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WELDING. Q 5. INTRODUCTION. Welding is the joining of parts by FUSING them together Fusion involves HEAT and PRESSURE between the parts being joined Some techniques require pressure Other techniques just require very high temperatures and no pressure. IDEAL CONDITIONS FOR WELDING.

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Welding

WELDING

Q 5


Introduction
INTRODUCTION

  • Welding is the joining of parts by FUSING them together

  • Fusion involves HEAT and PRESSURE between the parts being joined

  • Some techniques require pressure

  • Other techniques just require very high temperatures and no pressure


Ideal conditions for welding
IDEAL CONDITIONS FOR WELDING

  • SMOOTH joint surfaces that match each other

  • CLEAN joint surfaces, free from oxides, grease and dirt

  • Metals to be joined must have the same MICROSTRUCTURE (example: steel to steel)

  • Metals must be of good quality no internal impurities


Preparing joint edges
PREPARING JOINT EDGES

  • Large plates may have to be bevelled.

  • Cleaning is very important, sometimes it is cleaned chemically or mechanically.

  • OXIDATION – is when metals are heated to high temperatures their surfaces are more easily affected by the oxygen in the atmosphere

  • To prevent oxidation surfaces must be shielded from the atmosphere during the welding operation


Many welding techniques
MANY WELDING TECHNIQUES

YOU CAN TELL DIFFERENCE BETWEEN THEM BY:

  • The way the metal is heated

  • The way additional filler metal is fed into weld

    IMPORTANT TYPES OF WELDING

  • Gas Welding

  • Electric Arc Welding

  • Electric Resistance Welding


Gas welding
GAS WELDING

  • Gas welding involves the mixture of a fuel gas and oxygen

  • Fuel gas usually ACTEYLENE

  • ACETYLENE mixed with OXYGEN is - OXYACETYLENE WELDING



Oxy acetylene welding
OXY-ACETYLENE WELDING

  • Oxy-acetylene welding is a common gas welding method

  • It is a fusion weldingprocess

  • Gas is fed from two separate cylinders

  • The acetylene and oxygen mix with each other in torch where it will escape and be ignited and burn as a very hot flame - 3500ºC.

  • Intense heat is capable of melting the metal


  • Heat from the flame is capable of melting the joint edges until the metal melts and starts to flow

  • When molten metal from both edges meet, it fuses.

  • As the metal cools it becomes solid and the two parts will be permanently joined

  • Filler metal in rod form can be fed by hand into weld pool

  • During welding it is dipped constantly at regular intervals into weld pool


Oxy acetylene equipment
Oxy-acetylene Equipment until the metal melts and starts to flow.


Weld run on a flat sheet
Weld Run on a flat sheet until the metal melts and starts to flow.


Weld run on a flat sheet1
Weld Run on a flat sheet until the metal melts and starts to flow.


Types of flames
Types of flames until the metal melts and starts to flow.


Types of oxy acetylene flames
TYPES OF OXY-ACETYLENE FLAMES until the metal melts and starts to flow

  • NEUTRAL FLAME – has equal proportions of oxygen and acetylene.

  • Ratio 1:1

  • Used for welding, steel, stainless steel and cast iron


Types of oxy acetylene flames cont
TYPES OF OXY-ACETYLENE FLAMES Cont. until the metal melts and starts to flow

  • OXIDISING FLAME – this flame contains excess oxygen,

  • Ratio Oxygen to Acetylene = 1.5:1

  • Working temperature of up to 3,500ºc

  • It is used to weld copper and brass but not steel as it would oxidise and contaminate the joint


TYPES OF OXY-ACETYLENE FLAMES Cont. until the metal melts and starts to flow

  • CARBURISING FLAME – contains excess acetylene

  • Ratio Oxygen to Acetylene = 0.9:1

  • Working temperature of approximately 3150ºc

  • It is used to weld aluminium, special alloy steel and gives excellent protection against Oxidisation


3 welding flames
3 Welding Flames until the metal melts and starts to flow

CARBURISING OXIDISING NEUTRAL


Safety factors oxy welding
SAFETY FACTORS OXY-WELDING until the metal melts and starts to flow

