Friction stir welding

1. ISHTIAQUE AHMED
ROLL: 113217
MECHANICAL ENGINEERING
NATIONAL INSTITUTE OF TECHNOLOGY, WARANGAL.
FRICTION STIR WELDING

2. CONTENTS:
INTRODUCTION
CLASSIFICATION OF WELDING
WORKING PRINCIPLE OF FSW
STEPS OF FSW
TOOL USED
PIN DESIGN
MICROSTRUCTURE ANALYSIS
EFFECT OF ROTATIONAL SPEED ON WELD QUALTY
PLUNGE DEPTH AND TILT ANGLE
ADVANTAGES
DISADVANTAGES
CHALLENGES
APPLICATIONS
CONCLUSION
REFERENCES

3. INTRODUCTION:
 FSW is a solid state welding process performed at
temperatures lower than the melting point of the alloy.
 Friction Stir Welding (FSW) was invented by The
Welding Institute (TWI) in England in 1991.
 Weld is created by means of friction heating and
mechanical deformation.
 Unlike fusion welding here no filler material is used.
 Commonly used for aluminum and its alloys.

4. CLASSIFICATION OF WELDING
• Mainly welding is classified into two categories. They
are:
a)Fusion welding :
* heated to molten state
* no pressure required
* Example: Gas welding, Arc welding
b) Plastic welding:
*heated to plastic state
*pressure required
*Example: friction welding, forge welding

5. WORKING PRINCIPLE OF FSW

6. WORKING PRINCIPLE OF FSW(continued):

7. WORKING PRINCIPLE OF FSW(continued):
 FSW a cylindrical, shouldered tool with a profiled probe/pin is rotated and
slowly plunged into the joint line between two pieces butted together.
 The parts have to be suitably clamped rigidly on a backing bar to prevent the
abutting joint faces from being forced apart
 The length of the pin is slightly less than the required weld depth. The
plunging is stopped when the tool shoulder touches the surface of the job
 Frictional heat is generated between the wear resistant welding tool and the
material of the work pieces.
 The plasticized material is transferred the front edge of the tool to back edge
of the tool probe and it’s forged by the intimate contact of the tool shoulder
and pin profile.
 As the tool is moved along the seam the desired joint is created.

8. STEPS OF FSW PROCESS:
a) 1. Plunge stage
b) 2. Dwell stage
c) 3. Welding stage
d) 4. Pull out stage.

9. STEPS OF FSW PROCESS(continued):

10. MICROSTRUCTURE ANALYSIS OF ESW:
The macro and microstructural investigation reveal that the
friction stir weldment is composed of four different regions
namely
1. Weld Nugget (WN) or stirred zone,
2. Thermo-Mechanically Affected Zone (TMAZ),
3. Heat Affected Zone (HAZ) and
4. Unaffected material.

11. MICROSTRUCTURE ANALYSIS OF ESW(continued):
Unaffected material or parent metal
 This is material remote from the weld, which has not been deformed.
 it may have experienced a thermal cycle from the weld .but it is not affected by the
heat in terms of microstructure or mechanical properties.
Heat affected zone (HAZ)
 In this region the material has experienced a thermal cycle which has modified the
microstructure and/or the mechanical properties.
 However, there is no plastic deformation occurring in this area.

12. MICROSTRUCTURE ANALYSIS OF ESW(continued):
Thermo-mechanically affected zone (TMAZ)
 In this region, the material has been plastically deformed by the friction
stir welding tool.
 In the case of aluminum, there is generally a distinct boundary between
the recrystallized zone and the deformed zones of the TMAZ.
 In other materials, the distinct recrystallized region (the nugget) is absent,
and the whole of the TMAZ appears to be recrystallized.
Weld Nugget
 The recrystallized area in the TMAZ in aluminum alloys has traditionally
been called the nugget.
 this term is descriptive, it is not very scientific.

