An Investigation into Submerged An Investigation into Submerged Friction Stir WeldingFriction Stir Welding

Vanderbilt University Welding Automation Vanderbilt University Welding Automation Laboratory: Nashville, TNLaboratory: Nashville, TN

Thomas S. Bloodworth IIIThomas S. Bloodworth IIIPaul A. FlemingPaul A. FlemingDavid H. LammleinDavid H. LammleinTracie J. PraterTracie J. PraterDr. George E. CookDr. George E. CookDr. Alvin M. StraussDr. Alvin M. StraussDr. Mitch WilkesDr. Mitch Wilkes

Los Alamos National Laboratory: Los Los Alamos National Laboratory: Los Alamos, NM.Alamos, NM.

Dr. Thomas LienertDr. Matthew Bement

OverviewOverview

1.1. IntroductionIntroduction2.2. ObjectiveObjective3.3. VUWAL Test BedVUWAL Test Bed4.4. Experimental SetupExperimental Setup5.5. Materials TestingMaterials Testing6.6. Results and ConclusionsResults and Conclusions7.7. Future WorkFuture Work8.8. AcknowledgementsAcknowledgements

IntroductionIntroduction Friction Stir Welding (FSW)Friction Stir Welding (FSW)

Frictional heat with sufficient Frictional heat with sufficient stirring plasticizes weld-piece stirring plasticizes weld-piece (Thomas et al)(Thomas et al)

Advantageous to Advantageous to conventional welding conventional welding techniquestechniques No FumesNo Fumes Solid StateSolid State Non-consumable ToolNon-consumable Tool

Welds maintain up to 95% of Welds maintain up to 95% of UTS compared to parent UTS compared to parent materialmaterial

IntroductionIntroduction

Light weight materials used in production (e.g. Light weight materials used in production (e.g. Aluminum)Aluminum)

FSW is used primarily to weld Aluminum Alloys FSW is used primarily to weld Aluminum Alloys (AA)(AA)

Process currently becoming more prevalent:Process currently becoming more prevalent: Aerospace (e.g. Boeing, Airbus)Aerospace (e.g. Boeing, Airbus) Automotive (e.g. Audi)Automotive (e.g. Audi) Marine (SFSW / IFSW)Marine (SFSW / IFSW)

ObjectiveObjective

Submerged / Immersed FSW (SFSW / IFSW)Submerged / Immersed FSW (SFSW / IFSW)

Processing of the weld piece completely Processing of the weld piece completely submerged in a fluid (i.e. water)submerged in a fluid (i.e. water)

Greater heat dissipation reduces grain size in Greater heat dissipation reduces grain size in the weld nugget (Hofmann and Vecchio)the weld nugget (Hofmann and Vecchio) Increases material hardnessIncreases material hardness Theoretically increases tensile strengthTheoretically increases tensile strength

ObjectiveObjective Hofmann and Vecchio show Hofmann and Vecchio show

decrease in grain size by an decrease in grain size by an order of magnitudeorder of magnitude

Increase in weld quality in Increase in weld quality in SFSW may lead to prevalent SFSW may lead to prevalent use in underwater repair use in underwater repair and/or construction (Arbegast and/or construction (Arbegast et al)et al) Friction Stir Spot Welds Friction Stir Spot Welds

(FSSW)(FSSW) Repair of faulty MIG welds Repair of faulty MIG welds

(TWI)(TWI)

Process must be quantitatively Process must be quantitatively verified and understood before verified and understood before reliable uses may be attainedreliable uses may be attained

VUWAL Test BedVUWAL Test Bed

VUWAL CapabilitiesVUWAL Capabilities VUWAL Test BedVUWAL Test Bed: Milwaukee #2K Universal Milling : Milwaukee #2K Universal Milling

Machine utilizing a Kearney and Treker Heavy Duty Machine utilizing a Kearney and Treker Heavy Duty Vertical Head Attachment modified to accommodate high Vertical Head Attachment modified to accommodate high spindle speeds.spindle speeds.

4 – axis position controlled automation4 – axis position controlled automation

Experimental force and torque data recorded using a Experimental force and torque data recorded using a Kistler 4 – axis dynamometer (RCD) Type 9124 BKistler 4 – axis dynamometer (RCD) Type 9124 B

Rotational SpeedsRotational Speeds: 0 – 5000 rpm: 0 – 5000 rpm

Travel SpeedsTravel Speeds: 0 – 100 ipm: 0 – 100 ipm

VUWAL Test BedVUWAL Test Bed

Anvil modified for a Anvil modified for a submerged welding submerged welding environmentenvironment

Water initially at room Water initially at room temperaturetemperature

Equivalent welds run in Equivalent welds run in air and water for air and water for mechanical comparison mechanical comparison (i.e. Tensile testing)(i.e. Tensile testing)

Experimental SetupExperimental Setup Optimal dry welds run 2000 rpm, 16 ipmOptimal dry welds run 2000 rpm, 16 ipm

Wet welds speeds: 2000 – 3000 rpm, travel speeds 10 – Wet welds speeds: 2000 – 3000 rpm, travel speeds 10 – 20 ipm20 ipm

Weld samplesWeld samples AA 6061-T6: 3 x 8 x ¼” (butt weld configuration)AA 6061-T6: 3 x 8 x ¼” (butt weld configuration)

