Development Of The Digital Control System For Submerged-arc Welding Machine Basing On MSP430 MCU

The automatic submerged-arc welding has much merit, such as high efficiency of production, excellent quality of welding product, good circumstance of working field, etc. It is using widely, along with the developing science and technology, the users'demanding welding quality is getting higher, the analog control system of SCR submerged-arc welding machine couldn't satisfy the demand, so applying the digital control technique into the control system of submerged-arc welding machine has important academic meaning and practical purpose of appliance.On the base of MZ-1000A SCR automatic submerged-arc welding machine, we have designed the digital control system for submerged-arc welding, which control core is MSP430F149 MCU.In accord with request of automatic submerged-arc welding, here using menu to design a man-machine interactive system, the system has functions: Interface can easily be changed if user has operated; The welding parameters can be changed and modified conveniently; It can complete the function of forward and backward feed wire by manually operation; The parameters and status of power can be display and show dynamically. The whole man-machine interactive system has friendly interface, visualized display, convenient manipulation, and so on.The paper has designed the system circuit and software program for the digital control system for submerged-arc welding machine. The system circuit contains welding voltage and welding current sampling circuit, wire feeding device controlling and driving circuit, welding current presetting and driving circuit, welding tractor's velocity presetting and driving circuit, welding tractor's direction controlling circuit, etc. In the current and welding tractor's velocity's presetting section applying the digital potentiometers, this makes the digital giving parameters which is outputted by the MCU transfer to analog electric voltage which we need, thus finishing the function of original analog potentiometers. The power system employed the strategy of welding voltage feedback control alternate wire-feed system, finishing the design of PWM driving and controlling circuit for wire feeding device, and composing corresponding program.Welding voltage feedback control alternate wire-feed system employs the PI algorithm, uses Simulink in MATLAB to emulate the system, the result of the emulation can help to adjust the PI control parameters. According to the emulation and experiment , the PI control parameters was fixed at K_p =1.5, K_i=1000; The arc extinguishing control method is backgo arc extinguishing control method, it is through controlling standstill arcing time and backgo arcing time in arc extinguishing stage to control the effect of arc extinguishing.The welding experiment indicates the following conclusion. When limiting the duty ratio range of PWM in 0%~60%, we can use wide-ranging of welding voltage in range of rated welding voltage, the welding process is stable, the whole welding seams have good quality; Employing backgo arc extinguishing strategy can achieve good crater molding effect.