Q.What is the mean of Off time?

It is the interval from the end of the hold time to the beginning of the squeeze time for the next (resistance) welding cycle.

In automatic machines all these segments of times of times are controlled automatically whereas in manually operated machines, only the weld time is controlled automatically and the remaining time periods are adjusted by the operator himself.

Weld time can be controlled automatically by using a suitable (electronic) timer. Weld times range from one-half cycle of 50 cycle frequency for thinnest sheets to as long as several seconds for thicker plates, depending somewhat upon the metal are being welded.

Pressure or Electrode force

Pressure exerted on the work pieces by the welding electrodes does the following;
(i) It brings the various interfaces into intimate contact and thus affects the contact resistance between the two work pieces.

(ii) It ensures the completion of the electrical circuit between the electrodes and through the work.

(iii) It permits the weld to be made at lower temperatures.

pressure on the work piece is exerted by the electrodes extending form the arms of the welding machine.

Besides this, the other functions performed by electrodes ere;

(i) They carry the current which passes through and generates heat at the place where the two work pieces are in pressed contact.

(ii) Depending upon the area of the electrodes face or tip, they determine the current density in the weld zone.*

(iii) They dissipate the heat from the weld zone and thus prevent surface fusion of the work.