Abstract: The structure-borne acoustic emission signals in resistance spot welding on low carbon steel are detected in real time, and are used to characterize the expulsions occurred in welding process. The results show that the expulsion can be classified as three modes by the waveform of AE signals detected in welding process. The difference of expulsion mode indicates the difference of the equivalent weight of expulsion. The expulsion can be assessed by two characteristic parameters of expulsion event: positive peak and acoustic emission (AE) count. The positive peak and AE count are high, which indicates the expulsion amount released in welding is large; Conversely, the expulsion amount released in welding is small. The welding current is more important than the welding time and electrode pressure as inducing factors of expulsion. The equivalent weight of expulsion increases as the welding current and welding time increasing; but the equivalent weight of expulsion decreases as the electrode pressure increasing.

Key words: resistance spot welding;expulsion;acoustic emission;welding parameter