advance welding technology

02/05/2023 RAVI VISHWAKARMA 1

NME-055

ADVANCE WELDING TECHNOLOGY


Survey of Welding and Allied Processes

Manufacturing Processes

Shaping Processes

Surface Processing Operation

Particulate Processing

Material Removal

Deformation Processes

Solidification Processes

Processing Operation

Assembly Operation

Property Enhancing Processes

Coating & deposition Pro.

Cleaning & surface Treatm.

Heat Treatment

Adhesive bonding

Mechanical Testing

Permanent Joining Processes

Permanent Fastining

Threaded fasteners

Brazing & Soldering

Welding


WELDING

– Welding is a materials joining process which produces coalescence of materials by heating them to suitable temperatures with or without the application of pressure or by the application of pressure alone, and with or without the use of filler material.

– Welding is used for making permanent joints. – It is used in the manufacture of automobile bodies, aircraft frames,

railway wagons, machine frames, structural works, tanks, furniture, boilers, general repair work and ship building.


TYPES

• Plastic Welding or Pressure WeldingThe piece of metal to be joined are heated to a

plastic state and forced together by external pressure(Ex) Resistance welding

• Fusion Welding or Non-Pressure WeldingThe material at the joint is heated to a molten state and

allowed to solidify(Ex) Gas welding, Arc welding


Classification of welding processes:(i). Arc welding • Carbon arc• Metal arc• Metal inert gas• Tungsten inert gas• Plasma arc• Submerged arc• Electro-slag(ii). Gas Welding• Oxy-acetylene• Air-acetylene• Oxy-hydrogen(iii). Resistance Welding• Butt• Spot• Seam• Projection• Percussion

(iv)Thermit Welding(v)Solid State Welding

FrictionUltrasonicDiffusionExplosive

(vi)Newer WeldingElectron-beamLaser

(vii)Related ProcessOxy-acetylene cuttingArc cuttingHard facingBrazingSoldering


Arc welding

• Equipments:• A welding generator (D.C.) or Transformer (A.C.)• Two cables- one for work and one for electrode• Electrode holder• Electrode • Protective shield• Gloves • Wire brush• Chipping hammer• Goggles


Power Source in Arc Welding

• Direct current (DC) vs. Alternating current (AC) – AC machines less expensive to purchase and operate, but

generally restricted to ferrous metals– DC equipment can be used on all metals and is generally

noted for better arc control


Arc Welding Equipments


Arc Welding

Uses an electric arc to coalesce metals

Arc welding is the most common method of welding metals

Electricity travels from electrode to base metal to ground


Fusion Welding: Arc Welding (AW)

A fusion welding process in which coalescence of the metals is achieved by the

heat from an electric arc between an electrode and the work

1. Electric energy from the arc produces temperatures ~ 10,000 F (5500 C), hot enough to melt any metal.

2. Most AW processes add filler metal to increase volume and strength of weld joint.

3. A pool of molten metal is formed near electrode tip, and as electrode is moved along joint, molten weld pool solidifies in its wake


Arc and Power Source Characteristics inArc Welding

Arc CharacteristicsPower Source Characteristics


Two Basic Types of Arc Welding (Based on Electrodes)

1. Consumable electrodes consumed during welding process added to weld joint as filler metal in the form of rods or spools of wire

2. Non-consumable electrodes not consumed during welding process but does get

gradually eroded filler metal must be added separately if it is added


Arc welding (AW): Arc Shielding

1. At high temperatures in AW, metals are chemically reactive to oxygen, nitrogen, and hydrogen in air Mechanical properties of joint can be degraded by these

reactions Arc must be shielded from surrounding air in AW processes

to prevent reaction

2. Arc shielding is accomplished by Shielding gases, e.g., argon, helium, CO2

Flux


Arc welding (AW): Flux

A substance that prevents formation of oxides and other contaminants in welding, which comes from

1. granules that are created from the welded material.2. a coating on the stick electrode that melts during welding to

cover operation.3. a core that is within tubular electrodes and is released as

electrode is consumed.

Melts during welding to be liquid slag that hardens when cooled. The slag should be removed for a clean look by brushing or grinding off.


Consumable Electrode AW Processes

Shielded Metal Arc Welding (or Stick Welding)

Gas Metal Arc Welding (or Metal Inert Gas Welding)

Flux‑Cored Arc Welding

Electro-gas Welding

Submerged Arc Welding


Uses a consumable electrode consisting of a filler metal rod and coating around rod.

