Coligan_XX_XX_P

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This work was prepared by the National Center for Excellence in Metalworking Technology,

operated by Concurrent Technologies Corporation (CTC), under Contract No. N00014-00-C-0544 to the Office of Naval Research as part of the Navy ManTech Program. Approved for

public release; distribution is unlimited.

Examination of Material Flow in

FSW of Aluminum Using Stop-Action Techniques

Kevin Colligan

Concurrent Technologies Corporation

Johnstown, PA - USA


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Acknowledgements

This work was funded by:

The Boeing Company [1,2],

andConcurrent Technologies Corporation (CTC )

and the National Center for Excellence in

Metalworking Technologies (NCEMT),

operated by CTC [3].

1 - Colligan, K. “Dynamic Material Deformation During Friction Stir Welding of

Aluminum,” 1st International Symposium on Friction Stir Welding, Thousand Oaks,

California, June 1999.

2 - Colligan, K, “Material Flow Behavior During Friction Stir Welding of Aluminum,”

Welding Journal, July 1999.

3 - Colligan, K. and Chopra, S., “Examination of Material Flow in Friction Stir Welding of

Aluminum Using a Stop Action Technique,” 5th International Symposium on Friction Stir

Welding, Metz, France, September 2004.


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Agenda

Introduction

Stop Action for Cylindrical, Threaded Pins [1,2]

Stop Action for Frustum Pins with Reentrant

Features [3]

Conclusions


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Introduction -

Motivation for Material Flow Studies

Knowledge of material flow is useful for:

– understanding weld formation

– diagnosing defects

– predicting the effect of tool design changes

Modeling has given good insight, but

model verification can be difficult Experimental methods must be

developed to verify models


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Introduction

Flow visualization in FSW based on:

– Stop Action (Colligan, Guerra, McClure, Dickerson)

– Embedded Tracers (Colligan, Reynolds, Seidel,London, Ouyang)

Must be repeated as tool designs evolve

New methods needed for new tools & materials

– tools with reentrant features

– high-temperature FSW of steel, titanium, etc.


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Stop Action Technique - Rapid Retraction

Welds made on Mazak 3-axis mill

– Rigid frame

– Rapid axis acceleration

– 6.4mm 6061-T6 workpiece mounted at 3° tilt angle

– Threaded pin with no reentrant features

At end of weld, tool retracted at rate to “unscrew”

tool from keyhole, leaving keyhole intactShoulder Profile 7° cup, smooth

Shoulder Diameter, mm 5

Shoulder Material H13Pin Profile threaded, cylindrical

Pin Diameter, mm 6.4

Pin Length, mm 6.4Pin Material WC

Number of Flats 0

Spindle Speed, rev/min 1,540

Travel Speed, mm/min 216


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Pin Design - Conventional Threaded Pin

WC pin, ground with thread forms

1mm pitch, 6.4mm diameter, 6mm long

Shank ground concentric to pin

Collet used to hold tool

Shank ground

concentric to pin

Surrogate pin used

to hold tool during

grinding


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Post-Weld Procedures

Photograph intact keyhole using light microscope

Section keyhole and inspect interior wall using SEM

Section keyhole and inspect section surface using

light microscope


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LT Section View of Keyhole

Upper leading edge - material curling into thread spaces

Lower leading edge - material in filled thread spaces rotates with

pin Upper trailing edge - void behind pin

Lower trailing edge - material in filled thread spaces smeared

against keyhole wall


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Section View of Keyhole - rear wall LT section

Rear wall section shows

origin of “onion ring”

pattern Material in filled threads

smeared against lower

rear portion of keyhole

Material deposited at

bottom of keyhole causes

material from above to

rise to fill void from upper portion of the keyhole

Tool Motion


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Section View of Rear Keyhole -

higher magnification view

Thread-formed material shows

accumulation in thread space

on successive rotations?

– Etching contrast based on

variations in base plate chemistry?

– More inhomogeneity in lower

threads than in upper

– Etch contrast preserved in stir

zone macrostructure

– Change in vertical velocity

(rotation speed) of material in

thread spaces?


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Intact Keyhole -

view looking down into keyhole

Partially filled thread space

Filled thread rotates with

pin at some intermediate

speed

Leading edge of

keyhole, LT

section view Welded at 1540 rev/min, 610 mm/min


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Keyhole Interior Rear Wall -

SEM image of material from thread space

Suggests deposition of

material on keyhole

wall by smearing

action Suggests vertical

motion caused by

intermediate rotation

speed


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Plastic Deformation Processes -

Cylindrical Threaded Pin

Curling of material into thread spaces (upper leading edge of keyhole)

Rotation of material in filled thread spaces at intermediate

speed, combined with vertical motion (lower leading edge of

keyhole) Deposition of material by “smearing” action (rear of keyhole)

Deposition of material at bottom of pin, causing bulk of SZ

material to rise as shoulder passes


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Stop-Action Technique -

Frustum Pin w/ Reentrant Features - Rapid Stop

Perform bead-on-plate weld, 25.4mm 2195 Al-Li

Engage emergency stop control

Pour tap water on plate until cool

Remove shoulder piece Section through pin

Shoulder Profile flat shoulder with scrolls

Shoulder Diameter, mm 30.5Shoulder Material H13

Pin Profile threaded frustum with flats

Pin Root/Tip Diameters,mm

15.2/8.9

Pin Length, mm 24.6

Pin Material MP159

Number of Flats 3

Spindle Speed, rev/min 220

Travel Speed, mm/min 102


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Sectioning Procedure

End of weld was cut to 50mmsquare sample

Sample was then sectioned using

wire-EDM

SEM and light microscopes usedto study the keyhole wall

G-1G-2

G-3


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operated by Concurrent Technologies Corporation (CTC), under Contract No. N00014-00-C-0544 to the Office of Naval Research as part of the Navy ManTech Program. Approved for public release; distribution is unlimited.

Keyhole Interior Inspection

Inspection by light microscope

Inspection by SEM

Optical micrograph, specimen G3

Pin rotation

Trailing edge of flat

Leading edge of flat

G-1G-2

G-3

G3

Optical micrograph, specimen F2


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SEM Micrographs from G1 & G2

Generally replicates pin surface

Small voids observed between thread-shaped

features

G-1G-2

G-3

G2 G1

Specimen G1


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SEM Micrograph from G3

Less material carried in flat space than in G1 or G2 Thread-shaped material retains shape further into

flat space

Tool motionG-1G-2

G-3

G3

Arrows indicate edge of tool flat


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Plastic Deformation Processes -

Frustum Pins with Reentrant Features

4 plastic deformation processes proposed for

this type of tool:

– crushing and consolidation of thread-shaped material in

the flat space

– extrusion of material from flat space into next thread

space

– downward shear of material in thread spaces relative to

surrounding material

– shear of material in flat space relative to surrounding

material


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Conclusions

Threaded tools with reentrant features produce

different stir zone appearance, implying different

material flow

Stop-action techniques can yield insight into the

inner-workings of the FSW process

Different plastic deformation processes proposedfor two tool design classes

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