The Study Of Digitalized Control System For GMAW-P & Double GMAW-P Inverter

GMA welding becomes more and more important with the application anddevelopment of semi-automatic and automatic welding, it approximates 25% among allkinds of welding methods in china, and 50~80% in advanced industry countries. GMAwelding is of high efficiency and good quality, and PMIG/PMAG welding as onemethod of GMA is with wide process scope and good environmental protection effect.It is important to further improve PMIG/PMAG welding control performance andcorresponding process performance by full digital control design in welding machineresearch. The full digital controlled PMIG welding inverter (based on DSP) is studiedand a new sheet metal aluminum welding process-Double PMIG is tried in this paper. For constant current characteristic (I-I) PMIG/PMAG welding inverter, oneanolog chip is used for pulse current control in most conventional methods, which ishard to take account of control system dynamic and static performance in peak period,base period and arc-igniting period, so it is hard to get ideal pulse current waveformcontrol result. At the same time, the conventional pulse welding arc control designbased on micro-computer differs from the usual discrete sample system, the regulator isused in design and pulse frequency usually varies, which leads to arc-voltage samplesynchronized with pulse frequency becomes multirate sampling, Z transform can't beused for analyse of arc control system dynamic process. In addition, pulse arc model ishard to describe accurately, so regulator parameters is hard to set. Even if regulatorparameters has been set, it is hard to get ideal arc adjust characteristic in wide weldingcurrent scope. In order to solve the above problems, the full digital control system design ispresented for PMIG/PMAG welding inverter in this study. A PI regulator with variableparameters is adopted for flexible and accurate controlled pulse current-waveform. Theexperimental results validated pulse current's rising and falling edge can be adjustedrespectively and flexibly, the stable state precision of peak and base current is improved.So, compared with conventional pulse current control method, stable and accuratecontrolled drop transition is obtained over wide welding current scope, and arc is stableduring base period even if base current is small. In addition, a new pulse arc controlmethod, which is arc-length synchronization pulse control method is presented, and thehigher arc-length adjustment performance is achieved within a wide range. For sheetmetal aluminum welding, timely adjustment and effective control for arc-length is veryimportant for avoiding meltback events in the GMAW mass production in anautomated production line. －III－北京工业大学工学博士学位论文 The experimental results validated the above full digital control system design forPMIG welding inverter, the well repeatable drop transition, and stable arc are obtainedfor variable parameters PI regulator design in pulse current control, and the arc-lengthbecomes robust against the variations of welding conditions for completely new pulsearc control design in arc-length adjustment. The control performance andcorresponding process results improved greatly for full digital design. Double-pulsed gas metal arc (DPMIG) welding has been applied aboard becausebeautiful bead appearance can be got, pore and crack can be avoided to great extentusing this method in aluminum alloy welding. In this study, the wire-feed velocitykeeps constant during DPMIG welding. Only several foreign companies master thetechnique now, no correlative product and study in china. Full digital control systemdesign of DPMIG is presented on the basis of PMIG design in this study, and DPMIGprocess is studied too. The desirable control performance is achieved with therepeatable pulse current waveform, high-speed and stable arc-voltage adjustment. Theexperimental results validated even if arc length varies with hig...