PRESENTATION ONPRESENTATION ONWELDINGWELDING

BY

RISHIKESH KR. KAUSHIK

SEM.-VI

32nd BATCH

A Brief History of WeldingA Brief History of Welding

• Late 19th Century• Scientists/engineers apply advances in electricity to

heat and/or join metals (Le Chatelier, Joule, etc.)• Early 20th Century

• Prior to WWI welding was not trusted as a method to join two metals due to crack issues

• 1930’s and 40’s• Industrial welding gains acceptance and is used

extensively in the war effort to build tanks, aircraft, ships, etc.

• Modern Welding• the nuclear/space age helps bring welding from an art to

a science

INTRODUCTIONINTRODUCTION

• A welding is a permanent joint which is obtained by the fusion of the edges of the two parts to be joined together, with or without application of pressure and a filler material.

• The heat required for the fusion of material may be obtained by burning of gas or by an electrical arc.

Weldability of a MetalWeldability of a Metal

• Metallurgical Capacity• Parent metal will join with the weld metal without

formation of deleterious constituents or alloys

• Mechanical Soundness• Joint will be free from discontinuities, gas

porosity, shrinkage, slag, or cracks

• Serviceability• Weld is able to perform under varying conditions

or service (e.g., extreme temperatures, corrosive environments, fatigue, high pressures, etc.)

Welding ProcessesWelding Processes

BROAD CLASSIFICATIONBROAD CLASSIFICATION

• Welding processes that use heat alone e.g., fusion welding

• Welding processes that use combinat-ion of heat and pressure

e.g., forge welding

Types of WeldingTypes of Welding

Fusion Welding Pressure Welding

Homogeneous Heterogeneous

Brazing Soldering

Thermit Welding

Gas welding

High Energy Beam

Electric Arc

MIG

TIG

Shielded Metal Arc – “Stick”

Forge welding

Fusion Welding PrinciplesFusion Welding Principles

• Base metal is melted

• Filler metal may be added

• Heat is supplied by various means• Oxyacetylene gas• Electric Arc• Plasma Arc• Laser

Fusion WeldingFusion Welding

BASE METAL

WELD

SOLIDIFIED SLAG

ARC POOL

WELDING ATMOSPHERE

CORE WIRE

ELECTRODE COATING

ARC STREAM

PENETRATION DEPTH

Types of Fusion WeldingTypes of Fusion Welding

HOMOGENEOUS

• Thermit welding

• Gas welding

• Electrical arc welding

(i) Oxyacetylene Cutting/Welding

(ii)Shielded Metal Arc (“Stick”)

(iii)Metal Inert Gas (MIG)

(iv)Tungsten Inert Gas (TIG)

THERMIT WELDINGTHERMIT WELDING

• Mixture of iron oxide and aluminium called thermit is used.

• Weld section are molten at same time and weld cools uniformly, so minimum problem with residual stresses.

• Used in joining iron and steel parts that are too large to be manufactured in one piece.

e.g., rails,stern and rudder frames.

GAS WELDINGGAS WELDING

• Made by applying flame of gases like oxy-acetylene or hydrogen from a welding torch.

• A flux is being used to remove slag.

• Heating is slow so used on thinner materials.

ELECTRICAL ARC ELECTRICAL ARC WELDINGWELDING

• Work is prepared in same manner as in case of gas welding.

• Filler metal is supplied by metal welding electrode.

• An arc is strike by touching work of base metal with the electrode.

• Slag is brushed off after joint is cooled.

• Extensively used due to greater speed of welding.

• Protection of eye and face is reqd.

Oxyacetylene WeldingOxyacetylene Welding

• Flame formed by burning a mix of acetylene (C2H2) and oxygen

• Fusion of metal is achieved by passing the inner cone of the flame over the metal

• Oxyacetylene can also be used for cutting metals

Inner Cone: 5000-6300 deg F Combustion Envelope 3800 deg F

2300 deg FTORCH TIP

Shielded Metal Arc (Stick)Shielded Metal Arc (Stick)

• An electric arc is generated between a coated electrode and the parent metal

• The coated electrode carries the electric current to form the arc, produces a gas to control the atmosphere and provides filler metal for the weld bead

• Electric current may be AC or DC. • Used for welding of lighter steel structures

and Al-alloys.

Shielded Metal Arc (contd.)Shielded Metal Arc (contd.)

• Process:

• Intense heat at the arc melts the tip of the electrode

• Tiny drops of metal enter the arc stream and are deposited on the parent metal

• As molten metal is deposited, a slag forms over the bead which serves as an insulation against air contaminants during cooling

• After a weld ‘pass’ is allowed to cool, the oxide layer is removed by a chipping hammer and then cleaned with a wire brush before the next pass.

Inert Gas WeldingInert Gas Welding

For materials such as Al or Ti which quickly form oxide layers, a method to place an inert atmosphere around the weld puddle had to be developed

• Uses a consumable electrode (filler wire made of the base metal)

• Inert gas is typically Argon

• As argon is very costly, CO2 is used for shielding gas specially for mild steel

• Used in AL-deckhouses, liq. Methane gas tanks.

Metal Inert Gas (MIG)Metal Inert Gas (MIG)

BASE METAL PUDDLE

POWER SOURCE

DRIVE WHEELSCONSUMABLE ELECTRODE

ARC COLUMNSHIELDING GAS

• Tungsten electrode acts as a cathode which is non consumable• A plasma is produced between the tungsten cathode and the

base metal which heats the base metal to its melting point• Filler metal can be added to the weld pool

• Plate(generally of Al) of thickness less than 6mm is welded by this process

Tungsten Inert Gas (TIG)Tungsten Inert Gas (TIG)

BASE METAL PUDDLE

POWER SOURCE

ARC COLUMNSHIELDING GAS

TUNGSTEN ELECTRODE

+ +

BASE METAL (ANODE)

TUNGSTEN ELECTRODE

(CATHODE)

- - -

+ +

Types of Fusion WeldingTypes of Fusion Welding

HETEROGENEOUS

• Soldering

• Brazing

SOLDERINGSOLDERING

• Produces coalescence of materials by heating them to a suitable temperature.

