1) Seam Welding its neat labelled sketch:
Seam welding is nothing but series of continuous spot welding
Working: Job is kept in between two electrodes under pressure. This pressure is kept constant throughout. In this type intermittent current is used, it means current is ON for definite time and OFF for another time interval with the help of timer. If current is continuously passes then heat produced may cause burning of job. Heat is produced due to I2R losses where ‘R’ is the contact resistance. This heat is utilized to obtain welding temperature (to become a plastic state) When welding temperature is reached supply is cut down and external pressure is applied simultaneously across the job to complete weld.