How to make a 18650 cell welder from a microwave oven Part 1

Today I decided to build myself a welder for thin plates mainly for connecting 18650 cells.
As a standard, I will make it from a microwave transformer.
Out of curiosity, I also checked whether it is possible to make a welder from other transformers. Unfortunately, the effect was much worse.
You can buy a ready welder here: s.click.aliexp...
See also:
18650 cell welder: • Car Power Bank as a ba...
Capacitor welder: • Zgrzewarka z kondensa...
Parkside plasma cutter: • Parkside Lidl plasma c...