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SOLDERING, BRAZING & WELDING
INTRODUCTION
Some products cannot be manufactured as a single piece.
The desired shape and size of such products can be
obtained by joining two parts of same or different
materials. These parts are manufactured individually andare joined together to obtain the desired product.
For example, aircraft and ship bodies, welded machine
frames, furniture, computers, bridges and the transmission
or electric towers etc., are all fabricated by joining several
different parts.
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Classification of joining processes:
Temporary Joint
Permanent Joint
A temporary joint can be easily dismantled
separating the original parts without any damage to
them
In case it is a permanent joint, an attempt to separate
the parts already joined will result in the damage of theparts. In a permanent joint, the joint is made such that
it has properties similar to the base metal of the two
parts. These parts cannot be separated into their
original shape, size and surface finish 3
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Based on the process used for making the joint, the
joining processes can be further classified as:
Soldering.
Brazing.
Welding.
Mechanical Fasteners - bolts, nuts, rivets, screws
Adhesive bonding.
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Welding is one of the most extensively used
fabrication method. The joint strength obtained in
welding is being equal to or some times more thanthat of the parent metal.
Welding is not only used for making structures,
but also for repair work such as the joining of
broken castings.
The choice of a particular joining processdepends on several factors such as application,
nature of loads or stresses, joint design, materials
involved and size and shape of the components 5
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WELDING
Welding is a process of metallurgical joining of
two pieces of metals by the application of heat with
or without the application of pressure and addition
of filler metal. The joint formed is a permanent
joint.
It is extensively used in the fabrication work in
which metal plates, steel sections, castings offerrous metals are joined together. It is also used for
repairing broken, worn-out or defective metal parts.
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Modern methods of welding may be classified
under two broad headings.
Plastic or pressure welding process Fusion or non-pressure welding process
In plastic or pressure welding process the pieces
of metal to be joined are heated to a plastic state
and then forced together by external pressure. This
procedure is used in forge welding, resistance
welding, spot welding in which pressure is required.
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In the fusion or non-pressure welding, the material
at the joint is heated to a molten state and allowed to
solidify. This includes gas welding, arc welding
The surfaces of the metal which are to be joined by
any of the welding processes must be sufficiently clean
to permit clean metallic surfaces to come in to contact.
Fluxes are applied to the parts being welded to
dissolve the oxides or to prevent the formation ofoxides.
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GENERAL WELDING PROCEDURE
1. Surface Cleaning:
Surfaces of the parts to be welded need to bethoroughly cleaned to remove dust, dirt, oil, grease etc.
2. Edge Preparation:
Preparing a contour at the edges of the pieces to be
joined. It may involve beveling or grooving. This is
done in order to get the fusion or penetration through
the entire thickness of the member.
3. Clamping:
Pieces to be welded are clamped suitably so that there
are no undesirable movements during welding. 9
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4. Safety Devices:
Goggles & shields to protect the eyes, Apron to prevent
the sparks and flying globules of molten metal, shoes,
hand gloves etc.
5. Initial Weld:
Initial tack welds are done at the opposite corners of the
joint to secure the pieces together. Any cracks at this
stage must be removed as they cause residual stresses.
6. Intermediate and Final Welding:The weld joint is formed through various weaving
movements (weld beads). During this process, filler
metal and a suitable flux are used. After the
intermediate run of welding, final run is taken. 10
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7. Removal of Excess Material:
Extra material on the weld surface can be removed
using tongs and chipping hammer. The weld is allowedto cool and then cleaned.
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Classification of welding processes:
(i). Arc welding Carbon arc
Metal arc
Metal inert gas
Tungsten inert gas
Plasma arc
Submerged arc
Electro-slag
(ii). Gas Welding Oxy-acetylene
Air-acetylene
Oxy-hydrogen(iii). Resistance Welding
Butt
Spot
Seam
Projection Percussion
(iv)Thermit Welding
(v)Solid State Welding
Friction
Ultrasonic
DiffusionExplosive(vi)Newer Welding
Electron-beam
Laser
(vii)Related Process
Oxy-acetylene cuttingArc cutting
Hard facing
Brazing
Soldering
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Another criterion used for a classification of the welding
process is based on the composition of the joint
(i) autogeneous (ii) homogeneous, and (iii) heterogeneous
In autogeneous processes no filler material is added during
the joining. All types of solid phase welding and resistance
welding are examples of this category.
