1. An Investigation into Submerged Friction Stir Welding
Vanderbilt University Welding Automation Laboratory: Nashville, TN
Thomas S. Bloodworth III
Paul A. Fleming
David H. Lammlein
Tracie J. Prater
Dr. George E. Cook
Dr. Alvin M. Strauss
Dr. Mitch Wilkes
Los Alamos National Laboratory: Los Alamos, NM.
Dr. Thomas Lienert
Dr. Matthew Bement

2. Overview Introduction Objective VUWAL Test Bed Experimental Setup
Materials Testing
Results and Conclusions
Future Work
Acknowledgements

3. Introduction Friction Stir Welding (FSW)
Frictional heat with sufficient stirring plasticizes weld-piece (Thomas et al)
Advantageous to conventional welding techniques
No Fumes
Solid State
Non-consumable Tool
Welds maintain up to 95% of UTS compared to parent material

4. Introduction Light weight materials used in production (e.g. Aluminum)
FSW is used primarily to weld Aluminum Alloys (AA)
Process currently becoming more prevalent:
Aerospace (e.g. Boeing, Airbus)
Automotive (e.g. Audi)
Marine (SFSW / IFSW)

5. Objective Submerged / Immersed FSW (SFSW / IFSW)
Processing of the weld piece completely submerged in a fluid (i.e. water)
Greater heat dissipation reduces grain size in the weld nugget (Hofmann and Vecchio)
Increases material hardness
Theoretically increases tensile strength

6. Objective
Hofmann and Vecchio show decrease in grain size by an order of magnitude
Increase in weld quality in SFSW may lead to prevalent use in underwater repair and/or construction (Arbegast et al)
Friction Stir Spot Welds (FSSW)
Repair of faulty MIG welds (TWI)
Process must be quantitatively verified and understood before reliable uses may be attained

7. VUWAL Test Bed

8. VUWAL Capabilities
VUWAL Test Bed: Milwaukee #2K Universal Milling Machine utilizing a Kearney and Treker Heavy Duty Vertical Head Attachment modified to accommodate high spindle speeds.
4 – axis position controlled automation
Experimental force and torque data recorded using a Kistler 4 – axis dynamometer (RCD) Type 9124 B
Rotational Speeds: 0 – 5000 rpm
Travel Speeds: 0 – 100 ipm

9. VUWAL Test Bed Anvil modified for a submerged welding environment
Water initially at room temperature
Equivalent welds run in air and water for mechanical comparison (i.e. Tensile testing)

10. Experimental Setup Optimal dry welds run 2000 rpm, 16 ipm
Wet welds speeds: 2000 – 3000 rpm, travel speeds 10 – 20 ipm
Weld samples
AA 6061-T6: 3 x 8 x ¼” (butt weld configuration)
Tool
01PH Steel (Rockwell C38)
5/8” non – profiled shoulder
¼” – 20 tpi LH tool pin (probe) of length .235”
Clockwise rotation
Single pass welding

11. Experimental Procedure
Shoulder plunge and lead angle: .004” , 20
Fine adjustments in plunge depth have been noted to create significant changes in force data as well as excess flash buildup
Therefore, significant care and effort was put forth to ensure constant plunge depth of .004”
Vertical encoder accurate to 10 microns
Tool creeps into material from the side and run at constant velocity off the weld sample

12. Materials Testing
Tensile testing done using standards set using the AWS handbook
Samples milled for tensile testing
Three tensile specimens were milled from each weld run
½ “ wide x ¼ “ thick specimens were used for the testing

13. Materials Testing
Tensile specimens tested using an Instron Universal Tester
Recorded values included UTS and UYS in lbf

14. Results
Stress – Strain curves were generated from the data gathered from the tensile test
Weld pitch “rule” is not followed in IFSW (Revolutions / Inch)

15. Results IFSW run with weld parameters 2000 rpm, 10 ipm
Developed optimal tensile properties
Wet parameter set 3000 rpm, 15 ipm developed worm hole defect

16. Results

17. Results

18. Results

19. Results

20. Results Submerged welds maintained 90-95% of parent UTS
Parent material UTS of ksi compared well to the welded plate averaging UTS of ~41 ksi
Worm hole defect welds failed at 65% of parent UTS
effective dry weld equivalent tests not run
Optimal welds for IFSW required a weld pitch increase of 60%
Weld pitch of dry to wet optimal welds
Dry welds: wp = 2000/16 = 125 rev/inch
Wet welds: wp = 2000/10 = 200 rev/inch

21. Results Average torque increased from FSW to IFSW
FSW: 16 Nm
SFSW: 18.5 Nm
Elastic Modulus also increases for IFSW when compared to FSW
FSW: 1250 ksi
SFSW: 1450 ksi

22. Summary and Conclusions
Optimal submerged (wet) FSW’s were compared to conventional dry FSW
Decrease in grain growth in the weld nugget due to inhibition by the fluid (water)
Water welds performed as well if not better than dry welds in tensile tests
Elastic Modulus of the SFSW’s were considerably higher than that of traditional FSW
Leading to a less elastic and therefore less workable material
Dry FSW: E = ~1200 ksi
SFSW: E = ~1400 ksi

23. Future Work Fracture Surface Microscopy
Cross section work for electron microscopy
TEM
SEM
Hardness Testing for comparison
Further Mechanical testing
e.g. bend tests

24. Acknowledgements This work was supported in part by:
Los Alamos National Laboratory
NASA (GSRP and MSFC)
The American Welding Society
Robin Midgett for materials testing capabilities

25. References
Thomas M.W., Nicholas E.D., Needham J.C., Murch M.G., Templesmith P., Dawes C.J.:G.B. patent application No , 1991.
Crawford R., Cook G.E. et al. “Robotic Friction Stir Welding”. Industrial Robot (1)
Hofmann D.C. and Vecchio K.S. “Submerged friction stir processing (SFSP): An improved method for creating ultra-fine-grained bulk materials”. MS&E 2005.
Arbegast W. et al. “Friction Stir Spot Welding”. 6th International Symposium on FSW