Fundamentals of Welding Tech.ppt

7/29/2019 Fundamentals of Welding Tech.ppt

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WELDING

Definition :

A localizedJoining of materialwith or without the use offiller and also with or without the application of pressure.

or

Bringing twoperfectly smooth & clean material surfacesto

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

1G

2G3G

4G


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G - Positions on Pipe

1G

2G

5G

6G


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F- Positions on Plate

1F2F

3F

4F


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F - Positions on Pipe

1F2F

2FR

4F

5F


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Welding Processes

Following are the common Welding Processes Used in the Industries

1. Oxy- Gas Welding

2. Manual Metal Arc ( M.M.A ) Welding

3. Metal Inert Gas ( MIG), Metal Active Gas ( MAG ) Welding

4. Tungsten Inert Gas ( TIG) Welding

5. Plasma Arc Welding( PAW )

6. Submerged Arc Welding ( SAW )

7. Electroslag Welding


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OXY-GASWELDING


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OXY-GASWELDING

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-GASWELDING


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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

aluminum

The 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 high

Excessive penetration,

burn through,

porosity,

spatter,deep craters,

undercut,

electrode overheats,

high deposition (positional welding difficult).

Effect of Amperage too low

Poor 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 low

Poor penetration,

Electrode freezes to work

Possible stray arcsFusion defects

Slag inclusions

Unstable arc

Irregular bead shape.

Effect of Voltage too high

Porosity

Spatter

Irregular bead

Slag inclusion

Very fluid weld pool

positional welding difficult.


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Travel speed too slow

Excessive deposition

Cold lapsSlag inclusions

Irregular bead shape.

Travel speed too FastNarrow thin bead

Slag inclusion

Fast cooling

Undercut

Poor 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 material

It will result in:wide and shallow weld pool

Broad HAZ

Slow Rate of Cooling

Hydrogen IntrapmentAn 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 h.a.z.

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 MMA

Rutile: Titanium Dioxide, Clay , Sodium silicate

Cellulosic: Cellulose( wood pulp), Titanium Dioxide, Sodium silicate

Basic: Lime stone ( Calcium carbonate ), Titanium Dioxide, Sodium

silicate


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The m.I.g./m.a.g. 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 (m.i.g.) 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 transfer

The 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 flat

Characteristic.

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.

Fundamentals of Welding Tech.ppt

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