GOVERNMENT COLLEGE OF ENGINEERING

KALAHANDI BHAWANIPATNA
DEPARTMENT OF MECHANICAL ENGINEERING

A
SEMINAR REPORT
ON
FRICTION STIR WELDING (FSW)

SUBMITTED BY:

RABI SHANKAR MOHAPATRA

REGD. NO.:1601110194
 CONTENT
i. Introduction
ii. Working principle
iii. Description of the rotating tool pin
iv. Microstructure classification
v. Factors affecting weld quality
vi. Material suitability
vii. Other materials
viii. Joint geometrics
ix. Friction stir welding machines
x. Advantages of fsw
xi. Applications of fsw
xii. Limitations of fsw
xiii. Retractable pin tool
xiv. Fsw equipment manufacturers
xv. Areas of active development and research
xvi. Conclusion

1. Introduction

In late 1991 a very novel and potentially world beating welding method
was conceived at TWI. The process was duly named friction stir welding
(FSW), and TWI filed for world-wide patent protection in December of
 that year. TWI (The Welding Institute) is a world-famous institute in the
UK that specializes in materials joining technology. Consistent with the
more conventional methods of friction welding, which have been
practiced since the early 1950s, the weld is made in the solid phase, that
is, no melting is involved. Compared to conventional friction welding,
FSW uses a rotating tool to generate the necessary heat for the process.
Since its invention, the process has received world-wide attention and
today two Scandinavian companies are using the technology in
production, particularly for joining aluminium alloys. Also, FSW is a
process that can be automated. It is also a cleaner and more efficient
process compared to conventional techniques.

2. Working principle

In friction stir welding (FSW) a cylindrical, shouldered tool with a

profiled probe is rotated and slowly plunged into the joint line between two
pieces butted together. The parts have to be clamped onto a backing bar in a
manner that prevents the abutting joint faces from being forced apart. Frictional
heat is generated between the wear resistant welding tool and the material of the
work pieces. This heat causes the latter to soften without reaching the melting
point and allows traversing of the tool along the weld line. The maximum
temperature reached is of the order of 0.8 of the melting temperatures of the
material. The plasticized material is transferred from the leading edge of the
tool to the trailing edge of the tool probe and is forged by the intimate contact of
the tool shoulder and the pin profile. It leaves a solid phase bond between the
two pieces. The process can be regarded as a solid phase keyhole welding
technique since a hole to accommodate the probe is generated, then filled during
the welding sequence.

3. Description of the rotating tool pin

The non-consumable tool has a circular section except at the end where
there is a threaded probe or more complicated flute; the junction between the
cylindrical portion and the probe is known as the shoulder. The probe
penetrates the work piece whereas the shoulder rubs with the top surface.
The tool has an end tap of 5 in 6 mm diameter and a height of 5 to 6 mm
(may vary with the metal thickness). The tool is set in a positive angle of
 some degree in the welding direction. The design of the pin and shoulder
assembly plays a major role on how the material moves during the process.

4. Microstructure Classification: -
The first attempt at classifying microstructures was made by P L
Threadgill (Bulletin, March 1997). This work was based solely on
information available from aluminium alloys. However, it has become
evident from work on other materials that the behaviour of aluminium alloys
is not typical of most metallic materials, and therefore the scheme cannot be
broadened to encompass all materials. It is therefore proposed that the
following revised scheme is used. This has been developed at TWI, but has
been discussed with a number of appropriate people in industry and
academia, and has also been provisionally accepted by the Friction Stir
Welding Licensees Association. The system divides the weld zone into
distinct regions as follows:

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

5. Factors affecting weld quality

 Type of metal
 Angle of tool
  Traversing speed of the tool
 Spinning speed of tool
 Pressure applied by the pin tool

Research is going on to combine the above factors in order to control the

process in a better way.

