振動(dòng)，特別是當(dāng)電極長(zhǎng)時(shí)間超出引導(dǎo)裝置時(shí)。所有這些都會(huì)對(duì)加工間隙偏差產(chǎn)生不利影響。
當(dāng)脈動(dòng)幅度大于0.3MPa且時(shí)間在3/4時(shí)，入口處的電解液壓力幾乎為零。 電解液入口和出口之間存在零壓差，并且由電解液流動(dòng)驅(qū)動(dòng)的副產(chǎn)物去除停止。 隨著工具進(jìn)入孔中，這種現(xiàn)象變得更糟，這會(huì)對(duì)孔特性產(chǎn)生不利影響。
從結(jié)果中選擇一組最佳的脈動(dòng)流量參數(shù)。 當(dāng)頻率為5Hz，振幅為0.2MPa，平均壓力為0.5MPa時(shí)，得到25μm的最小加工間隙偏差。
4.4 施加電壓對(duì)深孔鉆削的影響
圖8顯示了施加電壓分別對(duì)恒定流量和脈動(dòng)流量的深孔鉆削的影響。 恒定壓力為0.5MPa，脈動(dòng)流頻率為5Hz，振幅為0.2MPa，平均壓力為0.5MPa。 電壓在22和25V之間變化。電極饋送速率為0.6mm / min。
圖8（a）顯示了施加電壓對(duì)加工間隙和最大加工深度的影響。 圖8（b）顯示了對(duì)加工間隙范圍的影響。 在這兩種流動(dòng)條件下，隨著施加電壓的增加，平均的加工間隙，加工間隙范圍和最大加工深度都增加。 當(dāng)電壓升高時(shí)，電流密度增加，單位時(shí)間的材料去除量增加，這意味著更大的加工間隙。
通過(guò)比較相同電壓下的結(jié)果，可以得出脈動(dòng)流動(dòng)加工間隙與恒定流動(dòng)加工間隙幾乎相同，而加工間隙范圍減小的結(jié)論。 即加工精度提高。 此外，脈動(dòng)流的最大加工深度明顯優(yōu)于恒定流的加工深度。 當(dāng)電壓為22 V時(shí)，以恒定流量鉆出的孔具有0.159 mm的間隙和0.016 mm的間隙范圍，而鉆有脈動(dòng)流的孔具有0.161 mm的間隙和0.013 mm的間隙范圍。 帶有脈動(dòng)流的加工深度為12.5毫米，比恒定流量（10.4毫米）深約20％。 當(dāng)電壓為24 V時(shí)，脈動(dòng)流的最大加工深度為20 mm，比恒流（15.3 mm）深30％。
4.5 電極進(jìn)給速度對(duì)深孔鉆削的影響
圖9分別顯示了電極進(jìn)給速率對(duì)恒定流量和脈動(dòng)流量深孔鉆削的影響。 恒定壓力是0.5MPa。 脈動(dòng)流頻率為5Hz，振幅為0.2MPa，平均壓力為0.5MPa。 電極進(jìn)給速率在0.6,0.8和1.0毫米/分鐘之間變化。 施加的電壓是24 V.
圖9（a）顯示了電極進(jìn)給速度對(duì)加工間隙和最大加工深度的影響。 圖9（b）顯示了對(duì)加工間隙范圍的影響。 在這兩種流動(dòng)條件下，隨著電極進(jìn)給速率的增加，平均加工間隙，加工間隙范圍和最大加工深度都減小。 當(dāng)電極進(jìn)給速率增加時(shí)，每單位長(zhǎng)度電流攻擊工件的時(shí)間減少，材料去除量減小，這意味著較小的加工間隙。
比較相同電極進(jìn)給速度下的結(jié)果，脈動(dòng)流的最大加工深度明顯優(yōu)于恒定流的加工深度。 當(dāng)進(jìn)給速率為0.6毫米/分鐘時(shí)，帶脈動(dòng)流的加工深度為20毫米，比恒流（15.5毫米）深30％。
4.6 鈦合金深孔鉆削
從第4節(jié)中的結(jié)果可以得出結(jié)論，使用高電壓和低電極進(jìn)給速率的參數(shù)組有助于提高最大加工深度。 另外，脈動(dòng)流動(dòng)對(duì)于提高最大加工深度和深孔直徑的均勻性是有效的。 利用5Hz頻率，0.2MPa振幅，0.5MPa平均壓力，25V施加電壓和0.6mm / min電極進(jìn)給速率的優(yōu)化參數(shù)，在鈦中機(jī)加工了深20mm深和平均直徑1.97mm的深孔 合金，如圖10所示。
5結(jié)論
本文提出了一種脈動(dòng)電解液流動(dòng)的電化學(xué)鉆井方法，并對(duì)脈動(dòng)流動(dòng)對(duì)深孔鉆削的影響進(jìn)行了實(shí)驗(yàn)研究。 結(jié)論可概括如下。
（1）隨著正弦規(guī)則變化的脈動(dòng)流動(dòng)對(duì)于加速副產(chǎn)物去除和減少絮凝產(chǎn)物與孔內(nèi)壁的粘附是有效的。
（2）脈動(dòng)頻率和振幅的正確增加可以提高副產(chǎn)物的去除率和加工間隙的均勻性，但過(guò)高的增加對(duì)工藝穩(wěn)定性有害。
（3）在提高最大加工深度和加工精度方面，脈動(dòng)流量?jī)?yōu)于恒定流量。
致謝
作者感謝國(guó)家自然科學(xué)基金和江蘇省自然科學(xué)基金提供的財(cái)政支持。
9
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
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脈沖電解液流動(dòng)鈦合金深小孔的電化學(xué)鉆削
1.簡(jiǎn)介
具有相當(dāng)高寬比的深孔，如渦輪葉片和葉片上的冷卻孔已廣泛應(yīng)用于航空航天領(lǐng)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(jī)械加工技術(shù)加工。不管材料的機(jī)械性能如何，大多數(shù)都使用非傳統(tǒng)加工技術(shù)。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(yīng)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(xué)鉆孔（ECD）可以達(dá)到較高的表面質(zhì)量，不會(huì)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(yīng)用中，開(kāi)發(fā)酸
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