Backing Gas Displacement Phase

The displacement phase describes the initial purging of ambient air located in closed cavities by the lighter or heavier backing gas. The duration of this phase depends on the volume and inlet geometry of the component to be purged.

The purge phase is the first step in forming. You blow the air out of the hollow body by letting in the shielding gas. The gas must completely displace the air, otherwise you'll get porosity in the weld and the part won't be right. If you purge too short, residual air remains and you get a bad root. If you purge too long, you create overpressure in the part, which can deform it. The correct purge time depends on the volume and geometry of the part; you need to develop a feel for it and stick to the specs.

MetallurgieSchweißtechnik