Arc Welding-Final

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Welding is a process of metal joining by applying heat and sometimes pressure WELDING

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Classification of welding processes welding Forge or Pressure Welding ( Under pressure without additional filler metal ) Fusion or non pressure welding ( With additional filler metal ) Forge or Pressure welding :- The work piece are heated to plastic state & then work pieces are joined together by applying pressure on them. In this case no filler material is used. Fusion or non- pressure welding :- Here edge of work piece to be joined & filler material both are heated to a temp. above the melting point of the metal & then allow to solidify

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Forge or pressure welding Welding heat created by Furnace Electric current friction Forge or furnace welding Resistance welding friction welding Spot seam projection flash butt

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Fusion or non pressure welding Welding heat created by gas Electric Arc chemical reaction Oxy-acetylene welding Thermit welding Carbon arc metal arc atomic hydrogen submerged arc plasma arc electro slag TIG MIG

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Other processes of welding are : Solid State welding : The solid state welding depends upon the theory that if two perfectly clean metallic surfaces are placed in an intimate contact , the cohesive force between atoms of the two surfaces is sufficient to hold them together. The various solid state welding process are: Friction Welding Ultrasonic Welding Diffusion Welding Explosive Welding Modern Welding Processes: Electron Beam Welding Laser Beam Welding

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Protects the weld from oxidizing with atmosphere by producing a shield of gas around the arc and weld pool Provide the slag which floats at the top of molten metal so as to protect the weld from rapid cooling and to protect weld from atmosphere. The slag is then brushed off after weld gets cooled. Terms used in welding : Weld Pool :- Nature of deposition of the filler material in fusion zone is know as weld pool Slag :- molten or fused flux is called as slag Flux :- mixture of Borax and sodium carbonate is coated to electrode for shielding purpose. Functions of Coated Electrodes( flux coated ) Electric arc between the electrode and work piece closes the electric circuit. The arc temperature may reach 10000°F (5500°C), which is sufficient for fusion the work piece edges and joining them.

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In conventional arc welding, the fluxes are used to shield atmosphere around the molten metal and arc. In inert gas welding, separate inert gas such as argon, helium, carbon dioxide are used for surrounding the electric arc and molten metal from the metal . Thus inert gas serves as a shielding gas which displaces the oxygen and nitrogen from the air surrounding the arc and molten metal. Thus it provides protective shield around arc and molten metal. Thus it eliminates formation of metal oxides and nitrides which lower weld metal ductility and toughness. Inert gas welding is of following types Gas tungsten arc welding (GTAW) or Tungsten inert gas ( TIG ) Gas metal arc welding ( GMAW ) or Metal inert gas ( MIG ) INERT GAS WELDING

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Similarities between TIG and MIG No fluxes are used to shield the atmosphere around molten metal Instead of that , both are using separate inert gas ( Argon, helium, Carbon dioxide ) for shielding purpose Differences between TIG and MIG INERT GAS WELDING TIG Arc is stuck between a non consumable tungsten electrode and work piece to be welded. 2. Filler material is added from a hand held filler rod or wire of the same composition as the work piece MIG Arc is struck between consumable electrode( which serves as a filler material ) and work piece to be welded. 2. The electrode / filler is a wire fed from a reel continuously to the welding zone. Consumable electrode is having the same composition as work piece material

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Uses a consumable electrode (filler wire made of the base metal) Inert gas is typically Argon Metal Inert Gas (MIG) BASE METAL WELD POOL POWER SOURCE DRIVE WHEELS CONSUMABLE ELECTRODE ARC COLUMN SHIELDING GAS

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torch electric power source shielding gas source wire spool with wire drive control GMAW ( MIG ) :- Main equipment Equipment required for the GMAW

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The heat is produced by an electric arc between the continuously fed metal electrode and the base metal. Both the base metal and the filler are melt. The weld area is protected by inert shield gases. Weldable metals: steel carbon steel low-allow steel stainless aluminum copper and its allows nickel and its allows magnesium reactive metal (titanium, zirconium, tantalum) The GMAW ( MIG ) process Characteristics of the weld joint by GMAW

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Metal Inert Gas Welding (MIG, GMAW) Metal Inert Gas Welding (Gas Metal Arc Welding) is the arc welding process, in which the weld is shielded by an external gas (argon, helium, CO2, argon + oxygene or other gas mixtures).Consumable electrode wire, having chemical composition simiilar to that of the parent material, is continuously fed from a spool to the arc zone. The arc heats and melts both the work pieces edges and the electrode wire. The fused electrode material is supplied to the surfaces of the work pieces, fills the weld pool and forms joint.Due to automatic feeding of the filling wire (electrode) the process is referred to as a semi-automatic. The operator controls only the torch positioning and speed.

