空心阴极真空电弧焊电子束磁约束及加速特性研究

发布时间：2018-09-09 08:53

【摘要】：真空保护是一种理想的金属熔化焊熔池保护方式,真空环境下的熔化焊接方法具有显著的技术优势。相对于其他真空环境下熔化焊接方法,空心阴极真空电弧焊具有焊接成本低和工艺操作简单的特点,是一种重要的真空环境下熔化焊方法。尽管空心阴极真空电弧焊接方法有很多优点,但是它存在着焊接熔化效率低和熔化深度浅的限制。针对这个问题,为了发挥真空保护熔池金属的优势,本文通过电场增强空心阴极真空电弧的电子能量,利用磁场提高加速间隙的电气绝缘强度,提出了一种磁约束空心阴极真空电弧电子束焊接方法,对电弧及电子束磁约束效应、电子束加速特性和焊缝成形规律进行了深入研究。基于空心阴极真空电弧放电和等离子体阴极电子发射原理,利用空心阴极真空电弧作为电子的粒子源,研制了具有输出高电流密度的磁约束空心阴极真空电弧电子束系统,有效地提高了空心阴极真空电弧的电子能量。在小孔引出系统结构下,利用磁场控制带电粒子运动轨迹,抑制碰撞等离子体自由膨胀,保证了电子束加速间隙电气绝缘,因此磁约束空心阴极真空电弧能够施加高加速电压而提高电子能量。基于IGBT逆变原理设计开发了空心阴极真空电弧放电电源和电子加速电源,实现了电弧放电和提高了电子能量。空心阴极真空电弧高频引弧研究结果表明,空心阴极真空电弧放电时电极材料存在老化现象,老化处理使空心阴极内表面粗糙度变大,进而容易实现场致电子发射。在夹持空心阴极的夹持器良好绝缘的基础上,电极材料老化处理显著地提高空心阴极真空电弧高频引弧的成功率,高频引弧成功率达到97%,高频引弧时间低于2 s。空心阴极真空电弧物理特性研究结果表明,随着气体流量降低,等离子体阻抗增加,电弧伏安特性曲线上移。与空心阴极真空电弧放电相比,磁场能够抑制空心阴极真空电弧粒子自由膨胀,增加空心阴极真空电弧放电电压,并且在低气体流量时放电电压增加更为明显,磁场强度由10 mT增加至110 mT,放电电压增加了161%。磁场能够约束空心阴极真空电弧,增强电子碰撞几率,进而提高了等离子体密度,相对于无磁场而言,当磁场强度20 mT时,氩离子谱线强度增加了4倍。光谱辐射强度分布存在不均匀现象,空心阴极真空电弧中心区域的光谱辐射强度高于边缘区域。磁场显著地约束空心阴极真空电弧分布半径,当约束磁场强度大于20 mT、电弧放电电流小于30 A和气体流量低于30 sccm时,电弧分布半径小于4.0 mm。采用PIC数值模拟方法对磁约束空心阴极真空电弧电子束磁约束及加速特性进行了数值模拟研究,加速电场通过引出电极孔渗透至等离子体内部,加速电场的引入可以降低电子引出势垒,实现空心阴极真空电弧电子发射过程。磁场能够压缩电子束直径。由于发射电子的等离子体面凹向电子束加速间隙,电子从等离子体内部引出后首先汇聚运动,然后迅速扩散运动。磁约束空心阴极真空电弧电子束加速特性表明,随着加速电压增加,引出电流表现为快速增加、缓慢增加及饱和的三阶段变化趋势。磁约束空心阴极真空电弧电子束加速特性具有恒定饱和特性,这有利于磁约束空心阴极真空电弧电子束焊接工艺的调控。磁约束空心阴极真空电弧电子束加速特性的实验结果表明:随着电弧放电电流和磁场强度增加,引出电流逐渐增加。电弧放电电流从15 A增大至25 A时,引出电流增大了56%。空心阴极真空电弧电子加速过程中,电子与气体分子碰撞效应导致碰撞等离子体密度增强,引出电流由等离子体发射电子和碰撞等离子体电子两部分构成。采用磁约束空心阴极真空电弧电子束焊接方法实现了金属材料的熔化焊接,相对于空心阴极真空电弧焊接,这种焊接方法有效提高了电子能量,克服了常规空心阴极真空电弧焊熔深浅、热效率低的不足。由于电子动能具有高能量利用率的特点,因此在相同热输入情况这种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.
【学位授予单位】：哈尔滨工业大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TG456.3

【相似文献】