Cause: Electrode Wear

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Definition
Electrode wear is a deformation of the tip face over time due to the resistance welding process.
Same as: mushrooming, or pitting.

Description
The electrode heating and force during the resistance welding process cause the surface area of the tip face to deform over time. The surface area increase causes the current density (amps/unit area) to decrease, potentially reducing the weld size. (The current density can be increased by using a current stepper.)

Electrode wear can also occur by the pitting of the tip face. In severe cases, localized current flow may result, potentially causing nonround welds.

(In either case tip dressing may address the effects of electrode wear.)

Fig. 1. Deformation of tip face over time

Fig. 2. Badly pitted tip face

Detection

• Expulsion/burn through
• Missing weld
• Nonround weld
• Poor Class A appearance
• Stuck weld
• Undersized weld
• Visual inspection of the tip face

Significance
Quality, Workplace Issues, Cost, Downtime, Maintenance, Throughput (cycle time; PPH), are all potentially affected by this condition. Special considerations are noted below:

Quality: Electrode wear is the primary cause of weld degradation.

Subordinate Causes

• Dirty material
• Hold time short
• Incorrect material/coating
• Incorrect workpiece selected
• Insufficient Cooling
• Squeeze time short
• Weld current high
• Weld force high
• Weld time long
• Incorrect Stepper Schedule