Cause: Weld Current Low

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Definition
The applied weld current is insufficient at the existing conditions to form an acceptable weld.
Same as: low heat, cold weld.

Description
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

where:
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.

Detection
Indirect indications of low weld current:

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.

Significance
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.

Subordinate Causes

  • 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).

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