Welding Lectures

8/10/2019 Welding Lectures

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Classification of

Manufacturing Processes

MEEG 217Biraj Singh Thapa

27, Aug, 2007


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Basic Classification of MP

Primary Shaping Process

Machining processes

Surface finishing processes Joining processes

Processes affecting the change in

properties


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Welding Technology


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Introduction

Welding is a process of joining two similar or

dissimilar metals by fus ion,

with or with out the application of pressure,

and with or with out use of f i l ler metal.

The fusion of metal take place by heat. The heat may be obtained from:

electric arc,

electric resistance, chemical reaction,

friction

or radiant energy


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Classification of Welding


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Classification of Welding


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Gas Welding


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Introduction Also called as oxy-fuel gas welding

Derives the heat from the combustion of a fuel gasincombination with oxygen.

Fusion welding process is obtained by complete meltingof parent metals.

Filler rod may be used. Useful fuel gases are:

Fuel Gas Chem Form. Flame Tem (C)

Acetylene C2H2 3200

Propylene C3H6 2500

Propane C3H8 2450

Hydrogen H2 2390

Natural Gas CH4 + H2 2350


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Oxy-Acetylene Welding Acetylene mixed with oxygen in correct

proportion in welding torch and ignited gives theflame of high temperature.

C2H2 + O2 = 2CO + H2 + Heat

2CO + H2 + 1.502 = 2CO2 + H2O + Heat


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Types of Flame

Neutral Flame 5900F (3200C)

Mild Steel, Stainless Steel, Copper, Cast Iron

Oxidizing Flame

6300F

Copper based alloys for protective layer of slag

Reducing Flame

5500F

Lead and for Carburizing (Surface hardening)


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Types of Flame


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Gas Welding Tools


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Gas Welding Techniques

The flame is pointed in the

direction of welding.

This position permits uniform

preheating of the plate edges

immediately ahead of themolten puddle.

Recommended for welding

material up to 1/8 in. (3.2

mm) thick. A great deal of pipe welding

is done using this technique.


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Gas Welding Techniques The torch precedes the welding

rod, away from the direction ofwelding.

The flame is directed at themolten puddle.

The welding rod is between the

flame and the molten puddle. Right hand welding may be used

with a slightly reducing flame,increasing the carbon content,which lowers the melting point ofa thin layer of steel and increaseswelding speed.

This technique increases speed ofmaking pipe joints where the wallthickness is 1/4 to 5/16 in. (6.4 to7.9 mm).


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Welding Torch


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Welding Torch


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The End


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Brazing, Braze Welding &

Soldering


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B i


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Brazing Process of joining two pieces of metals in which a non-

ferrous alloy is introduced in liquid state between work-

piece. Heating source may be various types.

Melting point of filler metal is above 450C but less

than parent material.

Filler metal is distributed between the surfaces of thejoint by capillary action.

Fluxes (combination of borax, boric acid, chlorides,

fluorides and other wetting agents) are also added to

remove any of the oxide present. Can join cast metals to wrought metals, dissimilar

metals and also porous components.

Used for pipe fittings, heat exchangers, electrical parts


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Brazing

Common Filler metals:

Aluminum Silicon Copper phosphorus

Copper Zinc

Silver

Magnesium

Nickel etc.

Advantages:

Less distortion, Quick finish, wide range of applicationLimitations:

Tight mating parts, Proper cleaning, Limited size,Costly, Poor color matching.


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Braze or Bronze Welding

Similar to the Brazing but the joint is not

produced by the capillary or fusion, but byadhesion.

Filler rod usually contain 60% copper and 40%

zinc.

Flux is applied to prevent oxidization.

Cheaper than Brazing but low in strength.

Both Brazing and Braze welding needs the pre

heating of the parent materials.

Both wildings are not successful at the elevated

temperatures.


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Soldering Similar to the Brazing but the filler metal used has

melting point less than 450C. The filler material is called solder.

Composition of Some Solder are:

Soft solder: Lead 37% and Tin 63%

Medium solder: Lead 50% and Tin 50% Electrician solder: Lead 58% and Tin 42%

Plumbers Solder: Lead 70% and Tin 30%

Some Fluxes are: Inorganic (Corrosive): Zinc and Ammonium chloride

Organic (Mild): Latic Acid, Stearic Acid etc.

Rosins (Non Corrosive): Gum extruded from pine trees.


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END


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Arc Welding


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Introduction

Heat Source is Electric Arc (Plasma) Without application of Pressure

With or without filler rod

AC Or DC Current supply can be used


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Arc welding Equipment


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AC / DC Machines

Step down transformers are used for AC

Machines to change the supply to 80-100

volts, 50-100 Amps.

DC machines are used for heavy works

and for the sites where AC source is not

available.

Straight and reverse polarity in DCMachines (67% in +ve terminal)


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Arc Crater

Small depression ofelectric arc into parentmetal.

Can be adjusted by

operator. Arc should not be broken.