  • Oxygen should never be used instead of compressed air

  • Special care when using pressurised flammable gases

  • Use goggles when welding

  • Ventilation


Safety features integrated into oxyacetylene equipment include
Safety features integrated into oxyacetylene equipment include:

  • Gas cylinders are colour-coded with acetylene having a maroon cylinder and oxygen having a black cylinder

    • Regulators cannot be interchanged with colour coding

    • Acetylene has left handed thread fittings

    • Flashback arrestors are placed on gas lines

    • Hoses are colour-coded

    • Regulators are fitted to cylinders with an over-ride valve

    • Adequate ventilation systems


Colour coding in oxyacetylene welding equipment
Colour Coding In Oxyacetylene Welding Equipment include:

  • Oxygen cylinder is black and acetylene is maroon, hoses and regulators are colour coded with oxygen as blue and acetylene as red.


Safety precautions in preparation of equipment and materials for oxyacetylene welding
Safety precautions in preparation of equipment and materials for oxyacetylene welding

  • Oil and grease needs to be removed to minimise reaction with welding process

  • Torch must be thoroughly cleaned before starting weld Flashback arrestors need to be in place on fuel and oxygen line

  • Correct colour coding of cylinders and hoses must be observed


Dissolved acetylene
DISSOLVED ACETYLENE for oxyacetylene welding

  • Acetylene is highly explosive when compressed, for this reason acetylene cylinders are packed with a porous material, which is filled with acetone

  • Acetone can absorb up to 25 time its own volume of acetylene for each atmosphere of pressure it receives


Acetylene in tank
Acetylene in Tank for oxyacetylene welding


Eletric arc welding
Eletric Arc Welding for oxyacetylene welding

4 Types

  • Manual metal arc (MMA) welding.

  • Metal inert gas (MIG) welding.

  • Tungsten inert gas (TIG) welding.

  • Submerged arc welding (SAW)

    All work on the same principal of electric arc.


Basic welding circuit
Basic Welding Circuit for oxyacetylene welding .


Manual metal arc mma welding
Manual Metal Arc (MMA) Welding for oxyacetylene welding


Shielded metal arc welding stick welding
Shielded Metal Arc Welding Stick Welding for oxyacetylene welding

  • Definition:

    • Consumable electrode coated with chemicals that provide flux and shielding

    • The filler metal (here the consumable electrode) is usually very close in composition to the metal being welded.


Manual metal arc wedling principle of operation
Manual Metal Arc Wedling Principle of Operation for oxyacetylene welding

  • Electricity is passed through an electrode which jumps between the electrode and the work piece.

  • This causes an arc which produces great heat melting the consumable electrode and the work piece causing the edges to fuse together.

  • The weld pool is protected from oxidation by the gasses produced by melting the chemicals on the electrode coating. This wire electrode also acts as a filler


  • material to fill the gap between the two parts being joined. A slag is formed which protects the weld area from oxidation and minimises cracking of the weld as it allows the joint cool slowly.

  • MMA welding is made more effective with the use of an adjustable transformer to allow for different thicknesses of steel to be welded.

  • MMA welding has many operational uses such as repair work on construction steel


Funtions of transformer
FUNTIONS OF TRANSFORMER A slag is formed which protects the weld area from oxidation and minimises cracking of the weld as it allows the joint cool slowly.

  • A TRANSFOREMR IS USED TO STEP DOWN THE MAINS VOLTAGE TO A SUITABLE LEVEL FOR ARC WELDING


Transformer
Transformer A slag is formed which protects the weld area from oxidation and minimises cracking of the weld as it allows the joint cool slowly.

  • A step-down transformer is used to change the mains voltage from 220V to a suitable level (80-100V) for welding.

  • This will provide the high current needed for welding.

  • This type of transformer has more turns on the primary coil than the secondary coil and will induce alternating current (AC) at a lower voltage.


Transformer with air core
Transformer With Air Core A slag is formed which protects the weld area from oxidation and minimises cracking of the weld as it allows the joint cool slowly.


