【作者】 刘强；

【导师】 宋永伦；

【作者基本信息】 北京工业大学 ， 机械电子工程， 2012， 博士

【摘要】 在焊接领域中,直流TIG焊接被公认为是一种优质的焊接方法，但由于其工艺及早期TIG焊机技术不够完善，应用范围受到了一定的限制。近年来，为充分挖掘TIG焊的潜在优势，许多科研人员和工程技术人员对TIG焊在能量输出和工艺等方面进行了大胆的探索，特别是晶体管逆变技术、微电子控制器件、微处理机、数字信号处理器和计算机软件技术在TIG焊机中的成功应用，全面提升了TIG焊接工艺水平和TIG焊机性能，其中脉冲TIG焊接技术因热输入量低、能量密度大、高效节能等优点，成为各重要工业制造部门焊接高质量不可缺少的现代加工手段。根据直流脉冲TIG焊接技术的特点，本文设计了一套直流脉冲TIG焊接系统，系统主要包括基值电源、脉冲电源和人机界面三部分。基值电源主回路采用双功率管并联BUCK结构，即提高了工作频率，减少了输出电流的波动，同时也降低了功率管的损耗，为TIG电弧提供稳定的维弧电流；脉冲电源主回路采用全桥二次逆变拓扑结构，对于不同工作频率都有很强的适应性。一次逆变采用双PI调节方式，实现精确快速地功率输出控制，二次逆变控制采用ARM+CPLD结构，实现脉冲的频率，占空比等功能控制。双PI方式可以实现精细控制，同时又具有较高的实时性，对短路、过流等故障具有较强的保护能力。控制软件是电源系统的核心，脉冲电源控制软件采用前后台+流水线的控制结构，将通信、MODBUS协议解析、电压信号的采集、电流信号的采集等任务放在流水线上，通过任务状态的查询，实现最短周期的调度。PI算法在前台实现，周期的更新PWM调节量。这种结构与传统的串行结构相比，具有更高的实时性、更合理的软件结构性和更高的CPU利用率。高频变压器作为焊接系统的主要器件，其设计方法众多，本文采用有效面积Ae和磁链路长度Le作为控制参数，根据电磁理论，提出了新的设计方法，并对设计方法进行了详细推导。最后根据实验需求，依据文中设计方法对主功率变压器进行设计，在实验中变压器工作良好，证明了此方法的有效性。在小电流条件下，通过脉冲TIG电弧电特性的测量与研究，发现平均电流相同的实验条件下，频率为2500Hz时输入功率出现最大值，此时平均电子密度最大，随频率的提高，使得脉冲电弧的脉动特性趋向直流特性。通过对脉冲电弧的基值、峰值以及上升沿的电特性分析，在脉冲由峰值电流跃变到基值电流后，电弧电压和动态电阻可由一个惯性环节描述；脉冲由基值电流跃迁到峰值电流，可由三阶系统描述。研究发现，电弧在基值时的状态对电弧的影响比较大，随电弧频率的提高增强。最后，采用文中设计的脉冲TIG焊接电源对0.8+1.5mm不锈钢（0Cr18Ni9）薄板进行叠焊工艺实验，保护气分别用Ar、A_r+H₂（1%）、A_r+H_e（5%）,实验结果表明，在A_r+H₂（1%）保护气氛围中，当脉冲频率为2500Hz时，脉冲TIG焊接方式能有效地降低工件热输入，减少工件焊接变形，使焊接质量显著提高。更多还原

【Abstract】 DC TIG welding is generally acknowledged to be a high quality welding methodin the field of welding, but its range of application is limited because of imperfect forthe welding process and the early TIG welding technology. In recent years manyscientific researchers and technical engineers have valiantly explored the method ofTIG welding to exploit its latent advantages. With the successful application of sometechnologies, such as transistor inverter technology, microelectronic control devices,microprocessor, digital signal processor and computer software technology, theoverall technical characteristics of TIG welding method and TIG welder raised.Among all the application, DC pulse TIG has been one of the indispensable modernmaterial processing means because its advantage of low heat input, high Abilitydensity, energy efficiency and so on. This technology has been used by almost all keymanufacturing industry sectors.According to the characteristics of the DC pulse TIG welding technology, A DCpulse TIG welding system is designed in this paper. The welding system mainlyconsists of three parts: the base power supply, pulse power supply, and user interface.The main circuit of base power source uses BUCK structure with dual power tubes.This structure not only reduces the fluctuations in the output current by improving theoperating frequency, but also reduces the loss of power tube. The main circuit ofpulsed power supply uses the twice full-bridge inverter topology. In the first inverterthe double PI regulator is used to achieve quickly and accurately power output control.In the second inverter the ARM+CPLD structure is applied to control the outputfunction. The double PI regulator not only achievesduanlu fine control, but also hashigh real-time with a strong ability to protect short circuit and overcurrent faults.The software is the core of the welding power control system. The interrupt andthe pipeline structure are used in the pulse power control software. The tasks,including the communication, MOBUS protocol analysis, and data acquisition and soon, are placed on the pipeline. The PI algorithm software running in the foregroundupdates PWM fixed cycle regulation. It is compared with the traditional serialstructure. The comparison indicates that this structure has higher real-time, morereasonable structure and the CPU utilization.High frequency transformer, which is the main components of the weldingsystem, has many design methods. In this paper, by adopting the Ae and Le as thecontrol parameters, a new design method based on electromagnetic theory ispresented and derived in detail. Finally, according to the needs of experiments, thetransformer is designed based on the method. The transformer works well in theexperiment and this indicates the effectiveness of this design method. By pulsed arc physical parameters measurement in the small current conditions,the arc input power and the average electron density reach the maximum value whenthe pulse frequency is2500Hz. While the arc input power and the average electrondensity decrease gradually with increasing frequency, the increasing influence of thethermal inertia makes the pulsed arc characteristics approach the DC characteristics.Through the electrical characteristics analysis of peak current, base current, and therising edge, arc voltage and dynamic resistance could be an one-order systemdescription after peak current transition to the base current, while arc current can be athird-order system description by the base current transition to peak current. Throughthe mode system study, it is found that the arc thermal inertia in the base current makea great impact on the arc and the impact is enhanced with the improvement of the arcfrequency. This show the response of the arc on the external power supply frequencydepends on the physical parameters of the base status.Finally, the experiments on the0.8+1.5mm of stainless steel （0Cr18Ni9） sheetsof the stitch welding procedure is done by using the pulsed TIG welding power sourcedesigned in this paper with the protective gas of Ar, Ar+H2（1%） and Ar+He （5%）.Experimental results show that, the Ar+H₂shielding gas pulsed TIG welding methodcan effectively reduce the heat input and the welding deformation of workpiece whenthe pulse frequency is2500Hz, while this method can also refine grains and improvethe quality of welding.更多还原