In homogeneous welding processes, the filler material used
to provide the joint is the same as the parent material. Arc,
gas, and thermit welding belong to this category
In third category of welding, a filler material different fromthe parent material is used. Soldering and brazing are two
such joining processes
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GAS WELDING
Gas welding is a fusion welding process
Flame produced by the combustion of gases is
employed to melt the metal
The molten metal is allowed to flow together thusforming a solid continuous joint upon cooling.
By burning pure oxygen in combination with other
gases, in special torches, a flame up to 33000C can be
attained.
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Principle
In oxy-fuel gas welding (OFW) the heat is obtained from the
combustion of a fuel gas such as acetylene in combination
with oxygen
The process is a fusion welding process wherein the joint is
completely melted to obtain the fusion.
The heat produced by the combustion of gas is sufficient to
melt any metal and as such is universally applicable
The fuel gas generally used is acetylene because of the high
temperature generated in the flame. This process is called
oxy-acetylene welding
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Principal Cont.
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Oxy-acetylene Gas Welding Equipment
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Oxy-acetylene Gas Welding Equipment
1. Welding torch & tip
2. An acetylene cylinder
15.5 bar, red or maroon3. An oxygen cylinder 125 bar. Blue or black
4. Pressure regulator Cylinder pressure to delivery
pressure
5. Pressure gauge- One shows cylinder pressure & the
other shows the working or delivery pressure
6. Rubber hoses - black/green hose for oxygen &
red/orange hose for acetylene7. Safety devices Goggle with coloured glasses, hand
gloves, helmet, apron, sleeves, shoes etc.
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The oxy-acetylene flame is used to pre heat the parts to
be welded around the joint and also to melt the filler
metal.
A jet of oxy acetylene flame issuing from the nozzle of a
burner is played on the junction of the two pieces to be
welded.
At the same time a filler rod is held in the zone of jet
and its melt is deposited on the fused junction.
A weld is obtained after the molten metal solidifies. The
coating on the filler rod acts as a flux to keep the joint
clean.23
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GAS WELDING FLAMES (OXY-ACETYLENE FLAMES)
(Based on Gas Ratio)
1. Neutral Flame: (Gas ratio is 1)
.A certain amount of oxygen is required for complete combustion of
fuel gases
When the oxygen supply varies, the flame appearance obtained
would also vary.
In neutral flame all the acetylene present is completely burned andthus all the available heat in the fuel gas is released.
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So this is the most desirable flame to be used in oxy-acetylene
welding.
Due to neutral flame no chemical change and no oxidation in
molten metal
This neutral flame is desired for most welding operations. Used
for welding steel, stainless steel, cast iron, Cu etc.
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2. Carburizing or Reducing Flame: ( Gas ratio 0.95 to 1)
Excess of acetylene is present, Low temp flame
The excess unburnt carbon is absorbed in ferrous metals,
making the weld hard and brittle.
An intermediate flame feather exists - reddish in colour.
The length of the flame feather is an indication of the excess
acetylene present.
Carbonizing flame is used for welding high carbon steels
and cast iron, alloy steel.
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Since this flame provides a strong reducing atmosphere in the
welding zone, it is useful for those materials which are readilyoxidize like oxygen free copper alloys.
It is also used for high carbon steels, cast iron and hard
surfacing with high speed steel and cement carbides.
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2. Oxidizing Flame: (Gas ratio 1.15 to 1.5)
Excess of oxygen is present, similar to the neutral flame
Inner white cone is some what small, giving rise to higher
tip temperatures. Excess of oxygen causes the metal to burn/oxidize quickly.
Used for brass, bronze
Widely used for oxyacetylene cutting and not suitable for
welding since the weld metal will be oxidised.
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Advantages of Oxy-acetylene Gas Welding
1.The equipment is inexpensive, simple and is easily portable and
versatile
2.The same equipment with a range of torches can be used for
oxygen cutting as well as for brazing
3. Source of heat is separate from the filler rod, filler metal and heat
can be properly controlling, giving rise to satisfactory result.
