Classification of

Manufacturing Processes

MEEG 217

Biraj Singh Thapa

27, Aug, 2007

Basic Classification of MP

• Primary Shaping Process

• Machining processes

• Surface finishing processes

• Joining processes

• Processes affecting the change in

properties

Welding Technology

MEEG 217

Biraj Singh Thapa

27, Aug, 2007

Introduction

• Welding is a process of joining two similar or

dissimilar metals by fusion,

– with or with out the application of pressure,

– and with or with out use of filler 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

Classification of Welding

Classification of Welding…

Gas Welding

MEEG 217

Biraj Singh Thapa

30, Aug, 2007

Introduction• Also called as oxy-fuel gas welding

• Derives the heat from the combustion of a fuel gas in combination with oxygen.

• Fusion welding process is obtained by complete melting of 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

Oxy-Acetylene Welding• Acetylene mixed with oxygen in correct

proportion in welding torch and ignited gives the

flame of high temperature.

C2H2 + O2 = 2CO + H2 + Heat

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

Types of Flame

• Neutral Flame

– 5900°F (3200°C)

– Mild Steel, Stainless Steel, Copper, Cast Iron

• Oxidizing Flame

– 6300°F

– Copper based alloys for protective layer of slag

• Reducing Flame

– 5500°F

– Lead and for Carburizing (Surface hardening)

Types of Flame

Types of Flame

Gas Welding Tools

Gas Welding Techniques

• The flame is pointed in the

direction of welding.

• This position permits uniform

preheating of the plate edges

immediately ahead of the

molten 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.

Gas Welding Techniques• The torch precedes the welding

rod, away from the direction of welding.

• The flame is directed at the molten 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 of a thin layer of steel and increases welding speed.

• This technique increases speed of making pipe joints where the wall thickness is 1/4 to 5/16 in. (6.4 to 7.9 mm).

Welding Torch

Welding Torch

The End…

Brazing, Braze Welding &

Soldering

MEEG 217

Biraj Singh Thapa

31, Aug, 2007

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 450°C but less

than parent material.

• Filler metal is distributed between the surfaces of the

joint 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

Brazing

Common Filler metals:

• Aluminum Silicon

• Copper phosphorus

• Copper Zinc

• Silver

• Magnesium

• Nickel etc.

Advantages:

• Less distortion, Quick finish, wide range of application

Limitations:

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

Braze or Bronze Welding

• Similar to the Brazing but the joint is not

produced by the capillary or fusion, but by

adhesion.

• 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.

Soldering• Similar to the Brazing but the filler metal used has

melting point less than 450°C.

• 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%

• Plumber’s 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.

END…

Arc Welding

MEEG 217

Biraj Singh Thapa

31, Aug, 2007

Introduction

• Heat Source is Electric Arc (Plasma)

• Without application of Pressure

• With or without filler rod

• AC Or DC Current supply can be used

Arc welding Equipment

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 DC

Machines (67% in +ve terminal)

Arc Crater

• Small depression of electric arc into parent metal.

• Can be adjusted by operator.

• Arc should not be broken.

• The distance through the center of the arc from the tip of the electrode to the bottom of arc is called arc length. It should be 2-4 mm

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.

Electrodes

• Consumable

– Electrode melts along with parent metal and get mixed to form a joint.

– Sevres as heat source and filler rod.

– Electrode material is close to that of parent material

• Non Consumable

– Separate filler rod required if necessary

– Better control of heat input and filler material

– Carbon Graphite for DC

– Tungsten for both AC and DC

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.

Flux Shielded Metal Arc Wielding

• Flux coated consumable electrodes produces the heat by electric arc (750 Am.)

• Temperature is in range 2400°C-2700°C

• AC or DC may be used

• Simple & cheap

• Limited length of electrode

• Chances of moisture and slag entrapment.

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

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

• Welding carried out in air or inert atmosphere with or with out filler rod.

• DC is usually used (Polarity!).

• Twin carbon electrode arc welding has better arc control. Arc is maintained between two carbon electrodes 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.

Carbon Arc Welding Cont..

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 and molten metal.

• The current from the welding machine is changed by changing the rate of feeding of the electrode wire:

– If arc length decreases, voltages decreases and current increases. Increased current melts the electrode at the faster rate normalizing arc length (Self adjusted arc).

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

MIG Operation

MIG Operation Contd…

MIG Operation Contd…

Advantages, Disadvantages &

applications of MIG

Tungsten Inert Gas (TIG)

• Welding heat is produced from an electric arc established between the non-consumable tungsten electrode and the job.