Coating composed of chemicals that provide flux and shielding. Low cost welding system: Power supply, connecting cables, and electrode

holder available for $300 to $400.

AW: Consumable: Shielded Metal Arc Welding (SMAW)


SMAW Applications

Used for steels, stainless steels, cast irons, and certain nonferrous alloys.

Not used or rarely used aluminum and its alloys, copper alloys, and titanium.

Can be used in windy weather. Can be used on dirty metals (i.e. painted or rusted surfaces). Good for repair work. Makes thick welds.


AR: Consumable: Gas Metal Arc Welding (GMAW) or Metal Inert Gas (MIG) Welding

Uses a consumable bare metal wire as electrode with shielding by flooding arc with a gas

1. Wire is fed continuously and automatically from a spool through the welding gun.

2. Shielding gases include argon and helium for aluminum welding, and CO2 for steel welding.

3. Bare electrode wire (no flux) plus shielding gases eliminate slag on weld bead. No need for manual grinding and cleaning of slag

4. Medium cost welding system: $1000 to $1200


Gas Metal Arc Welding


GMAW Advantages over SMAW

1. Continuous welding because of continuous wire electrode.

Sticks must be periodically changed in SMAW.

2. Higher deposition rates.

3. Eliminates problem of slag removal.

4. Can be readily automated.

5. Has better control to make cleaner & narrower welds than

SMAW.


GMAW Applications

1. Used to weld ferrous and various non-ferrous and metals.

2. Good for fabrications such as frames and farm equipment.

3. Can weld thicker metal (not as thick as SMAW).

4. Metal must be clean to start weld.


Non-consumable Electrode Processes

Gas Tungsten Arc Welding

Plasma Arc Welding

Carbon Arc Welding

Stud Welding


AW: non-consumable: Gas Tungsten Arc Welding (GTAW) or Tungsten Inert Gas (TIG) Welding

Uses a non-consumable tungsten electrode and an inert gas for arc shielding

1. Melting point of tungsten = 3410C (6170F).2. Used with or without a filler metal. When filler metal used, it

is added to weld pool from separate rod or wire.3. Applications: aluminum and stainless steel mostly.4. High cost for welding system: $4000.


Gas Tungsten Arc Welding

Filler rod


Advantages and Disadvantages of GTAW

Advantages:1. High quality welds for suitable applications

- Welds are cleaner and narrower than MIG2. No spatter because no filler metal through arc3. Little or no post-weld cleaning because no fluxDisadvantages:4. More difficult to use than MIG welding 5. More costly than MIG welding


GTAW Applications

1. Used to weld ferrous and various non-ferrous and metals.

2. Can weld various dissimilar metals together.

3. Good for fabrications such as aircraft or race car frames.

4. Used for welding thinner metal parts (not as thick as MIG).

5. Metal must be very clean to start weld.


Plasma Arc Welding


Advantages and Disadvantages of PAW

Advantages:• Good arc stability and excellent weld quality• Better penetration control than other AW processes• High travel speeds• Can be used to weld almost any metalsDisadvantages:• High equipment cost • Larger torch size than other AW processes

– Tends to restrict access in some joints


Ultrasonic Welding

Friction Welding

Diffusion Welding

Resistance Welding

Solid state welding processes

Friction Welding (Inertia Welding)

• One part rotated, one stationary• Stationary part forced against rotating part• Friction converts kinetic energy to thermal energy

• Metal at interface melts and is joined

• When sufficiently hot, rotation is stopped & axial force increased


Inertia Welding


Friction Welding (FRW)

SSW process in which coalescence is achieved by frictional heat combined with pressure

• When properly carried out, no melting occurs at faying surfaces

• No filler metal, flux, or shielding gases normally used• Process yields a narrow HAZ• Can be used to join dissimilar metals• Widely used commercial process, amenable to automation and

mass production


• (1) Rotating part, no contact; (2) parts brought into contact to generate friction heat; (3) rotation stopped and axial pressure applied; and (4) weld created

Friction Welding


Applications and Limitations of Friction Welding

Applications:• Shafts and tubular parts• Industries: automotive, aircraft, farm equipment, petroleum

and natural gas Limitations:• At least one of the parts must be rotational• Flash must usually be removed (extra operation)• Upsetting reduces the part lengths (which must be taken into

consideration in product design)


