Dr. Livingstone, I Presume WELDWISE 2400 - Manual (Page 22)

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0429-INS-400 Rev. C
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Effects of Different Factors
Each of the four main parameters— Current, Voltage, Force, and Displacement— affect the properties
of a weld.
Current, measured in KA, is typically set and expressed as a percentage of heat on weld controls used
by a number of manufacturers, although some of the more modern equipment allows a current setting
in KA instead of a percentage. Throughout the industry, the majority of welds are performed using
single-phase AC current, but there are other sources of welding current used as well. These include:
• Single and Three-phase rectified DC
• Mid-frequency DC (600-1,200 Hz)
• High-frequency DC (2,000-25,000 Hz)
• Capacitive Discharge DC
Whatever type of current is used, control of current density during welding is the most important factor
involved in making a quality weld. Without proper current density, too much heat can be generated,
leading to expulsion and/or part deformation. Conversely, there may be too little heat generated,
causing cold welds and/or incomplete weld nugget formation. Some people uphold the 'bake it longer'
theory, which prescribes lower weld heat for a longer time. While this reduces expulsion, the longer
weld time makes it much less efficient. Others think that in order to have good welds, expulsion is
necessary as an indicator that a weld is being made. However, tiny pieces of molten metal exploding
out of a weld cause the weld itself to be weaker than it would be without expulsion.
Voltage, measured in Volts, is also a key indicator during the weld process. As discussed earlier,
voltage is a relative measure in that the location of the measurement is important. The voltage in the
secondary of a welder can vary during operation due to a variety of factors, including:
• variances in the part fit-up;
• loose connections;
• line load variations within the plant;
• differences in power factor throughout the day.
Voltage variations at the tips due to worn or pitted electrodes, dirty materials, or insufficient surface
contact with the workpiece can also affect resistance and current density. As a partial solution, many of
today's controllers are equipped with an Automatic Voltage Compensation (AVC). If a voltage drop in
the factory line is detected, the control will adjust in an attempt to provide the same amount of energy
to the weld. Despite the adjustment, what comes out of the transformer is not necessarily what comes
out of the electrodes. The same conditions apply to constant current controls. Even though the amount
of current coming out of the transformer secondary is regulated, the amount at the tips may be variable.
Force, measured in pounds per square inch (psi), pounds (lbs.), or kilograms (kg), indicates the amount
of pressure being applied to the electrodes before, during and after the weld process. Electrode force is
typically provided by air, hydraulic, or spring pressure. Changes in force can result in a significant
increase or decrease in resistance as the weld is taking place. This is particularly true of welders using