friction stir welding
TRANSCRIPT
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WELDING PROCESS FOR ALUMINIUM
A presentation on
By Ummen Sabu13ETMMO8 M.Tech Materials Engineering
School of Engineering Sciences and Technology UNIVERSITY OF HYDERABAD
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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
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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
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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
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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.
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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:
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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