The Research On Square-wave Alternating Current In TIG Welding With MCU

As the further research on magnesium,aluminum and their alloys,and their entensive application on various areas,it is very important to launch the study of magnesium,aluminum and their alloys.Improving the weldability of magnesium, aluminum and their alloys to acquire excellent welding joints is crucial factors to expand their applied range.This paper introduces a digital IGBT inverter square wave AC TIG welding power sources,taking MCU as control core,so as to satisfy the need of positive current's fusion and negative current's cathode surface cleaning during the welding of magnesium,aluminum and their alloys.This paper emphasizes on the component parts and control principle of square wave AC TIG welding power sources.Main circuit,control circuit,protection circuit and drive circuit are respectively analyzed.Otherwise,the software and hardware are also interpreted.Main circuit,which applies IGBT full-bridge inverter structure,is made up of rectifier,filter,high-frequency transformer and the latter inverter.The key points and the parameters of design are discussed detailedly.High performance 16-bit microprocessor 80C196KC is adopted for control kernel.Using universal PWM method means to control output power and output characteristic through controlling IGBT switch on time.The digital signal from microprocessor are firstly converted into analogy signal,which is then modulated by pulse width modulate(PWM) chip SG3525 into two pulses not overlapped each other.At last the pulses are used to spring IGBT after they are magnified by exclusive drive module M57959L.The latter separate two pulses trigger IGBT after they are magnified by special circuit.The system samples output current in real time and bring it to MCU for A/D conversion.This paper also intruduces the resource distribution of microprocessor and the functions of peripheral circuit are given.Aim to typical problems in welding process: over current,over heat,over voltage and lack voltage,a corresponding protection circuit is designed.Reliability and noise resistance designs are also covered.Various noises probably appear in the whole system,as well as their causation,are analyzed systematically. Then,in order to reduce their bad infections,some hardware and software measures are adopted while designing schematic chart,PCB board,and compiling code.The stucture and function of main program and interrupt service subroutine are explained.Corresponding data and waveforms are recorded in the experiment,and problems occurred in experiment are investigated.The experiment results show that the inverter power source has rapid response-speed,high reliability,a strong ability of anti-jamming.At last,some advices on future research for the welding power are given,and they will make a found ground for tomorrow's research of digital welding power.