Heated Friction Stir Welding: An Experimental and Theoretical Investigation into How Preheating Influences Process Forces

Abstract

As friction stir welding (FSW) has expanded to welding higher strength materials, large process forces and extreme tool wear have become issues. One possible solution is introducing an additional heating source in front of the FSW tool which softens the material and reduces the tool loads. We investigate the advantages of elevating temperature. Bead on plate welds were performed with a Trivex tool in aluminum alloy (AA 6061) heated to initial material temperatures up to 300°C. Macrograph cross-sections of the welds revealed a slight increase in material flow with increasing temperatures. More significant, the welding forces were analyzed to reveal up to a 43% reduction in the axial force with even moderate heating. An intriguing trend is observed that the process forces do not decrease steadily with increasing initial temperature, as might be expected, but exhibit a more complex polynomial shape, which actually increases for some heating intervals.

Keywords:

• Aluminum alloys
• Assisted FSW
• Axial force
• Friction stir welding
• Force control
• Heat input
• Modeling
• Preheating
• Process force reduction
• Temperature

ACKNOWLEDGMENTS

This work was financially supported under a grant funded by the Tennessee Space Grant Consortium. We would also like to thank Kate Lansford of The University of Tennessee Space Institute for her assistance with this project.