• Good for dissimilar metals

Diffusion Welding

• Parts forced together at high temperature (< 0.5Tm absolute) and pressure

• Atoms diffuse across interface

• Heated in furnace or by resistance heating

• Bond can be weakened by surface impurities

•After sufficient time the interface disappears


Resistance Welding (RW)

A group of fusion welding processes that use a combination of heat and pressure to accomplish coalescence

• Heat generated by electrical resistance to current flow at junction to be welded

• Principal RW process is resistance spot welding (RSW)


Resistance Welding

• Resistance welding, showing components in spot welding, the main process in the RW group


Components in Resistance Spot Welding

• Parts to be welded (usually sheet metal)• Two opposing electrodes• Means of applying pressure to squeeze parts between

electrodes• Power supply from which a controlled current can be applied

for a specified time duration


Resistance Spot Welding (RSW)

Resistance welding process in which fusion of faying surfaces of a lap joint is achieved at one location by opposing electrodes

• Used to join sheet metal parts• Widely used in mass production of automobiles, metal

furniture, appliances, and other sheet metal products – Typical car body has ~ 10,000 spot welds – Annual production of automobiles in the world is

measured in tens of millions of units


• (a) Spot welding cycle

• (b) Plot of force and current

• Cycle: (1) parts inserted between electrodes, (2) electrodes close, (3) current on, (4) current off, (5) electrodes opened

Spot Welding Cycle


Advantages and Drawbacks of Resistance Welding

Advantages:• No filler metal required• High production rates possible• Lends itself to mechanization and automation• Lower operator skill level than for arc welding• Good repeatability and reliability Disadvantages:• High initial equipment cost• Limited to lap joints for most RW processes


Resistance Seam Welding (RSEW)

Uses rotating wheel electrodes to produce a series of overlapping spot welds along lap joint Can produce air‑tight joints.

Applications: – Gasoline tanks – Automobile mufflers – Various sheet metal containers


Resistance Seam Welding


Resistance Projection Welding (RPW)

A resistance welding process in which coalescence occurs at one or more small contact points on the parts

• Contact points determined by design of parts to be joined• May consist of projections, embossments, or localized

intersections of parts

02/05/2023 44

(1) Start of operation, contact between parts is at projections; (2) when current is applied, weld nuggets similar to spot welding are formed at the projections

Resistance Projection Welding

RAVI VISHWAKARMA


Other Resistance Projection Welding Operations

• (a) Welding of fastener on sheet metal and (b) cross-wire welding


Arc welding

Advantages– Most efficient way to join

metals– Lowest-cost joining

method– Affords lighter weight

through better utilization of materials

– Joins all commercial metals

– Provides design flexibility

Limitations• Manually applied, therefore

high labor cost.• Need high energy causing

danger• Not convenient for

disassembly.• Defects are hard to detect at

joints.


Comparison of A.C. and D.C. arc welding

Alternating Current (from Transformer)More efficiencyPower consumption less Cost of equipment is lessHigher voltage – hence not safeNot suitable for welding non ferrous metalsNot preferred for welding thin sectionsAny terminal can be connected to the work or electrode


Direct Current (from Generator)Less efficiencyPower consumption moreCost of equipment is moreLow voltage – safer operationsuitable for both ferrous non ferrous metalspreferred for welding thin sectionsPositive terminal connected to the workNegative terminal connected to the electrode


SMAW - DC Polarity

Straight Polarity Reverse Polarity

Shallow penetration(thin metal)

(+)

(–)

Deeper weld penetration

(–)

(+)

AC - Gives pulsing arc

- used for welding thick sections

Electric arc welding --Polarity


OXYFUEL WELDING

• OFW is the term to describe the group of fusion operations that burn various fuels mixed with oxygen to perform welding.

• The OFW processes employ several type of gases, which is the primary distinction among the members of this group.

• The most important OFW process is oxyacetylene welding. Filler materials are used to supply additional material to the weld zone. Flux is often used to clean the surfaces and to retard oxidation by providing inert gas shield around the weld area. It also helps in removing oxide and other impurities. Borax, is the most common flux, but sometimes other substances are added to improve its effectiveness.


