Chapter 3.0.1 All Welding Part 1.pdf

3.1 Metal joining processes
3.2 Classification of
Welding Processes
3.3 Forge Welding
3.4 Resistance Electric
Welding
3.5 Spot Welding
3.6 Seam Welding
3.7 Projection Welding
3.8 Butt Welding
3.9 Gas Welding
3.9.1 Oxy-acetylene Welding
3.9.2 Leftward welding
3.9.3 Rightward welding
3.9.4 Types of flames
3.9.5 Equipments
3.9.6 Electric Arc Welding
3.9.7 Arc Blow
3.9.8 A.C. and D.C. Arc Welding
3.9.9 Electrodes
3.9.10 Types of Welded Joints
3.9.11 Welding positions
3.9.12 TIG Welding
3.9.13 MIG Welding
Prepared By :- Prof. H. N. Patel (GECV Mech.)
Lecture Scheduled on 09th August 2022 [1:10 PM to 2:10 PM] &
11th August 2022 [2:10 PM to 3:10 PM]
B.E. Semester – V
Manufacturing Technology (3151912)

Recall welding processes
24 August 2022
Prepared By- Prof. H. N. Patel GECV
Mechanical
2
‘‘a localized coalescence of metals, wherein coalescence is obtained by heating to
suitable temperature, with or without the applications of pressure and with or
without the use of filler metal’’. –R. K. Rajput
➢The filler metal has a melting point approximately the same as the base metal.
➢The large bulk of materials that are welded are metals and their alloys, although
the term welding is also applied to the joining of other materials such as
thermoplastics.
➢Welding joins different metals/alloys with the help of a number of processes in
which heat is supplied either electrically or by means of a gas torch.

24 August 2022
Mechanical
3
➢ Soldering:- It is a process of joining two pieces of metal with a different fusible
metal applied in a molten state. The fusible metal is called ‘solder’.
OR
It is a process of joining two metals with low melting point metal.
➢ Brazing:- It is a process of joining two metal pieces in which a non-ferrous alloy is
introduced in the liquid state between the pieces to be joined and allowed to solidify.
➢ Soldering and brazing are two common solid/liquid-state bonding processes.
➢ These are different from welding as bonding here requires capillary action and that
some degree of alloying action between the filler and the base metal always occurs.
➢ Also the composition of filler metal is significantly different and its strength and
melting point are substantially lower than that of the base metal.
Recall Soldering and brazing :

24 August 2022
Mechanical
4
➢ — In ‘soldering’ (very similar to brazing) the filler material is usually a lead-tin based
alloy which has much lower strength and melting temperature (about 250°C).
➢ Also, less alloying action between the base and filler metals gives lower joint strength.
➢ Since in this process much lower temperatures are involved, it is usually carried out
with electric resistance heating.
➢ — In ‘brazing’ the joint is made by heating the base metal red hot and filling the gap
with molten filler metal whose melting temperature is above 427°C but below the
temperature of base metal.
➢ The filler metals, generally used for brazing are copper alloys.
➢ This process is usually carried out with a gas flame.

24 August 2022
Mechanical
5
❖ Base on the composition of the joint, the joining processes may be classified as
following :
➢ (i) Autogeneous process. In this type of joining process, no filler material is added
during the joining process as in the case of resistance welding, cold welding, friction
welding, diffusion welding and hot forge welding.
➢ (ii) Homogeneous process. This process make use of filler metal but of same
composition as the parent metal as in the case of arc, gas and thermit welding.
➢ (iii) Heterogeneous process. In this process the filler material is soluble in both the
parent metals which themselves are insoluble in each other.
Recall Joining processes:

24 August 2022
Mechanical
6
Following are the advantages and disadvantages of welding :
Advantages :
➢ 1. A large number of metals/alloys both similar and dissimilar can be joined by
welding.
➢ 2. Welding can join workpieces through spots, as continuous pressure tight seams,
end-to-end and in a number of other configurations.
➢ 3. A good weld is as strong as the base metal.
➢ 4. Welding permits considerable freedom in design.
➢ 5. General welding equipment is not very costly.
➢ 6. Portable welding equipments are available.
Recall Advantages, Disadvantages and
Applications of Welding:

24 August 2022
Mechanical
7
Advantages :
➢ 7. Welding results in a good saving of material and reduced labour content of
production.
➢ 8. Low manufacturing costs.
➢ 9. Welding is also used as a method for repairing broken, worn or defective metal
parts. Due to this, the cost of reinvestment can be avoided.