• A shielding gas (argon, helium, nitrogen etc.) is used to avoid oxidation.

• Argon requires a lower arc voltage, easier arc starting.

• 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 with a scrap tungsten or by using high frequency unit.

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

TIG Operation

TIG Contd…

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 large electrodes (12mm), for plates with 75mm thick in butt at a single pass.

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

• Economical for larger works only.

SAW Operation

SAW Operation Contd…

Electroslag Welding

• Welding heat is produced by the molten slag,

which melts the filler metal and welding

surface.

• Arc initiated between electrode and the work

is extinguished after flux is melted and the

molten conditions maintained by the its

resistance to current flow between electrode

and work.

• Temperature of molten slag is 1650 º-1950º.

• Water-cooled shoe or dam plate fastened to

the sides of the workpeice prevents the

molten metal from running off.

Electroslag Welding Operation

Electroslag Welding Operation

Advantages, Disadvantages &

applications of Electroslag Welding

Electrogas Welding

• Similar process electroslag welding, but an inert gas is used for shielding.

• Flux cores wire is automatically fed to the molten weld pocket and an electric arc is continuously maintained.

• Welding Shoes are used to confine the weld metal for the vertical positions.

Electrogas Welding Operation

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 ºC can be

obtained.

Plasma Arc Welding

Operation

Plasma Arc Welding Operation

Plasma Arc Welding Operation

Plasma Arc Welding Types

Plasma Arc Welding…

Comparison Between PAW &

TIG

END OF

ARC WELDING

Resistance Welding

MEEG 217

Biraj Singh Thapa

07, Sept, 2007

Introduction• Welding heat is obtained from resistance of the

work to the flow of electric current and by the

application of pressure.

• No filler metal or flux is added.

• Heat balance is essential: Sizing electrode

proportional 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• Overlapping sheets

are joined by local fusion at one or more spots by the heat and pressure is applied by the electrodes one above and another below the workspace.

• Low cost, no edge preparation, semi-automatic.

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

Spot Welding Operation

Spot

Welding

Operation

Seam Welding

• Overlapping sheets are joined by local fusion progressively along a joint by rotating the circular electrodes.

Seam Welding

Projection Welding

• Advancement of spot welding.

• One of the electrode is provided with number of projections to help to localize the current at a predetermined spot.

• Projections of the order of 0.8 mm can be obtained.

• All the projections should be of same height

Resistance Butt Welding

(UPSET)

• Job pieces to be

joined are held

tightly together and

current is applied

heating the entire

surface area.

• Pressure is

increased when the

welding temperature

is reached.

• For butt joints of

pipes, tubes etc.

Resistance

Butt

Welding

Flash Butt Welding

• Similar to upset,

except the heat

required for melting

is obtained by

means of an arc

rather than simple

resistance heating.

• Cheap, faster and

consumes less

current

Flash Butt

Welding

Percussion Welding

• Welding heat is obtained by arc produced by rapid discharge of stored electrical energy, using capacitors.

• Higher temp, Costly devices

END

Other Welding…

MEEG 217

Biraj Singh Thapa

7, Sept, 2007

Solid State Welding

• Unlike the fusion welding, no molten phase is present in the joint.

• Two clean surfaces are brought into atomic contact with each other under sufficient pressure to form the bond and strong joint.

• Strength depends upon pressure, temp and time of contact.

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

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

– Popular with black smiths works

– For low carbon steels; flux is needed to prevent oxides

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, Aerospace

engineering, Tools

manufacture

Solid State WeldingDiffusion Welding:

• Strength of joint results primarily from diffusion and secondarily 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.

Diffusion Welding

Thermo Chemical Welding

• Fusion takes by heat from exothermic reaction.

Atomic Hydrogen welding:

• Welding heat is obtained from electric arc maintained between two tungsten electrodes in an atmosphere of hydrogen, which also acts as shielding gas.

• Electric current breaks down molecular hydrogen into atomic hydrogen, which reforms molecule as touches relatively cold surface producing large heat.

• Filler metal may or may not be used.

Atomic Hydrogen welding

Operation

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 narrow beam electrons.

• The kinetic energy of the electrons is converted into heat 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 in atmosphere.

• Used for reactive metals as titanium, tungsten etc.

• Chances of x-ray exposure.

Electron Beam Welding Operation

Radiant Energy Welding

Laser beam Welding:

• Utilizes a high power laser beam as the source of

heat.

• 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

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

End of chapter 2 (Welding) (7hrs.)

Next chapter Foundry (8 hrs.)