welding notes 1

7/28/2019 Welding Notes 1

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4ME-6 MANUFACTURING PROCESS – II

Unit – IV

Powder Metallurgy Power manufacturing and Conditioning, Production of Sintered Structural Components Self

lubricating bearing, Cemented Carbides, Ceramics, Sintered Carbide cutting tools Composite Materials,

Classification , Different types of composite material and its applications. [6 Hrs]

Unit – V: Joining Process :

Introduction to Welding, Soldering Brazing Process Types of Welding Arc Welding & Gas Welding Process,Defect & Inspection of Welding Joints, Electrodes, Weldability of Metals, Welding equipments of Fixtures. [8

Hrs]

Unit – VI

Processing of Plastics, Thermoplastic, Thermosetting plastics, general properties & applications of

Thermosetting & Thermo Plastics. General Plastics Processes: Extrusion, Injection Moulding Compression

Moulding, Transfer Moulding Blow Moulding, Calendering Wire Drawing Embossing . [7 Hrs]

Unit – V: Joining Process

Definition and Classification

Welding is the process of permanently joining two or more metal parts, by melting both

materials. The molten materials quickly cool, and the two metals are permanently bonded.

Welding is carried out by the suitable combination of temperature, pressure and metallurgical

conditions. Depending upon the combination of temperature and pressure from a high

temperature with no pressure to a high pressure with low temperature, also with or without

added metal.

It is used in the manufacture of automobile bodies, aircraft frames, railway wagons, machine

frames, structural works, tanks, furniture, boilers, general repair work and ship building.

Welding Processes can be classified as: -

1. Gas Welding

Oxyacetylene

Oxy-hydrogen

Air- acetylene

2. Arc Welding

Carbon arc

Metal arc

Gas metal arc (MIG)

Gas tungsten arc (TIG)

Plasma arc

Submerged arc

Electro-slag

Flux-cored arc

3. Resistance Welding

Spot

Seam

Projection

Butt Induction Welding



4. Radiant Energy Welding

Electron BeamWelding

Laser Beam Welding

5. Solid State Welding

Friction Welding

Ultrasonic Welding Forge and Diffusion Welding

Explosive Welding

6. Related Processes

Oxyacetylene Cutting

Arc Cutting

Brazing

Soldering

Oxyacetylene Welding

The oxyacetylene welding process uses a combination of oxygen and acetylene gas to provide a high temperature flame; this is done with the help of welding torch which is used to

weld metals. It is a manual process which is incorporated when two pieces are heated to a

temperature that produces a shared pool of molten metal. The molten pool is generally

supplied with additional metal called filler. Filler material depends upon the metals to be

welded.



Some Key Features:-

Sound weld is obtained by selecting proper size of flame, filler material and

method of moving torch.

Temperature generated during the process is 33000c.

When the metal is fused, oxygen from the atmosphere and the torch combineswith molten metal and forms oxides, results defective weld

Fluxes are added to the welded metal to remove oxides

Common fluxes used are made of sodium, potassium. Lithium and borax.

Flux can be applied as paste, powder, liquid.solid coating or gas.

Gas Welding Equipment

1. Gas Cylinders

Pressure

Oxygen – 125 kg/cm2

Acetylene – 16 kg/cm2

2. Regulators

Working pressure of oxygen 1 kg/cm2

Working pressure of acetylene 0.15 kg/cm2

Working pressure varies depends upon the thickness of the work pieces

welded.



3. Pressure Gauges

4. Hoses

5. Welding torch

6. Check valve

7. Non return valve

Types of Flames

• Oxygen is turned on, flame immediately changes into a long white inner area

(Feather) surrounded by a transparent blue envelope is called Carburizing flame

(30000c)

• Addition of little more oxygen give a bright whitish cone surrounded by the

transparent blue envelope is called Neutral flame (It has a balance of fuel gas and

oxygen) (32000c).It is used for welding steels, aluminium, copper and cast iron.

• If more oxygen is added, the cone becomes darker and more pointed, while the

envelope becomes shorter and more fierce is called Oxidizing flame. Has the highest

temperature about 34000c. It is used for welding brass and brazing operation.



Three basic types of oxyacetylene flames used in oxyfuel-gas welding and cutting operations:

(a) neutral flame; (b) oxidizing flame; (c) carburizing, or reducing flame.

Advantages of Oxy-Acetylene Welding It's easy to learn.

