Spatter

Spatter is metal that leaves the process without becoming weld. In short-circuit transfer, the wire touches the weld pool, the circuit shorts, and the resulting current surge can vaporise the bridge violently enough to eject droplets before a clean transfer occurs; in globular transfer, gravity detaches oversized drops irregularly rather than at a controlled rate. Both mechanisms are sensitive to arc voltage, inductance and shielding gas composition, which is why a change in any of them shows up as a change in spatter rate before it shows up anywhere else.

That sensitivity is why spatter is worth more attention than its cosmetic reputation suggests. A weld can be structurally sound and still be throwing spatter, but a rising spatter rate during an otherwise unchanged production run is one of the earliest visible symptoms of arc instability — a wandering arc length, a feed fault, or shielding gas drifting out of specification — the same instability that, left uncorrected, goes on to disturb pool geometry and raise the risk of porosity and inconsistent fusion. Camera-based process monitoring increasingly reads spatter rate as exactly this kind of leading indicator rather than only as a cleanliness metric.

Adherent spatter that fuses onto the finished surface is a distinct condition from loose spatter that brushes off, because adherent particles can sit close enough to the joint to interfere with subsequent NDT or coating adhesion. It is conceptually related to an arc strike in that both put unwanted metal or heat outside the intended weld path, though the mechanisms differ: spatter is ejected molten filler, while an arc strike is localized melting of the parent material itself.