20
THROAT DEPTH
Clearance distance from center line of electrodes to frame of machine.
WELD STAND BY
Machine in ready to weld condition; power on, sequence reset, pneumatic and electrical controls adjusted
for weld, and electrodes open but brought down to weld stroke opening.
WELD STROKE
Stroke that opens electrodes for minimum clearance, typically just enough to allow work to be moved to
next weld location.
TYPICAL SEQUENCE
A resistance welding sequence consists of two associated sub-sequences; electrode force and weld
current. Each consists of timed intervals. The main difference between the spot and seam weld sequences
occurs at the beginning and near the end of the sequence. The actual weld current part of the sequence is
similar.
The basic weld sequence consists of three timed intervals; SQUEEZE, WELD and HOLD.
Intervals in the weld sequence can also be referred to as functions. Squeeze provides time for the electrode
force to be applied and for the pressure system to stabilize before a weld current is applied. Weld is the
Interval during which the main weld current is applied; the nugget is formed and parts fused. Hold is a
current off interval for the part to cool before the electrode force is released. A fourth interval is added if
more than one weld is to be made. During OFF time, the electrodes are opened allowing the work piece to
be moved to the next location.
SEQUENCE OPTIONS
Precompression, pre-heat, quench and temper are four typical optional intervals or functions that
may be supplied with your sequence. The sequence will consist of the following intervals in the indicated
order; Squeeze, Pre-Heat, Weld Time, Quench, Temper, Hold and OFF.
CONTROLLING ELECTRODE FORCE
Electrode force is controlled by pressurizing one, or both sides of the weld cylinder. Pressure
applied to the upper chamber of the weld cylinder provides the main electrode force. Pressure applied to
the lower part of the cylinder provides a bucking force. Total electrode force results from the difference
between these pressures.
In this arrangement, maximum electrode force is obtained when the lower chamber exhausted and
the upper chamber is pressurized; such as during recompression and forge. When electrode force drops to
the lower weld level, both sides of the weld cylinder are pressurized.
The arrangement of pressurizing both sides of the weld cylinder to control electrode force is used
in machines with Variable Pressure/Constant Pressure selection. In these machines, the arrangement is
used in Variable Pressure and Constant Low modes. Bucking pressure can be used in these modes to reduce
the electrode force to a minimum level. However, this level should be lower than the pressure applied to
the upper chamber to allow the head to be brought down.
In a Constant High mode, the lower chamber of the weld cylinder is exhausted and pressure is
applied to only the upper chamber. This arrangement provides the maximum electrode force.