Patent ID: 7432466

Claim:
A method of welding comprising: contacting a metal sheet with at least one electrode having a first contact surface area at a force to provide a pressure to a contact surface of the metal sheet, wherein the first contact surface area has a starting position displaced from the contact surface by a stroke dimension, wherein the stroke dimension is equal to a difference in the starting position and a position of the electrode tip when the electrode tip makes contact to the contact surface of the metal sheet; applying a current through the at least one electrode to the metal sheet; measuring a dimensional change of the stroke dimension; correlating the dimensional change in the stroke dimension to the change in the first contact surface area of the at least one electrode using a mathematical algorithm, D 2 to D 1 area ratio=0.0977(Δ X 2 )+0.625(Δ X )+1.0 wherein D 1 is equal to a first diameter of an electrode tip of the at least one electrode, D 2 is equal to a second diameter of the electrode tip of the at least one electrode, ΔX is equal to the dimensional chance of the stroke dimension, and the at least one electrode has a 45 degree truncated electrode tip geometry; and adjusting the force to compensate for the dimensional change in the first contact surface area of the at least one electrode to maintain the pressure applied to the contact surface of the metal sheet.