Before I respond,
Does the acceptance criteria for your weld require flash to be present, which some Mil specs do not require if mechanical testing can prove the electrical parameters (voltage, squeeze time, etc) will provide a specific bond strength?
I use different processes and equipment but have similar problems from time to time... protecting the threads is cheaper than an investment in expensive equipment... have you tried appropriate bolt threaded into the nut before welding? Copper or brass may be superior but common steel hardware serves my purpose. I find any kind of grease or anti-sieze helps spin them out.
I'd like to know if it works for you too... good luck.
regards, dee
IS THIS FOR PRODUCTION WELDING? DEPENDING ON WHAT STANDARD YOU USE FOR EXAMPLE CATERPILLAR ALLOWS FOR MIG WELDING NUTS ON IF RESISTANCE WELDING IS NOT FEASIBLE AT THE TIME. PLEASE GIVE MORE INFORMATION. THE OTHER POSTED REMEDIES ALSO WORK.