Spot welding electrode and method for welding coated metals therewith

A spot welding electrode comprising:

• (a) a housing having an open end and a closed end, the housing having a cavity formed therein extending from the open end partially toward the closed end;
• (b) a mounting portion for mounting to an electrode adaptor, the mounting portion being disposed proximate the open end of the housing;
• (c) a tip portion, the tip portion integral the mounting portion and being disposed proximate the closed end of the housing, the tip portion having a cooling wall and an integral end wall surrounding and defining the cavity within the tip portion, the tip portion having an outer surface and an inner surface, the inner surface being substantially parallel to the outer surface;
• (d) a plurality of cooling fins disposed within the cavity and integrally formed with the wall, the fins having a first and second edge and a first end and a second end, the second edge of the fins extending partially inward toward the center of the closed end of the housing, the spaces between the fins defining a plurality of cooling paths;
• and
• wherein the cavity, the tip portion, the cooling fins and the parallel surfaces of the cooling wall and end wall cooperate to define a non-alloying contact surface.

A method of welding comprising the steps of:

• (a) applying a clamping pressure upon at least two coated metal workpieces with axially opposing heat stabilizing electrode workpieces formed to each other to eliminate any air spaces at a welding location at the interface of the workpieces;
• (b) applying a cooling liquid into the cavity of at least one of the electrodes such that the temperature at the electrode-workpiece interface remains stabilized below the melting point of the coating material on the surface of the workpieces during the weld cycle;
• (c) applying an electrical current to the workpieces through the electrodes sufficient to create a temperature which, in cooperation with the cooling liquid, is below the melting point of the coating at the interface of the electrode and the associated workpiece and which is at at least the melting point of the substrate of the workpiece at the interface of the workpieces, to form a molten weld nugget at the weld location at the interface of the workpieces;
• (d) discontinuing the electric current and continuing to apply the clamping pressure and the cooling liquid to the electrodes such that the weld nugget has a balanced cooling and solidification;
• (e) disengaging the clamping pressure from the cooled workpieces, and
• wherein, the cooling liquid and the at least one electrode cooperate to prevent the alloying of the coating material to the electrode during the application of electrical current and the forming of the weld nugget.