ArtMetal

Great question, Richard! (Translated: I haven't been asked that before!)

Q: Why does 100 amps when stick welding melt deeper than 100 amps on TIG or MIG?

A: The electrode diameter is the main reason. Also the way the heat is transfered across the arc.

The arc that comes off the stick welding electrode is a larger volume arc than the other two processes. It is a wider "stream" of electrons and also there are larger size "beads" of molten metal that are transferred from the electrode to the base metal.

When MIG welding, you are using a smaller diameter electrode. Less amps are needed to melt the electrode and send the molten "bullets" of metal across the arc. These molten bullets and the small diameter of the electrode make a forceful arc that penetrates deeply into the base metal. (provided the volts and wire feed speed are within a proper range for the base metal thickness and gas used)

In TIG welding, there is a small diameter electrode, but there is no metal transfered across the arc. It is an intense, narrow arc which concentrates the heat in a small area. On thin (<1/8") steel or stainless steel, a molten puddle is established quickly. Aluminum conducts the heat so well that much more amperage is needed to obtain a molten puddle. This is true even though the melting temperature is half that of steel or stainless!

 FYI: In MIG, volts and wire feed are the variables set on most power sources.