Precision Resistance Welding
Control System is general equipment to assure more
perfect resistance welding process. A microprocessor
with a powerful software is the core control unit,
and the software is special design for resistance
welding. From a single phase power supply, the low
frequency welding control
utilizes an inversed parallel pair of Silicone Controlled
Rectifiers (SCR) to control the output the welding
power transformer. SCRs are turned on by pulsing
a gate with a voltage signal. The welding control
uses predictive algorithms to determine the best
point to pulse the gate of the SCRs during the half
cycle of the alternating current supply. The SCRs
are turned off only when the alternating current
supply is below the threshold point called "minimum
holding current". This occurs near the zero crossing
point of the AC power supply. Every welding moment
is controlled precision from power cycle.
Resistance welding is an electromechanical process
that is used to assemble metallic parts. A basic
understanding of the electrical and mechanical components
of the process will provide the foundation for developing
control algorithms that benefit the users of this
assembly method. It is a good practice to design
welding tools beginning at the requirements of the
weld nugget and progressing outwards to the controls.
Mistakes can be made if one decides first on controls
before considering the weld results that are needed.
The progression shown on the left starting with
the welding process (i.e. spot or projection) then
continuing on to mechanical tools, then power transformers,
then finally welding controls is the order to follow.