OXYFUEL WELDING

• The heat is obtained by combustion of acetylene and oxygen. Here primary combustion occurring in the inner zone gives:

C2 H2 + O2 → 2CO + H2 + Heatand the second reaction in the outer zone gives:

2CO + H2 + 1.5O2 → 2CO2 + H2 O + Heat

• The maximum temperature at the tip of inner cone reaches up to 3000-3500°C. Therefore, most gas welding is performed by keeping this inner zone tip just above the metal to be welded so that maximum temperature is available for welding.


GAS WELDING EQUIPMENT...

1. Gas CylindersPressure

Oxygen – 125 kg/cm2Acetylene – 16 kg/cm2

2. RegulatorsWorking pressure of oxygen 1 kg/cm2Working pressure of acetylene 0.15 kg/cm2 Working pressure varies depends upon the thickness of the

work pieces welded.3. Pressure Gauges4. Hoses5. Welding torch 6. Check valve7. Non return valve


Oxy-Acetylene welding


TYPES OF FLAMES…

• Oxygen is turned on, flame immediately changes into a long white inner area (Feather) surrounded by a transparent blue envelope is called Carburizing flame (30000c)

• Addition of little more oxygen give a bright whitish cone surrounded by the transparent blue envelope is called Neutral flame (It has a balance of fuel gas and oxygen) (32000c)

• Used for welding steels, aluminum, copper and cast iron• If more oxygen is added, the cone becomes darker and more

pointed, while the envelope becomes shorter and more fierce is called Oxidizing flame

• Has the highest temperature about 34000c• Used for welding brass and brazing operation


Three basic types of oxyacetylene flames used in oxyfuel-gas welding and cutting operations: (a) neutral flame; (b) oxidizing flame; (c) carburizing, or reducing flame.


TEMPERATURE DISTRIBUTION ALONG THE FLAME


TYPES OF FLAMES…

• A neutral flame is obtained when the ratio of is oxygen and acetylene is 1. Most gas welding operations are carried out by this flame.

• An oxidizing flame is obtained when this ratio is more than 1. This type of flame is not suitable for welding of steels since excess oxygen present reacts with carbon in steel and is generally used for welding of copper and its alloys.

• When the ratio in mixture is less than 1 a carburizing flame is obtained. In this type of flame acetylene decomposes into carbon and hydrogen and the flame temperature gets reduced. Joining operations such as brazing and soldering which require lower temperature generally use this flame


Weld defectsClassification of Weld Joint Discontinuities

Geometric• Misalignment• Undercut• Concavity or Convexity• Excessive Reinforcement• Improper Reinforcement• Overlap• Burn-through• Backing left on• Incomplete Penetration• Lack of Fusion• Shrinkage• Surface Irregularities

Other• Arc Strikes• Slag Inclusions• Tungsten Inclusions• Oxide Films• Spatter• Arc Craters


POROSITY

• Porosity is the entrapment of small volumes of gas in solidifying weld metal

• Prevention– Drying consumables– Cleaning, degreasing

material being welded– Electrode or filler metals

with higher level of deoxidants

– Sealing air leaks, reducing excess shielding gas flow


Molten weld metal is able to hold more gas than solid weld metal. For this reason, gas bubbles tend to evolve as the liquid metal solidifies. These gas bubbles trapped within the solid weld metal are referred to as porosity. Although porosity is sometimes noted at the surface of a weld, visual inspection cannot detect internal porosity. Radiography and ultrasonic methods are required. Localized regions of porosity can be cut from a weld; a repair is then made. For general porosity throughout a weld, the entire weld must be gouged out and rewelded.


SLAG INCLUSIONS

• Slag inclusions, as the name implies, are small pieces of welding slag which are trapped in the weld metal. Unlike porosity, which is usually spherical, slag inclusions are irregularly shaped. Since these are internal discontinuities, radiography or ultrasonic testing is required for detection. Weld regions containing slag inclusions must be cut out and rewelded.

Slag inclusions are irregularly shaped, not spherical like porosity Prevention

Position work and/or change electrode/flux to increase slag controlBetter slag removal between passesDress weld surface smooth if it is likely to cause slag trapsRemove heavy mill scale on plate


LACK OF FUSION

• Lack of fusion is caused by incorrect welding conditions

• Prevention– Procedure for complete

fusion should be verified by testing

– Increased energy input– Correct electrode angle

and work position

• Lack of fusion can occur at the weld sidewall, root, or between individual passes. Magnetic particle and dye or fluorescent penetrant may be used to detect this discontinuity if it reaches the surface. Otherwise, radiography or ultrasonic methods must be used. Affected regions must be cut out and rewelded.


