GTAW Cold Wire Penetration Depth

When TIG welding without current on the filler wire, you're talking about the cold penetration depth – i.e., how deep the arc melts into the base material before you feed the wire. If you have too little depth, the wire won't melt in cleanly and you'll get porosity or lack of fusion. Too deep is also not good, then the material overheats and the structure becomes brittle. So you need to get a feel for how strongly you melt the base material before you put the wire in – and adjust that depending on sheet thickness and position. Check the weld regularly, then you'll quickly see if you're on the right track.