REGISTRATION SEMINARBY

KANCHAN KUMARI(10ME90R20)UNDER THE GUIDANCE OF

DR. SURJYA K. PALDepartment of Mechanical Engineering

Indian Institute of Technology, Kharagpur

� INTRODUCTION� FRICTION STIR PROCESSING� LITERATURE REVIEW� OBJECTIVES� EXPERIMENTAL SETUP� RESULT AND DISCUSSION� FUTURE WORK� CONCLUSION

� Friction stir welding (FSW) is a solid state joining process.

� Invented at The Welding Institute (TWI) of Cambridge, UK in 1991.

� Utilizes a non consumable rotating tool consisting of a concentric threaded tool pin and tool shoulder.

� Transforms the metal from a solid state into a “Plastic like” state and the mechanically stir the materials together under pressure to form a welded joint.

Schematic representation of FSW

Contd.

SEQUENCE OF OPERATION

Contd.

Contact of the pin produces friction and deformational heating.Contact of shoulder to the work piece increases the work piece heating and expands the zone of softened material and constrained the deformed material.

A. Unaffected material B. Heat affected zone (HAZ) C. Thermo-mechanically affected zone (TMAZ) D. Weld nugget (Part of thermo-mechanically affected zone)

� Aerospace � Ship building� Railway industries� Automobiles� Some of the parts are-

Ø Fuel tank for space launch vehicles.Ø Roofing for railway carriages.Ø Bodies and floors for coaches, buses.Ø Wings and fuselage panels of aircraft.Ø Wheel assemblies.Ø Connectors.

� Retain near-parent material properties across the weld.

� Join similar and dissimilar material, difficult by conventional processes.

� Weld quality is excellent (no porosity).� No melting of material.� Low residual stresses.� No fumes, no filler material, no shielding gases.� Easily automated on simple milling machine-low

setup cost and less training.

Machine variable Tool variable Other variable

Welding speedSpindle speedPlunge force

Tool tilt angle

Tool materialPin and shoulder diameter

Pin lengthThread pitch

Shoulder and tool feat

Joint designMaterial Type and sizeProperty of work piece

materialType of fixture material

PROCESS VARIABLES IN FSW

�Tool rotation rate and traverse speed are the most important welding parameters in FSW.�The tool rotation results in stirring and mixing of the

material around the tool pin and the traverse speed results in movement of material from the front to back and complete welding process.�High rotation results in high temperature due to high

frictional heating. With increase in temperature frictional coupling occur between the tool surface and work piece. Therefore monotonic increases in heating with increasing tool rotation rate is not expected as the coefficient of friction at interface will change with increasing tool rotation rate.

Author Year Findings

Sato et al. 2002 Significant rise of temperature with rise of rotational speed.

Peel et al. 2006 Both torque and extent of material mixing in the SZ zone displays a much stronger dependence on the rotational speed than the traverse speed.

Meran et al. 2006 With const.rpm and varying welding speed finding out the optimum parameter for defect-free joint

Kwo et al. 2009 Onion ring structure becomes wider as rpm increased. but grain size decreased with decrease in rpm.

Rodrigues et al. 2009 Hot weld obtained with maximum rpm and minimum traverse speed have improved mechanical properties relative to cold weld.

Raja manickram et al.

2008 Temperature under the tool was strongly dependent on the tool rotation rate than the welding speed.

Azizieh et al. 2011 With high rpm, higher heat input occur and simultaneously more shattering effect of rotation cause better nano-particle distribution.

�Tool geometry is the most influential aspect of process development which plays a critical role in the material flow and in turn governs the traverse rate at which it can be conducted.

� FSW tool consist of a pin and a shoulder..�Selection of tool material is also very important. Tool steel, cobalt-nickel base alloy, tungsten-base alloy, nickel alloy, PCBN alloy are the different tool materials used for FSW.

Contd.

Schematic drawing of FSW tool

Contd.

A selection of tools designed at TWI

Contd.

Tool shoulder geometries, viewed from underneath the shoulder

Author Year Findings

Scialpi et al. 2007 Used 3 different shoulder geometry (scroll with fillet, cavity with filet, only fillet)and found that best joint has been welded by shoulder with fillet.