4. Gas flame temperature is lower and easy controllable which is
necessary for the delicate work. Therefore it is extensively used for
sheet metal fabrication
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Disadvantages of Oxy-acetylene Gas Welding
1. Equipment must always be handled carefully as in certain
circumstances acetylene is explosive as oxygen when used inan oily atmosphere (such as an old dirty garage floor pit).
2. A high temperature flame from a hand held torch is
dangerous when handled carelessly.
3. It is much slower than electric arc welding and does notconcentrate the heat close to the weld. Thus, the heat treated
area is larger, which causes more distortion.
4. Highly skilled operators are required to produce a good
weld.5. If electric arc welding is available gas welding is seldom
used for work over 3.2mm thick.
6. The process is not satisfactory for heavy sections
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Applications:
For joining of thin materials.
For joining materials in whose case excessively high
temperature or rapid heating and cooling of the job
would produce unwanted changes in the metal. For welding both ferrous and non-ferrous metals.
In automotive &aircraft industries, project site works,
workshops etc.
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IT 208 Chapter 14 33
GAS WELDING
Oxygen-Hydrogen Welding
The oxygen-hydrogen torch can reach temperatures much higher than the
oxy-acetylene torch.
More expensive than oxy-acetylene welding and involves the flammability
risk with hydrogen.
Plasma Welding
Hydrogen plasma burns even hotter than hydrogen gas, permitting the
welding of extremely high-melting-point metals.
Very clean procedure that results in very little slag or foreign matter in theweld.
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Gas Cutting
It is possible to rapidly oxidise (burn) iron and steel when it is
heated to a temperature between 800 to 10000 C
When a high pressure oxygen jet with a pressure of the order
of 300 KPa is directed against a heated steel plate, the oxygen
jet burns the metal and blows it away causing the cut
This process is used for cutting steel plates of various
thicknesses (can go up to 2 m) mainly because the equipment
required is simple and can be carried anywhere without
handling the heavy steel plates.
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Here the torch tip has a provision for preheating the plate as
well as providing the oxygen jet. Thus the tip has a central
hole for oxygen jet with surrounding holes for preheating
flames
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GAS CUTTING
Manual Gas Cutting
http://en.wikipedia.org/wiki/Image:Railway-cutting-2-a.jpghttp://images.google.co.in/imgres?imgurl=http://www.abadibaru.com/images/pgcm/BA200.jpg&imgrefurl=http://www.abadibaru.com/pgcm.htm&h=262&w=250&sz=96&hl=en&start=34&um=1&usg=__hpdNn71Q6qsWntqU57VLIdd-S_U=&tbnid=VSaymAYCQvGiTM:&tbnh=112&tbnw=107&prev=/images?q=Gas+cutting&start=18&ndsp=18&um=1&hl=en&sa=N8/4/2019 Welding DS8
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Arc Welding Equipments
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Arc Welding Setup
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ARC WELDING
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ARC WELDING
Joining of metals with heat produced by an electric
arc.
Heat necessary to melt the edges of the metal to be
joined is obtained from an electric are struck betweenthe electrode (filler rod) and the work, producing a
temperature of 50000C, in the welding zone.
The heat of the arc melts the base metal or edges ofthe parts fusing them together.
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Filler metal, usually added melts and mixes with
molten base metal to form the weld metal.
The weld metal cools and solidifies to form the
weld.
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What is an Electric Arc?
An arc is an electric current flowing between twoelectrodes through an ionized column of gas.
It is sustained by an ionized column of gas(plasma) through which the current flows
To initiate the arc in AW, electrode is brought intocontact with work and then quickly separatedfrom it by a short distance
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ARC WELDING MACHINE: AC or DC
AC Arc Welding Machine:
A step down transformer - receives the AC supply
between 200 to 440volts and transforms it to the
required low welding voltage in the range of 80 to100volts.
A high current of 100 to 400A will be suitable for
general arc welding work.
In AC arc welding, there is no choice of polarity
since they change in every cycle. 42
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DC Arc Welding Machine:
In DC welding, the workpiece is connected to the
positive pole of a DC generator and the electrode to
the negative pole in order to melt greater mass of the
metal in the base material. This is called straight
polarity.
When the less heat is required at the base material, the
polarity is reversed. This is called reversed polarity.
