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WELDINGDefinition :

A localized Joining of material with or without the use of filler and also with or without the application of pressure.

or

Bringing two perfectly smooth & clean material surfaces to an intimate contact, which is an atomic distance, indeed, between the two, is known as welding.

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Welding Joint Terminology

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Types of Common Welded Joints

• Single Vee Butt Joint• Fillet Joint• Spot Welded Joint• Plug Welded Joint• Edge Joint

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Types of Common Welded Joints

• Butt Joint• Fillet Joint• Lap Joint• Open Corner Joint• Closed Corner Joint

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Types of Fillet Welds

• Mitre Fillet• Convex Fillet• Concave Fillet

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Leg length

Reinforcement

Designed throat

Actual Throat

Face

Leg Hieght

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Weld Positions

• Weld Slope• Weld Rotation• Flat Position• Horizontal Vertical Position• Horizontal Position• Over Head Position• Vertical Up Position• Vertical Down Position• Inclined Position

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G - Positions on Plate

1G2G3G4G

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G - Positions on Pipe

1G2G5G6G

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F - Positions on Plate

1F2F3F4F

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F - Positions on Pipe

1F2F2FR4F5F

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Welding Processes

Following are the common Welding Processes Used in the Industries

1. Oxy- Gas Welding2. Manual Metal Arc ( M.M.A ) Welding 3. Metal Inert Gas ( MIG), Metal Active Gas ( MAG ) Welding4. Tungsten Inert Gas ( TIG) Welding5. Plasma Arc Welding( PAW )6. Submerged Arc Welding ( SAW )7. Electro slag Welding

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OXY-GAS WELDING

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OXY-GAS WELDING

• It is a fusion welding process • Uses a fuel gas and oxygen to provide a flame hot enough to melt the materials to be joined.• Suitable for almost all thicknesses and types of ferrous and most non-ferrous metals. • All positions welding is possible • Relatively cheep method• Reasonable ease of operation

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This Method is suitable for

• Welding of most metals including carbon steels, stainless steels, cast iron, bronze, copper, aluminum etc.• Metals less than 5 mm thickness

The main disadvantages are

• Slow speed of travel• High heat input

OXY-GAS WELDING

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Process Technique

• A flame temperature of 31000 C is produced• This high temperature flame is used to bring a small area of parent metal tip to melting point.• Separate filler wire is then dipped into the molten pool• The filler is melted off and mixes with the base metal to produce the weld

OXY-GAS WELDING

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The neutral flame• Equal quantities of oxygen and acetylene• Distinct inner white cone with a rounded tip• Suitable for all carbon steel, cast irons, low alloy steels and aluminumThe carburizing (carbonizing) flame• Slight excess of acetylene.• Feather around the inner white cone. • Used for welding of high carbon steels and for hard surfacing. The oxidizing flame• Has an excess of oxygen • Inner white cone is shorter and sharper than the neutral cone. • This flame is suitable for brass, bronze, zinc applications, • Used for bronze welding and brazing

There are three distinct flame used in this method

OXY-GAS WELDING

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Three Distinct Flame

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Manual Metal Arc Welding

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Manual Metal Arc Welding

• Most Versatile Welding Process• Suitable for almost all types of metals and all positions• Its operation is comparatively easy• It is a fusion welding• The heat being provided by electric arc• The arc has an average temperature of around 6,000 degree C• M.M.A welding is carried out using either a.c. or d.c.• In case of d.c. current + ve or – ve polarity may be used• A high open circuit voltage (o.c.v.) required is 65-90 volts• Lower welding voltage required is 20-40 volts• Reasonable range of current must be available; 30-350 amps

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Effect of Amperage too highExcessive penetration, burn through, porosity, spatter, deep craters, undercut, electrode overheats, high deposition (positional welding difficult).

Effect of Amperage too lowPoor penetration or fusion, unstable arc, irregular bead shape, slag inclusion, porosity, electrode freezes to the weld, possible stray arc strikes.

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Effect of Voltage too lowPoor penetration,Electrode freezes to workPossible stray arcsFusion defectsSlag inclusionsUnstable arcIrregular bead shape.

Effect of Voltage too highPorosity SpatterIrregular beadSlag inclusionVery fluid weld poolpositional welding difficult.

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Travel speed too slowExcessive depositionCold lapsSlag inclusionsIrregular bead shape.

Travel speed too FastNarrow thin beadSlag inclusionFast cooling UndercutPoor fusion and Penetration

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An electrode connected to the d.c.+ve pole will have two thirds of the available energy.The remaining one third of the energy in the parent materialIt will result in:wide and shallow weld poolBroad HAZSlow Rate of CoolingHydrogen Intrapment

An electrode connected to the d.c. –ve pole has One third of the energy develops at the electrode and two thirds of the energy in the parent material. This will result in Weld pool which is narrow, deep and fast freezing limited HAZ.May lead to hydrogen entrapment and a brittle metallurgical structure

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In A.C. The polarity is reversing 100 times per second (50 c.p.s.).Effect of equalizing the heat distributionHeat at the electrode and half in the parent material.

Types of Consumables used in MMARutile: Titanium Dioxide, Clay , Sodium silicateCellulosic: Cellulose( wood pulp), Titanium Dioxide, Sodium silicateBasic: Lime stone ( Calcium carbonate ), Titanium Dioxide, Sodium silicate

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The MIG./MAG. welding process uses a bare wire consumable electrode .The wire, typically 0.8-1.6 mm diameter, is continuously fed from a coil through a specially designed welding gun.

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Eliminate the possibility of atmospheric contamination by introducing a shielding gas.Argon is an efficient shielding gas, being inert, it doesnot chemically react with the weld metal.When an inert gas is used for shielding the welding process is know as metal inert-gas (MIG) welding.

Deoxidizers must exist in the wire.This process is widely referred to as CO2 welding is also called metal active-gas (m.a.g.) welding.

Metal transfer modes Spray or free flight transfer, Dip transfer (semi-short circuiting arc), Globular transfer, Pulsed transfer.

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Spray or free flight transferThe weld metal transfers across the arc in the form of a fine spray.High deposition rates and deep penetration welds.Suited to thick materials,The flat or horizontal welding positions.

Dip transfer (semi-short circuiting arc)Amperage and low arc volts are required.Used on thinner sections for all positional welding, Vertical down welding

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For m.I.g./m.a.g. welding is usually electrode d.c. +ve of a flatCharacteristic.

Advantages minimal wastage of consumable electrode, no frequent changing of consumable electrode, little or no interpass cleaning required (no slag produced) heavier weld beads are produced, faster welding process, low hydrogen process – preheat may not be required.

Disadvantages increased risk or porosity – due to displacement of the gas shield, more maintenance of plant involved, high risk of lack or fusion.