The applied weld current is insufficient at the existing conditions to form an acceptable weld.
Same as: low heat, cold weld.
Weld current provides the heating required to melt the metals during welding. The heating is a result of the resistance of the workpieces and interfaces to the flow of current. The heat developed in the weld area is described by the following equation:
Q = I2Rt
Q = heat generated in joules
I = current in amperes
R = resistance in ohms
t = duration of current in seconds
Part of the heat generated is used to make the weld and part is lost to the surrounding metal and electrodes.
Direct indication of low weld current:
A secondary current reading meter may be used to determine weld current for comparison with a previously established reference value. Another method is to measure the welding transformer primary current (either directly with a weld current meter or by observing the primary current indicated by the weld controller) and multiplying that number by the welding transformer’s turns ratio to determine welding current.
Indirect indications of low weld current:
Quality, Workplace Issues, Cost, Downtime, Maintenance, Throughput (cycle time; PPH), are all potentially affected by this condition. Special considerations are noted below:
Downtime: Poorly welded parts may break and jam downstream stations.
- Shunting of guns or parts
- Incorrect weld schedule program (weld current set too low)
- Weld controller setup parameters incorrectly adjusted (such as steppers, voltage compensation, and constant current)
- High workpiece resistance
- High welding loop resistance and/or impedance
- Incorrect weld force
- Insufficient power supply capacity
- Poor line voltage regulation
Note: The same symptoms may occur if weld time is too short (see Weld Time Short).