We've been using Wivco Spot-Eze spot weld cutter for about three years (100+ cuts). The bits have had to be replaced a few times but the cutter is still sharp.

Tim

http://www.toolsource.com/spot-weld-drill-p-105368.html

https://www.autobodytoolmart.com/2856-wivco-spot-eze-pro-p-11596.aspx