The equipment is cheaper than most other types of welding rigs (e.g. TIG welding) The equipment is more portable than most other types of welding rigs (e.g. TIG

welding)

OA equipment can also be used to "flame-cut" large pieces of material.

Disadvantages of Oxy-Acetylene Welding OA weld lines are much rougher in appearance than other kinds of welds, and require

more finishing if neatness is required.

OA welds have large heat affected zones (areas around the weld line that have had their

mechanical properties adversely affected by the welding process)

Gas MIG (GMAW):

Very clean welds with no slag or spatter.

Wire is less expensive.

Direct-Current, Electrode Positive polarity (DCEP) Wire size down to 0.023: (0.6mm), great for thin metal.



Uses a consumable wire electrode during the welding process that is fed from a spool,

Uses a shielding gas, usually – argon, argon - 1 to 5% oxygen, argon - 3 to 25%

CO2 and a combination argon/helium gas,

Is considered a semi-automatic welding process,

Allows welding in all positions,

Requires less operator skill than TIG welding, Allows long welds to be made without starts or stops,

Needs little cleanup.

Provides a uniform weld bead

Working of MIG Welding

MIG weld welding requires three things, electricity to produce heat, an electrode to fill the

joint, and shielding gas to protect the weld from the air. MIG welding is done using a very

small electrode that is fed continuously, The wire is fed via from a roll wire feeder to the gun

while the operator controls the amount of weld being done. In some cases when a robot takes

over this process, it becomes automatic welding. MIG is the easiest process to learn, but

requires gas and a wire feeder so it is not as portable. MIG is great for thin metal especially

auto body work.



Advantages of MIG welding

High quality welds can be produced much faster

Since a flux is not used, there is no chance for the entrapment of slag in the weld

metal resulting in high quality welds

The gas shield protects the arc so that there is very little loss of alloying elements.

Only minor weld spatter is produced

MIG welding is versatile and can be used with a wide variety of metals and alloys

The MIG process can be operated several ways, including semi and fully automatic

Disadvantages of MIG welding

The MIG welding cannot be used in the vertical or overhead welding positions

because of the high heat input and the fluidity of the weld puddle

The equipment is complex.



Tungsten Inert Gas (TIG) Welding

An arc is struck between a tungsten electrode (non-consumable) and the sheet metal

to be welded. An inert gas shields the arc from the ambient to prevent oxidation. A

filler material is optional

Carbon steels, low alloy steels, stainless steels, most aluminum alloys, zinc based

copper alloys and non-ferrous metals such as aluminum and magnesium can be

welded using this process. TIG is quite suitable for welding dissimilar materials,

but usual cautions of galvanic corrosion still apply.

Uses a non-consumable tungsten electrode that is used to melt two metals together

in the presence of shielding gas.

Uses a number of shielding gases including helium (He) and argon (Ar),

Is easily applied to thin materials,

Produces very high-quality, superior welds,

Welds can be made with or without filler metal,

Provides precise control of welding variables (i.e. heat),

Leaves no slag or splatter.

The TIG process is a slower process compared to the MIG process, but the quality

of weld is cosmetically better. There is no weld spatter, and the quality of welds is

higher than MIG welding.

Also different types of power sources are used for different types of metal.

Working of TIG Welding:

In TIG welding, an arc 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. If

filler wire is used, it is added to the weld pool separately.

GTAW is most commonly used to weld thin sections of stainless steel . The process grants

the operator greater control over the weld than competing processes such as shielded metal

arc welding and gas metal arc welding, allowing for stronger, higher quality welds.

http://en.wikipedia.org/wiki/Aluminum

http://en.wikipedia.org/wiki/Magnesium


http://en.wikipedia.org/wiki/Stainless_steel

http://en.wikipedia.org/wiki/Shielded_metal_arc_welding


http://en.wikipedia.org/wiki/Gas_metal_arc_welding

http://en.wikipedia.org/wiki/Gas_metal_arc_welding



http://en.wikipedia.org/wiki/Stainless_steel


http://en.wikipedia.org/wiki/Aluminum



Uses of TIG welding

• Oil Pipelines

• Medical Industry (SS)

• Exhaust piping

• Aluminum radiators



Disadvantages of TIG vs MIG

• Cost of filler material and shielding gas are similar

• Higher skilled/paid employees are required for TIG

• More time for TIG

• Harder to automate a TIG process

• Outside welding is more difficult since the shielding gas can be blown away

Advantages of TIG vs MIG

• TIG is irreplaceable in critical applications

• TIG has higher strength and heat resistance

• TIG is cleaner

• Can weld nearly any metal

• Can weld extremely thin materials (0.1mm)

• Can join metals without additional filler material in many cases.

