【作者】 易小林；

【导师】 单平； 胡绳荪；

【作者基本信息】 天津大学 ， 材料加工工程， 2003， 博士

【摘要】 根据目前国内外在等离子弧焊接过程、质量控制方面的研究可知，等离子弧 焊接过程中电弧的稳定性，焊接质量的稳定性是人们关心的热点，而在小孔等离 子弧焊接中，检测小孔状态并对此进行控制，从而提高焊接质量是该领域的前沿。 本文根据等离子弧与熔池之间的相互作用，分析了等离子云（等离子弧反翘） 产生的机理，并根据焊接熔池形状的变化，分析了等离子云形态变化的机理。根 据等离子弧喷射速度和等离子弧对熔池作用力，分析当工件没有熔透时，在焊接 反方向，沿着熔池上表面最大切线角喷射，形成等离子云的机理。建立了仿真模 型，通过研究，得出等离子云喷射角（等离子弧反翘角）和熔深随焊接电流、焊 接速度等工艺参数之间的变化规律。 根据等离子体鞘层理论，得出了探针在等离子云中所产生鞘层电位的计算公 式，等离子云鞘层电压到达伏级，很容易检测。为了检测等离子云喷射角，提出 了一种用无电源探针检测等离子云的新方法。通过检测等离子云中不同温度、不 同等离子云喷射角下的电压值，可以检测等离子云喷射角进行熔深控制。 研究了探针在高温等离子云中的烧损和熔化规律，结果表明，只要探针位置 放置适当，完全可以用探针检测高温等离子体，因此采用无电源探针法可以检测 高于探针熔点的等离子体温度。 设计了无电源探针法检测等离子云装置，该装置简单、可靠，具有很好的工 业应用前景。通过试验，验证了鞘层理论的正确性，验证了焊接电流、焊接速度 以及探针位置对鞘层电压的影响，并分析了探针位置，焊接电流，焊接速度对等 离子云喷射角的影响规律。 在理论和试验的基础上，将模糊控制理论引入到等离子弧焊接熔深的控制中， 建立了模糊控制器模型，提出了一种通过检测等离子云喷射角，并用电流补偿的 方法，保证等离子云喷射角恒定,进行熔深控制的新方法。仿真研究表明，可以 实现焊接熔深及熔透的智能控制。更多还原

【Abstract】 Nowadays, the stability of arc and welding quality plays a crucial role on the plasma arc welding from the research of the controls of welding process in the world. And it is uneasy to maintain the process of stable welding and to gain a good quality of welding line.The control of welding process and quality is an important problem in the keyhole plasma arc welding. Therefore, controls of the keyhole are an urgent task by means of detecting the state of the keyhole. It is a short cut to improve the welding quality in the plasma arc welding. So people are focused on detecting the size of the keyhole. On the basis ofinterplay between the plasma arc and penetration, the paper analyzes the formation of the plasma cloud in plasma arc welding. The state of plasma cloud is changed when the shape of the pool is changed. The relation between plasma cloud and the shape of pool is pointed out. If work piece is not yet penetrated, the plasma cloud must be existed above the work piece on theoppose direction of welding velocity; On the other hand, if work piece is penetrated, the plasma cloud can.t be existed while plasma efflux must be existed.With the help of the phenomenon, if plasma cloud can be detected, work piece is penetrated, or the work piece is not penetrated. The paper analyzes that the welding time, welding current and welding velocity have an influence on the penetration.From views of plasma arc velocity and plasma arc force, plasma cloud is ejected from the maximal tangent angle of molten pool in the oppose direction of welding velocity when work piece is unpenetrated. The formation of the pool and penetration can determine the angle of plasma cloud ejection.Therelations between the welding current and angle of ejection plasma cloud are fit out by least double multiplication. If the probe is located in the plasma, there is a negative electromotive force in the probe. The paperfirst introduces the model of plasma sheath to explain the mechanism of phenomenon. It offers the formula to compute plasma cloud voltage. The value has only something to do with temperature and plasma component. It is up to the level of voltage and easy to be detected. On the above basis, a device of detecting plasma cloud without power is designed. It is simple and reliable, and has a good future of application in industry. The angle of plasma cloud can reflect the penetration. The location tungsten probe, welding velocity and welding current can change the angle of plasma cloud. The paper studies the rule of melting probe in high temperature plasma cloud. The II<WP=5> Abstract result indicates that the device without power can detect the high temperature plasma if the location of probe is sound. The experiment proves the theory of the sheath. The welding current, welding velocity, and the location of probe can change sheath voltage on the experiment. According to the formula between welding current and the angle of plasma cloud ejection, the theory of fuzzy control is introduced to plasma welding. Detection of更多还原