An Investigation into Submerged Friction Stir Welding

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

1. Introduction
2. Objective
3. VUWAL Test Bed
4. Experimental Setup
5. Materials Testing
6. Results and Conclusions
7. Future Work
8. 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 44.88 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) FSWs 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 SFSWs 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. 9125978.8, 1991.
• Crawford R., Cook G.E. et al. Robotic Friction
  Stir Welding. Industrial Robot 2004 31 (1)
  55-63.
• Hofmann D.C. and Vecchio K.S. Submerged friction
  stir processing (SFSP) An improved method for
  creating ultra-fine-grained bulk materials. MSE
  2005.
• Arbegast W. et al. Friction Stir Spot Welding.
  6th International Symposium on FSW. 2006.