WELDING PROCESS FOR ALUMINIUM

A presentation on

By Ummen Sabu13ETMMO8 M.Tech Materials Engineering

School of Engineering Sciences and Technology UNIVERSITY OF HYDERABAD

CONTENTS

What is friction stir weldingTheory of FSWFSW processDifficulties of welding aluminium by fusion welding Microstructure details of FSW Advantages of the processDis-advantages of the process Applications of FSWMain FSW machines in IndiaNeed for indigenously developed machineriesConclusionReference

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Friction stir welding is a solid state welding process

Weld is created by means of friction heating and mechanical deformation

Unlike fusion welding here no filler material is used

Commonly used for aluminium and its alloys

WHAT IS FRICTION STIR WELDING

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Friction Stir Welding transforms the metals from a solid state into a plastic state( For Al a temperature of 350-450℃ is required )

The tool mechanically stirs the materials together under pressure to form awelded joint.

FSW uses a rotating, non consumable tool moved along the length of the joint.

The rotation of the tool heats up and plasticizes the materials in contact with tool

A substantial forging force is applied to the weld region by the tool

THEORY OF FSW

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FRICTION STIR WELDING PROCESS

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TOOL USED

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COMMONLY USED TOOL MATERIALSHigh speed steelEN SteelPCBN

shoulder

probe

Ds

Dp

H

FSW tools must be made out of material that is significantly harder and stronger than the material to be joined to maintain rigidity

EFFECT OF ROTATIONAL SPEED ON WELD QUALTY

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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

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Oxide formation at the surface

High thermal conductivity of Aluminium

High solidification shrinkage on cooling

Absence of color change on heating

DIFFICULTIES OF WELDING ALUMINIUM BY FUSION PROCESS

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Aluminium reacts with oxygen in the air to produce a thin film of Aluminium

oxide on the surface

Aluminium oxide melts at about 2050oC, which is almost three times the melting

point of pure Aluminium, 660oC

Due to high thermal conductivity of aluminium it is difficult to concentrate the

heat on a local area near the weld

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Aluminium welds decrease about 6% in volume when solidifying from the

molten state on cooling

Aluminium is different from steels it does not exhibit color as it approaches

its melting temperature

It requires good skilled and experienced operator to weld Aluminium by

fusion welding process

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

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MICRO STRUCTURE FEATURES

The friction stir welded joints possess four mutually distinct microstructural regions.

UNAFFECTED ZONE

Region starting from outside towards the center of the weld, this region is the un-affected zone i.e. the base metal.

No microstructural changes occur in this zone.

HEAT AFFECTED ZONE

It is called heat affected zone or HAZ.

A very little microstructural changes occur in the HAZ due to the heat of welding

No plastic deformation of base takes place in this zone.

The microstructure in this zone consists of coarse grained structure.

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THERMOMECHANICALY AFFECTED ZONE

It is the region adjacent to weld zone

TMAZ undergoes plastic deformation but no recrystallisation occurs

The grains are elongated in nature

STIR ZONE

The weld region that has direct interaction with the tool probe

Extreme strain and elevated temperature cause recrystallisation of material

Therefore this region consists of very fine equi-axed grains.

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Parent metal HAZ

TMAZ Stir zone

Materials Transactions, Vol. 45,No.5pp. 1700 to 1705 The Japan Institute of Metals

Microstructural Variation of 6061 Al Alloy Joints by Friction Stir WeldingWon-Bae Lee, Yun-Mo Yeon and Seung-Boo JungDepartment of Advanced Materials Engineering,Sungkyunkwan, Korea

Welds a wide range of alloys

Eliminates consumables and common fusion weld defects

Welds in all positions and creates straight or complex-shape welds

Does not create hazards such as welding fumes, radiation, high voltage,

liquid metals, or arcing

Environmentally clean process

ADVANTAGES

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DIS-ADVANTAGES

Work pieces must be rigidly clamped

Keyhole at the end of each weld

Cannot make joints which required metal deposition

Initial cost of the machine is very high compared to fusion welding

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APPLICATIONS OF FSW

Aerospace applications

Ship building and automotive works

Structural fabrication works

Personal computers

Apple applied friction stir welding on the 2012 iMac to effectively join the bottom to the back of the device.

1. HAL, Aerospace division, Bangalore

2. BHEL, Thiruchirapally

3. Indian Institute of Science, IISC Bangalore(locally designed and fabricated)

4. Center for materials joining and research, Annamalai university

MAIN FSW MACHINES IN INDIA

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After POKHRAN 2 and AGNI 2 was tested United Nations Security Council Resolution was imparted on India

India was called to stop nuclear weapons programmes, development of ballistic missiles and fissile materials

All countries were urged to prohibit, export of machineries, equipments, materials and technology that assist research programmes in India

To overcome similar situations in future and to smoothen working of defence and space organisations India should be capable of producing advanced machineries and materials

NEED FOR INDIGENOUSLY DEVELOPED FSW AND OTHER MACHINERIES

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CONCLUSION

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An alternative welding process to fusion welding of aluminium

Safe and eco friendly operation is ensured in FSW

FSW can used for a wide variety of applications

Friction stir welding is:

REFERENCES

[1]. Richard.L.Little, Welding and Welding technology, Tata McGraw hill

[2]. O.P.Khanna, A Text book of welding technology,Dhanapath Rai publications

[3] http://www.twi.co.uk/technical-knowledge/published-papers/friction-stir-welding-of-aluminium-alloys/

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Thank you