Plasma Arc Welding

A plasma is a gas which is heated to an extremely high temperature and ionized so that it

becomes electrically conductive. Similar to GTAW (Tig), the plasma arc welding process

uses this plasma to transfer an electric arc to a work piece. The metal to be welded is melted

by the intense heat of the arc and fuses together.

In the plasma welding torch a Tungsten electrode is located within a copper nozzle having a

small opening at the tip. A pilot arc is initiated between the torch electrode and nozzle tip.

This arc is then transferred to the metal to be welded.

By forcing the plasma gas and arc through a constricted orifice, the torch delivers a highconcentration of heat to a small area. With high performance welding equipment, the plasma

process produces exceptionally high quality welds.

Plasma gases are normally argon. The torch also uses a secondary gas, argon, argon/hydrogen

or helium which assists in shielding the molten weld puddle thus minimizing oxidation of the

weld.

Temperatures in PAW reach 28,000C (50,000F), due to constriction of arc, producing a plasma jet of small diameter and very high energy density.



Advantages:

Good arc stability and excellent weld quality

Better penetration control than other AW processes

High travel speeds

Can be used to weld almost any metals

Requires less operator skill due to good tolerance of arc to misalignments;

Disadvantages:

High equipment cost

Larger torch size than other AW processes

Tends to restrict access in some joints.

Submerged Arc Welding

Its a common arc welding process which requires a continuously fed consumable solid or

metallic (flux cored) electrode. A granular blanket fusible containing lime, manganese oxide,

silica, calcium fluoride and other component are used for shielding the arc zone and molten

weld from atmospheric contamination.

The arc heats and melts both the work pieces edges and the electrode wire. The molten

electrode material is supplied to the surfaces of the welded pieces, fills the weld pool and joins the work pieces.



Since the electrode is submerged into the flux, the arc is invisible. The flux is partially melts

and forms a slag protecting the weld pool from oxidation and other atmospheric

contaminations.

The flux close to the arc melts and intermixes with the molten weld metal and helps purifyand fortify it. The flux forms a glasslike slag that is lighter in weight than the deposited weld

metal and floats on the surface as a protective cover. The weld is submerged under this layer

of flux and slag- hence the name submerged arc welding.



Advantages of Submerged Arc Welding (SAW): Very high welding rate;

The process is suitable for automation;

High quality weld structure.

High productivity with true deposition rates as high as 100 pounds per hour Travel speeds up to 150 inches per minute single wire or as high as 220 inches per

minute with multiple electrodes

Operating factor approaching 100%

Deepest penetration, up to 1 1/2 inches thick in a single pass

High operator comfort, no visible arc or spatter

High weld quality and repeatable results

Usually fully automated process, exceptional control

Environmentally friendly

Disadvantages of Submerged Arc Welding (SAW): Weld may contain slag inclusions;

Limited applications of the process - mostly for welding horizontally located plates.

http://www.substech.com/dokuwiki/doku.php?id=grain_structure&DokuWiki=e30d930e597f60491f065c539a09b4d0






Spot Welding

Resistance spot welding description:

The process is used for joining sheet materials and uses shaped copper alloy electrodes to

apply pressure and convey the electrical current through the workpieces. Heat is developed

mainly at the interface between two sheets, eventually causing the material being welded to

melt, forming a molten pool, the weld nugget.

Spot welding is one of the oldest welding processes. It can be used on very thin foils or thick

sections but is rarely used above about 6mm thickness. It is used in a wide range of industries

but notably for the assembly of sheet steel vehicle bodies where more than 100 million welds

are made per day in Europe alone. High quality welds can also be made in stainless steels,

nickel alloys, aluminium alloys and titanium for aerospace application.

Process of Spot Welding:

The two work pieces to be joined are cleaned to remove dirt, grease and other oxides either

chemically or mechanically to obtain a sound weld.

The work pieces are then overlapped and placed firmly between two water cooledcylindrically shaped copper alloy electrodes, which in turn are connected to a secondary

circuit of a step-down transformer. The electrodes carry high currents and also transmit the

force/pressure to the work pieces to complete the weld.

In operation, the welding current is switched ON. As the current passes through theelectrodes, to the work piece, heat is generated in the air gap at the point of contact of the two

work pieces.

