Why do electrodes stick to the work piece?

Electrode sticking to the work piece generally is caused by excessive heating between the electrode and the work piece. In the Relative Resistivity Diagram RC has become too large. Any factor which would cause this is an issue that must be addressed to prevent this manufacturing problem. In many cases this condition is accompanied with excessive surface expulsion.

Electrode Sticking

Conditions which can lead to this are:
Short Squeeze Times – Current initiates before force is fully applied.
Long Weld Time – The weld nugget grows too large and reaches the surfaces of the parts.
Low Weld Force – This causes the contact resistance between the electrode and the part to be high and make the surface very hot.
High Weld Current – Too much current and the weld nugget grows too large and reaches the surface.
Dirty/Scaley Material – The dirt and scale can be expelled from the surface.
Short Hold Time – The nugget is still molten when the force is released.

Other issues which could be factors in surface expulsion but not as prevalent as the above are electrode misalignment, poor heat balance, low conductivity electrodes, insufficient edge distance, metallurgy of the material being welded, coatings on the material, poor head follow up, poor voltage regulation, poor air pressure regulation, poor water flow or cooling.

Reference: CMW Welding Product Catalog

                  RWMA - Resistanc Welding Manual 4th Edition

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