6. Material suitability

TWI has concentrated most of its efforts to optimizing the process for the
joining of aluminium and its alloys. Subsequent studies have shown that cast to
cast and cast to extruded (wrought) combinations in similar and dissimilar
aluminium alloys are equally possible. The following aluminium alloys could
be successfully welded to yield reproducible high integrity welds within defined
parametric tolerances:

 2000 series aluminium (Al-Cu)

 3000 series aluminium (Al-Mn)
 4000 series aluminium (Al-Si)
 5000 series aluminium (Al-Mg)
 6000 series aluminium (Al-Mg-Si)
 7000 series aluminium (Al-Zn)
 8000 series aluminium (Al-Li)

7. Other Materials
The technology of friction stir welding has been extended to other materials
also, on which researches are going on. Some of them are as follows-

 Copper and its alloys

 Lead
 Titanium and its alloys
  Magnesium and its alloys
 Zinc
 Plastics
 Mild steel
Companies practicing and developing FSW are spending a lot of money on
improving its use for plastics. It has been demonstrated that FSW is a much
more efficient and cleaner process than conventional adhesive bonding in
plastics. But it is yet to be made cost and material effective. Ceramics is another
field where FSW could be very useful in the future.

8. Joint Geometrics

The above figure shows friction stir welded parts

FSW is independent of gravity. Hence, it can be used to weld in any position-
vertical, horizontal and even annular. For this reason, FSW has been used to
make circumferential annular welds in fuel tanks for spaceships. Besides these
FSW can also be utilized for normal fillet and corner welds and also double v-
butt joints etc.

9. FSW of Mild Steel

Steel can be friction stir welded, but the essential problem is that tool materials
wear rapidly. The sample becomes red hot during welding (as shown in the
figure). Since the tool gets red hot it is necessary to protect it against the
environment using a shielding gas. So generally, FSW is avoided for mild steel.
This is not such a great disadvantage since there are more efficient methods to
weld mild steel. The weld shown is made by Hitachi of Japan.

10. Friction stir welding machines: -

10. 1 ESAB Super Stir TM machine FW28

The machine has a vacuum clamping table and can be used for non-linear joint
lines.

 Sheet thickness: 1mm-25mm aluminium.

 Work envelope: Approx. 5 x 8 x 1m.
 Maximum down force: Approx. 60kN (6t).
 Maximum rotation speed: 5000rev/min.

10. 2 Modular machine FW22 to weld large size specimens

A laboratory machine was built in October 1996 to accommodate large

sheets and to weld prototype structures. The modular construction of FW22
enables it to be easily enlarged for specimens with even larger dimensions.

 Sheet thickness: 3mm-15mm aluminium

 Maximum welding speed: up to 1.2m/min
 Current maximum sheet size: 3.4m length x 4m width
 Current maximum working height: 1.15m

10. 3 Moving gantry machine FW21

The purpose-built friction stir welding machine FW21 was built in 1995.
This machine uses a moving gantry, with which straight welds up to 2m long
can be made. It was used to prove that welding conditions can be achieved
which guarantee constant weld quality over the full length of long welds.

 Sheet thickness: 3mm-15mm aluminium.

 Maximum welding speed: up to 1.0m/min.
 Current maximum sheet size: 2m length x 1.2m width.

10. 4 Heavy duty Friction Stir Welding machines FW18 and FW14

Two existing machines within TWI's Friction and Forge Welding Group
have been modified exclusively to weld thick sections by FSW. The following
thickness range has been experimentally investigated but the machines are not
yet at their limits.

 Sheet thickness: 5mm-50mm aluminium from one side 10mm-100mm

aluminium from two sides 5mm thick titanium from one side
 Power: up to 22kW
 Welding speed: up to 1m/min

10. 5 High rotation speed machine FW20

For welding thin aluminium sheets TWI equipped one of its existing machines
with an air-cooled high-speed head which allows rotation speeds of up to
15,000rev/min.

 Sheet thickness: 1.2mm-12mm aluminium.

 Maximum welding speed: up to 2.6m/min, infinitely variable.

10. 6 Friction Stir Welding demonstrator FW16

TWI's small transportable machine produces annular welds with

hexagonal aluminium alloy discs. It has been exhibited on fairs in USA,
Sweden, Germany, and the United Kingdom in recent years. It is an eye catcher
which enables visitors to produce their first friction stir weld themselves. It can
be operated with 110V or 220V-240V and has been used by TWI and its
member companies to demonstrate the process.

11. Advantages of FSW

 The process is environment friendly since no fumes or spatter is generated

and no shielding gas is required.
 A non-consumable tool is used.
 Since the weld is obtained in solid phase, gravity does not play any part and
hence the process can be done in all positions (vertical, horizontal, overhead
or orbital).
 No grinding, brushing or pickling is required.
 Since the temperature involved in the process is quite low, shrinkage during.
solidification is less.
 One tool can be typically used for up to 1000 metres of weld length (6000
series aluminium alloy).
 No fusion or filler materials is required.
 No oxide removal necessary as in fusion welding.
 The weld obtained is of superior quality with excellent mechanical properties
and fine micro structure.
 The process is cost effective since mechanical forming after welding can be
avoided.
 Dissimilar metals can be welded.
 Automation is possible.

