【作者】 刘超英；

【导师】 黄石生；

【作者基本信息】 华南理工大学 ， 材料加工工程， 2011， 博士

【摘要】 埋弧焊(Submerged arc welding /SAW)以其高效率的特点广泛应用在许多工业场合。多丝焊接也主要采用埋弧焊工艺,多丝焊接又可以分为多电源多丝焊接和单电源多丝焊接两种,单电源多丝焊接工艺中由于焊接电源只有一个,或者说总的热输入量是有限的,焊丝在导电嘴中的摆放位置主要用于热的分布分配。多电源多丝焊接工艺中几个焊丝在一个熔池内燃烧,总的热量输入是单丝焊接热量输入的若干倍,使单位时间内金属的熔化量大大提高,从而可以明显提高焊接生产率。本文所讨论的多丝焊接是指这种多电源多丝焊接。近些年,一种新型的电子控制的焊接电源,开关模式焊接电源出现在许多工业应用领域。这种焊接电源的外特性可以很好的控制为恒压或恒流特性,本文将研究这种电源组成的埋弧焊接系统的电弧动力学模型与稳定机理。一个埋弧焊接系统主要由三部分组成:用于提供热源的焊接电源;用于控制焊接速度的行走机构;用于调节和控制焊接电压和电弧的控制箱。在焊接过程中,焊丝一边连续不断的燃烧,一边由送丝机不断地把焊丝送到燃烧区,两者之间只有达到动态平衡状态才能形成良好的焊缝。在焊接电弧的引弧阶段,电弧从产生到稳定也要经过一段时间的暂态过渡。本文以焊接电弧电压为主要参数,结合焊接电源、送丝机、以及具有PWM控制特性的送丝机电源,建立了具有恒流特性自动埋弧焊接过程中的机(送丝机)电(焊接电弧)一体化动力学模型。模型准确地反映了焊丝在一边燃烧、一边送进过程中的动态平衡关系。模型中得到一个复合时间常数,该常数不仅与控制电路特性有关,也与送丝机特性、电弧特性有关。从理论上为后续自动埋弧焊接的数字化控制奠定了基础。论文通过拉扑拉斯变换从S域对系统模型进行了稳定性分析。由于焊接电源极性的不同以及强电磁场的存在,焊接过程中焊接电源之间的相互隔离、电弧之间的相互协同配合成为多丝焊接协同控制器需要主要考虑的问题。根据上述特点和要求,除了采用传统的继电器隔离技术和变压器隔离技术外,选择光隔离技术作为各电源之间信号/命令的传输媒体,明显提高了系统的抗电磁干扰能力,也提高了系统的灵活性、减小了设备的体积。另一方面,机械设备的数字化和智能化已经成为当今工业社会的主要发展趋势,论文提出了一种适用于多台设备同步协调控制的程序结构,即任务-作业-进程程序结构。在这种程序结构下,多设备的数字化同步控制变的清晰明了。根据理论,设计了模块结构的多丝焊接协同控制电路,电路布置在一个20cm*30cm的PCB(印刷线路板)板上。电路中包括两个方便控制的共地式Buck结构直流/直流电源,一个用于焊接速度(即行走小车)的控制,一个用于电弧和送丝速度的动态平衡控制。论文还报告了一种基于集成电路SG3525的PWM信号发生器及其调节方法、比例放大器系数的整定与选择、复合时间常数的估计与设计等。在实际设计的控制电路中,还考虑了几个子焊接系统的级联问题、电源的软启动和过流保护、电弧收弧阶段防止焊丝插入熔池的控制方法等。根据实验结果,双丝焊的焊接速度可以提高到1.4-2.0(m/min),三丝焊的焊接速度可达到2.5-2.8(m/min),符合理论分析结果和有关文献报道的结果。更多还原

【Abstract】 Submerged arc welding (SAW) is a popular welding method used in many industrial fields because it has the property of high productivity. The technique of multi-electrode welding, or multi-wire welding, is commonly used in submerged welding processing. Multi-electrode welding can also be classified into two groups, single-power-supplied (SPS) multi-electrode welding and multi-power-supplied (MPS) multi-electrode welding. In SPS multi electrode welding system, the heat supplied from one single power, the total heat input being limited in a definite value, wires are used for heat distribution in welding processing. In MPS multi-electrode system, two or more welding arcs burning in one molten pool, the heat input is several times of single power supply. It greatly incases the welding productive because the amount of melting metal in a unit time is increased. In this paper, we refer to this kind of welding scheme as multi-electrode welding.In recent years, a new type of electronic controlled welding power supplies, switch-mode welding power is emerged and used in industrial field. The output character of this power can be well controlled ether in constant voltage (CV) mode or in constant current mode (CC). The dynamic model and the stability of welding arc under this power supply in submerged arc welding are studied in this paper.Generally, a submerged welding system consists of three parts, a power supply for heat input, a bogie for welding speed control, and a control unit for welding arc adjusting. In the welding processing, wire is burned in the arc, and is sent into the arc by the wire feeder at same time. A smooth welding seam could be obtained only if a balance were reached between the speed of wire burning and the speed of wire sending. In the period of arc initiation, a transient is existed from the time of arc igniting to the time of arc stable. Taking welding arc voltage as major a parameter, cooperated with power supply and wire feeder, an electron-mechanical dynamic model of submerged arc welding in constant current condition is established. Under this model, the balance relationship between wire burning and wire sending is depicted. A compound time constant, which is derived from control circuit, wire feeder, and welding arc, is obtained. It is the theoretical foundation for the further designing of numerical controller. The stability of the system is analyzed in S domain through Lap lace’s transformation.Due to the defference of electronic poles in defferent power supplies and the electron-magnetic interference (EMI) in multi-electrode system, the isolation schemes among powers and the coordination method among arcs become the major problems which need to be solved in multi-electrode welding. According to the character and request above, optical isolation technique is used for the transmission of signals or instructions among equipments besides the traditional relay- and transformer-isolation schemes. The ability of anti-EMI of the system is increased. And it also enhances the adaptability and reduces the bulk of the system. Furthermore, the trend today goes towards numerical equipments in mechanical field. A task/job/procedure program structure for several devices working coordinately is reported in the paper. Under this structure, the method of numerical synchronization for several devices becomes easy and clear.Based on the theory, a module structured multi-electrode welding coordinate control circuit, which is placed on a 20cm*30cm printed circuit board (PCB), is designed. Two DC-DC converters, which derived from Buck converter but power ground and gate drive signals ground are common earthed, are designed on it. One is designed for the bogie speed control, and another is for the balance of welding arc and wire feeder control. The principle of a pulse width modulation (PWM) generator and its adjusting method based on integrated circuit SG3525 is reported. The method of the parameters selection of operation amplifier, estimate and design of time constant, are reported as well. Some of the specific questions, such as the method of series connection of several sub-systems, soft start, over current protection, and the prevention of wire inserting into the molten pool during wind up are discussed.According to the experimental results, the welding speeds reached to 1.4-2.0(m/min.) in double-wire welding, and to 2.5-2.8(m/min.) in three-wire welding. The results tally with the theoretical analysis, as well as the reported results in some related references.更多还原