【作者】 牛永；

【导师】 曾周末； 宋永伦；

【作者基本信息】 天津大学 ， 精密仪器及机械， 2010， 博士

【摘要】 脉冲TIG焊在提高能量密度、热输入控制、焊缝成形以及焊接质量等方面具有独特的优点,近年来在制造业中的应用日益广泛。但目前脉冲电弧的应用频率一般在30kHz以下。论文针对脉冲频率提高以后,电弧可能出现的新现象、新特性以及对焊接工艺的影响进行深入研究,以期探求进一步改善脉冲TIG弧焊性能的技术措施。深入研究了TIG弧的电学特性。通过对弧-源系统的高频特性分析,建立了TIG弧动态阻抗模型,导出了传递函数,发现了高频电弧的二阶共振特征。围绕改善弧-源系统的高频特性,研制了TIG弧主电源,搭建了基于直流+高频交流的TIG电源、动态阻抗测试机构的实验平台,测试输入不同频率激励电流条件下的TIG弧电弧响应电压,分析电弧的动态阻抗。实验研究证明,小电流TIG弧的电特性具有明显的二阶惯性环节的振荡特征;电弧谐振点的频率与阻抗受到电流基值与弧长的影响;在电弧谐振点,电弧功率最大。采用电子密度作为研究电弧热力学状态的特征量,研究电弧的热力学特性,研究电弧电特性变化对电弧热力学特性的影响。构建了高频脉冲电弧发射光谱同步观测平台,利用Stark展宽原理和Griem公式,明确了电子密度基值和波动幅值随频率变化的规律,并将电弧热所产生的光谱信号与电弧的电压电流信号相对应,测试了不同频率下TIG弧的电子密度,验证了电子密度与电弧功率具有相同的变化特征,电弧电子密度的基值与波动幅值在谐振点处达到最大。明确了电弧功率、电弧谐振、电子密度三者之间的关系。研究了高频小电流脉冲TIG弧焊的工艺特性。经过对304不锈钢的实际焊接后发现:在电弧谐振频率上,焊缝的熔深、熔宽都为最大;与直流情况相比熔宽基本不变,而熔深却增大一倍以上;晶粒度在谐振点附近达到最细,结晶方向消失。这一实验结果充分体现了电弧谐振特性的工程意义与实用价值。更多还原

【Abstract】 Pulsed TIG welding is an advanced technology on impoving energy density, controlling input energy, welding seam shape and metallurgy quality. It plays a unique and important role in engineering in resent years. However, the knowledge about the pulsed TIG arc plasma is very limited currently for the low pulsing frequency which is below 30KHz. This work focuses on studying the characteristics of pulsed TIG arc plasma and application of them when the pulsed frequency continues to increase in order to promote the development of pulsed TIG welding and deepen the understanding of plused TIG arc plasma.The electrical characteristics of pulsed TIG arc plasma is investigated. After analyzation, a new dynamic model of TIG arc is established, and a transfer function is deduced too. And then, some of the equipment are designed, including main power supply and power amplifier, as well as the platform. The dynamic impedance of TIG arc plasma is obtained through measuring the response voltage when input the different exciting current to the TIG arc plasma. The results show that the electrical characteristics of the low current high frequency TIG arc plasma is not first-order link, but second-order link with an obvious shock. Subsequently, the shock characteristic of TIG arc plasma is investigated under different based values of current and arc length. It is found that the frequency and impedance of resonant point on TIG arc plasma is influenced by base current and arc length. It also shows that the power of pulsed TIG arc is the highest at resonant point.Electron density is one of the most important thermodynamics quantities. The electron density is calculated using Griem’s method independent of the assumption of LTE (Local Thermodynamic Equilibrium), and the spectral line width at half maximum is got by Lorentz fitting. The electron density of pulsed TIG arc plasma under different frequency was tested using synchronizer designed on this work to make sure the synchronization of the spectral signal and the signals of arc voltage as well as current. The results show that the base value and fluctuation amplitude of electron density reach the maximum at the resonance point. It keeps a good agreement with the result derived from the arc power calculation. Low current pulsed TIG arc welding technology is studied. After 304-stainless steel is welded, it can be found that the welding penetration depth and bead width are the largest at the resonant frequency point on the pulsed TIG arc plasma. Compared to the DC TIG arc plasma, the weld penetration depth and bead width are increasing relatively, especially the former. It is twice as large as that by DC TIG arc plasma, and grain size is the smallest without directionality at resonant point. The whole study shows that the resonance phenomenon has engineering significance and practical value.更多还原