The heat at this contact point is maximum with temperature varying from 815-930 degreecentigrade, and as a result melts the work pieces locally at the contact point to form a spot

weld.



In order to obtain a strong bond, external pressure is applied to the work piece, throughthe electrode, by means of a piston-cylinder arrangement. The current is switched OFF.

In some cases, external pressure is not required and the holding pressure of the two

electrodes is just sufficient to create a good joint.

Heat dissipates throughout the work piece which cools the spot weld causing the metal to

solidify. The pressure is released and the work piece is moved to the next location to make

another spot weld.

In some spot welding machines, the work piece remains stationary while the electrode

moves to the next location to make a weld.

Copper is used for electrodes because it has a low resistance and high thermal conductivitycompared to most metals. This ensures that the heat is generated in the workpieces instead of the

electrodes.

The heat generated depends on the electrical resistance and

thermal conductivity of the metal, and the time that the

current is applied. The heat generated is expressed by the

equation: E=I2*R*t

where E is the heat energy, I is the current, R is the

electrical resistance and t is the time that the current is

applied.

Note:

The duration of current flow varies from a fraction of second to a few seconds. Both the

current and the duration of current flow form the important parameters in spot welding and

depend on the thickness and type of the work pieces being welded.



Advantages of Spot Welding:

Efficient energy use.

Limited work piece deformation. Also, work piece is not melted to a larger extent. Heat is

concentrated only at the spot to be welded.

High production rates.

Suitable for automation.

Filler metals are not required. Hence, no associated fumes or gas. This results in clean

weld.

Disadvantages of Spot Welding:

Weld strength is significantly lower when compared to other processes. This makes the

process suitable for only certain applications.

Silver and copper are difficult to weld because of their high thermal conductivity.

Applications of Spot Welding:

Extensively used for welding steels and especially in the automotive industry for cars that

requires several hundred spot welds made by industrial robots

Seam Welding

Seam Welding is a Resistance Welding (RW) process of continuous joining of overlapping

sheets by passing them between two rotating electrode wheels. Heat generated by the electric

current flowing through the contact area and pressure provided by the wheels are sufficient to

produce a leak-tight weld.

http://www.substech.com/dokuwiki/doku.php?id=resistance_welding_rw








Seam Welding is high speed and clean process, which is used when continuous tight weld is

required (fuel tanks, drums, domestic radiators).

Resistance seam welding

Description

The seam welding process is an adaptation of resistance spot welding and

involves making a series of overlapping spot welds by means of rotating copper

alloy wheel electrodes to form a continuous leak tight joint. The electrodes are not

opened between spots. The electrode wheels apply a constant force to the work

pieces and rotate at a controlled speed. The welding current is normally pulsed to

give a series of discrete spots, but may be continuous for certain high speed

applications where gaps could otherwise occur between individual spots.

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Wide wheel seam

Applications:-

Containers, radiators and heat exchangers, pressure vessels, tanks, water floats, nuclear

components, appliance drums, brewery tanks,motor shells, etc.



Advantages

Efficient energy use, with little pollution Fast processing times

Easily automated

No required filler materials

Economical

Adaptable to a variety of electrically conductive materials

Ability to produce leak-tight welds

Can be performed by unskilled operators

For certain high strength aluminum alloys, it is practically the only process applicable

Low fumes

Disadvantages

Limited by component shape and wheel access

Initial equipment costs

Lower tensile and fatigue strengths

Thickness of welded sheets is limited - up to 1/4” (6 mm)



Electron Beam Welding

Electron beam welding (EBW) is a fusion welding process in which a beam of high-

velocity electrons is applied to the materials being joined. The workpieces melt as the kinetic

energy of the electrons is transformed into heat upon impact, and the filler metal, if used, also

melts to form part of the weld. The welding is often done in conditions of a vacuum to

prevent dispersion of the electron beam.

The electrons are small particles of matter with small mass.When they are accelerated they

hit the piece transferring their kinetic energy into thermal energy ensuring metal melting

creating plasma of metallic vapours.

This transformation is stable in the high 90% range for all metals regardless of whether the

electrons hit the surface at a perpendicular or shallow angle. As a practical matter, this

physical behaviour makes the process very robust and reliable!

