FRICTION STIR WELDING

Introduction

Welding using friction as the major resource

No filler material involved Welds created by,

a) Frictional heating

b) Mechanical deformation

History

Invented by TWI in 1991 in England

28 organizations worldwide use FSW

Friction Welding

Heat from mechanical energy conversion

Linear friction weldingRotary friction welding

Friction Stir Welding

Shoulder which creates friction heatand welding pressure

Probe which Stir the material

Sufficient downward force to maintain pressure and to create friction heat

Rotating probe provides friction heat and pressure which joins the material Sufficient downward force to maintain pressure and to create friction heat

Microstructure Analysis

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

Microstructure analysis

Optical micrographs of regions (a), (b) and (c) of the stir nugget.

Joint Geometries

It can be used in all positions,

Horizontal Vertical Overhead Orbital

Material Suitability

Copper and its alloys Lead Titanium and its alloys Magnesium alloys Zinc Plastics Mild steel Stainless steel Nickel alloys

Welding Steel using FSW

Tools Parameters

Common Tools

Fixed Pin ToolSelf Reacting Pin Tool

Adjustable Pin Tool Retractable Pin Tool

Some of the FSW Machines

ESAB SuperStir TM machine FW28

ESAB Machine

Advantages Diverse materials: Welds a wide range of alloys, including

previously un-weldable (and possibly composite materials)

Durable joints: Provides twice the fatigue resistance of fusion welds.

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

Retained material properties: Minimizes material distortion

Safe operation: Does not create hazards such as welding fumes, radiation, high voltage, liquid metals, or arcing

No keyholes: Pin is retracted automatically at end of weld

Tapered-thickness weld joints: Pin maintains full penetration

Comparison with other joining processes

FSW vs Fusion Welding FSW vsRivetting » Improved Mechanical

Properties » Reduced Distortion » Reduced Defect Rate » Parent Metal Chemistry » Simplifies Dissimilar Alloy Welding » Fewer Process Variables » Eliminates Consumables » Reduces Health Hazard

» Reduced Part Count » Reduced Production Time» Reduced Defect Rates » Increase in Load Carrying Capability» Improved Fracture Performance » Eliminates Consumables » Less Operator Dependent

Disadvantages

Work pieces must be rigidly clamped

Backing bar required (except where self-reacting tool or directly opposed tools are used)

Keyhole at the end of each weld

Cannot make joints which required metal deposition (e.g. fillet welds)

Barriers for FSW

Special clamping system necessary Only for simple joint geometries (e.g. butt

joint) License required from TWI Few applications in the construction industry Corrosion protection is needed

Future Developments

Laser-assisted friction stir welding Possible use of induction coil and

other mechanism

Conclusion

An alternative to fusion welding Advanced technologies are in the

offing

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