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Joining Processes Welding

Joining is an important process in manufacturingFor products impossible to manufacture in a single pieceMany product are cheaper to fabricate as many individual components and join laterMany product have to be dissembled for repairsAutomobile assemblyElectronic devices etc. Different parts of a product might have different design requirementsIt is cheaper and practical to transport assemblies to site before assembling it.e.g. machines,home products.

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Joining Processes Welding

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    1. Joining Processes Welding

    2. Joining is an important process in manufacturing For products impossible to manufacture in a single piece Many product are cheaper to fabricate as many individual components and join later Many product have to be dissembled for repairs Automobile assembly Electronic devices etc

    3. Different parts of a product might have different design requirements It is cheaper and practical to transport assemblies to site before assembling it.e.g. machines,home products

    5. Liquid state Process Usually involves fusion resulting due to melting of metal particles – Filler metals E.g. Oxy-Fuel Welding, laser welding, chemical, electrical, optical Solid State process Ultrasound,friction,explosion No filler metal is used here Joining occurs due to external pressure and heat source.

    6. Liquid – Solid State process Braze metal, Soldering, Adhesive bonding Liquid metal applied to solid base metals to join parts Mechanical means Fasteners, bolts, nuts screws, seaming etc Easy to dissemble.

    7. Types of Welding Based on filler metals Autogenous No filler metal, electrode acts as filler metal Homogenous Filler metal used is same as base metal Heterogeneous Filler of different metal, soldering, brazing etc.

    8. Important factors governing fusion welding process Characteristic of heat source Nature of filler material Heat flow characteristics in the joint Gas metal / slag metal (reaction in the fusion zone) Cooling of the fusion zone with associated contraction, residual stresses and crystal changes

    9. Principles of fusion welding Metallurgically there are three distinct zones Fusion zone Heat affected unmelted zone Unaffected original part

    10. Arc Welding Consumable electrode: first developed in mid 1800 Heat developed by electric energy Arc between tip of the electrode and the work piece to be welded Uses both AC/DC power supplies Temperature 5000-30000 °C ,very high!!

    11. Shielded metal arc welding Most common and versatile method,electrodes are thin long sticks Heat melts the electrode, base metal and coating on the electrode,all of this weld in the weld bead Current: AC or DC(sheet metals etc) Electrodes can be Straight polarity ( electrode -ve) DCSP Work Piece is positive Reverse polarity (electrode +ve) DCRP

    12. Shielded metal arc welding (SMAW)

    14. Arc Welding (contd.) Current ranges between 50-300 amps. Power 10 KW Choice of electrodes,current, power etc depends upon the metal to be welded Advantages Simple Versatile Small variety of electrodes Few basic equipment Used in ship building, pipe lines,construction, fabrication etc.

    15. Welding practices Can be used to weld both ferrous and nonferrous material Economical for < 0.25 inch

    16. Submerged Arc Welding ( SAW) Welding arc is shielded by a granular flux consisting of lime,silica,manganese oxide,calcium fluoride Flux: insulates weld area,allows deep thermal penetration Prevents spatter and spark over molten metal Shielded glass etc is unnecessary 300 –2000 Amp Speed 5 m/min Thick plate welding – 4 to 10 times more weld material than SMAW. Carbon, allow, stainless steel etc

    17. Submerged Arc Welding

    18. Gas metal arc welding (GMAW) Also known as metal inert gas welding Weld area is shielded by an external source or inert gas Argon,CO2 , or mixture Multiple layers can be applied without cleaning surface Three types of GMAW processes Spray transfer : spray small droplets – High DC Pulsed Arc. Globular transfer: using pressure – Thick Metals Short circuiting: individual droplets, 50/s Consumable electrode wires of 1/16 to 3/8 inch diameter 600-2000 A (AC/DC) at 440 V

    19. Advantages Quality of weld is very good Good ductility and toughness Uniform properties in weld

    20. Flux core arc welding (FCAW) Tubular electrode filled with flux Electrodes usually 1/16 to 3/32 inch diameter Combines good feature of Shield metal arc welding and gas metal arc welding (electrode feeding feature) We can alloying element in the flux Can be automated

    21. Flux Cored Arc welding Process

    22. Summary Liquid Welding Solid Welding Liquid-solid welding Arc welding – Fusion welding – Consumable electrode Shielded Metal Arc Welding (SMAW) Submerged Arc Welding (SAW) Gas Metal Arc Welding Flux cored arc welding

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