Definition
The electrode tips do not move towards each other quickly enough during
the forging phase of the weld sequence.
Description
During welding, the temperature of the parent material increases due
to resistive heating. This heating causes expansion of the workpiece
between the tips, moving the electrodes apart. The parent material temperature
continues to increase until the material softens and can no longer resist
the applied force of the electrodes. At this point the tips start to
move towards each other, forging the softened weld material together.
If this electrode movement (follow-up) is too slow, surface and interfacial
expulsion may occur, and the granular structure within the button may
be flawed.
The follow-up characteristics of a welder are influenced by many factors,
including the flowrate capacity of the air/hydraulic feeder system,
the weld cylinder characteristics (size, friction, mass), electric gun
characteristics (feedback control circuit, motor, gear train), design
of the welder, its condition, and the weld force in use.
Detection
Detectable evidence may include:
Significance
Quality, Workplace Issues, Cost, Downtime, Maintenance, Throughput (cycle
time; PPH), are all potentially affected by this condition. Special
considerations are noted below:
Workplace Issues: Poor follow-up may result
in excessive expulsion.
Subordinate Causes
WeldHelp: To Issue/Cause
Matrix
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