Electronic Circuits used in Resistance Welding System
There are many electronic control circuits used in the resistance welding process, they are as follows :
The line contactor :
The line contactor is basically an electronic switch. The line contactor connects and disconnects the primary winding of the welding transformer across the ac mains supply.
The contactor is like a switch, the status of which is controlled by the control signals coming from control circuit.
Heat control circuit :
The line contactor circuit uses thyratron tubes or thyristors. By controlling their firing angle in each half cycle of the ac mains, it is possible to control the amount of heat transferred to the load. (load is the metal pieces to be welded together).
The sequence timer :
Welding cycle : One complete welding cycle can be divided into four time periods as shown in Figure.
The four important time periods in one welding cycle are :
- Squeeze time
- Hold time and
- Weld time
- Off time
In order to execute this welding cycle, four different timers are required, they are :
- The squeeze timer, i.e. the time required for pressure to build up before the line contactor is closed.
- A weld timer.
- A timer to determine the “hold time,” i.e. the time required for the material to cool before releasing the pressure.
- A timer to determine the “OFF time,” i.e. the time for which the welding electrodes are left unenergised before the next welding cycle begins.
All these timers are clubbed together to form a timer called sequence timer or sequential timer.
It is a timer which decides (controls) the number of cycles for which the welding current flows and the number of cycles for which it is disallowed.