24 August 2022
Mechanical
8
Disadvantages :
➢ 1. Welding results in residual stresses and distortion of the workpieces.
➢ 2. Welding heat produces metallurgical changes. The structure of the welded joint is
not same as that of parent metal.
➢ 3. Jigs and fixtures are generally required to hold and position the parts to be welded.
➢ 4. A welded joint, for many reasons, needs stress-relief heat treatment.
➢ 5. Welding results in residual stresses and distortion of the workpieces.
➢ 6. Welding gives out harmful radiations (light), fumes and spatter.
➢ 7. For producing a good welding job, a skilled worker is a must.

24 August 2022
Mechanical
9
Applications :
➢ The welding process finds wide applications in almost all branches of industry and
construction.
➢ Extensively employed in the fabrication of :
— Structural members of bridges and buildings, etc ;
— Vessels of welded-plate construction e.g., steel reservoirs, boilers, pressure
vessel tanks and pipelines, etc.
— Concrete reinforcement.
➢ Chief means of fastening panels and members together into automobile bodies and in
aviation industry.

24 August 2022
Mechanical
10
A. The welding processes may be classified
as follows :
I. Pressure Welding :
➢ 1. Forge welding.
➢ 2. Resistance electric welding.
(i) Butt welding
(ii) Flash welding
(iii) Spot welding
(iv) Seam welding
(v) Projection welding
(vi) Percussion welding.
➢ The characteristics of a pressure weld is
that the metal joined is never brought to
a molten stage, it is heated to a welding
temperature and the actual union is
brought about by application of pressure.
Recall Classification of Welding Processes:

24 August 2022
Mechanical
11
as follows :
II. Fusion Welding :
➢ 1. Gas welding.
➢ 2. Electric arc welding.
(i) Metallic arc welding
(ii) Carbon arc welding
(iii) Atomic hydrogen welding
(iv) Shielded arc welding.
➢ 3. Thermit welding.
➢ The characteristic of a fusion weld is that
the material being joined is a actually
melted and the union is produced on
subsequent solidification.

24 August 2022
Mechanical
12
as follows :
III. Modern/Miscellaneous Welding
Techniques :
➢ (i) Tungsten inert-gas (TIG) welding or
GTAW (Gas tungsten arc welding)
➢ (ii) Metal inert-gas (MIG) welding
➢ (iii) Submerged arc welding
➢ (iv) Electro-slag and electro-gas welding
➢ (v) Electron-beam welding
➢ (vi) Ultrasonic welding
➢ (vii) Plasma arc welding
➢ (viii) Laser beam welding
➢ (ix) Friction welding
➢ (x) Explosive welding
➢ (xi) Diffusion welding
➢ (xii) Induction welding
➢ (xiii) Cold welding
➢ (xiv) Stud-arc welding
➢ (xv) Hydrodynamic welding.
Allied Processes :
➢ 1. Soldering
➢ 2. Brazing

24 August 2022
Mechanical
13
B. The welding processes may also be
classified as follows :
1. Solid-state welding processes :
(i) Forge welding
(ii) Friction welding
(iii) Explosive welding
(iv) Ultrasonic
(v) Diffusion.
2. Liquid-state (or fusion) welding
processes :
(i) Gas welding
(ii) Electric arc welding
(iii) TIG welding
(iv) Resistance welding
(v) Thermit welding, etc.
3. Solid/liquid-state bonding processes :
(i) Soldering
(ii) Brazing.
Note : For ISO 4063 classification of welding
processes