The distance through thecenter of the arc from the

tip of the electrode to thebottom of arc is called arclength. It should be 2-4mm


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Arc Blow

Wandering of arc due to electromagnetic

fields.

Present in DC Machines.

More at the ends of job.

Results porosity and other defects.

Ground connections should be placed as far

as possible.

Arc length and current should be reduced.


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Electrodes Cont

Bare Electrodes:

Additional flux is added if necessary

For carbon and Tungsten.

Striking of arc is difficult.

Coated Electrodes:Available in form of stick of length 350 or 450 mm.

Gas forming flux: Starch, wood pulp etc

Slag forming flux: Manganese, Titanium ores Reducing components, Alloys, Stabilizing and

binding components are also present.


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Flux Shielded Metal Arc Wielding

Flux coated consumable electrodes produces

the heat by electric arc (750 Am.)

Temperature isin range 2400C-2700C

AC or DC maybe used

Simple & cheap

Limited length ofelectrode

Chances ofmoisture andslag entrapment.


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Carbon Arc Welding Heat is obtained by electric struck in between a

non consumable carbon electrode and the workpiece. Graphite rod is also used.

Welding carried out in air or inert atmospherewith or with out filler rod.

DC is usually used (Polarity!).

Twin carbon electrode arc welding has better arccontrol. Arc is maintained between two carbonelectrodes held in special holder. (Movibility!)

Used for cast iron, steel, copper, bronze, rough

cutting material. Simple & better control. But high arc blow and

chances of carbon infiltration in base metal.

C b A W ldi C t


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Carbon Arc Welding Cont..

M l I G (MIG)


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Metal Inert Gas (MIG) Welding heat is produced from continuously fed

metal electrode and the job. Ar, He, Co2 or mixture gas shields the arc andmolten metal.

The current from the welding machine is

changed by changing the rate of feeding of theelectrode wire:

If arc length decreases, voltages decreases andcurrent increases. Increased current melts the

electrode at the faster rate normalizing arc length(Self adjusted arc).

Electrode feeding motor is controlled by the arcvoltage, change in arc length is thus adjusted bychange in feed rate (Self controlled arc).


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MIG Operation


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MIG Operation Contd


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MIG Operation Contd

Advantages Disadvantages &


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Advantages, Disadvantages &

applications of MIG

T t I t G (TIG)


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Tungsten Inert Gas (TIG)

Welding heat is produced from an electric arc

established between the non-consumabletungsten electrode and the job.

A shielding gas (argon, helium, nitrogen etc.) isused to avoid oxidation.

Argon requires a lower arc voltage, easier arcstarting.

Carbon dioxide is used for low temp, economical.

Helium can withstand higher arc voltage.

Filler material if required is fed separately. Arc is struck either by touching the electrode witha scrap tungsten or by using high frequency unit.

Both AC and DC power source can be used(Polarity)


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TIG C td


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TIG Contd

S b d W ldi (SAW)


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Submerged arc Welding (SAW)

Welding heat is produced from an electric arc

set up between bare metal electrode and job. Arc, end of electrode and molten metal remain

submerged under a granular material

Initially flux is insulator but once melted it acts

as good conductor to maintain the electricity. Continuously fed bare metal acts as filler rod.

For very faster rate welding (5m/min), with largeelectrodes (12mm), for plates with 75mm thickin butt at a single pass.

4000 A current can deposit metal up to 20kg/hr

Economical for larger works only.

SAW O ti


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SAW Operation

SAW Operation Contd


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SAW Operation Contd


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Electroslag Welding


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Electroslag Welding

Welding heat is produced by the molten slag,

which melts the filler metal and weldingsurface.

Arc initiated between electrode and the work

is extinguished after flux is melted and themolten conditions maintained by the its

resistance to current flow between electrode

and work.

Temperature of molten slag is 1650 -1950. Water-cooled shoe or dam plate fastened to

the sides of the workpeice prevents the

molten metal from running off.

El t l W ldi O ti


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Electroslag Welding Operation

El t l W ldi O ti


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Electroslag Welding Operation

Advantages Disadvantages &


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Advantages, Disadvantages &

applications of Electroslag Welding

El t W ldi


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Electrogas Welding

Similar processelectroslag welding, butan inert gas is used forshielding.

Flux cores wire isautomatically fed to themolten weld pocket andan electric arc is

continuously maintained. Welding Shoes are usedto confine the weld metalfor the vertical positions.

Electrogas Welding Operation


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Electrogas Welding Operation

Plasma Arc Welding


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Plasma Arc Welding

Plasma is formed when inert gase get ionized

after passing through arc and nozzle. Welding heat is obtained from a constricted arc

set up between a tungsten electrode and water

cooled nozzle (non-transferred arc) or between

the electrode and job (transferred arc). The process employs two inert gases, one forms

the arc plasma and the second shields the arc

plasma.

Filler metal may or may not be used.

Temeperature of the order 11000 C can be

obtained.