Transformer with iron core
Transformer With Iron Core A slag is formed which protects the weld area from oxidation and minimises cracking of the weld as it allows the joint cool slowly.


Function bridge rectifier
FUNCTION BRIDGE RECTIFIER A slag is formed which protects the weld area from oxidation and minimises cracking of the weld as it allows the joint cool slowly.

  • A bridge rectifier permits current to flow in one direction only

  • For MMA WELDING it converts AC to DC.

  • This is used to supply Direct Current when Arc Welding

  • The Voltage is rectified by using the rectifier which consists of 4 Diodes- (A Diode allows current to flow in one direction only)


Rectifier
Rectifier A slag is formed which protects the weld area from oxidation and minimises cracking of the weld as it allows the joint cool slowly.

  • The rectifier changes alternating current (AC) to direct current (DC). It

  • consists of four diodes which allows two of the diodes to conduct on each

  • half-cycle of the AC supply


Transformer rectifier circuit
Transformer-Rectifier Circuit A slag is formed which protects the weld area from oxidation and minimises cracking of the weld as it allows the joint cool slowly.


Single phase bridge converter
Single Phase Bridge Converter A slag is formed which protects the weld area from oxidation and minimises cracking of the weld as it allows the joint cool slowly.

  • During one half –cycle of the AC supply, diodes D1 and D3 are conducting.

  • During the next half cycle, diodes D2 and D4 are conducting.

  • The Diodes are arranged to allow current to flow across the arc in the same direction regardless of the polarity of the AC supply


Capacitor
Capacitor A slag is formed which protects the weld area from oxidation and minimises cracking of the weld as it allows the joint cool slowly.

  • The capacitor is employed to provide a smooth supply of low voltage DC.


Tungsten inert gas welding tig
Tungsten Inert Gas Welding (TIG) A slag is formed which protects the weld area from oxidation and minimises cracking of the weld as it allows the joint cool slowly.

  • Definition:

    • TIG welding is an arc that is formed between a non-consumable tungsten electrode and the metal being welded.

    • Gas is fed through the torch to shield the electrode and molten weld pool.

  • Benefits:

    • Welds with or without filler metal

    • Precise control of welding variables (heat)

    • Low distortion

  • Shielding Gases:

    • Argon


Tungsten inert gas welding tig cont
Tungsten Inert Gas Welding (TIG) Cont. A slag is formed which protects the weld area from oxidation and minimises cracking of the weld as it allows the joint cool slowly.

  • Applications

    • Most commonly used for aluminum and stainless steel

    • For steel

      • Slower and more costly than consumable welding

      • Except for thin sections or where very high quality is needed


Why use tungsten inert gas when welding aluminium
Why use Tungsten Inert Gas When Welding Aluminium? A slag is formed which protects the weld area from oxidation and minimises cracking of the weld as it allows the joint cool slowly.

  • Aluminium oxidises very quickly when heated. This tenacious oxide layer is overcome with the use of an inert gas, such as argon, and the cathodic action of the arc on the work-piece. Aluminium can be welded successfully in this way by TIG welding.


Gas metal arc welding mig
Gas Metal Arc Welding (MIG) A slag is formed which protects the weld area from oxidation and minimises cracking of the weld as it allows the joint cool slowly.

  • Definition:

    • The heat source is formed by creating an electric arc between the work piece and a wire, which is fed continuously into the weld pool.


Gas metal arc welding mig cont
Gas Metal Arc Welding (MIG) Cont. A slag is formed which protects the weld area from oxidation and minimises cracking of the weld as it allows the joint cool slowly.

  • Benefits:

    • Long welds can be made without starts and stops

    • Minimal skill required

    • Minimal cleaning of surface before weld

    • Allows welding in all positions


Gas metal arc welding mig1
Gas Metal Arc Welding (MIG) A slag is formed which protects the weld area from oxidation and minimises cracking of the weld as it allows the joint cool slowly.

  • Shielding Gases:

    • Inert

      • Argon, Helium

        • Used for aluminum alloys and stainless steels.

