The Study Of Digital Controlled Double PMIG Welding Process For Aluminium Alloy

Abstract Aluminum alloy is of light, high strength, anti-erode and can be recycled. It isimportant to study aluminum alloy welding technique for its wide application in car,high-speed train and ship. Double-pulsed gas metal arc (DPMIG) welding is a newprocess for Aluminum alloy welding, it has been applied aboard because beautiful beadappearance can be got, pore and crack can be avoided to great extent using this methodin aluminum alloy welding. Only several foreign companies master the technique now,no correlative product and study in china. On the base of MCU+DSP technique, Fulldigital control system design of DPMIG is presented on the basis of PMIG design inthis study, and DPMIG process is studied too. One anolog chip is used for pulse current control in most conventional method,which is hard to take account of control system dynamic and static performance inpeak period, base period and arc-igniting period, so it is hard to get ideal pulse currentwaveform control result. The development of digital control technique and DSP'sappearance provide base of matter for studying digital welding power. Compared withconventional pulse current control method, the full digital control system design ispresented for PMIG/PMAG welding inverter in this study. A PI regulator with variableparameters is adopted for flexibly and accurately controlled pulse current-waveform.The experimental results validated pulse current's rising and falling edge can beadjusted respectively and flexibly, the stable state precision of peak and base current isimproved. Arc-length control is the core of welding process stability. A new arc-lengthsynchronization pulse control method is presented and the higher arc-length adjustmentperformance is achieved within a wide range. For sheet metal aluminum welding,timely adjustment and effective control of arc-length is very important in order to avoidmelt back events in the GMAW mass production in an automated production line. The experimental results validated that the desirable control performance isachieved with the repeatable pulse current waveform, high-speed and stable arc-voltageadjustment. Even if arc length varies with higher frequency and large amplitude in －III－北京工业大学工学硕士学位论文DPMIG, the welding process is very stable. Spatter can be avoided with new arc lengthcontrol design and suitable process parameters. In addition, arc ignition program isdesigned and the stable arc ignition process is achieved.