Cause: Weld Force Low
The interfacial welding force is less than that required by the applicable specification.
Description
Weld force brings the metal between the electrodes together and provides electrical continuity, the required welding pressure, and forging force, so that a weld may be generated. The lower the force, the higher the interfacial resistances, resulting in higher heat generation at the tip to sheet and sheet to sheet interfaces.
On a microscopic scale, the surfaces of electrodes and workpieces consist of peaks and valleys. When subjected to low force, the metal-to-metal contact will be only at the contacting peaks. The resulting contact area is less than that produced by an appropriate force. Contact resistance will therefore be higher, causing a greater amount of heat to be generated.
Measured weld force: That value of weld force set, for example, using a force gage, before the workpiece is introduced.
Interfacial weld force: That force actually present at the sheet to sheet interface. This is equal to the measured weld force minus the force required to overcome poor fit up.
Detection
The condition may be indicated by:
- Cracks & holes
- Expulsion/burn through
- Poor Class A appearance
- Sticking/stuck tips
- Short electrode life
Significance
Quality, Workplace Issues, Cost, Downtime, Maintenance, Throughput (cycle time; PPH), are all potentially affected by this condition.
Subordinate Causes
- Poor mechanical connection
- Wrong cable/shunts
- Air or hydraulic fitting loose
- Air or hydraulic leak
- Air or hydraulic pressure low
- Contaminated bearings or bushings
- Kinked or broken hose
- Leaking cylinder – Piston or rod seals bad
- Wrong electrodes or shanks installed (too short for the cylinder stroke)
- Wrong force selected for the material/stack-up
