Research On Pulsed Ultrasound Assisted Arc Shape Of GTAW And Droplet Transfer Of GMAW

Pulsed ultrasonic assisted arc welding is a novel welding method based on continuous ultrasonic assisted arc welding.In the previous study,there are two main problems: one of them is that the pulse frequency is very low(0-15 Hz),and there is a large difference between the drop frequency(around 100 Hz)and the droplets;and another is that the application of pulsed ultrasound is random.These two problems make it difficult to analysis of experimental phenomena in-depth.Regarding the above problem,the thesis takes improving the ultrasonic generator as an entry point.The pulsed ultrasonic frequency is raised to 200 Hz by changing the pulse generation way of the ultrasonic generator,which reaching the same magnitude as the frequency of droplet transfer.The main research object in the thesis is the change of arc shape during welding process and droplet transition in the process of aluminum alloy MIG welding.In the TIG welding process,pulse frequency,emitter height and welding current are the main experimental parameters,the influence of parameters on arc shape is studied.In the MIG welding process,the pulse frequency and emitter height are the main experimental parameters,the influence of the parameters on the droplet transfer mode,droplet size,and arc shape is studied.For different experimental methods,suitable research objects are different.For example,TIG welding does not have droplet transfer without filling the wire;during the MIG welding process,the feeding speed of the wire cannot be completely the same as the melting speed.Therefore,the arc shape change drastically,and it is difficult to analyze the arc quantificationally.Therefore,the experimental method in the thesis is not be limited,which is selected according to different research object.For TIG welding,the arc is stable during the welding process,so the parameters of the arc shape is analysed quantificationally.For the MIG welding of aluminum alloys,the study mainly focuses on the typical projected transfer process,and studies the dynamic changes of the arc shape.Based on the above,the thesis further proposed pulsed ultrasonic wave assisted GMAW(PU-GMAW).In the pulse GMAW process,the droplet transfer mode could realize “one drop per pulse” by adjusting the welding parameters,which means that the droplet transfer process has a corresponding relationship with the pulse current signal.By collecting the pulsed GMAW current signal,information such as the droplet transfer duration and the droplet transfer start time can be obtained.The current signal could be processed as a control signal,so that the ultrasonic generator could output an ultrasonic signal,having a certain correspondence relationship with the control signal,which means a relatively clear correspondence relationship between the ultrasonic action time and the droplet transition is established.This study focuses on the effects of different matching modes of pulsed ultrasound and pulsed GMAW on the arc shape and droplet transition during welding,fully excavating the potential of ultrasonic in the welding process,and laying the foundation for “the noncontact control” of the droplet transition process.