    • Active

      • 1 to 5% Oxygen, 3 to 25% CO2

        • Used for low and medium carbon steels

  • Applications

    • Gas Metal Arc Welding (MIG) is used to weld all commercially important metals, including steel, aluminum, copper, and stainless steel.


  • Mig versus tig welding
    MIG versus TIG WELDING A slag is formed which protects the weld area from oxidation and minimises cracking of the weld as it allows the joint cool slowly.

    • MIG (MAGS) welding is a very versatile process and can be used to weld

    • light sheet metal as well as heavy plate. It can also be automated for welding by robots on car and other assembly line products.


    Mig versus tig welding cont
    MIG versus TIG WELDING CONT. A slag is formed which protects the weld area from oxidation and minimises cracking of the weld as it allows the joint cool slowly.

    • TIG (TAGS) welding is a more specialised welding process, that features a

    • non-consumable electrode and demands the feeding of a filler metal, it has

    • made the welding of aluminium and stainless steel feasible.


    Why tig weld aluminium
    Why TIG Weld Aluminium? A slag is formed which protects the weld area from oxidation and minimises cracking of the weld as it allows the joint cool slowly.

    • Aluminium oxidises very quickly when heated.

    • This tenacious oxide layer is overcome with the use of an inert gas, such as argon, and the cathodic action of the arc on the work-piece. Aluminium can be welded successfully in this way by TIG welding.


    Submerged arc welding
    Submerged Arc Welding. A slag is formed which protects the weld area from oxidation and minimises cracking of the weld as it allows the joint cool slowly.

    • Bare wire electrode is used.

    • Flux is in a powder form which is poured over and completely covered the weld pool.

    • Used in long, uninterrupted weld runs.

    • E.G. large steel reinforcing beams. (I beams)


    Submerged arc welding1
    Submerged Arc Welding A slag is formed which protects the weld area from oxidation and minimises cracking of the weld as it allows the joint cool slowly.


    Section of weld run
    Section of Weld Run A slag is formed which protects the weld area from oxidation and minimises cracking of the weld as it allows the joint cool slowly.


    Submerged arc welding2
    Submerged Arc Welding A slag is formed which protects the weld area from oxidation and minimises cracking of the weld as it allows the joint cool slowly.

    • In submerged arc welding, a bare wire electrode is used.

    • It is fed automatically from a spool and generates an electric arc to heat the metal.

    • The flux, in powder form, is fed from a hopper to completely cover the joint and the tip of the electrode.

    • The arc creates the heat to melt the joint, flux and electrode. A slag is formed to provide a protective coating for the weld. process.


    Submerged arc welding3
    Submerged Arc Welding A slag is formed which protects the weld area from oxidation and minimises cracking of the weld as it allows the joint cool slowly.

    • A slag is formed to provide a protective coating for the weld.

    • The excess flux powder can be collected and used again.

    • Submerged arc welding is a fully automated process.


    Submerged arc welding applications
    Submerged arc Welding Applications A slag is formed which protects the weld area from oxidation and minimises cracking of the weld as it allows the joint cool slowly.

    • used for large scale straight line welds such as steel reinforcing beams, shipbuilding and bridge construction


    Resistance welding spot welding
    RESISTANCE WELDING SPOT WELDING A slag is formed which protects the weld area from oxidation and minimises cracking of the weld as it allows the joint cool slowly.

    • PRESSURE, HEAT AND ELECTRICAL CURRENT

    • Components to be joined placed between 2 copper electrodes and the resistance of this current causes local rapid heating at interface, resulting in a nugget type spot weld


    APPLICATIONS A slag is formed which protects the weld area from oxidation and minimises cracking of the weld as it allows the joint cool slowly.Use to weld overlapped sheet metal, commonly used in the motor industry or where small scale spot welds are needed ie orthodontics- re-sizing molar brands

    ADVANTAGES

    Energy efficient, limited work deformation, high production, easy automation, no filler metal requirements.


    Resistance welding seam welding
    RESISTANCE WELDING SEAM WELDING A slag is formed which protects the weld area from oxidation and minimises cracking of the weld as it allows the joint cool slowly.