We can select the polarity depending upon the type of
the job. Hence, in DC arc welding, it is possible to melt
many metals which require more heat to melt. 43
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DC arc welding
it is generally preferred because of the control of the heat
input offered by it. If more heat is required at the workpiece
side, such as for thicker sheets or for the work materials
which have higher thermal conductivity such as aluminium
and copper, the workpiece can be made as anode, liberatinglarge heat near it
For thinner materials where less heat input is required in the
weld zone, the polarity could be reversed by making theworkpiece as negative
Sl N A t AC W ldi DC W ldi
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Sl No. Aspect AC Welding DC Welding
1. Arc Stability Lower/ Unstable Higher/Stable
2. Cost Low High
3. Electrodes Only Coated Both Bare & Coated
4 Electrical
energy
Consumption
Less energy consumption per
kg of the metal deposited (3
to 4 kWh)
More energy consumption
per kg of the metal deposited
(6 to 10 kWh)
5. Efficiency High Low
6. Polarity No choice of polarity Straight or reversed polarity
can be used depending on thetype of job and heat required
at the base metal
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ARC WELDING ELECTRODES
1. Consumable Electrodes: Melt along with the
workpieces & fills the joint.
They are either Bare or Coated.
When the bare electrodes are used, the globules of
the molten metal while passing from the electrodes
absorb oxygen and nitrogen from the atmospheric
air to form non-metallic constituents which gets
trapped in the solidifying weld metal and thereby
decreasing the strength of the joint.
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Coated Electrodes facilitate:
1. Protection of molten metal from oxygen and
nitrogen of the air by providing a gaseous shield
around the arc and the molten metal pool.
2. To establish & maintain the arc throughout welding
3. The formation of slag over the joint, thus protects
from rapid cooling.
4. Addition of alloying elements
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2. Non-consumable Electrodes:
When non-consumable electrodes are used, an
additional filler material is also required. The
advantage of using this type of electrode is that the
amount of the metal deposited by the filler rod can be
controlled.
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Advantages of Arc Welding
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Advantages of Arc Welding
1.Applicable to an infinite variety of work & can be
executed in any position.
2.It produces strong sound and ductile welds.
3.Satisfactory welds can be produced in heavy & light
sections.
4.Low cost process & Low accuracy in setting up required.
5.Excellent joint properties can be obtained in mild, low
alloy and stainless steels, nickel and copper-base alloys.
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Di d t f A W ldi
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Disadvantages of Arc Welding
1.Basically a manual process requiring adequate operator
skill for good results.
2.Electrodes require frequent changing.
3.Multi run welds necessary on thick plate-slag chipping
necessary after each run.
4.The principal disadvantage has been the high heat of themetal arc which makes it unsuitable for use on materials
less than 1.55 mm thick.
5.High initial cost of welding equipment. 50
Th b hi ld d b i h d h
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The arc must be shielded because - as it hardens the
molten metal combines with oxygen and nitrogen to
form impurities that weaken the weld.
The electrodes are usually coated with a flux. This
coating forms a gaseous cloud that shields the molten
metal from the atmosphere.
The coating also forms a protective slag. The slag
floats on the molten pool and hardens as the weld
cools. This keeps impurities out of the weld.
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Arc Shielding
At high temperatures in AW, metals arechemically reactive to oxygen, nitrogen, andhydrogen in air
Mechanical properties of joint can be seriously degradedby these reactions
To protect operation, arc must be shielded fromsurrounding air in AW processes
Arc shielding is accomplished by: Shielding gases, e.g., argon, helium, CO2 Flux
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Flux
A substance that prevents formation of oxides
and other contaminants in welding, or
dissolves them and facilitates removal
Provides protective atmosphere for welding
Stabilizes arc
Reduces spattering
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Various Flux Application Methods
Pouring granular flux onto welding operation
Stick electrode coated with flux material that
melts during welding to cover operation
Tubular electrodes in which flux is contained
in the core and released as electrode is
consumed
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Shielded Metal Arc Welding
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Shielded Metal Arc Welding
(SMAW)
An arc welding process that produces a
coalescence of metals by heating with an arc
between a covered metal electrode and the
work pieces
Stick Welding
Shielding is obtained from decomposition of
the electrode covering.
