【摘要】：真空保護(hù)是一種理想的金屬熔化焊熔池保護(hù)方式,真空環(huán)境下的熔化焊接方法具有顯著的技術(shù)優(yōu)勢(shì)。相對(duì)于其他真空環(huán)境下熔化焊接方法,空心陰極真空電弧焊具有焊接成本低和工藝操作簡(jiǎn)單的特點(diǎn),是一種重要的真空環(huán)境下熔化焊方法。盡管空心陰極真空電弧焊接方法有很多優(yōu)點(diǎn),但是它存在著焊接熔化效率低和熔化深度淺的限制。針對(duì)這個(gè)問題,為了發(fā)揮真空保護(hù)熔池金屬的優(yōu)勢(shì),本文通過電場(chǎng)增強(qiáng)空心陰極真空電弧的電子能量,利用磁場(chǎng)提高加速間隙的電氣絕緣強(qiáng)度,提出了一種磁約束空心陰極真空電弧電子束焊接方法,對(duì)電弧及電子束磁約束效應(yīng)、電子束加速特性和焊縫成形規(guī)律進(jìn)行了深入研究�；诳招年帢O真空電弧放電和等離子體陰極電子發(fā)射原理,利用空心陰極真空電弧作為電子的粒子源,研制了具有輸出高電流密度的磁約束空心陰極真空電弧電子束系統(tǒng),有效地提高了空心陰極真空電弧的電子能量。在小孔引出系統(tǒng)結(jié)構(gòu)下,利用磁場(chǎng)控制帶電粒子運(yùn)動(dòng)軌跡,抑制碰撞等離子體自由膨脹,保證了電子束加速間隙電氣絕緣,因此磁約束空心陰極真空電弧能夠施加高加速電壓而提高電子能量�；贗GBT逆變?cè)碓O(shè)計(jì)開發(fā)了空心陰極真空電弧放電電源和電子加速電源,實(shí)現(xiàn)了電弧放電和提高了電子能量�？招年帢O真空電弧高頻引弧研究結(jié)果表明,空心陰極真空電弧放電時(shí)電極材料存在老化現(xiàn)象,老化處理使空心陰極內(nèi)表面粗糙度變大,進(jìn)而容易實(shí)現(xiàn)場(chǎng)致電子發(fā)射。在夾持空心陰極的夾持器良好絕緣的基礎(chǔ)上,電極材料老化處理顯著地提高空心陰極真空電弧高頻引弧的成功率,高頻引弧成功率達(dá)到97%,高頻引弧時(shí)間低于2 s�？招年帢O真空電弧物理特性研究結(jié)果表明,隨著氣體流量降低,等離子體阻抗增加,電弧伏安特性曲線上移。與空心陰極真空電弧放電相比,磁場(chǎng)能夠抑制空心陰極真空電弧粒子自由膨脹,增加空心陰極真空電弧放電電壓,并且在低氣體流量時(shí)放電電壓增加更為明顯,磁場(chǎng)強(qiáng)度由10 mT增加至110 mT,放電電壓增加了161%。磁場(chǎng)能夠約束空心陰極真空電弧,增強(qiáng)電子碰撞幾率,進(jìn)而提高了等離子體密度,相對(duì)于無磁場(chǎng)而言,當(dāng)磁場(chǎng)強(qiáng)度20 mT時(shí),氬離子譜線強(qiáng)度增加了4倍。光譜輻射強(qiáng)度分布存在不均勻現(xiàn)象,空心陰極真空電弧中心區(qū)域的光譜輻射強(qiáng)度高于邊緣區(qū)域。磁場(chǎng)顯著地約束空心陰極真空電弧分布半徑,當(dāng)約束磁場(chǎng)強(qiáng)度大于20 mT、電弧放電電流小于30 A和氣體流量低于30 sccm時(shí),電弧分布半徑小于4.0 mm。采用PIC數(shù)值模擬方法對(duì)磁約束空心陰極真空電弧電子束磁約束及加速特性進(jìn)行了數(shù)值模擬研究,加速電場(chǎng)通過引出電極孔滲透至等離子體內(nèi)部,加速電場(chǎng)的引入可以降低電子引出勢(shì)壘,實(shí)現(xiàn)空心陰極真空電弧電子發(fā)射過程。磁場(chǎng)能夠壓縮電子束直徑。由于發(fā)射電子的等離子體面凹向電子束加速間隙,電子從等離子體內(nèi)部引出后首先匯聚運(yùn)動(dòng),然后迅速擴(kuò)散運(yùn)動(dòng)。磁約束空心陰極真空電弧電子束加速特性表明,隨著加速電壓增加,引出電流表現(xiàn)為快速增加、緩慢增加及飽和的三階段變化趨勢(shì)。磁約束空心陰極真空電弧電子束加速特性具有恒定飽和特性,這有利于磁約束空心陰極真空電弧電子束焊接工藝的調(diào)控。磁約束空心陰極真空電弧電子束加速特性的實(shí)驗(yàn)結(jié)果表明:隨著電弧放電電流和磁場(chǎng)強(qiáng)度增加,引出電流逐漸增加。電弧放電電流從15 A增大至25 A時(shí),引出電流增大了56%。空心陰極真空電弧電子加速過程中,電子與氣體分子碰撞效應(yīng)導(dǎo)致碰撞等離子體密度增強(qiáng),引出電流由等離子體發(fā)射電子和碰撞等離子體電子兩部分構(gòu)成。采用磁約束空心陰極真空電弧電子束焊接方法實(shí)現(xiàn)了金屬材料的熔化焊接,相對(duì)于空心陰極真空電弧焊接,這種焊接方法有效提高了電子能量,克服了常規(guī)空心陰極真空電弧焊熔深淺、熱效率低的不足。由于電子動(dòng)能具有高能量利用率的特點(diǎn),因此在相同熱輸入情況這種焊接方法的焊接熔化效率增加。
[Abstract]:Vacuum protection is an ideal pool protection method for metal melting welding, and melting welding method in vacuum environment has obvious technical advantages. Compared with other melting welding methods in vacuum environment, hollow cathode vacuum arc welding has the characteristics of low welding cost and simple process operation, and is an important melting welding in vacuum environment. Methods. Although the hollow cathode vacuum arc welding method has many advantages, it has the limitation of low melting efficiency and shallow melting depth. To solve this problem, in order to give full play to the advantages of vacuum protection of molten pool metal, this paper uses the electric field to enhance the electronic energy of the hollow cathode vacuum arc, and uses the magnetic field to increase the electric field to accelerate the gap. Based on the principle of hollow cathode vacuum arc discharge and plasma cathode electron emission, the hollow cathode vacuum arc is used as the welding material. A magnetic confined hollow cathode vacuum arc electron beam system with high current density was developed by using a particle source of electrons. The electron energy of the hollow cathode vacuum arc was effectively increased. Under the structure of a small hole extraction system, the trajectory of charged particles was controlled by a magnetic field, and the free expansion of collision plasma was suppressed, thus ensuring the electron beam addition. The vacuum arc with magnetic confinement hollow cathode can