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Advantages of Metal Inert Gas Welding (MIG, GMAW): Continuous weld may be produced (no interruptions); High level of operators skill is not required; Slag removal is not required (no slag); High welding speed and can be easily automated Disadvantages of Metal Inert Gas Welding (MIG, GMAW): Expensive and non-portable equipment is required; Outdoor application are limited because of effect of wind, dispersing the shielding gas.

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Gas Tungsten Arc Welding

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Tungsten Inert Gas Arc Welding (TIG, GTAW) Tungsten Inert Gas Arc Welding (Gas Tungsten Arc Welding) is the welding process, in which heat is generated by an electric arc struck between a tungsten non-consumable electrode and the work piece.The weld pool is shielded by an inert gas (argon, helium, nitrogen) protecting the molten metal from atmospheric contamination. The heat produced by the arc melts the work pieces edges and joins them. Filler rod may be used, if required.Tungsten Inert Gas Arc Welding produces a high quality weld of most of metals. Flux is not used in the process.

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Advantages of Tungsten Inert Gas Arc Welding (TIG, GTAW): Weld composition is close to that of the parent metal; High quality weld structure Slag removal is not required (no slag); Thermal distortions of work pieces are minimal due to concentration of heat in small zone. Flux is not used; therefore, finished welds do not require cleaning of corrosive residue. Disadvantages of Tungsten Inert Gas Arc Welding (TIG, GTAW): Low welding rate; Relatively expensive; Requres high level of operators skill

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Plasma Arc Welding

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Plasma Arc Welding (PAW) PAW is the next step in GTAW. Plasma Arc Welding is a welding process utilizing heat generated by a constricted arc (plasma jet ) struck between a tungsten non-consumable electrode and either the work piece (transferred arc process) or water cooled constricting nozzle (non-transferred arc process).Plasma is a high temperature ionised gas which is a mixture of positive ions, electrons and neutral gas molecules. The gas is forced past an electric arc thtough a constricted openining at the end of water cooled nozzle.Due to this gas gets heated and becomes ionised which is a plasma. As the arc is constricted proportion of ionised gas increases and plasma jet is created. This results in a more concentrated heat source at a higher temperature that greatly increases the heat transfer efficiency, allowing for faster travel speeds. This plasma jet will take a narrow, columnar shape that make it ideal for welding This process uses two inert gases , one forms the plasma and second shield the arc weld metal. Filler rod may or may not be supplied.

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Transferred arc process produces plasma jet of high energy density and may be used for high speed welding and cutting of Ceramics, steels, Aluminum alloys, Copper alloys, Titanium alloys, Nickel alloys. Arc is struck between tungsten non-consumable electrode Non-transferred arc process produces plasma of relatively low energy density. It is used for welding of various metals and for plasma spraying (coating). Arc is struck between non consumable electrode and water cooled constricted nozzle. Since the work piece in non-transferred plasma arc welding is not a part of elctric circuit, the plasma arc torch may move from one work piece to other Plasma Arc Welding (PAW)

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Advantages of Plasma Arc Welding (PAW): Ensures greater arc stability Requires less operator skill due to good tolerance of arc to misalignments; High welding rate; High penetrating capability (keyhole effect); Disadvantages of Plasma Arc Welding (PAW): Expensive equipment; High distortions and wide welds as a result of high heat input.

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Electroslag Welding (ESW) Electroslag Welding is the welding process in which the heat is generated by an electric current passing between the consumable electrode (filler metal) and the work piece through a molten slag, which covers the weld surface.Prior to welding the gap between the two work pieces is filled with a welding flux. Electroslag Welding is initiated by an arc between the electrode and the work piece (or starting plate). Heat, generated by the arc, melts the fluxing powder and forms molten slag. The slag, having low electric conductivity, is maintained in liquid state due to heat produced by the electric current.The slag reaches a temperature of about 3500°F (1930°C). This temperature is sufficient for melting the consumable electrode and work piece edges. Metal droplets fall to the weld pool and join the work pieces.Electroslag Welding is used mainly for steels.

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Advantages of Electroslag Welding: High deposition rate - up to 45 lbs/h (20 kg/h); Low slag consumption (about 5% of the deposited metal weight); Low distortion; Unlimited thickness of work piece. Disadvantages of Electroslag welding: Coarse grain structure of the weld; Low toughness of the weld; Only vertical position is possible.

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