• Uses a filler metal having a liquidus not exceeding 450oC (840oF) and below the solidus of the base materials.

• The filler metal is distributed between the closely fitted surfaces of the joint by capillary action.

BRAZINGBRAZING

• Same as soldering only difference is that it uses a filler metal, having a liquidus above 450oC and below the solidus of the base materials.

• A braze is a very special form of weld, the base metal is theoretically not melted.

• Relates to welding processes using brass or bronze filler metal, where the filler metal is not distributed by capillary action.

Weld Metal ProtectionWeld Metal Protection

• During fusion welding, the molten metal in the weld “puddle” is susceptible to oxidation

• Must protect weld puddle (arc pool) from the atmosphere

• Methods• Weld Fluxes• Inert Gases• Vacuum

Weld FluxesWeld Fluxes

• Typical fluxes• SiO2, TiO2, FeO, Go, Al2O3

• Produces a gaseous shield to prevent contamination

• Act as scavengers to reduce oxides• Add alloying elements to the weld• Influence shape of weld bead during solidification

Inert GasesInert Gases

• Argon, helium, nitrogen, and carbon dioxide

• Form a protective envelope around the weld area

• Used in• MIG• TIG• Shield Metal Arc

Vacuum Vacuum

• Produce high-quality welds

• Used in electron beam welding

• Nuclear/special metal applications

• Reduces impurities by a factor of 20 versus other methods

• Expensive and time-consuming

Welding PositionsWelding Positions

FLATFLAT

HORIZONTALHORIZONTAL

VERTICALVERTICAL

OVERHEADOVERHEAD

INCREASING DIFFICULTY

Weld DefectsWeld Defects

• Undercuts/Overlaps

• Grain Growth• A wide T will exist between base metal and HAZ. Preheating

and cooling methods will affect the brittleness of the metal in this region

• Blowholes• Are cavities caused by gas entrapment during the

solidification of the weld puddle. Prevented by proper weld technique (even temperature and speed)

• HAZ is transition between liquid recrystalisation and base (usually cold-worked) metal most shrinkage occurs here, so most brittle →This is where welds usually fail.

Weld Defects(contd.)Weld Defects(contd.)

• Inclusions• Impurities or foreign substances which are forced into the weld

puddle during the welding process. Has the same effect as a crack.

Prevented by proper technique/cleanliness.

• Segregation• Condition where some regions of the metal are enriched with an

alloy ingredient and others aren’t. Can be prevented by proper heat treatment and cooling.

• Porosity• The formation of tiny pinholes generated by atmospheric

contamination. Prevented by keeping a protective shield over the molten weld puddle.

Residual StressesResidual Stresses

• Rapid heating and cooling results in thermal stresses detrimental to joint strength.

• Prevention• Edge Preparation/Alignment – beveled edges and space between

components to allow movement• Control of heat input – skip or intermittent weld technique• Preheating – reduces expansion/contraction forces (alloys) and

removes moisture from the surface• Peening – help metal stretch as it cools by hitting with a hammer.

Use with care since it may work harden the metal• Heat Treatment – “soak” the metal at a high temperature to relieve

stresses• Jigs and Fixtures – prevent distortion by holding metal fixed• Number of Passes – the fewer the better.

Joint DesignJoint Design

BUTT JOINTBUTT JOINT

STRAP JOINT

LAP JOINT

FILLET JOINT

CORNER JOINT

Generalized Welding SymbolGeneralized Welding Symbol

FAR SIDE DETAILS

ARROW SIDE DETAILS

Field weld symbol

Weld all-around for pipes, etc.

L1-L2

L1-L2

D = Weld Depth (usually equal to plate thickness)

L1 = Weld Length

L2 = Distance between centers for stitched welds

The Field Weld Symbol is a guide for installation. Shipyardsnormally do not use it, except in modular construction.

ElectrodeMaterial

D

D

Weld Geometry

Example of Welding SymbolExample of Welding Symbol

1/2” 1/2”

1/2

1/2

One-sided welds are max 80% efficientTwo sided are 100% efficient

Geometry symbol for V-groove

Weld Symbols (Butt Joints)Weld Symbols (Butt Joints)

Backing

Weld Symbol (Fillet Joints)Weld Symbol (Fillet Joints)

Weld Symbol (Corner Joints)Weld Symbol (Corner Joints)

WELD TESTINGWELD TESTING• For economic reasons much of the weld

testing in shipbuilding is carried out visually by trained inspectors.

• For important welds radiographic equipment is used for spot check in merchant ships.

• Welding material undergoes coprehe- nsive tests by classification society before approval.

• But for accuracy in the test NDT is used.

ADVANTAGES OF ADVANTAGES OF WELDINGWELDING

FOR SHIPBUILDERWelding lends itself to the prefabrication

techniques.Easier to obtain water tightness and oil

tightness. Joints produced more quickly.Less skilled labor is required.

ADVANTAGES OF ADVANTAGES OF WELDING(contd.)WELDING(contd.)

FOR SHIPOWNERReduced hull steel weight ;so more

deadweight.Less maintenance.Smoother hull reduced skin friction

resistance which reduces fuel costs.

THANK YOU!!!!!

QUESTIONS???