Zhang et al. 2011 Tool with three spiral flute w/o pin gives better result than inner concave flute and concentric circle flute.

Forcellese et al. 2012 Used two different tool configuration with different values of shoulder diameter, both with and w/o pin.Large shoulder diameter w/o pin gives strong beneficial effect on both ductility and strength.

Forcellese et al. 2012 Investigated the plastic flow behavior and formability of FSW AZ31 thin sheet using pin-less tool configuration.

Galvao et al. 2012 Used scrolled and conical shoulder tool. Found that different geometry had completely different morphology and intermetallic content using same process parameter.

Galvao et al. 2013 Further researched to see the influence of 3 different geometry (flat, conical, scrolled) on 1 mm thick copper plate..

� In FSW, heat generated by friction between the tool and work piece.

� The temperature within and around the stirred zone influence the microstructure of the weld and resultant mechanical properties.

� Temperature data acquisition done by 4 K-type thermocouples.

� It shows that the temperature is uniform and starts from the rim of the pin to the edge of the work piece.

� FSW process can be defined as a metal working process of five conventional metal working zones.� Preheat� Initial deformation� Extrusion� Forging� Post heat / cool down

Contd.

(a) Metal flow pattern and (b) Metallurgical processing zones developed during friction stir welding

� The microstructure and consequent property distribution produced during FSW depends on following factors :� Alloy composition� Alloy temper� Welding parameters� Other geometric factors (Shoulder size, Plate gauge,

etc)

Author Year Findings

Guerra et al. 2003 Studied the flow of metal using faying surface tracer and a nib frozen in place during welding. Material is moved around the nib by two processes both having different thermo mechanical histories and properties.

Hamilton et al. 2008 Proposed a model of material flow during FSW. They observed that NZ is the combination of interleaved layers of particle rich and particle poor material.

Sato et al. 2002 Grain size in the nugget region is determined predominantly by the peak temperature in the weld. Higher the peak temperature larger is the grain size.

Formation of defects are mainly due to improper material flow or due to geometric factors.

� Lack of penetration� Lack of fusion� Surface grooves� Excessive flash� Surface galling� Tunnels� Voids� Nugget collapse� Kissing bonds

� Too cold welding condition results in work hardening of the material.

� Causes dry slip between the tool and work piece.� Lack of surface fills/ voids, channel defects are the

main defects due to insufficient heat generation.� The insufficient heat generation causes improper

material mixing and thus responsible for non-bonding.Author Year Findings

Kim et al. 2006 Evaluate that at lower rotational speed and high welding speed insufficient heat input is generated resulting in cavity/ groove like defects

� FSW is capable of producing welds with less defects but still complete elimination of process upset is not possible.

� Much researchers has been devoted to understand the effect of process parameters on defect formation in order to optimize the process parameters for FSW. Still optimization of process parameters is mostly done by trial and error.

� In the past few decades, there has been research going on in the field of MP FSW/ FSP where it is more desirable to repair the defective portion of the weld than to throw as a scrap.

� One of the technique is to repair the defects is simply RE-WELDING using nominal process parameter.

Author Year Findings

Brown et al. 2009 Significant reduction in feed force when welding is done over the previous weld. Grain size,hardness,temperature remains unaffected with passes. Gradual reduction of residual stress with increasing pass number.

Nataka et al. 2006 Reported an improvement in mechanical properties of Al die casting alloy of MP FSP compared to as-cast BM.

Ma et al. 2006 No effect of overlapping passes on size, aspect ratio or distribution of Sic particle while performed five pass with 50% overlap FSP on cast A356.

Leal et al. 2008 Used two different alloy. Quality and strength is not just a function of parameters but also depend on type of material and condition of treatment.

Surekha et al. 2008 Investigated that MP FSP showed better corrosion resistance compared to base metal irrespective of process parameters.

� As FSP is one of the technique for grain refinement, removing flaws,defects,many researchers used MP FSP to improve the properties of as-cast material.

Author Year Findings

Johannes et al.