24 August 2022
Mechanical
14

24 August 2022
Mechanical
15
➢ In this method of welding the surfaces to be joined are heated in an open hearth until
they reach the welding temperature of metal, which is below its melting point.
➢ The blacksmith will judge this temperature by the colour of the metal, which may be
between red-hot and white-hot.
➢ The parts are then placed on an anvil and hammered together.
➢ In this welding process there is a risk of oxide and other inclusion when the metal is
heated in an open fire and accurate judgement of the temperature is called for if the
structure of metal is not to be changed.
➢ Modern alloy steels can be ruined by injudicious heating.
Recall Forge Welding:

24 August 2022
Mechanical
16
➢ When the wide range of light alloys is considered, it becomes imperative to use a
more scientific method.
➢ However, this process is still widely used for heavier classes of work, such as
manufacture of anchor chains, while controlled heating furnaces and automatic
forging machines have been designed to replace the open-forge fire and the
blacksmith’s anvil.
A modern version of welding in this category is manufacture of butt-welded
pipes. In this process, the skulp heated up to the required welding temperature is pulled
through a die which forces the two edges of a heated skulp to come into contact under
pressure and get welded.

24 August 2022
Mechanical
17
Advantages :
➢ 1. Inexpensive equipment.
➢ 2. Semi-skilled operation.
Limitations :
➢ 1. Poor joint strength
➢ 2. Labour intensive process (low production rate).
➢ 3. Weld quality dependent on operator’s skill.
➢ 4. Can be used only when hammering is possible.

24 August 2022
Mechanical
18
Advantages :
➢ 1. Inexpensive equipment.
➢ 2. Semi-skilled operation.
Limitations :
➢ 1. Poor joint strength
➢ 2. Labour intensive process (low production rate).
➢ 3. Weld quality dependent on operator’s skill.
➢ 4. Can be used only when hammering is possible.

24 August 2022
Mechanical
19
GENERAL ASPECTS:
➢ It is the method of uniting two pieces of metal by the passage of a heavy electric
current while the surfaces are pressed together.
➢ The fusing temperature is obtained by placing the surfaces to be joined in contact
with one another, and passing a current of two to eight volts, at a high amperage
through them.
➢ The heat is developed around the point to which they touch, forcing them together (by
pressure mechanically applied), and at the same time switching off the current,
completes the weld.
➢ A special feature of resistance welding is the rapid heating of the surface being
welded (in hundredths of a second) due to application of currents of high amperage.
Recall Resistance Electric Welding:

24 August 2022
Mechanical
20
General Aspects:
➢ Successful operation of a resistance welding process depends upon correct
application and proper control of the following factors :
(i) Welding current.
(ii) Welding pressure.
(iii) Time of application (cycle time) :
— Weld time
— Squeeze or forge time
— Hold time
— Off-time
(iv) Contact area of electrodes.

24 August 2022
Mechanical
21
Electrodes:
The electrodes in resistance welding should have higher electrical conductivity as well
as higher hardness.
➢ Steel though strong, do not have conductivity required for electrodes. Hence, copper
in alloyed form is generally used for making electrodes (Pure copper is poor in
mechanical properties).
➢ Copper cadmium (0.5 to 1.0%) alloys have the highest electrical conductivity with
moderate strengths and are used for welding non-ferrous materials such as
aluminium and magnesium alloys.
➢ Copper chromium (0.5 to 0.8%) alloys have slightly lower electrical conductivities
than the above but better mechanical strength. These are used for resistance welding
of low strength steels such as wild steel and low alloy steels.

24 August 2022
Mechanical
22
Advantages and disadvantages/Limitations of resistance welding process :
Advantages :
➢ 1. The heat is localised, action is rapid and no filler metal is needed.
➢ 2. The operation requires little skill and can be easily mechanised and automated.
➢ 3. A high degree of reliability and reproducibility can be achieved.
➢ 4. Very well suited for mass production (owing to high production rate).
➢ 5. Very economical process.
➢ 6. It is possible to weld dissimilar metals as well as metal plates of different
thicknesses.
➢ 7. Heating of workpiece is confined to a very small part which results in less
distortion.

