Patent ID: 8222560

Claim:
A method of forming one or more electrical resistance spot welds in an assembly of overlying sheet metal layers, the method comprising: forming a pair of welding electrodes, the electrodes having welding faces for engaging opposing outer surfaces of an assembly of overlying sheet metal layers, the welding faces being sized and shaped for forming at least one predetermined electrical resistance spot weld for joining the overlying sheets at a spot weld site, and at least one of the welding faces being spherically rounded and having a protrusion or intrusion in the spherically rounded welding face for forming an weld site image in the outer surface of the sheet metal layer contacted by the spherically rounded welding face, the protrusion or intrusion having surfaces that are shaped with a contact angle between the protrusion or intrusion and the outer surface of the sheet metal layer contacted by the spherically rounded weld face to minimize retention of sheet metal layer material; pressing the welding electrodes against the opposing outer surfaces of the overlying sheet metal layers with a central contacting area of the spherically rounded weld face that is free from the protrusion or intrusion contacting its respective outer surface prior to current flow through the electrodes; and passing an electrical current between the electrodes through the sheet metal layers to form a welding nugget between the sheet metal layers and to deform the outer surface of the sheet metal layer contacted by the spherically rounded welding face with the weld site image formed as the obverse shape of the protrusion or intrusion on the spherically rounded welding face.