Reverse Polarity in Welding

Reverse polarity for DC welding is called DCEP (DC Electrode Positive). Electrode is positive, work piece is negative. Electrons flow from work piece to electrode. This makes sense from first principle analysis of the underlying physics. Deeper penetration is obtained - as the electrons in the work piece are more energetic prior to jumping to the electrode. The work piece is hotter - and you want the heat at the work piece, not electrode.

https://www.everlastgenerators.com/blog/ac-dcen-and-dcep-when-use-them-when-not-use-them-part3