10-04-2017, 08:53 PM
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FRICTION STIR WELDING
Welding process
Welding is a process of joining of different or similar material.
Advantages
Economical, considerable freedom in designing, large no. of dissimilar or similar materials joined, weld as strong as the parent metal.
Different type of welding processes
1. Arc welding.
2. Oxy fuel gas welding.
3. Resistance welding
4. Solid state welding
Arc welding
Carbon arc welding
Electro gas welding
Gas metal arc welding
Gas tungsten arc welding
Plasma arc welding
Shielded metal arc welding
Submerged arc welding
2.Oxyfuel gas welding
Air acetylene welding
Oxy acetylene welding
Oxy hydrogen welding
Pressure gas welding
3. Resistance welding
Projection welding
Resistance seam welding
Resistance spot welding
4. Solid state welding
Cold welding
Diffusion welding
Explosion welding
Roll welding
Hot pressure welding
Friction welding
Friction stir welding
Friction stir welding process
Friction stir welding is a new solid state joining process.
Here a cylindrical shouldered tool along with a profiled probe is rotated and fed at a constant traverse rate in to the joint.
Frictional heat generated between the wear resistant welding tool and the workpiece along with mechanical mixing heat causes the stirred material to soften without reaching the melting point and allows the traversing of the tool along the weld line.
The plasticised material is transferred from the leading edge of the tool to its trailing edge and is forged by the intimate contact of the tool shoulder and the pin profile thus leaving a solid bond between two phases
Materials and thickness
Friction stir welding can be used for joining
2000, 5000,6000,7000 series aluminium.
Aluminium based metal matrix composites
Copper and its alloys (up to 50mm in one pass).
Lead.
Titanium and its alloys.
Zinc, plastic, stainless steel and nickel alloys.
Process advantages
Low distortion, even in long welds.
Excellent mechanical properties as proven by fatigue, tensile and bend tests.
No arc, fume, spatter and porosity
low shrinkage.
Can operate in all positions.
Non consumable tool.
No filler wire, gas shielding.
Can weld aluminium and copper of >50mm thickness on one pass
Applications of friction stir welding
1. Ship building and marine industries
Panels for decks, bulk heads and floors
Hulls and superstructures
Helicopter landing platforms
Mast and booms (sailing boat)
2. Aerospace industry
cryogenic fuel tank for space vehicles
Aviation fuel tanks
Military and scientific rockets
Various primary and secondary structural component
3. Railway and Land transport.
high speed trains
railway tankers and goods wagon
wheel rims
motor cycle and bicycle frames
Limitations of Friction stir welding
Workpieces must be rigidly clamped
Backing bar required (except for self reacting and directly opposed tools)
Key holes at the end of each weld
Cannot make joints that require metal deposition
Less flexible than manual and arc processes
Conclusion
New technology with vital application in aerospace an marine
Presently limited to aluminium ,its alloys and related metals
FSW of steel and titanium alloys are developed and they are in the nascent stage
Will emerge as a better welding technology