Research Of Waveform Digital Control Method Of A Low Spatter Pulse GMAW Welding Machine

Pulse GMAW has been widely used in manufacturing industry as its advanteages of strong flexibility, high efficiency and energy saving. It can achieve high qulity welding beam in larger current adjusting range. But the disadvantage is that the complexity and randomicity of droplet would make transfer hard to keep its status and form, so it is harder to a control accurately heat input during the stage. The spatter that generated by explosive liquid medal due to asymmetrical and unsteady of droplet in uncertain transition stage would cause welding defects. So the effective method will be needed to control the droplet transfer in stable condition which is good for enhancing welding appearance of GMAW.The research is carried out under support of National Natural Science Foundation(Grant NO.:E51375173). A new type of digital pulse GMAW welding machine was built, and welding process is controlled accurately through medium current control method. The prototype is been designed with four working modes:normal pulse, middle medium pulse, rear mediulm pulse, constant voltage.The thesis firstly introduced backgrounds of issue, analysed present situation and development trend of pulse GMAW welding, then discussed the influence of welding beam by droplet transfer and analysed the influence of process parameters and reason for spatter. Secondly, according to the characteristic and requests of GMAW, accomplished prototype based on core of ARM micro processor belongs to Cortex-M4, including the hardware design such as full bridge inverter circuit, the structure of control system, power module and minimum system of chip, then the program dedign of main control board and digital panel based on RTOS(RTX). Finally, completed lots of process test with the help of oscilloscope, voltage regulator and manipulator. Observed and compared welding quality in different modes, especially the case of spatter, thus to analyse the effectiveness of control method.It turns out that, the welding beam under medium current control method is superior to that of normal pulse modes, the droplet transfer of former one is more stable and regular, better beam formation with uniform width and sufficient depth, and spatter is significantly reduced. The formation sort is as follow:rear mediulm pulse, middle medium pulse, normal pulse, constant voltage.