Lower Chatter Friction Pull Plug Welding (FPPW)

Lower Chatter Friction Pull Plug Welding (FPPW) (MFS-TOPS-69)
New plug design reduces chatter and stalling
FPPW is the process that is necessary to plug the hole that is left behind as a friction stir weld (FSW) joint is completed and the pin tool of the welder retracts from the joint. FPPW involves a small, rotating part (plug) being spun and simultaneously pulled (forged) into a hole in a larger part. When the plug enters the hole, there is often chatter, and, sometimes, the machine stalls completely. NASA discovered that by optimizing the design of the pull plug, including angling the shoulder edge of the plug precisely, it makes contact with the hole in such a way that the chatter issue is improved. NASA has made the new design as an adaptation to make FPPW more practical and robust. The new plug has been used to make space-qualified parts at NASA, and the plug welds are as strong as initial welds.

The Technology
The new friction pull plug design is optimized to reduce chatter that results as a fast rotating plug enters the hole in the part. The plug design is based on a shank with multiple frustoconical sections shown in the figure to the right. The sections are carefully sized to ensure that the spinning plug contacts the edge of the hole at just the right position to minimize chatter. It keeps the machine from stalling when the plug enters the hole. This new design makes FPPW more practical, perhaps even as a future rivet replacement.
front image This chart shows the spindle speed and torque of the pull plug before the new design (red lines) and after (green lines). Note how the red lines draw close to each other, indicating that stalling is possible.
  • Eliminates stalling related to plug rotation
  • Enables FPPW on thicker plates; NASA has used the plug on a 0.5 inch-thick weld and also a 0.627 inch-thick weld
  • Broadens the applicability of FPPW to more alloys; the plug helps make FPPW practical for 2015 and 2019 aluminum

  • Potential rivet replacement
  • FPPW: for repair of spot ruptures and pin tool exit holes
  • Aerospace: NASA, military/defense applications
  • Future commercial ships: large aluminum vessels for transport
  • Naval ships and littoral combat ships that also use thick aluminum plates
  • Army lightweight vehicles and hybrid armor (e.g., Humvee)
  • High-speed trains made of thick aluminum
Technology Details

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