Research On Automatic Control Of Underwater Wet Weld Forming In Shallow Water

Underwater welding is one of the key technologies for marine industry and underwater structure maintenance. With the urgent demand of exploiting deep-sea resources, the industry put forward higher requirements for underwater welding. Wet welding which has advantages in monitoring costs, environment adaptability and operational flexibility is the most widely used underwater welding technology. However, currently, most wet welding operations were completed manually by diving welder, the welding efficiency was low and it was difficult to guarantee the weld quality. Automation is the development trend of engineering and manufacturing. The combination of wet welding and automation technology is an important method for improving welding quality and working efficiency, and it has broad prospects.Flux cored arc welding(FCAW) is an important developing direction for underwater wet welding automation. This paper established a wet FCAW underwater welding test platform and the welding parameters were accurately controlled. In the meantime, the real-time acquisition and storage of welding information was realized. Then, an electrical signal processing program was designed for voltage and current signals collection. This program provided waveform filtering and statistical analysis processing, and extracted characteristic parameters reflecting the welding process quality. In order to measure the forming value of weld seam, a wet welding active vision sensor system with laser source was designed and the corresponding image processing algorithm was developed.The effect of weld forming is one of the key standards for measuring the quality of weld joints. In this paper, the influence factors of weld forming and welding stability in shallow water environment were studied through wet FCAW welding tests. Using the orthogonal test method, the mathematical model of welding parameters(voltage, current, welding speed) and weld geometry morphology(width, reinforcement) were established. Through the statistical analysis and evaluation of the fitting degree of three types of mathematical model, exponential model displayed smaller standard residuals, higher credibility and better regression significance, and it was suitable for the weld automation control.PID control and fuzzy control were devised to improve the forming effect of wet FCAW weld. In contrast of the simulation results, the fuzzy control program was designed, and the closed-loop control system of the weld bead was established. For testing the effectiveness of the fuzzy control system, changing of height of the torch position experiments and the voltage changing experiments were conducted. The experiments results and electrical signal analysis showed that the wet FCAW welding control system improved the stability of welding process with quick response adjustment. Undercuts, slags inclusion, overlaps and other welding defects were eliminated, the fluctuation of weld formation was weakened and the stability coefficient of weld bead was improved over 100% on average. Above all, the established system showed remarkable effects in improving weld forming quality.