24 August 2022
Mechanical
23
Advantages and disadvantages/Limitations of resistance welding process :
Disadvantages/Limitations :
➢ 1. High cost of equipment.
➢ 2. Certain resistance welding processes are limited only to lap joints.
The various resistance welding processes are :
➢ Resistance spot welding.
➢ Resistance seam welding.
➢ Resistance projection welding.
➢ Resistance butt welding :
(i) Upset welding
(ii) Flash butt welding
Lap joints used
Butt joints used

24 August 2022
Mechanical
24
RESISTANCE SPOT WELDING:
➢ Spot welding is the simplest and most commonly used resistance-welding process.
➢ Refer to Fig. 1. Spot welding, as the name implies, is carried out by overlapping the
edges of two sheets of metal and fusing them together between copper electrode tips
at suitably spaced intervals by means of a heavy electrical current.
➢ The resistance offered to current as it passes through the metal raises the
temperature of the metal between the electrodes to welding heat.
➢ The current is cut-off and mechanical pressure is then applied by the electrodes to
forge the welds.
➢ Finally the electrodes open.

24 August 2022
Mechanical
25

24 August 2022
Mechanical
26
➢ When sheets of unequal thickness are joined, the current and pressure setting for the
thinner sheets are used.
➢ Similarly four thickness may be welded, using the same settings as for two thickness.
➢ Currents usually range from 3000 A to 40,000 A, depending on the materials being
welded and their thickness. Modern equipment for spot welding is computer
controlled for optimum timing of current and pressure, and the spot-welding guns
are manipulated by programmable robots.
➢ Steel, brass, copper and light alloys can be joined by this method, which forms a cheap
and satisfactory substitute for riveting. The area of fusion at each spot weld, in fact, is
approximately equal to the cross-sectional area of the rivet which would be employed
for a similar gauge of material.

24 August 2022
Mechanical
27
Applications :
➢ Spot welding is widely used for fabricating sheet-metal products. Examples of its
applications
➢ range from attaching handles to stainless-steel cookware to rapid spot welding of
automobile bodies, using multiple electrodes.
Advantages :
➢ 1. High production rate.
➢ 2. Very economical process.
➢ 3. High skill not required.
➢ 4. Most suitable for welding sheet metals.
➢ 5. Dissimilar metals can be welded.

24 August 2022
Mechanical
28
➢ 6. No edge preparation is needed.
➢ 7. Operation may be made automatic or semi-automatic.
➢ 8. Dependability.
➢ 9. Small heat affected area.
➢ 10. More general elimination of warping or distortion of parts.

24 August 2022
Mechanical
29
Limitations :
➢ 1. Suitable for thin sheets only.
➢ 2. High equipment cost.
Spot welding machines :
The following three types of spot welding machines are in common use :
➢ 1. Standard machines.
— Rocker arm type
— Press type spot or projection welders
➢ 2. Special multiple-electrode machines.
➢ 3. Portable welders.

24 August 2022
Mechanical
30
RESISTANCE SEAM WELDING:
➢ Refer to Fig. 2. Seam welding is analogous to spot welding with the difference the
electrodes are in the form of rollers ; and the work moves in direction perpendicular
to roller axis.
➢ The current is interrupted 300 to 1500 times a minute to give a series of overlapping
spot welds.
➢ The welding is usually done under water to keep the heating of the welding rollers
and the work to a minimum, and thus to give lower roller maintenance and less
distortion of the work.
➢ Welding currents range from 2000 A to 5000 A while the force applied to the rollers
may be as high as 5 kN to 6 kN.
➢ The typical welding speed is 1.5 m/min for thin sheet.
➢ With intermittent application of current to the rollers a series of spot welds at
various intervals can be made along the length of the seam, a procedure called roll
spot welding.