Plasma Arc Welding


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Plasma Arc Welding

Operation


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Plasma Arc Welding Operation


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Plasma Arc Welding Operation

Pl A W ldi T


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Plasma Arc Welding Types

Plasma Arc Welding


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Plasma Arc Welding

Comparison Between PAW &


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Comparison Between PAW &

TIG


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Resistance Welding

MEEG 217

Biraj Singh Thapa

07, Sept, 2007

Introduction


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Introduction Welding heat is obtained from resistance of the

work to the flow of electric current and by theapplication of pressure.

No filler metal or flux is added.

Heat balance is essential: Sizing electrodeproportional to thickness and thermal

conductivity.

Types:1. Spot welding 4. Resistance butt welding

2. Seam welding 5. Flash butt welding

3. Projection welding 6. Percussion welding

Spot Welding


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Spot Welding Overlapping sheets

are joined by localfusion at one or morespots by the heat andpressure is applied bythe electrodes one

above and anotherbelow the workspace.

Low cost, no edgepreparation, semi-automatic.

Used for automobiles,house hold furniture's,containers etc.

Spot Welding Operation


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Spot Welding Operation


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Seam Welding


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Seam Welding

Projection Welding


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Projection Welding

Advancement ofspot welding.

One of the electrodeis provided withnumber ofprojections to helpto localize thecurrent at apredetermined spot.

Projections of the order of 0.8 mm can beobtained.

All the projections should be of same height

Resistance Butt Welding


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(UPSET)

Job pieces to bejoined are held

tightly together and

current is applied

heating the entiresurface area.

Pressure is

increased when the

welding temperature

is reached.

For butt joints of

pipes, tubes etc.


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Fl h B tt W ldi


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Flash Butt Welding

Similar to upset,except the heat

required for melting

is obtained by

means of an arcrather than simple

resistance heating.

Cheap, faster andconsumes less

current


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Flash ButtWelding


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Other Welding

MEEG 217

Biraj Singh Thapa

7, Sept, 2007

Solid State Welding


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Solid State Welding

Unlike the fusion welding, no molten phase is

present in the joint. Two clean surfaces are brought into atomic

contactwith each other under sufficient pressureto form the bond and strong joint.

Strength depends upon pressure, temp and timeof contact.

Forge Welding: The ends of the parts to be joined are heated to a

temperature slightly below the solidus temp andpressure is applied to obtain the fusion.

Popular with black smiths works

For low carbon steels; flux is needed to preventoxides

Solid State Welding


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Solid State Welding

Friction Welding: Welding heat is obtained

by the friction between

the ends of the two parts

to be joined. Center Lathe like

machine is used.

Used for joining different

metals, Aerospaceengineering, Tools

manufacture

Solid State Welding


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Solid State Welding

Diffusion Welding:

Strength of joint results primarily from diffusion andsecondarily from plastic deformation.

Required temp is 0.5 MP, Usually Vacuum is preferred

Bonded interface has same mechanical and physical

properties. Diffusion Welding is able to bond dissimilar metals,

which are difficult to weld by other welding processes:

Steel to tungsten; Steel to niobium;

Stainless steel to titanium;

Gold to copper alloys.


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Thermo Chemical Welding


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Thermo Chemical Welding

Fusion takes by heat from exothermic reaction.Atomic Hydrogen welding:

Welding heat is obtained from electric arcmaintained between two tungsten electrodes in

an atmosphere of hydrogen, which also acts asshielding gas.

Electric current breaks down molecular hydrogeninto atomic hydrogen, which reforms molecule as

touches relatively cold surface producing largeheat.

Filler metal may or may not be used.

Atomic Hydrogen welding


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Atomic Hydrogen welding

Operation

Radiant Energy Welding


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Radiant Energy Welding The heat for fusion is obtained from the kinetic

energy of a dense beam.

Electron Beam Welding:

Heat of fusion is obtained from high velocity narrowbeam electrons.

The kinetic energy of the electrons is converted intoheat as they strike the work piece.

Depth to width ratio is between 10:1 to 30:1

No filler metal or flux is needed.

Can be done in Hard / Partial vacuum or inatmosphere.

Used for reactive metals as titanium, tungsten etc.

Chances of x-ray exposure.

Electron Beam Welding Operation


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Electron Beam Welding Operation

Radiant Energy Welding


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gy g

Laser beam Welding:

Utilizes a high power laser beam as the source ofheat.

Very high energy density and deep penetrating

capability.

Welding can be done inside plastic or glass casing.

Laser as light can be conversed, focused and

reflected.

Slow process and dangerous for health. Used for cutting and joining: wires, sheets etc

Used for welding: Copper, nickel, titanium, tungsten

Laser beam Welding


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Laser beam Welding

Assignment 1


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Assignment 1

Prepare a table (in a chart paper) to show: Classification,

Working principle,

Working temperature and materials,

Advantages and disadvantages,

Operation figures of all the welding systems

studied.

Identify welding defects, their causes and remedies.

Dead line: Friday, 21, September, 2006


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End of chapter 2 (Welding) (7hrs.)Next chapter Foundry (8 hrs.)

Welding Lectures

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