【作者】 古金茂；

【导师】 殷树言； 黄鹏飞；

【作者基本信息】 北京工业大学 ， 机械电子工程， 2009， 博士

【摘要】 焊接是一种将材料永久连接,并成为具有给定功能的制造技术。随着近年经济的迅速发展,全球制造业的竞争越来越激烈,汽车、集装箱等生产企业大量采用薄板和超薄板以降低成本,因此对焊接过程提出了低热输入的要求。为了迎合这种趋势,交流短路过渡这种低成本、低热输入的焊接方法被提出并受到关注。然而,目前该方法还处在发展初期,国外可参考的资料很少,而国内对此研究目前还尚处于空白阶段。因此,对交流短路过渡方法的控制以及能量分配原理进行学术深入研究,提出理想控制方案,并成功研制出焊接系统平台,成为当前焊接技术发展的一个重要课题。为了满足交流短路过渡焊接方法的工艺要求,设计了基于DSP和CPLD的交流短路过渡焊接电源系统,并成功研制出用于薄板焊接的交流短路过渡焊接电源系统平台。整个系统由主电路部分、控制电路部分以及送丝系统组成。其中主电路部分采用二次逆变结构,并且为了实现焊接过程中的电弧再引燃,增加了全桥高压稳弧电路。控制系统主要由DSP(TMS320F2812)和CPLD(EPM7192S)联合控制实现,其中DSP承担着整个系统所有时序控制和主要控制计算功能,是整个系统的核心,而CPLD则承担着DSP绝大部分与外部进行联系的信号的传递和分配,并实现电平兼容。同时,CPLD还有另外一个重要的功能,即将DSP计算输出的PWM数值,通过运算转变为相应脉冲宽度的数字PWM信号进行输出,实现PWM控制的数字化。由于薄板焊接过程对能量输入非常敏感,送丝系统的稳定与否将极大地影响着整个系统的精度及过程稳定,因此,如何提高送丝系统的精度和动态性能是焊接中不可回避的一个重要问题。本文通过采用DSP(TMS320F2808)和光电码盘,直接采集送丝电机的转速来实现送丝速度反馈控制,使控制目标更加合理。为了进一步提高送丝的整体性能,系统采用模糊数字PI算法进行设计。试验结果表明,送丝系统的静态和动态性能均高于一般电枢电压反馈控制,能够完美地实现送丝稳定性。交流短路过渡焊接方法作为一种新型低热输入焊接方法,由于其提出的时间较短,人们对此种方法的认识还并不深入,此方法在我国尚属空白。本论文从电弧物理的角度出发,分别对焊接过程中不同阶段焊丝和工件的加热情况进行分析、计算,并得出影响交流短路过渡焊接过程热输入的各种参数。根据此理论研究,并结合实际的焊接波形分析,确定并提出了本周期交流短路过渡焊接方法,使焊接过程的能量调节在一个短路燃弧周期之内完成,在保证焊接过程稳定的同时,实现了低热输入控制。为了适应交流短路过渡焊接方法,焊接过程采用了全新的波形控制方案。在短路阶段采用多曲率波形控制,完美实现焊接电流上升曲率的控制,降低焊接过程的飞溅;燃弧时期的EN阶段采用恒流控制,保证了电流稳定;在燃弧的EP阶段,采用多阶梯电压控制,通过电弧的自调节作用实现焊接弧长控制。论文针对所提出的本周期交流短路过渡焊接方法,采用双闭环控制原理,并配合变参数数字PI算法,成功实现焊接过程不同焊接状态的稳定、快速控制。通过合理设计相关程序,保证焊接极性转变过程中的时序要求,以及实现焊接过程中的引弧、焊接过程控制、断弧处理以及高压稳弧等相关过程的处理功能。由于所采用的本周期交流短路过渡焊接方法在一个周期中存在两次电流过零的时刻,因此如何保证过零时刻电弧的再引燃是实现焊接过程能够稳定进行的关键所在。本文通过施加高压稳弧脉冲的方法成功解决了再引燃的问题。并且,为了更好地了解所施加高压稳弧脉冲对过零电流再引燃情况的影响,通过改变稳弧电压的幅值、脉冲宽度、施加时刻、过零前电流大小等条件进行了相关研究,得出了电弧过零稳定的规律,并确定最终高压稳弧方案。为了对论文所提出的理论和公式进行验证,本文进行了大量的试验研究。试验结果证明本周期交流短路焊接方法是一种低热输入的焊接方法。同时论文还针对该方法焊接过程中各种参数大小对能量分配的实际影响作用进行相关试验研究,并得出相应了的规律。通过实际焊接过程中所测得的电流、电压波形、数值、焊缝成形、高速摄像等不同角度,对其进行论证,进一步证实了理论分析结果。更多还原