INCOMPLETE ROOT PENETRATION

• Incomplete root penetration can be caused by– Excessively thick root face,

insufficient root gap– Incorrect welding conditions– Misalignment of second weld

• Prevention– Improved joint preparation– Test weld verifications for

correct parameters– Reassessment of back

gouging

• Incomplete root penetration is the failure of a weld to extend into the root of a joint. For a double weld, it is an internal discontinuity and can be detected only by radiography or ultrasonic testing. It can be detected by magnetic particle, and dye or fluorescent penetrant methods if the root side is accessible. A long pipeline would be an example of when the weld root (inside the pipe) would not be accessible. This defect is repaired by cutting it out and rewelding.


OVERLAP

• Overlap is an imperfection at the weld toe or root caused by metal flowing onto the surface of the base metal without fusing to it

• Prevention– Adjust electrode

manipulation to ensure fusion of base metal

– Limit size of fillet to 9-mm leg length

• Overlap is often associated with horizontal welding; welding in the flat position can help to eliminate this problem. Overlap can be detected visually and can be supplemented with dye penetrant. It is corrected by cutting back to sound weld metal. Rewelding may be necessary


UNDERCUT

• Undercut is an irregular groove at the weld toe in the parent metal or previous pass caused by– excessive weaving– melting of top edge of fillet

weld with high current• Prevention

– Weld in flat position– Change shielding gas to one

which produces better wetting– Terminate welds so they don’t

finish at a free edge

• Undercut is another defect that can be associated with horizontal welding among other factors such as high current and excessive weaving. Flat position welding can aid in eliminating this discontinuity. It is detected visually and measured by a depth gauge. Deep undercut is ground out and weld repaired


SPATTER

• Spatter consists of small droplets of electrode material that land beside the weld and may or may not fuse to the base material

• Prevention– Reduce energy input– Shorter arc length– Reposition current return

clamp to reduce magnetic arc blow or switch to AC current

• As metal drops transfer from the electrode to the weld pool, some are blown clear of the weld and form drops of spatter on the base plate. All open arc consumable electrode processes produce some spatter.

• Spatter can occur when the energy input is too high or when the arc length is excessive. Arc blow can also cause spatter, as can insufficient inductance in GMAW or CO2 welding.

• Spatter can be detected visually. It can be removed by scraping or by light grinding. Anti-spatter coatings are available on the market that prevent spatter from adhering to the base material.


GAS CUTTING

• Ferrous metal is heated in to red hot condition and a jet of pure oxygen is projected onto the surface, which rapidly oxidizes

• Oxides having lower melting point than the metal, melt and are blown away by the force of the jet, to make a cut

• Fast and efficient method of cutting steel to a high degree of accuracy

• Torch is different from welding• Cutting torch has preheat orifice and one central orifice for oxygen

jet• PIERCING and GOUGING are two important operations• Piercing, used to cut a hole at the centre of the plate or away from

the edge of the plate• Gouging, to cut a groove into the steel surface


Flame Cutting

• Metal is merely melted by the flame of the oxyfuel gas torch and blown away to form a gap or kerf.

• When ferrous metal is cut, actually burning of iron takes place according to one or more of the following reactions

Fe+ O Feo+ Q3Fe+2 O2 Fe3 O4+ Q

4Fe+3 O2 2Fe2 O3 + Q


• Because, these reactions cannot take place below 815°C oxyfuel flame is first used to raise the metal temperature where burning can be initiated. Then a stream of pure oxygen is added to the torch (or the oxygen content of the oxyfuel mixture is increased) to oxidize the iron. The liquid iron and iron oxides are then expelled from the joint by the kinetic energy of the oxygen gas stream.

• Low rate of heat input, and need of preheating ahead of the cut, oxyfuel produces a relatively large heat affected zone and thus associated distortion zone.

• The process is suitable when edge finish or tolerance is not critical.• Theoretically heat generated due to burning of Fe is sufficient to continue cutting however

due to losses additional heat supply is needed. If the work is already hot due from the other processes, supply of oxygen through a small diameter pipe is needed to continue cut. This is called Oxygen Lance Cutting. A work piece temperature of 1200°C is needed to sustain the cutting.