Electron Beam is capable to weld work pieces with thickness from 0.0004” (0.01 mm) up to

6” (150 mm) of steel and up to 20” (500 mm) of aluminum. Electron Beam Welding may be

used for joining any metals including metals, which are hardly weldable by

other welding methods: refractory metals (tungsten, molybdenum, niobium) and chemically

active metals (titanium, zirconium, beryllium). Electron Beam Welding is also able to join

dissimilar metals.

Working of Electron Beam Welding In an electron beam welder electrons are "boiled off" as current passes through a filament

which is in a vacuum enclosure. An electrostatic field, generated by a negatively charged

filament and bias cup and a positively charged anode, accelerates the electrons to about 50%

to 80% of the speed of light and shapes them into a beam. Due to the physical nature of the

electrons - charged particles with an extremely low mass - their direction of travel can easily

be influenced by electromagnetic fields. Electron beam welders use this characteristic to

electromagnetically focus and very precisely deflect the beam at speeds up to 10 kHz. Recent

machine developments make it possible even to go up to 200 kHz.

Advantages of the electron beam welding:

• very small deformations after welding,

• very thick materials (exceeding 60 mm with steel) in one pass,

• possi bility to weld all the steel, copper, nickel materials, aluminium,

metals sensitive to oxygen and other gases as zirconium, titanium…

• no filler metal and no gas,

• high welding quality. The welds obtained are exceptionally pure,

• high reliability,

http://en.wikipedia.org/wiki/Welding



http://en.wikipedia.org/wiki/Charged_particle_beam



http://en.wikipedia.org/wiki/Electron



http://en.wikipedia.org/wiki/Kinetic_energy




http://en.wikipedia.org/wiki/Vacuum



http://en.wikipedia.org/wiki/Dispersion



http://www.substech.com/dokuwiki/doku.php?id=steels_and_cast_irons

http://www.substech.com/dokuwiki/doku.php?id=aluminum_alloys

http://www.substech.com/dokuwiki/doku.php?id=classification_of_welding_processes

http://www.substech.com/dokuwiki/doku.php?id=titanium_alloys

http://www.substech.com/dokuwiki/doku.php?id=titanium_alloys

http://www.substech.com/dokuwiki/doku.php?id=classification_of_welding_processes

http://www.substech.com/dokuwiki/doku.php?id=aluminum_alloys

http://www.substech.com/dokuwiki/doku.php?id=steels_and_cast_irons










• high reproducibility,

• high productivity

EBW Limitations

• High equipment cost

• Work chamber size constraints

• Time delay when welding in vacuum

• High weld preparation costs

• X-rays produced during welding

• Rapid solidification rates can cause

cracking in some materials



Laser Beam Welding

It is a commercial welding process which is used to weld two workpieces. In this the laser

beam is focussed over a area which causes the material to change from solid to liquid, after

cooling it forms a solid joint. There are many advantages which initiates this process

popularly like minimizing heat inputs, deep weld penetration, no need of shielding gas, no

need of pressure; these advantages are all connected to economic reasons (cost saving). There

are two types of laser beam welding i.e. solid state laser and gas laser. If the thinner metal is

to welded then lower, powered, pulsed solid state lasers are used, if the part is thicker then

higher power input, gas lasers like CO2 lasers are used.

The most popular solid state laser is neodymium doped yttrium aluminium garnet laser (Nd:YAG)

Laser is an acronym for light amplification by stimulated emission of radiation. Under normal

conditions, most atoms or molecules remain at their lowest energy level or ground state. But

if these particles are excited into higher energy states by an intense flash of light, by an

electric charge, or by any other means, they will emit incoherent light, when dropping back to

the normal ground state. In a laser cavity, such emitted photons (particles of light) are trapped

between highly polished and parallel mirrors, forcing them to bounce back and forth in the

cavity.



Whenever photon passes close to another excited particle of the same wave length, the

second particle will also be stimulated to emit a photon that in identical in wave length, phase

and spatial coherence to the first. Both photons are now capable of stimulating the emission

of more photons like themselves. This results in a growing wave between the parallel mirrors.

If one of the mirrors is partially transparent, a highly disciplined, intense and now coherentlaser beam is emitted.

Types of laser

Gas Solid-State

Argon

Carbon-dioxide

Helium-cadmium

Helium-Neon

Synthetic Ruby

Gallium-Aluminium-arsenide

Gallium-Arsenide

Nd: Glass(Neodymium: Glass)

Nd : YAG(Neodymium: Yttrium-

Aluminium-Garnet)



Characteristics of the laser beam

Monochromatic,Coherent &Collimated

welding notes 1

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