plasma arc welding

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FACTORS AFFECTING HEAT AFFECTED ZONE IN PLASMA ARC WELDING :

FACTORS AFFECTING HEAT AFFECTED ZONE IN PLASMA ARC WELDING N.Raghu ram, Roll no:RM2115A02, Regd no:11103395.

Contents:

Definition of PAW Contents

Definition of PAW:

Plasma arc welding is an arc welding process that produces coalescene of metals by heating them with a constricted arc between an electrode and the work piece(transferred arc) or between the electrode and the constricting nozzle(non transferred arc) . Definition of PAW

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Fig: plasma arc torch terminology, ref: (1)

APPLICATIONS OF PAW::

Welding of tubes of stainless steels, titanium alloys with high production rate. Used for low current range applications even < 100A, to allow welding of foil thickness material. Also used for making small welds on weldments for instrument manufacturing and other small components made of thin metal. Used in the place of electron beam welding but with much low cost. APPLICATIONS OF PAW:

Advantages of PAW:

High energy density during constricted arc. Optimum arc stability even with lower amperages. Insensitive to changes in torch-to-work distance Narrow HAZ causes less distortion of the work piece. Higher welding speeds in comparision with TIG welding. Deeper penetration. Advantages of PAW

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Fig: plasma arc on the left and a TIG arc on the right. COMPARISION BETWEEN PAW & TIG

Heat affected zone :

The heat-affected zone (HAZ) is the area of base material, either a metal or a thermoplastic, which has had its microstructure and properties altered by welding or heat intensive cutting operations The heat from the welding process and subsequent re-cooling causes this change in the area surrounding the weld. Heat affected zone

FACTORS INFLENCING HAZ::

Weld heat input. Cooling rate of welded metal. Thickness of weld. FACTORS INFLENCING HAZ:

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AFFECT OF WELD HEAT INPUT & COOLING TIME : Ref : (2)

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Feature of fracture morphology in the HAZ of HQ130 steel (SEM, 400): (a) t8/5 = 5 s, (b)t8/5 = 10 s, (c) t8/5 = 20 s and (d) t8/5 = 40 s. ref(2) MICRO STRUCTURE FOR DIFFERENT COOLING RATES :

CONCLUSION::

The increase in weld heat input results in the decrease of mechanical properties in HEAT AFFECTED ZONE. The increase in cooling time also reduces the mechanical properties of the HAZ. The fracture morphology changes from ductile to brittle. CONCLUSION:

Still to be done :

Key hole application of PAW High precision welding of thin plates using PAW. Role of tungsten electrode in PAW. Recent developments in PAW. Still to be done

References:

S.E.Barhorst , E.H.Daggest 1997 plasma arc welding AWS WHB-2 90.330 -336. WANG JUAN, LI YAJIANG and LIU PENG 2002 Effect of weld heat input on toughness and structure of HAZ of a new super high strength steel,bull mater. Sci., vol. 26, No.3,april 2003, 301-304. J.Dobranszky,2009 high precision plasma arc welding of thin stainless steel plates, international conference_innovative technologies for joining advanced materials,1-6. http//en.wikipidia.org/wiki/ plasma_arc_welding . References

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