Reinforcement of friction plug welds

An apparatus configured to reinforce a friction plug weld in a workpiece, the apparatus comprising:

• a chuck configured to rotate a plug and to force the plug through a hole through the workpiece, the hole comprising a first width on a root side of the workpiece and a second width on a face side of the workpiece;
• the plug configured to:
• forge weld to the workpiece, and plastically deform to comprise:
• a weld land surrounding a root side end of the plug, and a coin surrounding the weld land;
• and
• an anvil adapted to be placed against a root side of the workpiece, the anvil comprising:
• a first cavity configured to receive a tip of the plug, the first cavity being further from the workpiece than a second cavity and a third cavity;
• the second cavity configured to substantially surround the first cavity and extrude a first plasticized portion of the plug to form the weld land, the second cavity comprising a width and a depth that are larger and smaller respectively relative to the first cavity, the width of the second cavity being greater than the first width of the hole;
• and
• the third cavity configured to extend outward around the second cavity and extrude a second plasticized portion of the plug to form the coin, such that the third cavity comprises a height that is less than a width of the third cavity.