ToolTool 01PH Steel (Rockwell C38)01PH Steel (Rockwell C38) 5/8” non – profiled shoulder5/8” non – profiled shoulder ¼” – 20 tpi LH tool pin (probe) of length .235”¼” – 20 tpi LH tool pin (probe) of length .235” Clockwise rotationClockwise rotation Single pass weldingSingle pass welding

Experimental ProcedureExperimental Procedure Shoulder plunge and lead Shoulder plunge and lead

angle: .004” , 2angle: .004” , 200

Fine adjustments in plunge depth Fine adjustments in plunge depth have been noted to create have been noted to create significant changes in force data significant changes in force data as well as excess flash buildupas well as excess flash buildup

Therefore, significant care and Therefore, significant care and effort was put forth to ensure effort was put forth to ensure constant plunge depth of .004”constant plunge depth of .004” Vertical encoder accurate to 10 Vertical encoder accurate to 10

micronsmicrons

Tool creeps into material from the Tool creeps into material from the side and run at constant velocity side and run at constant velocity off the weld sampleoff the weld sample

Materials TestingMaterials Testing Tensile testing done Tensile testing done

using standards set using using standards set using the AWS handbookthe AWS handbook

Samples milled for tensile Samples milled for tensile testingtesting

Three tensile specimens Three tensile specimens were milled from each were milled from each weld runweld run ½ “ wide x ¼ “ thick ½ “ wide x ¼ “ thick

specimens were used for specimens were used for the testingthe testing

Materials TestingMaterials Testing

Tensile specimens Tensile specimens tested using an tested using an Instron Universal Instron Universal TesterTester

Recorded values Recorded values included UTS and included UTS and UYS in lbfUYS in lbf

ResultsResults Stress – Strain curves were generated from the data Stress – Strain curves were generated from the data

gathered from the tensile testgathered from the tensile test

Weld pitch “rule” is not followed in IFSW (Revolutions / Weld pitch “rule” is not followed in IFSW (Revolutions / Inch)Inch)

ResultsResults IFSW run with weld IFSW run with weld

parameters 2000 rpm, 10 parameters 2000 rpm, 10 ipmipm Developed optimal tensile Developed optimal tensile

propertiesproperties

Wet parameter set 3000 Wet parameter set 3000 rpm, 15 ipm developed rpm, 15 ipm developed worm hole defectworm hole defect

ResultsResults

ResultsResults

ResultsResults

ResultsResults

ResultsResults Submerged welds maintained 90-95% of parent UTSSubmerged welds maintained 90-95% of parent UTS

Parent material UTS of 44.88 ksi compared well to the Parent material UTS of 44.88 ksi compared well to the welded plate averaging UTS of ~41 ksiwelded plate averaging UTS of ~41 ksi

Worm hole defect welds failed at 65% of parent UTSWorm hole defect welds failed at 65% of parent UTS effective dry weld equivalent tests not runeffective dry weld equivalent tests not run

Optimal welds for IFSW required a weld pitch increase of Optimal welds for IFSW required a weld pitch increase of 60%60%

Weld pitch of dry to wet optimal weldsWeld pitch of dry to wet optimal welds Dry welds: wp = 2000/16 = 125 rev/inchDry welds: wp = 2000/16 = 125 rev/inch Wet welds: wp = 2000/10 = 200 rev/inchWet welds: wp = 2000/10 = 200 rev/inch

ResultsResults

Average torque increased from FSW to Average torque increased from FSW to IFSWIFSWFSW: 16 NmFSW: 16 NmSFSW: 18.5 NmSFSW: 18.5 Nm

Elastic Modulus also increases for IFSW Elastic Modulus also increases for IFSW when compared to FSWwhen compared to FSWFSW: 1250 ksiFSW: 1250 ksiSFSW: 1450 ksiSFSW: 1450 ksi

Summary and ConclusionsSummary and Conclusions Optimal submerged (wet) FSW’s were compared to conventional Optimal submerged (wet) FSW’s were compared to conventional

dry FSWdry FSW

Decrease in grain growth in the weld nugget due to inhibition by the Decrease in grain growth in the weld nugget due to inhibition by the fluid (water)fluid (water)

Water welds performed as well if not better than dry welds in tensile Water welds performed as well if not better than dry welds in tensile teststests

Elastic Modulus of the SFSW’s were considerably higher than that Elastic Modulus of the SFSW’s were considerably higher than that of traditional FSWof traditional FSW Leading to a less elastic and therefore less workable materialLeading to a less elastic and therefore less workable material Dry FSW: E = ~1200 ksiDry FSW: E = ~1200 ksi SFSW: E = ~1400 ksiSFSW: E = ~1400 ksi

Future WorkFuture Work Fracture Surface MicroscopyFracture Surface Microscopy

Cross section work for electron Cross section work for electron microscopymicroscopy TEMTEM SEMSEM

Hardness Testing for Hardness Testing for comparisoncomparison

Further Mechanical testingFurther Mechanical testing e.g. bend testse.g. bend tests

AcknowledgementsAcknowledgements

This work was supported in part by:This work was supported in part by:

Los Alamos National LaboratoryLos Alamos National Laboratory

NASA (GSRP and MSFC)NASA (GSRP and MSFC)

The American Welding SocietyThe American Welding Society

Robin Midgett for materials testing capabilitiesRobin Midgett for materials testing capabilities

ReferencesReferences 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”. Crawford R., Cook G.E. et al. “Robotic Friction Stir Welding”. Industrial Robot 2004 31 (1) 55-63.Industrial Robot 2004 31 (1) 55-63.

Hofmann D.C. and Vecchio K.S. “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. 2006.