unfortunately I have no ideaMy guess would be... Unobtainable, unless the machine's been built from a chip manufacturer's data sheet and its sample circuit in the back.
If it's a special made for the manufacturer, you'll probably have to buy the complete PCB and still won't know why it blew in the first place), if it's generic (and the manufacturer will tell you what it is) you'll still need to know why it blew...
What's the board do? what (if you know) happened as it was blowing the chip off the board (always a bad sign)?
Makes two of us... Any chance you could take a pic of the other side of that board? it looks like it may be the welding current output board (one of the thick cables goes off through what looks like a current sensor - do they go to the DINSE terminals for torch and earth?), looks like it'd come off the chassis with 5 (and a missing) PK screws on the top and bottom edges, be careful with any connectors on the invisible side! Take photos as you go along!unfortunately I have no idea