Abstract: The theory and related algorithm of the nonlinear parameter approximate entropy are introduced. A method for analysing the stability in short-circuiting transition arc welding is put forward based on approximate entropy, which can be helpful to select the welding conditions. With welding variables matched, the current data in short-circuiting transition arc welding are acquired and the approximate entropy of current is calculated. Referring to the traditional theoretical analysis of the best stable arc, the association features between app- roximate entropy and stability are studied by comparing value and standard deviation of approximate entropy. The results show that the better welding conditions are characterized by larger approximate entropy and lower standard deviation, and the lowest standard deviation among the better matching welding conditions indicates the best stable arc.

Key words: Best stable arc, Approximate entropy, Short-circuiting transition, Welding conditions