FRICTION STIR WELDING

Introduction

Welding using friction as the major resourceNo filler material involvedWelds created by, a) Frictional heating b) Mechanical deformation

HistoryInvented by TWI in 1991 in England28 organizations worldwide use FSW

Friction WeldingHeat from mechanical energy conversionLinear friction weldingRotary friction welding

Friction Stir WeldingShoulder which creates friction heat and welding pressureProbe which Stir the materialSufficient downward force to maintain pressure and to create friction heatRotating probe provides friction heat and pressure which joins the material Sufficient downward force to maintain pressure and to create friction heat

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

Microstructure analysisOptical 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 ToolsFixed Pin ToolSelf Reacting Pin ToolAdjustable Pin ToolRetractable Pin Tool

Some of the FSW MachinesESAB SuperStir TM machine FW28

ESAB Machine

AdvantagesDiverse 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 processesFSW 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 DevelopmentsLaser-assisted friction stir welding Possible use of induction coil and other mechanism

Conclusion

An alternative to fusion weldingAdvanced technologies are in the offing

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