2007 Create large area of super plastic materials with properties using MP FSP.Grain boundary sliding is the most important mechanism to achieve super plastic deformation.

Ma et al. 2009 Two pass FSP resulted in an enhancement in super plastic elongation with a optimum rate in the nugget zone of the second pass and a shift to higher temperature in both central of second pass as well as transitional zone between passes.

Jana et al. 2010 All single pass runs showed some extent of abnormal grain growth which was removed with multi-pass.Higher rotational speed was found to be beneficial for controlling AGG.

Author Year Findings

Barmouz et al. 2011 Found that MP FSP reduces the Sic particle size, improve dispersion and separation of Sic particle by severe stirring action in the NZ.

Ni et al. 2011 MP overlapping FSP transforms the coarse cast Nab alloy base metal to get defect free fine micro structure.

Izadi et al. 2012 Study the effect of MP FSP on distribution and stabilty of carbon nano-tube and to fabricate a MMC based on Al 5059 and MWCNTs.

� Requires less clamping and improves the welding speed

� Improves the weld integrity� Produces further break-up and disposal of oxides

with no loss of mechanical properties� Faster travel speeds

� To determine the effect of two contra rotating FSW tool (Tandem Twin-stir) on the friction stir processing/welding region of different types of aluminium alloys.

� Fixture design

Pictorial view of fixture (a) Fixture installed over milling machine bed (b) Welding plates clamped over fixture

� Twin tool setup

Twin tool attachment

Contd.

� Tool dimension

FSP/FSW tool dimensions

Contd.

� Machines used during experiments

Twin tool attachment

Contd.

�

� Work piece size – 200 mm x 50 mm x 2.5 mmChemical composition (weight %) of work piece material

Si Fe Cu Mn Mg Cr Ni Zn Ti Others, eachRemainder Aluminium

0.494 .656 .0207 0.0498 0.0045 0.00094 0.0014 < 0.001 0.0265 Max. 0.05% 98.7

Mechanical properties of base metal

Yield Strength in MPa Ultimate strength in MPa Elongation in % ageHardness at 200 gmf load in

VHN

58.44 97.92 46.08 45-55 HV

�

� Shoulder diameter – 16 mm �

� Pin length – 2 mm�

Chemical composition (weight %) of Tool Material SS316

Si P Mn Cr Ni Mo Fe2.13 0.27 8.95 16.29 0.2 0.14 72.01

FSP/FSW tool dimensions

�

� Rotational speed – 4�

� Total weld - 12Process parameters Values

Rotational speed (rpm) 900, 1120,1400,1800Welding speed (mm/min) 16,20,25D/d ratio of tool 3.2Pin length (mm) 2Tool shoulder, D (mm) 16Pin diameter (mm) 5

� Metallographic Observations (Macrostructure Analysis)

Optical microstructure (LEICA DFC-295)

Variable speed grinder polisher

� Micro hardness

Vickers micro hardness testing apparatus

Contd.

� Tensile test specimen

Dimension of the tensile test specimen

Contd.

� Tensile properties

(a): Universal Testing Machine (INSTRON) (b): Specimen mounted over UTM

Contd.

� Following weld joints properties were studied:� Macrograph� Micro-hardness� Ultimate tensile strength� Yield strength� % elongation� Joint efficiency� Temperature� Surface appearance

Contd.

Sl. No Rotational speed

Welding speed

FSP using single tool FSP using twin tool

1 900 16

2 1120 16

3 1400 16

4 1800 16

5 900 20

Contd.

Sl. No Rotational speed

Welding speed

FSP using single tool FSP using twin tool

6 1120 20

7 1400 20

8 1800 20

9 900 25

10 1120 25

Contd.

Sl. No Rotational speed

Welding speed

FSP using single tool FSP using twin tool

11 1400 25

12 1800 25

Contd.

Tool Welding speed

Rotation speed – 900 mm

Rotation speed – 1120 mm

Rotation speed – 1400 mm

Rotation speed – 1800 mm

Single tool

16

Single tool

20

Single tool

25

Twin tool

16

Twin tool

20

Twin tool

25

Contd.

Average micro hardness of 12 samples and base metal using single tool as well as twin tool

Contd.

