Analysis and improvement of underwater wet welding process stability with static mechanical constraint support

A process variant of underwater wet welding (UWW), i.e., mechanical constraint-assisted UWW process, was developed. Through the visual sensing of arc bubble and welding electrical signals, the optimum parameters of mechanical constraint system were determined. Variations of arc stability, arc burning process, and weld morphology with arc voltage were investigated under the same mechanical constraint condition. Results indicated that the coefficients of variation for the two processes initially dipped to a minimum and then gradually increased to a higher value with increasing arc voltage, but the change rate of variation coefficient in UWW was much more pronounced than that in mechanical constraint-assisted UWW (MC-UWW). When the arc voltage was lower, the proportion of short circuiting process was so high. Thus, there was room for further reduction by mechanical constraint. But the further reduction room became still effective when the arc voltage was larger because the proportion of arc extinction process was already large enough. Weld morphology results showed that the increment of weld penetration decreased from 0.91 mm to 0.18 mm with the increase of arc voltage when mechanical constraint was applied. In addition, the increment trend was very significant when arc voltage was within the range of 20 V to 28 V. For the welding conditions in this study, a suitable voltage range in conjunction with optimum mechanical constraint condition can be determined to achieve a more stable welding process in MC-UWW.