24 August 2022
Mechanical
31
RESISTANCE SEAM WELDING:
Applications :
➢ It is employed on many types of pressure (light or leak proof) tanks, for oil switches,
transformers,
➢ refrigerators, evaporators and condensers, aircraft tanks, paint and varnish
containers, etc.

24 August 2022
Mechanical
32
RESISTANCE PROJECTION WELDING:
Refer to Fig. 3. It is in effect, a form of multi-spot welding in which a number of welds are
made simultaneously.
➢ The pieces to be welded are arranged between two flat electrodes which exert
pressure as the current flows.
➢ The projections, and the areas with which they make contact, are raised to welding
heat and are joined by the pressure exerted by the electrodes.
➢ The projections are flattened during the welding.

24 August 2022
Mechanical
33

24 August 2022
Mechanical
34
Applications :
➢ The process is used chiefly to join pressings together since it is relatively simple to
make the press-tools so that the projections are produced during the main forming
operation in the press.
➢ The materials like brass and aluminium cannot be projection welded satisfactorily.
➢ The same principle is used in the cross welding of a number of wires or rods to make
a mesh.

24 August 2022
Mechanical
35
RESISTANCE BUTT WELDING:
There are two types of butt welding : Upset and Flash
Upset welding:
➢ Refer to Fig.4. In this type of welding which is employed to join bars and plates
together end-to-end, one bar is held in a fixed clamp in the butt welding machine ;
and the other bar in a movable clamp, the clamp being electrically insulated, the one
from the other, and being connected to a source of current.
➢ When the two ends to be joined are brought into contact and current is switched on,
the resistance at the joint causes the ends to heat up to welding temperature.
➢ Current is then switched off and the movable clamp forced up, so that pressure
applied upsets or forges the parts together.

24 August 2022
Mechanical
36
Upset welding:
➢ The voltage applied across the clamps is a low one, from 2 to 6 volts, and the current
is usually alternating.
➢ If the bars being joined are different in cross-section the amounts they project from
their clamps may have to be adjusted so as to modify the heat losses and ensure both
bars being brought to the welding temperature simultaneously.
Applications :
➢ Upset welding is used principally on non-ferrous materials for welding bars, rods,
wire.
➢ This process is being used for welding such things as steel rails whose cross-sectional
area is as much as 6.25 cm2.

24 August 2022
Mechanical
37
Upset welding:

24 August 2022
Mechanical
38
Flash welding:
➢ Refer to Fig.5. In this process, the parts to welded are clamped to the electrode
fixtures, as in butt welding but the voltage is applied before the parts are butted
together.
➢ As the parts touch each other, an arc is established which continues as long as the
parts advance at the correct speed.
➢ This arc bursts away a portion of the material from each piece.
➢ When the welding temperature is reached, the speed of travel is increased, the power
switched off and weld is upset.

24 August 2022
Mechanical
39
Flash welding:
▪ The upsetting action forces out the impurities caused by flashing. The forced-out
metal is called flash. The inner weld is then sound and free of oxides and cast metal.
▪ Many different materials and combination can be flash butt welded ; steels and the
ferrous alloys other than cast iron are probably the most easily welded. Those
materials which cannot be flash butt welded are lead, tin, zinc, antimony, bismuth
and their alloys, and the copper alloys in which these metals are present in large
percentage.

24 August 2022
Mechanical
40
Flash welding:
Flash welding claims the following advantages over upset method of welding :
(i) Power consumed is less once the arc creates more heat with a given current.
(ii) The weld is made in clean virgin metals as the surfaces are burned away.
(iii) More quicker.

24 August 2022
Mechanical
41
Flash welding:

24 August 2022
Mechanical
42
Flash welding:
Applications :
➢ It is widely used in automobile construction on the body, axles, wheels, frames and
other parts.
➢ It is also employed in welding motor frames, transformer tanks and many types of
sheet steel containers such as at barrels and floats.