13. TOOL USED:
 Wear resistance
 Chemical stability
 Should withstand high temperature.
 Commonly used tool materials:
• High speed steel
• EN Steel
• PCBN

14. PIN DESIGN:
Tool pin the most important part of FSW arrangement. It mainly
perform the stirring function and also frictional heating. Some of
popular pin profile is described below:
a) Round bottom cylindrical pin
b) Flat bottom cylindrical pin
c) Truncated cone pin
d) Whorl pin
e) MX Triflute pin

15. PIN DESIGN(continued):
a) Round bottom cylindrical pin:
 The pin consists of a cylindrical threaded pin with a round bottom.
 Threads are used to transport material from the shoulder down to the
bottom of the pin.
 A round or doomed end to the pin tool reduces the tool wear upon plunging
and improves the quality of the weld root directly underneath the bottom of
the pin.
b) Flat bottom cylindrical pin:
 The bottom pin is currently the most commonly used pin design.
 Flat bottom pin has higher surface velocity than round bottom pin. so it has
higher affect on the material below it.
 It is easier to machine.

16. PIN DESIGN(continued):

17. PIN DESIGN(continued):
c) Truncated cone pin:
 Cylindrical pins were found to be sufficient for aluminium plate
up to 12mm thick, but to weld thicker plates at fast travel
speeds it is not sufficient.
 This can be done by a simple modification of the cylindrical pin
i.e, Truncated cone pin.
 Truncated cone pins have lower traverse loads (when compared
to a cylindrical pin) and the largest moment load on a truncated
cone is at the base, where it is the strongest.

18. PIN DESIGN(continued):
d) Whorl pin:
 The whorl pin reduces the displaced volume of a cylindrical pin
of the same diameter by 60%.
 Reducing the displaced volume also decreases the traverse
loads, which enables faster tool travel speeds.
 The key difference between the truncated cone and the whorl
pin is the design of the helical ridge on the pin surface. In the
case of a whorl pin, the helical ridge is more than an external
thread, but the helical ridge acts as an auger, producing a clear
downward movement.
e) MX Triflute pin:
 The MX Triflute pin is a further refinement of the whorl pin. In
addition to the helical ridge, the MX Triflute pin contains three
cut into the helical ridge.
 The flutes reduced the displaced volume of a cylindrical pin by
70% and supply additional deformation at the weld line

19. PIN DESIGN(continued):

20. EFFECT OF ROTATIONAL AND TRAVEL SPEED:
 An optimum range of rotational speed exists for better quality
of the weld (For commercial aluminium 1200-1400 RPM is the
range)
 If the speed is lower than this value the friction heat produced
is less sufficient and quality of weld decreases.
 If the speed is higher than the optimum range excessive heat
produced results in cracking and quality of weld decreases.

21. TOOL TILT ANGLE AND PLUNGE DEPTH:
• Plunging the shoulder below the plate surface
increases the pressure below the tool and helps ensure
adequate forging of the material at the rear of the tool.
• Tilting the tool by 2–4 degrees, has been found to
assist this forging process.

22. ADVANTAGES:
• Good mechanical properties .
• Improved safety due to the absence of toxic fumes or the
spatter of molten material.
• No consumables and no filler or gas shield is required for
aluminium.
• Easily automated on simple milling machines — lower setup
costs and less training.
• Can operate in all positions (horizontal, vertical, etc
• Generally good weld appearance and minimal thickness
under/over-matching, thus reducing the need for expensive
machining after welding.
• Low environmental impact.

23. DISADVANTAGES:
 Exit hole left when tool is withdrawn.
 Large down forces required with heavy-duty clamping
necessary to hold the plates together.
 Less flexible than manual and arc processes (difficulties with
thickness variations and non-linear welds).
 Initial cost of the machine is very high compared to fusion
welding

24. CHALLENGES OF FSW:
• Main applications of FSW remain limited to
Aluminium and its alloys.
• It also faces challenges from welding of
dissimilar metals.
• Recently researches have been made on steel
and dissimilar metals by changing the process
parameters. The results are satisfactory.

25. APPLICATION:
Shipbuilding and Offshore
Aerospace
Automotive
Railways
Fabrication
Robotics
Personal Computers

26. CONCLUSION:
Friction Stir Welding is a promising process and has clear
advantages in terms of the mechanical properties of the welded
material. FSW has already found great applications in the
Aluminium industry. Therefore it becomes imperative to try to
use it with other materials including stainless steels.

27. REFERENCES:
• Welding and Welding technology, Richard.L.Little, Tata
McGraw hill
• Friction Stir Welding and Processing by Rajiv S. Mishra,
Murray W. Mahoney
• A Text book of welding technology, O.P.Khanna, Dhanapath
Rai publications