Effect of welding speed on average micro hardness of FSP zone using single and twin tool

1 2 3 438

39

40

41

42

43

44

Single toolTwin tool

AVERAGE MICRO HARDNESS, SPEED - 16 mm / min

5 6 7 838394041424344454647

Single toolTwin tool

AVERAGE MICRO HARDNESS, SPEED - 20 mm / min

9 10 11 1241

41.542

42.543

43.544

44.545

45.5

Single toolTwin tool

AVERAGE MICRO HARDNESS, SPEED - 25 mm / min

Contd.

Effect of rotational speed on average micro hardness of FSP zone using single and twin tool

1 5 938

39

40

41

42

43

44

Single toolTwin tool

AVERAGE MICRO HARDNESS, RPM - 900

2 6 103940414243444546

Single toolTwin tool

AVERAGE MICRO HARDNESS, RPM - 1120

3 7 11383940414243444546

Single toolTwin tool

AVERAGE MICRO HARDNESS, RPM - 1400

4 8 1238394041424344454647

Single toolTwin tool

AVERAGE MICRO HARDNESS, RPM - 1800

Contd.

Effect of welding speed on UTS, YS, Elongation and joint efficiency of FSP zone using single and twin tool

1S 2S 3S 4S 1T 2T 3T 4T0

10

20

30

40

50

60

70

80

90

100

110

YS UTS ELNG JointEff.

WELDING SPEED- 16 MM/MIN

5S 6S 7S 8S 5T 6T 7T 8T0

10

20

30

40

50

60

70

80

90

100

110

YS UTS ELNG JointEff

WELDING SPEED- 20 MM/MIN

Contd.

Effect of welding speed on UTS, YS, Elongation and joint efficiency of FSP zone using single and twin tool

1 2 3 4 5 6 7 845

50

55

60

65

70

75

80

YS-SYS-T

1 5 2 6 3 7 4 845

50

55

60

65

70

75

80

YS-SYS-T

Contd.

Effect of rotational speed on UTS, YS, Elongation and joint efficiency of FSP zone using single and twin tool

1S 5S 1T 5T0

10

20

30

40

50

60

70

80

90

100

110

YS UTS ELNG JointEff

ROTATIONAL SPEED = 900 RPM

2S 6S 2T 6T0

10

20

30

40

50

60

70

80

90

100

110

YS UTS ELNG JointEff

ROTATIONAL SPEED= 1120 RPM

Contd.

Effect of rotational speed on UTS, YS, Elongation and joint efficiency of FSP zone using single and twin tool

3S 7S 3T 7T0

10

20

30

40

50

60

70

80

90

100

110

YS UTS ELNG JointEff

ROTATIONAL SPEED= 1400 RPM

4S 8S 4T 8T0

10

20

30

40

50

60

70

80

90

100

110

YS UTS ELNG JointEff

ROTATIONAL SPEED= 1800 RPM

� Welds made with twin tool shows some higher value of hardness than the single pass FSP. Maximum hardness value of 46.36 HV is recorded at 1800 rpm with 20 mm/min welding speed using twin tool.

� Both the YS and UTS decreases with twin tool processing. At 900 rpm and 16 mm/min, the tensile strength is 107.48 MPa and joint efficiency is 109.8% which is maximum using single tool. On the other hand with the same parameter using twin tool exhibits the lowest tensile strength of 90.07 MPa and joint efficiency of 92.0%

� It is also observed that both YS and UTS is more with the joints fabricated by twin tool at 1800 rpm and 16 mm/min welding speed than the single tool

� Different types of shoulder design to be used to find out the optimum design for the twin tool experiment

� Optimization of process parameter (speed, feed rate, tilt angle) has to be done for better UTS. Design of experiment technique should be incorporated to select the appropriate combination of process parameters viz. Speed, feed rate and tilting in twin tool operation

� Temperature measurement has to be done throughout the welding operation by using both infrared thermograph and thermocouple method

� Power consumption during welding (both in conventional welding as well as using twin tool) has to be finding out by acquiring the data using power sensor with Lab view

� Comparison has to be done between multi pass welding and twin tool system

Contd.