    • Copper disc electrodes are used to provide a continuous run of overlapped spot welds as the current is activated at set intervals. E.G. Sewing machine

    • A time interval controlled so that these spots


    Functions of electrode coating
    FUNCTIONS OF ELECTRODE COATING A slag is formed which protects the weld area from oxidation and minimises cracking of the weld as it allows the joint cool slowly.

    • To generate a shield of carbon dioxide gas to protect weld joints from contamination by oxygen and nitrogen in the air

    • Forms a slag coating which shields the weld from oxidation and slows the cooling rate therefore preventing cracks and brittleness

    • Facilitates the striking of the arc between the work and the electrode


    Functions of slag
    FUNCTIONS OF SLAG A slag is formed which protects the weld area from oxidation and minimises cracking of the weld as it allows the joint cool slowly.

    • To form a coating which protects the weld from oxidation

    • It ensures a slow cooling rate for the weld

    • It prevents cracking and brittleness

    • It minimises impurities in the weld.


    Preventing atmospheric contamination of weld area
    Preventing atmospheric contamination of weld area: A slag is formed which protects the weld area from oxidation and minimises cracking of the weld as it allows the joint cool slowly.

    In manual metal arc welding (MMA), the flux electrode coating melts and gives off a gas to protect the weld from the surrounding air, protective slag coating forms on top of the weld.In oxy-acetylene welding the flame protects the weld area.

    MIG and TIG welding use a gaseous shield to protect the weld area.SAW covers the weld area with a powdered flux.


    Multi run welds
    Multi – Run Welds A slag is formed which protects the weld area from oxidation and minimises cracking of the weld as it allows the joint cool slowly.

    • A series of welds are run across the metals to be joined in multi-run welding. A superior weld is produced as each weld has a post heating effect on the previous run. The finished weld is stronger and more refined in structure than single run welds.


    Installing a safe school welding room
    Installing a safe school Welding Room A slag is formed which protects the weld area from oxidation and minimises cracking of the weld as it allows the joint cool slowly.

    • A ventilation system must be incorporated to efficiently remove the gases produced by welding.

      • The welding station should be shielded to protect others in the workshop from the intense light produced by welding.

    • Personal safety equipment (masks, apron, gloves, etc.) must be available.

      • The hazards of the area must be highlighted by signs.


    Hazards and remedies when welding
    HAZARDS AND REMEDIES WHEN WELDING A slag is formed which protects the weld area from oxidation and minimises cracking of the weld as it allows the joint cool slowly.

    • HAZARD = ELECTRIC SHOCK

    • REMEDY – Ensure conditions are DRY,

      and use well maintained machinery, where cables are properly secured, insulated and earthed.


    • HAZARD = UV LIGHT RADIATION A slag is formed which protects the weld area from oxidation and minimises cracking of the weld as it allows the joint cool slowly.

    • REMEDIES – use correct facial equipment/visors with dark UV resistant face plates

      Use a welding curtain to protect fellow colleagues/classmates from exposure to UV light


    • HAZARD – INHALATION OF FUMES AND GASES A slag is formed which protects the weld area from oxidation and minimises cracking of the weld as it allows the joint cool slowly.

    • REMEDY – Proper ventilation system


    • HAZARD = EXPOSURE TO EXTREME HEAT AND TEMPS A slag is formed which protects the weld area from oxidation and minimises cracking of the weld as it allows the joint cool slowly.

    • REMEDY – Wear protective clothing, leather gloves, aprons, etc


    Brazing
    Brazing A slag is formed which protects the weld area from oxidation and minimises cracking of the weld as it allows the joint cool slowly.

    • Definition:

      • A process which a filler metal is placed at or between the faying surfaces, the temperature is raised high enough to melt the filler metal but not the base metal.

        • The molten metal fills the spaces by capillary attraction.

    • Torch Brazing

      • Oxy-fuel torch with a carburizing flame

      • First heat the joint then add the filler metal


    Brazing examples
    Brazing Examples A slag is formed which protects the weld area from oxidation and minimises cracking of the weld as it allows the joint cool slowly.


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