Research On Fractional Order Control Of The Droplet Transfer In Double Wire Pulsed MIG Welding

One of the most basic methods to improve welding efficiency is the multi-wire welding.Twin-wire welding is the basic way of multi-wire welding. So research on twin-wire weldingis of great significance. Many domestic and abroad researchers focused their study on doublewire welding droplet transfer process and the formation of weld pool. The existing resultshave demonstrated that the control of droplet transfer behavior will control the weldingquality. It is certain that in-depth study to double wire pulse welding control method andwelding droplet transfer process as well as the weld pool taking shape will provide the theoryfor new control technology and improve welding performance.Twin-wire pulsed MIG welding is a high efficient welding method which has a widerange of practical applications.Thus the study of double wire pulsed MIG welding hastheoretical and practical significance. On the basis of the mechanism of pulsed welding,wepointed out the most basic as well as the most important parameters which affect the droplettransfer in pulsed welding are the peak current Ip, peak time Tp, base current Iband basic timeTb. These parameters are associated with the duty cycle, thus to control these parameters canbe achieved by controlling the duty cycle. By using the state space variable method to analysethe chaotic characteristics of inverter arc welding system,we noted that the root cause for theneeds of the specification parameters match in arc welding system is determined by its chaoticnature of the tie. Also the feed-forward&feedback control principle of the self-developedsoft-switching inverter is analysised. Then a small signal model of the welding system isestablished based on the method of three-terminal-switching device modeling.This article first introduced the hot spot in control field---fractional theory into the arccontrol and pointed out using the fractional-order PID controller in the control system of arcwelding.Then the application of the fractional theory in arc welding control field is discussed,and a range-graphic method of design on fractional order controller is put forward. A kind ofintegral type of fractional order controller (PIλ) is designed depend of the model, andcompared with the traditional integer order controller (PI) in simulation. The simulationresults show that the fractional order controller is better than the integer order controller in theregulation of dynamic performance, less overshoot5%. It improves the double wire weldingtechnology dynamic performance. The single wire welding test using the fractional ordercontroller is done, the test effect is better than the integer order controller.A high-speed dual-wire pulse welding system and high-speed photography experimentplatform are built. The double wire welding experiment platform is composed of a two-wire torch with water cooling system, of two inverter power supplies1250A and1000A. Thebacklight shadow method is used to photograph the droplet transfer behavior in the high speedphotography system. The backlight light comes from a high power semiconductor laser. Thecamera's type is FASTCAM Super-10KC color digital high speed camera, which can take10,000pictures per second. That can fully meet the experimental requirements. By high speedphotograph system, the welding droplet transfer process can easily be observed and analyzed.Large-current high-speed welding process of twin-wire test is studied. Under somewelding conditions, it is studied that the current phase relationships between the host andslave in double wire pulsed MIG welding, and the influences of droplet transfer and weldformation when pulse current frequency changes. The research results are:(1) the arc shape offormer and rear wire is not effect and is showing cone shape while their pulse current phaseschange by turn;(2) the arc shape is showing peach-shaped while their pulse current phaseschange synchronously, and the reason is the appeal caused by the same direction weldingcurrent of two wires;(3) the weld quality while their pulse current phases change random isbetween that in synchronization and by turn.The pulse current frequency will change the droplet transfer method of the former wireand the rear wire. With the welding specification of current phase changing by turn, thedroplet transfer manner of former wire is shot drops, and that of rear wire is jet transition withhigher frequency. The droplet transfer manners of former wire and rear wire are shot dropstransition with lower frequency. The droplet transfer manners of former wire and rear wire arejet transition with medium frequency. The droplets behave almost one-pulse-one-drop whilepulse current frequency changes around middle frequency. The welded shape is good whenthe pulse current frequency changes between50Hz and100Hz, and the welded shape qualitywill change depend on the pulse frequency.