24 August 2022
Mechanical
43
Percussion welding :
➢ It is a very fast method of welding.
➢ It consists of holding the parts at a small distance with their end faces opposite to
each other, bringing them closer at a fast speed after switching on the current, thus
creating an arc between their end faces just before they come in contact and
completing the weld under impact.
➢ Some of the metal may squeeze out of the joint, but it is very small.
➢ The use of this process is limited to very thin wires, with their diameters ranging
between 0.05 mm and 0.38 mm.
➢ It can also be used for joining wire of dissimilar metals, such as copper to nichrome
and copper to stainless steel.

24 August 2022
Mechanical
44
FUSION WELDING:
General Aspects:
➢ In fusion (or liquid state) welding the material around the joint is melted in both the
parts to be joined.
➢ If necessary a molten filler metal is added from a filler rod (or otherwise).
➢ The important zones in fusion welding are :
(i) Fusion zone ;
(ii) Heat affected unmelted zone around the fusion zone.
(iii) The unaffected original part.
➢ The characteristics of a fusion weld is that the metal being joined is actually melted
and the union is produced on subsequent solidification.
3.9 Gas Welding:

24 August 2022
Mechanical
45
FUSION WELDING:
General Aspects:
Factors affecting fusion welding process :
(i) Nature of weld pool.
(ii) Chemical reaction in the fusion zone.
(iii) Characteristics of heat source.
(iv) Contraction, residual stresses and metallurgical changes.
(v) Heat flow from the joint.
The fusion welding group includes :
1. Gas welding ;
2. Electric arc welding ;
3. Thermit welding.
3.9 Gas Welding:

24 August 2022
Mechanical
46
FUSION WELDING:
General Aspects:
Gas welding :
➢ It is a method of fusion welding in which a flame produced by a combustion of gases is
employed to heat and melt the parent metal and filler rod of a joint. It can weld most
common materials.
3.9 Gas Welding:

24 August 2022
Mechanical
47
FUSION WELDING:
General Aspects: Gas welding
Advantages and Disadvantages of Gas Welding :
Advantages :
➢ 1. The oxy-acetylene torch is versatile. It can be used for brazing, bronze welding,
soldering, heating, heat treatment, metal cutting, metal cleaning, etc.
➢ 2. It is portable and can be moved almost everywhere for repair of fabrication work.
➢ 3. The oxy-acetylene flame is easily controlled and not as piercing as metallic arc
welding, hence, extensively used for sheet metal fabrication work.
➢ 4. Welder has considerable control over the temperature of the metal in the weld
zone. When the rate of heat input from the flame is properly coordinated with the
speed of welding, the size, viscosity and surface tension of the weld puddle can be
controlled, permitting the pressure of the flame to be used to aid in positioning and
shaping the weld.
3.9 Gas Welding:

24 August 2022
Mechanical
48
FUSION WELDING:
Advantages :
➢ 5. The cost and maintenance of the gas welding equipment is low when compared to
that of some other welding processes.
➢ 6. The rate of heating and cooling is relatively low. In some cases, this is an
advantage.
➢ 7. Good weld quality.
3.9 Gas Welding:

24 August 2022
Mechanical
49
FUSION WELDING:
Disadvantages :
➢ 1. As compared to arc welding, it takes considerably longer time for the metal to heat
up.
➢ 2. Owing to prolonged heating harmful thermal effects are aggravated which results
in a larger heat affected area, increased grain growth, distortion and less of
corrosion resistance.
➢ 3. Oxygen and acetylene gases are expensive.
➢ 4. Flux applications and the shielding provided by the oxy-acetylene flame are not so
positive as those supplied by the inert gas in TIG, MIG or CO2 welding.
3.9 Gas Welding:

24 August 2022
Mechanical
50
FUSION WELDING:
Disadvantages :
➢ 5. The handling and storing of gas necessitate lot of safety precautions.
➢ 6. Heavy sections cannot be joined economically.
➢ 7. Flame temperature is less than the temperature of the arc.
➢ 8. Skilled operator required.
➢ 9. Difficult to prevent contamination.
➢ 10. Large heat affected zone
3.9 Gas Welding:

