Modeling And Analysis Of Weld Pool Vibration Characteristics In Pulsed Gas Metal Arc Welding

Pulsed metal inert gas arc welding(P-MIG)is a new kind of technology which joins weldment using periodic variation pulsed current and it conquers the shortcoming exists in MIG that there are many difficulties in the space position welding such as overhead,vertical welding.It is suitable for sheet metal,thermal sensitive material and spatial position component.The biggest characteristic of P-MIG is that it can control the droplet transfer process and the size of welding heat input for the sake of obtaining the best quality of weld.Therefore,pulsed metal inert gas arc welding has been widely used in modern industrial production.The quality of weld is largely determined by the weld pool vibration in the welding process.So in order to control the welding process in real time,it is very important to grasp the information of weld pool vibration.In the past,the study on vibration of molten pool is mainly focused on the extraction of natural oscillation frequency for the relatively stable tungsten inert gas shielded arc welding.But for P-MIG,molten dropping makes the molten pool vibration more complex,so it is rarely in this research.In this paper,a new perspective of wave theory is established to try to understand the mechanism of P-MIG molten pool vibration,which provides a preliminary theoretical basis for the control of P-MIG in real time in the future.Firstly,in this paper,an experimental platform is set up,which is composed of three systems,namely,welding system,high speed image acquisition system and electric signal acquisition system.Through the trigger signal,the high-speed camera and electrical signal acquisition system can work synchronously.Clear weld pool boundary can be got through digital image processing on original pictures taken by high-speed photography,and the measured oscillation information of each point along weld pool for every image is analysed in time domain and frequency domain.Then,real amplitude of each point and the distribution of it along the boundary can be obtained.Based on simple harmonic wave model and wave group theory in the water wave dynamics,a new model of molten pool vibration is presented,which regards the molten pool vibration caused by pulsed arc and droplet transfer as a superposition of several simple harmonic waves.Meanwhile,the parameters of the established modelsuch as attenuation factor,amplitude,wave number,angular frequency and phase angle are determined.Eventually,the vibration characteristics of DC-MIG,one pulse one droplet and one pulse multi droplets for P-MIG are comparatively analysed through the model.Simulation results accord with the fact,which shows that,with increasing of the distance from the center of arc column,the amplitude distribution of the points along the boundary of weld pool is linear decreasing trend for DC-MIG,but a fluctuation decreasing trend for one pulse one droplet and one pulse multi droplets.