One of the most used / common tools is a Rotabroach

The most used size is 3/8 inch.

Rotabroach Spot Weld Cutter Kit
https://www.google.com/search?q=Rotabroach+Spot+Weld+Cutter+Kit&ie=utf-8&oe=utf-8

https://www.google.com/search?q=Rotabroach+Spot+Weld+Cutter+Kit&source=lnms&tbm=isch&sa=X&ei=Egq_VJKAFI2xyASuyILQCg&ved=0CA kQ_AUoAg&biw=1280&bih=891

FYI: Most automotive prototype shops require mechanics have in your toolbox, and know how to use at least a basic Rotabroach® Cutter Kit like this.
5/16, 3/8, 7/16, 1/2, 9/16, 5/8, & 3/4" Cutters, Arbor, (2) Extra Pilots, & Center Punch

This is the easy way of removing spot welded parts, look at the videos.

https://www.youtube.com/watch?v=lk3s4ucJg7k

https://www.youtube.com/watch?v=P7FrgdyuhVA

https://www.youtube.com/user/blairequip

.

__________________
ASE Master Mechanic
https://whunter.carrd.co/

Prototype R&D/testing:
Thermal & Aerodynamic System Engineering (TASE) Senior vehicle instrumentation technician.
Noise Vibration and Harshness (NVH).
Dynamometer.
Heat exchanger durability.
HV-A/C Climate Control.
Vehicle build.
Fleet Durability
Technical Quality Auditor.
Automotive Technical Writer

1985 300SD
1983 300D
2003 Volvo V70

https://www.boldegoist.com/

good info thank you