12. Applications of FSW

12. 1 Shipbuilding and marine industries

The shipbuilding and marine industries are two of the first industry
sectors which have adopted the process for commercial applications. The
process is suitable for the following applications:

 Panels for decks, sides, bulkheads and floors

 Aluminium extrusions
 Hulls and superstructures
 Helicopter landing platforms
 Marine and transport structures
 Masts and booms, e.g. for sailing boats
 Refrigeration plant

12. 2 Aerospace industry

At present the aerospace industry is welding prototype parts by friction

stir welding. Opportunities exist to weld skins to spars, ribs, and stringers for
use in military and civilian aircraft. This offers significant advantages compared
to riveting and machining from solid, such as reduced manufacturing costs and
weight savings. Longitudinal butt welds and circumferential lap welds of Al
alloy fuel tanks for space vehicles have been friction stir welded and
successfully tested. The process could also be used to increase the size of
commercially available sheets by welding them before forming. The friction stir
welding process can therefore be considered for:

 Wings, fuselages, empennages

 Cryogenic fuel tanks for space vehicles
 Aviation fuel tanks
 External throw away tanks for military aircraft
 Military and scientific rockets
 Repair of faulty MIG welds

12. 3 Railway industry

The commercial production of high-speed trains made from aluminium

extrusions which may be joined by friction stir welding has been published.
Applications include:

 High speed trains

 Rolling stock of railways, underground carriages, trams
 Railway tankers and goods wagons
 Container bodies

12. 4 Land transportation

The friction stir welding process is currently being experimentally assessed

by several automotive companies and suppliers to this industrial sector for its
commercial application. Potential applications are:

 Engine and chassis cradles

 Wheel rims
 Attachments to hydro formed tubes
 Tailored blanks, e.g. welding of different sheet thicknesses
 Space frames, e.g. welding extruded tubes to cast nodes
 Truck bodies
 Tail lifts for lorries
 Mobile cranes
 Armour plate vehicles
 Fuel tankers
 Caravans
 Buses and airfield transportation vehicles
 Motorcycle and bicycle frames
 Articulated lifts and personnel bridges
 Skips
 Repair of aluminium cars
 Magnesium and magnesium/aluminium joints

12. 5 Construction industry

The use of portable FSW equipment is possible for:

 Aluminium bridges
 Facade panels made from aluminium, copper or titanium
 Window frames
 Aluminium pipelines
 Aluminium reactors for power plants and the chemical industry
 Heat exchangers and air conditioners
 Pipe fabrication

12. 6 Electrical industry

The electrical industry shows increasing interest in the application of friction

stir welding for:

 Electric motor housings

 Busbars
 Electrical connectors
 Encapsulation of electronics

12.7 Other industry sectors

Friction stir welding can also be considered for:

 Refrigeration panels
 Cooking equipment and kitchens and furniture
 Gas tanks and gas cylinders, connecting of aluminium or copper coils in
rolling mills

13. Limitations

 Welding speeds are moderately slower

 Work pieces must be rigidly clamped
 Backing bar required
 Keyhole at the end of each weld
 Requirement of different length pin tools when
 welding materials of varying thickness

14. FSW equipment manufacturers

Some of the manufacturers of friction stir welding machines are:

 Friction stir welding link, U.S.A

 General tool company, U.S.A
 Hitachi limited, Japan
 Smart technology limited, U.K

15. Areas of active development and research

 Development of new tool design

 Use of process at higher speeds
 Research in the use of other materials
 Investigation of fundamental characteristics of FSW created joints

16. Conclusion

Such has been the interest in FSW, which was patented not so long ago
that considerable effort is being made in transferring the technological benefits
from aluminium to other materials. Efforts are on to make the process more
flexible. In the new millennium there is no doubt that the automotive sector will
find an increasing number of uses for this process as its cost effectiveness and
ability to weld dissimilar material combinations with minimal distortion is more
widely appreciated. The process has been an excellent substitute for alloys that
have inherent fusion welding problems

Name: RABI SHANKAR MOHAPATRA

Reg. no.: 1601110194
Section: ‘B’
Branch: Mechanical Engineering