• Low carbon steel from 5 to 75 mm can be cut.


GAS CUTTING…

Automatic Gas Cutting Manual Gas Cutting

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Weld joints


SOLID / LIQUID STATE BONDING

• Low temperature joining methods are used when the metal to be joined cannot withstand high temperature, or intricate sections are to be joined, or dissimilar metals are to be joined, or weldability of material is poor.

• In these methods, the gap between the metal pieces to be joined is filled with molten filler material after heating the base metal. Melting point of filler material is much lower than base metals.

• The bonding is not due to melting of parent metal and fusion.


• Filler material is drawn into the gap between the metal pieces to be joined by capillary action and the bond formation is initiated when the molten filer metal comes under intimate contact with the solid surface as in solid state welding.

• The nature of bond formed is much complex here, and invariably there is some degree of intersolubility between filler and base metals.

• This inter-diffusion at the base metal surface and resulting alloy has a strength which is very close to that the base metal.


• For a good joint strength the liquid filler metal; must flow into the gap between the metal pieces to be joined and cover the entire surface area, without gaps or blow holes. The following usually insures good bonding:

– Clean base metal surfaces– Maintain optimum gap– Heat the joining area above meltingtemperature of the filler material– Use fluxes for welding of base metalsurfaces.• Joint strength is sensitive to the gap and

there exists an optimum gap for a filler material.


Brazing and Soldering

• Brazing It is a low temperature joining process. It is performed at

temperatures above 840º F and it generally affords strengths comparable to those of the metal which it joins. It is low temperature in that it is done below the melting point of the base metal. It is achieved by diffusion without fusion (melting) of the base

Brazing can be classified asTorch brazingDip brazing

Furnace brazingInduction brazing


BRAZING

Brazing methods(a) Torch and filler rods

(b) Ring of filler metal atentrance of Gap

(c) Foil of filler metal between flat part surfaces


• In brazing the joint is made by heating the base metal red hot and filling the gap with molten metal whose melting temperature is typically above 450°C but below melting temperature o base metal. The filler metals are generally copper alloys. Cu-Zn and Cu-Ag alloys are used for brazing because they form alloy with iron and have good strength.


VARIOUS BRAZING JOINTS

(a) Conventional butt(b) Scarf joint(c) Stepped joint(d) Increased crossest ion

(a)Conventional Lap(b) Cylindrical part(c) Sandwiched part(d) Use of sleeve


Brazing


Advantages & Disadvantages

Advantages• Dissimilar metals which can not be welded can be joined by brazing• Very thin metals can be joined• Metals with different thickness can be joined easily• In brazing thermal stresses are not produced in the work piece.

Hence there is no distortion• Using this process, carbides tips are brazed on the steel tool holdersDisadvantages• Brazed joints have lesser strength compared to welding• Joint preparation cost is more• Can be used for thin sheet metal sections


SOLDERING

• Soldering is very similar to brazing except that filler material is usually a lead-tin based alloy which has much lower strength and melting temperature around 250°C.

• In this process less alloying action between base metal and filler material as compared to brazing takes place hence the strength of joint is lesser.

• It is carried out using electrical resistance heating

Soldering • It is a low temperature joining

process. It is performed at temperatures below 840ºF for joining.

• Soldering is used for,• Sealing, as in automotive

radiators or tin cans• Electrical Connections• Joining thermally

sensitive components• Joining dissimilar metals



THERMIT WELDING (TW)

FW process in which heat for coalescence is produced by superheated molten metal from the chemical reaction of thermite

• Thermite = mixture of Al and Fe3O4 fine powders that produce an exothermic reaction when ignited

• Also used for incendiary bombs • Filler metal obtained from liquid metal• Process used for joining, but has more in common with casting

than welding


• (1) Thermit ignited; (2) crucible tapped, superheated metal flows into mold; (3) metal solidifies to produce weld joint

Thermit Welding


TW Applications

• Joining of railroad rails• Repair of cracks in large steel castings and forgings• Weld surface is often smooth enough that no finishing is

required


WELDING METALLURGY

• In fusion welded joint, where three distinct zones can be identified:-

• The base metal• The heat affected Zone• The fusion Zone


Two major concerns occur in the heat affected zone which effect weldability these are, a.) changes in structure as a result of the thermal cycle experienced by the passage of the weld and the resulting changes in mechanical properties coincident with these structural changes, and b.) the occurrence of cold or delayed cracking due to the absorption of hydrogen during welding.