apply high acceleration voltage to improve the electronic energy because of the electrical insulation of the high speed gap.Based on IGBT inverter principle,the vacuum arc discharge power supply with hollow cathode and the electronic acceleration power supply are designed and developed,which can realize the arc discharge and improve the electronic energy.Research results of high frequency arc ignition with hollow cathode The results show that there is an aging phenomenon of electrode materials during hollow cathode vacuum arc discharge, and the surface roughness of hollow cathode increases with aging treatment, which makes it easy to realize field emission. The results show that with the decrease of gas flow rate, the plasma impedance increases, and the arc voltage-ampere characteristic curve moves up. Compared with the vacuum arc discharge of the hollow cathode, the magnetic field can restrain the free expansion of the particles in the vacuum arc of the hollow cathode. The discharge voltage of the hollow cathode vacuum arc increases by 161% when the magnetic field intensity increases from 10 mT to 110 mT at low gas flow rate. The magnetic field can restrain the hollow cathode vacuum arc, enhance the probability of electron collision, and then increase the plasma density compared with no magnetic field. When the magnetic field intensity is 20 mT, the intensity of argon ion spectrum increases four times. The distribution of spectral radiation intensity is inhomogeneous. The spectral radiation intensity in the central region of vacuum arc of hollow cathode is higher than that in the edge region. The distribution radius of the arc is less than 4.0 mm when the gas flow rate is less than 30 sccm. The magnetic confinement and acceleration characteristics of the magnetic confinement hollow cathode vacuum arc electron beam are numerically simulated by PIC method. The accelerated electric field penetrates into the plasma through the electrode hole, and the accelerated electric field can reduce the barrier of the electron extraction. A magnetic field can compress the electron beam diameter. As the electron emitted from the plasma surface concave to the electron beam acceleration gap, the electrons first converge and then diffuse rapidly from the plasma. The electron beam acceleration characteristics of magnetic confinement hollow cathode vacuum arc have constant saturation, which is beneficial to the control of magnetic confinement hollow cathode vacuum arc electron beam welding process. The experimental results show that with the increase of arc discharge current and magnetic field intensity, the induced current increases gradually. When the arc discharge current increases from 15A to 25A, the induced current increases by 56%. In the process of electron acceleration in vacuum arc with hollow cathode, the collision effect between electrons and gas molecules results in the increase of collision plasma density, and the induced current is from 15A to 25A. Electrons emitted by plasma and collision plasma are composed of two parts. The melting welding of metal materials is realized by using magnetic confinement hollow cathode vacuum arc electron beam welding method. Compared with hollow cathode vacuum arc welding, this welding method effectively improves the electron energy and overcomes the penetration depth of conventional hollow cathode vacuum arc welding. Because the electron kinetic energy has the characteristic of high energy utilization, the welding melting efficiency of this welding method increases under the same heat input.
【學(xué)位授予單位】：哈爾濱工業(yè)大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2015
【分類號(hào)】：TG456.3

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