【Abstract】 Welding is a set function manufacturing technology and makes the materials for permanent connection. With the rapid development of economy, the global competitiveness of manufacturing is growing up, especially in automotive, container and etc., more and more sheet thin plate are used, so low-energy requirement is put up for the welding of thin plates. In order to adapt to this rising demand, the short-circuit arc welding as low-cost and low-energy got attention, and can be tried to make more reasonable. However, this method is still in early stage of development, it has few information can be found at home and abroad. Therefore, it is hard and important to study the principle of control AC short-circuit transfer and energy distribution, to bring up an ideal control scheme and build up a welding system.In order to meet the process requirement of AC short-circuit arc welding, the system for welding thin plates based on DSP and CPLD was designed and investigated. The entire welding system included main circuit, control circuit and wire feed system. The main circuit was used of two inverters and high-voltage full-bridge arc stability circuit to re-igniting the arc. The control circuit was to achieve by DSP (TMS320F2812) and CPLD (EPM7192S), all sequential control and many core computing in the system were controlled by DSP, while CPLD was to transmit and distribute the signals from the DSP to external parts, as well as implement level compatibility. At the same time, CPLD had another important function, which is to transform the processed data from the DSP to digital PWM output signals.Energy input is a very sensitive factor, and the stability of wire feed system is a great impact on the accuracy and stability of the entire system, therefore, it can not be avoided to how to improve the accuracy and dynamic performance of wire feeding system. In this thesis, the closed-loop control of the wire feeding system was achieved through DSP (TMS320F2812) and electro-optical encoder to acquire the electrical wire feed speed directly. In order to improve the overall performance of system, the fuzzy PI algorithm was applied. The results showed that it had a perfect wire feeding stability, furthermore, the static and dynamic performance of the system were better than ordinary one.It is too hard to bring up a best project about the energy distribution on the short-circuit arc welding, because the welding method is new. In this thesis, a variety of factors impacting heat input were analyzed during different stages of the welding process. According to the theoretical study and combining to the analysis of actual welding waveform, a new and flexible AC short-circuit arc welding was brought up. It can complete the energy regulation in one short-circuit arcing cycle, make sure the stability of the welding process and increase the flexibility of energy regulation at the meantime.A new waveform control project was proposed to better transfer different welding process in the AC short-circuits arc welding. At the short circuit stage, multi-curvature waveform control was to control the ascending curvature of welding current to reduce spatter; at EN stage, constant current control was to make sure the current stability; at EP stage, multi-step voltage control was to implement welding arc length control through self-regulation of arc.Based on dual closed-loop control and varying parameters PI algorithm, a new AC short-circuit arc welding method was brought up to achieve stable and rapid control successfully during different status of welding process. Furthermore, rational procedures were designed to make sure the requirement of time sequence at polarity transferring, and complete the control of generating the arc, arc interruption, high-voltage arc stability and other related functions.There exits two current zero during one cycle in AC short-circuit arc welding, so it is a key to make sure arc re-ignition and stability at welding process. In the thesis, high-voltage pulse was to re-ignite arc successfully. In addition, in order to better understand the impact on arc re-ignition, the voltage amplitude, pulse width, the imposition of time and the current before zero-point were investigated to determine the best program.Many experiments were carried out for study the relation between the welding parameters and energy distribution in the AC short-circuit arc welding. The results of theoretical analysis were confirmed through measurement of welding current and voltage, the welding shape, high-speed camera pictures and etc.更多还原