Patent ID: 8011560

Claim:
A method for assuring a predetermined bottom thickness at an actual position in an operating region of at least one workpiece by a friction stir spot welding system having a weld gun, comprising: monitoring system deflection occurring substantially along a rotational axis of the weld gun; determining a zero position; calculating a plunge distance relative to said determined zero position based upon at least a predetermined stack-up thickness, the bottom thickness, and said monitored system deflection; causing a weld tool to enter the operating region at a predetermined plunge force and a predetermined plunge speed and causing relative rotational movement about said rotational axis between said weld tool and the at least one workpiece, while plunging up to said plunge distance, whereby pressure and frictional heat is generated, thereby causing the material in the operating region to plasticize; and causing said weld tool to exit the operating region after said bottom thickness has been reached, wherein the operating region is allowed to cool and the plasticized material to harden, thereby completing a single weld on the workpiece.