Filler metal is obtained from the electrode.
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Figure 31.3 Shielded metal arc welding (SMAW).
Shielded Metal Arc Welding
Gas Metal Arc Welding
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Gas Metal Arc Welding
(GMAW)
An arc welding process that produces
coalescence of metals by heating them with
an arc between a continuous filler metal
(consumable) electrode and the work
MIG welding
Shielding is obtained entirely from an
externally supplied gas or gas mixture.
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GMAW Weld Diagram
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Gas Metal Arc Welding (GMAW)
Uses a consumable bare metal wire aselectrode and shielding accomplished byflooding arc with a gas
Wire is fed continuously and automaticallyfrom a spool through the welding gun
Shielding gases include inert gases such asargon and helium for aluminum welding,and gases such as CO2 for steel welding
Bare electrode wire plus shielding gaseseliminate slag on weld bead - no need formanual grinding and cleaning of slag
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GMAW Advantages over SMAW
Better arc time because of continuous wireelectrode Sticks must be periodically changed in SMAW
Better use of electrode filler metal thanSMAW End of stick cannot be used in SMAW
Higher deposition rates
Eliminates problem of slag removal
Can be readily automated
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Submerged Arc Welding (SAW)
Uses a continuous, consumable bare wireelectrode, with arc shielding provided
by a cover of granular flux
Electrode wire is fed automaticallyfrom a coil
Flux introduced into joint slightly ahead
of arc by gravity from a hopper
Completely submerges operation, preventing
sparks, spatter, and radiation
Submerged Arc Welding
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Submerged Arc Welding
(SAW)
An arc welding process that uses an arcbetween a bare metal electrode and the weldpool. The arc and molten metal are shielded
by a blanket of granular flux. a process in which welding is done by an
automatic electrode feeding machine whereinthe tip of the electrode is submerged into a
granular flux which shields the arc and themolten metal.
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SAW operations
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SAW Applications and Products
Steel fabrication of structural shapes (e.g.,
I-beams)
Seams for large diameter pipes, tanks, and
pressure vessels
Welded components for heavy machinery
Most steels (except high C steel)
Not good for nonferrous metals
Non-consumable Electrode
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Processes
Gas Tungsten Arc Welding
Plasma Arc Welding
Carbon Arc Welding
Stud Welding
Gas Tungsten Arc Welding
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Gas Tungsten Arc Welding
(GTAW)
An arc welding process that produces
coalescence of metals by heating them with
an arc between a tungsten (non-consumable)
electrode and the work piece. TIG welding
Shielding is obtained from an externally
supplied gas or gas mixture.
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GTAW or TIG process
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Gas Tungsten Arc Welding (GTAW)
Uses a non-consumable tungstenelectrode and an inert gas for arcshielding
Melting point of tungsten = 3410 C
(6170 F) Used with or without a filler metal
When filler metal used, it is added to weld poolfrom separate rod or wire
Applications: aluminum and stainlesssteel most common
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Advantages / Disadvantages of GTAW
Advantages:
High quality welds for suitable applications
No spatter because no filler metal through arc
Little or no post-weld cleaning because no flux
Disadvantages:
Generally slower and more costly than consumable
electrode AW processes
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Plasma Arc Welding (PAW)
Special form of GTAW in which a constricted
plasma arc is directed at weld area
Tungsten electrode is contained in a nozzle that
focuses a high velocity stream of inert gas (argon)into arc region to form a high velocity, intensely
hot plasma arc stream
Temperatures in PAW reach 28,000 C (50,000 F),due to constriction of arc, producing a plasma jet
of small diameter and very high energy density
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Figure 31.10 Plasma arc welding (PAW).
