An Investigation in to Tool Wear Detection in Friction Stir Welding

1. Paul Fleming Thomas Bloodworth David Lammlein Tracie Prater George E. Cook Alvin Strauss D. M. Wilkes David DeLapp Thomas Lienert Matt Bement An Investigation in to Tool Wear Detection in Friction Stir Welding

2. Friction Stir Welding • Recently (1991) developed solid state welding technique • Uses mechanical stirring to join metals • Yields high weld strength • Can be used to join aluminum

3. The FSW Tool • Numerous tool designs exist • Smooth • Threaded • Fluted (Khaled)

4. FSW Tool Wear • There is extensive study of tool wear in related fields such as cutting tool wear and milling tool wear, but little for FSW • This is because of both FSW's newness and also because FSW is currently typically used on soft metals and wear is often neglible. • However this may not always be the case

5. FSW Tool Wear • The paper “Tool wear in the friction-stir welding of aluminum alloy 6061 20% Al2O3: a preliminary study“ investigates FSW tool wear for a threaded tool • When welding the above metal, an FSW tool of 01 steel hardened to a Rockwell C hardness of 62 showed the following wear patterns

6. FSW Tool Wear (Prado)

7. Detecting Tool Wear • This research focuses on means of discovering tool wear in FSW automatically to prevent the use of a worn tool to be allowed to proceed unnoticed.

8. Experimental Design • An FSW tool was constructed out of a mild tool steel to increase the wear rate • Bead on plate welds were run repeatedly and the forces incurred were recorded

9. Experimental Design

10. Show Movie

11. Results • After 20 welds the tool had worn to the point shown (compared with unused tool) • Worn tool on left • Threads have been worn down

12. Analysis • Dynamometer collects data at 1000Hz: • Fx, Fy, Fz, Mz • The average force for each direction was calculated and plotted across runs

13. AnalysisFx

14. Analysis • The progression appears to be a decrease in the force experienced by the dynamometer • This trend is demonstrated in each direction

15. AnalysisFz

16. AnalysisTorque

17. Analysis • This decreasing force and torque can probably be directly related to the loss of threads • This decrease would then serve as a good indicator of tool wear • However, it is also shown that the forces involved vary for other reasons and make a precise estimator based on this alone impractical

18. Frequency Based Analysis • The frequencies in the recorded force signals could also serve as indicators of tool wear • The following shows the recorded forces for the recorded wear runs

19. Frequency Based Analysis

20. Other Possibilities • Acoustic Emissions • Computer Vision

21. Detection of Tool Wear in FSW • This automatic detection is important for the increased industrial application of FSW, as joining of more difficult materials will become more common • Forces recorded during the weld can serve as indicators of tool wear when forces involved in welding have dropped below a certain threshold

22. References • George E. Cook, Reginald Crawford, Denis E. Clark, and Alvin M. Strauss. Robotic friction stir welding. Industrial Robot, 31(1):55–63, November 2004. • Terry Khaled. An outsider looks at friction stir welding. Technical report, Federal Aviation Administration, 2005. • R. A. Prado, L. E. Murr, D.J. Shindo and K.F. Soto. Tool wear in the friction stir welding of aluminum alloy 6061 + 20% Al2O3: a preliminary study. Scripta Materialia. 2001