Research On Double-wire MIG Welding Digital Controlling System Based On DSP-PIC

Welding technology was the key technology in modern shipbuilding, and the welding efficiency directly affected the cost of shipbuilding and shipbuilding cycle. Currently, the FCB welding was widely used in the shipbuilding industry. But it had many shortcomings of narrow soldering conditions, complex welding equipment, high production costs, and quality problems. Therefore, it had some practical significance to research and develop a new efficient welding method to replace the FCB method which would improve the welding quality of steel plate and reduce the production costs. In this paper, based on the theoretical analysis, a set of DSP-PIC based on the double wire MIG welding control system was proposed, for improving the welding efficiency and welding quality, and this had a great significance to replace the FCB welding method.Firstly, single-wire and double-wire pulsed MIG welding theory were analyzed from the arc shape, the droplet transfer, and the pool characteristic, and the overall program of the double-wire pulsed MIG welding system had been identified, which was coordinated by master-slave controlling mode. For each of the arc welding power sources, TMS320F2812 DSP chip was responsible for signal processing,and PIC16F877A microcontroller was responsible for establishment and management of the process parameters. Asynchronous serial communication had been used between DSP and PIC,and CAN bus communication protocol was used between the master and the slave DSP system. For the simple structure, good reliability, timeliness and good flexibility, CAN bus ensure the master-slave system work coordinately.Based on the function of the whole double-wire MIG welding power, controlling circuit system had been designed containing the DSP as the core, PWM signal generating circuit, IGBT driving circuit, the signal sampling circuit and feedback circuit, wire driving circuit, fault detecting and protecting circuits and some other hardware. PIC microcontroller had been used for parameter input and output, controlling the keyboard and LCD and digital tube display, and through personalized control panel showed the management of welding parameters.Then according to DSP and PIC system, software programs had been developed respectively in CCS3.3 and MPLAB7.50 environments to achieve the controlling functions of DSP-PIC. Compiled programs included system initializing program, the main welding program, A/D conversion program, interrupt service routine, keyboard scanning program, LCD and digital displaying programs.Finally, simulated experiments for hardware and software of the system had validated the feasibility of the design. DSP had generated the ideal PWM output waveform for driving the power switching devices IGBT. Through the liquid crystal display and multistage menu type operation it realized DSP-PIC digital MIG welding parameter setting and management. It had realized coordination communication between the the double DSPs, and controlled two sets of DSP systems producing synchronous and asynchronous and random waveform, thereby ensuring the system could work in the three modes. Considering the interference sources in welding sites, the corresponding hardware and software anti-interference had been designed.