Controls and/or timers for resistance welding are simple, "in order" timers. They
control, or time, the events of the process and all programmed numbers are either
a time, normally in cycles with one "cycle" equal to 1/60th of a second, or the current
firing angle which is the %heat, %current, weld heat etc. depending upon
the timers. If the control of the machine is working with a PLC as a master
then the RW unit should be called a "weld timer" so as not to confuse the PLC
programmers. If it is the only "control" on the machine, as is the case for
stand alone machines, then it should be called the control. It is refered to here as the
timer to make things simpler.
The basics of the timer is to complete the following events in order: Squeeze,
Weld, %heat, Hold, and Off. These events are the primary events and other
events can be found in the Controls Extras page.
These are ordered events. The following are the defintitions:
- Squeeze: This is the time from the initiation of the air valve, or force
mechanism, to the time of the weld. It should be long enough for the FORCE of
the process to develop to an acceptable level. If the timer has a pressure
switch or simalure input then the signal is in this event and waits for the
satisfaction prior to continuing.
- Weld: This is the duration of TIME in which the CURRENT flows. The weld
TIME is very important in the physics of heating the weld nugget. The shorter
the WELD TIME the better.
- The Percent Current is also a time but in a different sense. It is the time
at which the CURRENT is allowed to flow after the "zero cross over point" is
detected in the individual half cycle of the process voltage. It controls the
amps, or amount of amps, in the RW welding process on a per cycle basis.
- Hold: This is the time after the welding TIME and CURRENT flow for the
FORCE to remain in place while the weld nugget(s) solidifies or strenthens. It
should be about 2-3 times the weld TIME due to thermodynamics. If a weld
checker is built into the timer, release of the FORCE may be an input at this
location as a quality matter.
- Off: Off time is after hold and prior to re-initiation of the air valve
in Repeat Mode. This is used in conjuntion with repeat and can help speed the RW
process in production when multiple welds are made, with the same settings,
and can be operator dependent.