Plasma Arc Welding
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Advantages / Disadvantages of PAW
Advantages: Good arc stability
Better penetration control than other AW
High travel speeds
Excellent weld quality Can be used to weld almost any metals
Disadvantages: High equipment cost
Larger torch size than other AW
Tends to restrict access in some joints
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Other Fusion Welding Processes
FW processes that cannot be classified as arc, oroxyfuel welding
Use unique technologies to develop heat formelting
Applications are typically unique
Processes include: Electron beam welding
Laser beam welding Electroslag welding
Thermit welding
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Thermit Welding (TW)
FW process in which heat for coalescence isproduced by superheated molten metal from thechemical reaction of thermite
Thermite = mixture of Al and Fe3O4 fine powders
that produce an exothermic reaction whenignited
Also used for incendiary bombs
Filler metal obtained from liquid metal
Process used for joining, but has more incommon with casting than welding
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Figure 31.25 Thermit welding: (1) Thermit ignited; (2) crucible tapped,
superheated metal flows into mold; (3) metal solidifies to produce weld
joint.
Thermit Welding
l
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TW Applications
Joining of railroad rails
Repair of cracks in large steel castings and
forgings
Weld surface is often smooth enough that no
finishing is required
Electroslag Welding (ESW)
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Electroslag Welding (ESW)
Electroslag Welding is a welding process, in which the heat isgenerated by an electric current passing between theconsumable electrode (filler metal) and the work piecethrough a molten slag covering the weld surface.
Prior to welding the gap between the two work pieces is filledwith a welding flux
Electroslag Welding is initiated by an arc between theelectrode and the work piece (or starting plate)
Heat, generated by the arc, melts the fluxing powder and
forms molten slag. The slag, having low electric conductivity,is maintained in liquid state due to heat produced by theelectric current.
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The slag reaches a temperature of about 3500F (1930C).This temperature is sufficient for melting the consumable
electrode and work piece edges. Metal droplets fall to the
weld pool and join the work pieces.
Electroslag Welding is used mainly for steels.
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Ad t f El t l W ldi
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: Advantages of Electroslag Welding
High deposition rate - up to 45 lbs/h (20 kg/h); Unlimited thickness of work piece.
Disadvantages of Electroslag welding:
Coarse grain structure of the weld;
Low toughness of the weld;
Only vertical position is possible.
R i W ldi (RW)
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Resistance Welding (RW)
A welding processes that use a combination ofheat and pressure to accomplish coalescence
Heat generated by electrical resistance to
current flow at junction to be welded
Principal RW process is resistance spot
welding (RSW)
P i i l
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Principal
In resistance welding(RW), a low voltage(typically 1 V) andvery high current(15000 A) is passed through the joint for a
very short time (typically 0.25 sec)). This high amperage heats
the joint, due to contact resistance at the joint and melts it.
The pressure on the joint is continuously maintained and themetal fuses together under this pressure. The heat generated
in resistance welding can be expressed as
H=k* I2*R*t
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Where H= the total heat generated in the work,J
I=electric current,A
t = time for which the electric current is passing through the joint,s
R= resistance of the joint
K=a constant to account for the heat losses from the welded joint
The resistance of the joint, R is a complex factor to know because it
is composed of
a) the resistance of the electrode
b)the contact resistance between the electrode and work piecec) the contact resistance between the two work piece plates
d) the resistance of the work piece plates
Resistance Welding
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Figure 31.12 Resistance
welding, showing the
components in spot
welding, the main
process in the RW group.
Resistance Welding
Components in Resistance Spot
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p p
Welding
Parts to be welded (usually sheet metal)
Two opposing electrodes
Means of applying pressure to squeeze parts
between electrodes
Power supply from which a controlled current
can be applied for a specified time duration
Ad t / D b k f RW
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Advantages / Drawbacks of RW
Advantages: No filler metal required
High production rates possible
Lends itself to mechanization and automation
Lower operator skill level than for arc welding
Good repeatability and reliability
Disadvantages:
High initial equipment cost Limited to lap joints for most RW processes
R i t S t W ldi (RSW)
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Resistance Spot Welding (RSW)
Resistance welding process in which fusionof faying surfaces of a lap joint isachieved at one location by opposingelectrodes
Used to join sheet metal parts using aseries of spot welds
Widely used in mass production ofautomobiles, appliances, metal furniture,and other products made of sheet metal Typical car body has ~ 10,000 spot welds Annual production of automobiles in the world is
measured in tens of millions of units
Spot Welding Cycle
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Figure 31.13 (a) Spot welding cycle, (b) plot of squeezing force & current incycle (1) parts inserted between electrodes, (2) electrodes close, force
applied, (3) current on, (4) current off, (5) electrodes opened.