Heat Affected Zone

• The Heat-Affected Zone (HAZ) is an area of a base metal which, while not melted, still has had its chemical properties altered by high temperature heat. This phenomenon primarily occurs during welding or high-heat cutting. The high temperature from the welding process and eventual re-cooling causes this change from the weld interface to the end of the sensitizing temperature in the metal. These areas can be varying sizes and levels of severity.

• The metallurgical changes that can occur at the HAZ tend to cause stresses that reduce the strength of the material. The HAZ can also suffer from a decreased resistance to corrosion and/or cracking (i.e, sensitization). These metallurgical changes can also lead to the formation of nitrides at the HAZ, which can affect weldability. In addition, the microstructure at the HAZ can be altered in a way that increases its hardness compared to the surrounding material. Hardness, sensitization, and high local stresses in or near the HAZ may be mitigated by practices such as controlled pre- and post-weld heat treatment and solution annealing.


How much these changes in metallurgical and physical properties can affect the HAZ of the material is dependent on a number of factors, including the base material, the weld filter metal, and the amount and concentration of heat input during the welding process.


Hardfacing

Hard facing is a metalworking process where harder or tougher material is applied to a base metal. It is welded to the base material, and generally takes the form of specialized electrodes for arc welding or filler rod for oxyacetylene and TIG welding. Powder metal alloys are used in (PTA) also called Powder plasma welding system and Thermal spray processes like HVOF, Plasma spray, Spray and Fuse, etc.


• Hard facing may be applied to a new part during production to increase its wear resistance ,or it may be used to restore a worn-down surface. Hard facing by arc welding is a surfacing operation to extend the service life of industrial components, pre-emptively on new components, or as part of a maintenance program. The result of significant savings in machine down time and production costs has meant that this process has been adopted across many industries such as Steel, Cement, Mining, Petro chemical, Power, Sugar cane and Food. According to the results of an experimental study, the SMAW (Shielded Metal Arc Welding) and the GMAW (Gas Metal Arc Welding)hard facing processes were effective in reducing the wear on the mould board ploughshare. With the SMAW and GMAW hard facing processes, the life span of the ploughshare was increased approximately 2 times.


Cladding

Cladding is the bonding together of dissimilar metals. It is different from fusion welding or gluing as a method to fasten the metals together. Cladding is often achieved by extruding two metals through a die as well as pressing or rolling sheets together under high pressure.


Microstructure Welding

The microstructural studies of friction welding helps in understanding microstructural changes occurred during friction welding process. High temperature and strain during friction welding process changes the microstructure of the parent material.


Welding Symbols

Representation of welds on drawings requires the use of following elements-1. A basic symbol to specify each type of weld.2. A reference line and an arrow to indicate the location the weld in a

joint.3. Supplementary symbols to mark weld-all-round, finish of welds

etc.4. Weld dimensions in cross-section and in length.


Basic Weld Symbols

FILLET

SQUARE BUTTSINGLE V-BUTT

AND MANY MORE SYMBOLS…..


WELDING DESIGN

Before an arc can be struck on metal, the product must be designed to serve its purpose, the material chosen and the method of welding determined in more or less detail.The weldment design engineer must I. Know the limitations and specific requirements of the processes as well

as the equipment available on the shop floor.II. Have a good working knowledge of the shop problems of shrinkage and

distortion.III. Have accurate knowledge not only of suitability but also of availability of

materials or the costs of extras.IV. Be able to calculate stresses, strengths and determine weld sizes and put

these together to work out a design that meets all service requirements.


Welding Joint Design

since, welding joins metals, design for welding is chiefly concerned with joints-when to use a joint, how to weld it, where to place it, what to do and what not to do.Selection and preparation of weld joints is an important step in the fabrication of a weldment.Selection of correct joint design is very essential if welded members are to perform within the load service, corrosive atmosphere and safety requirements.


Welding

Fusion Welding (FW)

Solid State Welding (SSW)

Consumable electrodes Non-consumable electrodes

Summary

Shielding

Flux

Various welding processes (AW) are developed to address the two issues: shielding and flux

Arc weldingOxyfuel welding


THANKS

advance welding technology

Engineering