A Study On The Small Current Plused TIG Welding Power Source And The ARC Physical Characteristics

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.