Spot Welding Cycle
Resistance Seam Welding (RSEW)
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Resistance Seam Welding (RSEW)
Uses rotating wheel electrodes toproduce a series of overlapping
spot welds along lap joint
Can produce air-tight joints Applications:
Gasoline tanks
Automobile mufflers
Various other sheet metal containers
Resistance Seam Welding
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Figure 31.15 Resistance seam welding (RSEW).
Resistance Seam Welding
Resistance Projection Welding (RPW)
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Resistance Projection Welding (RPW)
A resistance welding process in whichcoalescence occurs at one or more small
contact points on parts
Contact points determined by design of partsto be joined
May consist of projections, embossments, or localized
intersections of parts
Resistance Projection Welding
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Figure 31.17 Resistance projection welding (RPW): (1) start of operation, contact
between parts is at projections; (2) when current is applied, weld nuggets
similar to spot welding are formed at the projections.
Resistance Projection Welding
Solid State Welding Processes
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Solid State Welding Processes
Forge welding Cold welding
Roll welding
Hot pressure welding Diffusion welding
Explosion welding
Friction welding Ultrasonic welding
Forge Welding
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Forge Welding
Welding process in which components to be joinedare heated to hot working temperature range andthen forged together by hammering or similarmeans
Historic significance in development ofmanufacturing technology Process dates from about 1000 B.C., when blacksmiths learned
to weld two pieces of metal
Of minor commercial importance today exceptfor its variants
Friction Welding (FRW)
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Friction Welding (FRW)
SSW process in which coalescence is achieved byfrictional heat combined with pressure
When properly carried out, no melting occurs atcontact surfaces
No filler metal, flux, or shielding gases normallyused
Process yields a narrow HAZ
Can be used to join dissimilar metals
Widely used commercial process, amenable toautomation and mass production
Friction Welding
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Figure 31.28 Friction welding (FRW): (1) rotating part, no contact; (2) parts
brought into contact to generate friction heat; (3) rotation stopped and
axial pressure applied; and (4) weld created.
Friction Welding
Applications / Limitations of FRW
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Applications / Limitations of FRW
Applications: Shafts and tubular parts
Industries: automotive, aircraft, farm equipment,
petroleum and natural gasLimitations:
At least one of the parts must be rotational
Flash must usually be removed
Upsetting reduces the part lengths (which mustbe taken into consideration in product design)
Soldering
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Soldering
Soldering is a method of joining two metal work pieces bymeans of a third metal (solder) at a relatively low
temperature, which is above the melting point of the solder
but below the melting point of either of the materials being
joined. Flow of the molten solder into the gap between the work
pieces is driven by the capillary force
The solder cools down and solidifies forming a joint.
The parent materials are not fused in the process.
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Soldering is similar to Brazing. The difference is in the melting pointof the filler alloy: solders melt at temperatures below 840F
(450C); brazing filler materials melt at temperatures above this
point.
in the welding processes edges of the work pieces are either fused
(with or without a filler metal) or pressed to each other without any
filler material; soldering joins two parts without melting them but
through a soft low melting point solder.
Traditional lead containing solders consist of tin (Sn) and lead (Pb).
Brazing
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Brazing is a method of joining two metal work pieces bymeans of a filler material at a temperature above its melting
point but below the melting point of either of the materials
being joined.
Flow of the molten filler material into the gap between thework pieces is driven by the capillary force.
The filler material cools down and solidifies forming a strong
metallurgical joint, which is usually stronger than the parent
(work piece) materials. The parent materials are not fused in the process.
Brazing filler materials
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Copper filler alloys: Used for brazing Copper alloys, steels,Nickel alloys.
Aluminum filler alloys: Used for brazing Aluminum alloys.
Silver filler alloys: BAg-4 (40Ag-30Cu-28Zn-2Ni)
Used for most of metals and alloys except aluminum and
magnesium alloys.
Weldability
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Weldability
Capacity of a metal or combination of metalsto be welded into a suitably designedstructure, and for the resulting weld joint(s) topossess the required metallurgical propertiesto perform satisfactorily in intended service
Good weldability characterized by: Ease with which welding process is accomplished
Absence of weld defects Acceptable strength, ductility, and toughness in welded
joint