24 August 2022
Mechanical
51
FUSION WELDING:
Applications of Gas Welding:
➢ 1. To join most ferrous and non-ferrous metals, e.g., carbon steels, alloy steels, cast
iron, aluminium, copper, nickel, magnesium and its alloys, etc.
➢ 2. To join thin materials.
➢ 3. To join materials in whose case excessively high temperatures would cause certain
elements in the metal to escape into the atmosphere.
➢ 4. To join materials in whose case excessively high temperatures or rapid heating and
cooling of the job would produce unwanted or harmful changes in the metal.
➢ 5. Automative and Aircraft industries.
➢ 6. Sheet metal fabricating plants, etc.
3.9 Gas Welding:

24 August 2022
Mechanical
52
FUSION WELDING:
Oxy-acetylene Welding:
➢ The oxy-acetylene welding process can be used for welding almost all metals and
alloys used in engineering practice.
➢ The advantage of using acetylene, instead of other fuels, with oxygen is that it
produces a comparatively higher temperature and also an inert gas envelop,
consisting of CO2 and water vapours, which presents the molten metal from oxidation.
➢ Refer to Fig.6. The principle of oxy-acetylene welding is the ignition of oxygen and
acetylene gases, mixed in a blow pipe fitted with a nozzle of suitable diameter ; this
flame is applied to the edges of the joint and to a wire filler of the appropriate metal,
which is thereby melted and run into the joint.
3.9 Gas Welding:

24 August 2022
Mechanical
53
FUSION WELDING:
➢When the acetylene is burned in an atmosphere of oxygen an intensely hot flame with
a temperature of about 3300°C is produced.
➢As the melting point of steel is approximately 1300°C, the metal is fused very rapidly
at the point at which the flame is applied.
There are two systems of oxygen acetylene welding :
➢(i) High pressure system:- In this method both oxygen and acetylene are derived for
use from high pressure cylinders.
➢(ii) Low pressure system:- In this system oxygen is taken as usual form a high pressure
cylinder but acetylene is generated, by action of water on carbide (usually calcium
carbide), in a low pressure acetylene generator.
3.9 Gas Welding:

24 August 2022
Mechanical
54
FUSION WELDING:
➢ The use of an oxy-acetylene flame is the most widely employed method of welding
iron, steel, aluminium, cast-iron and copper, the equipment required (Fig.6.) being
considerably cheaper and simpler than that needed for electric welding.
➢ For a certain class of mass production work, however, electric welding will always
prove superior both in quickness and cheapness.
There are two methods of welding by means of the oxy-acetylene blow pipe :
➢ (i) Leftward or forward welding.
➢ (ii) Rightward or backward or backhand welding.
3.9 Gas Welding:

24 August 2022
Mechanical
55
FUSION WELDING:
3.9 Gas Welding:

24 August 2022
Mechanical
56
FUSION WELDING:
(i) Leftward (or forward or forehand) welding :
➢In leftward welding after suitable preparation of the joint the weld is commenced at
the right-hand side of the joint and blow pipe is given a steady forward movement, with
a slight sideways motion, zigzagging along the weld towards the left as shown in Fig.7.
➢The blow pipe is kept at an angle of 60° to 70° to the surface of the work so that the
flame plays ahead of it, and the filler rod held at an angle of 30° to 40°, is held just
ahead of the flame and progressively fed into it.
3.9 Gas Welding:

24 August 2022
Mechanical
57
FUSION WELDING:
(i) Leftward (or forward or forehand) welding :
▪ Vertical joints are welded by this technique. (This technique is restricted to welding of
mild steel plates upto 5 mm thick, cast iron and non-ferrous metals.)
3.9 Gas Welding:

24 August 2022
Mechanical
58
FUSION WELDING:
(ii) Rightward (or backward or backhand) welding :
➢ In this welding technique the flame is directed towards the completed part of the joint
and welding proceeds from left to right as shown in Fig.8. The filler rod is given a
circular movement as it is fed into the flame.
▪ Horizontal and overhead welding are usually done by the backhand technique. (The
technique is used for thicker materials, chiefly steel.)
3.9 Gas Welding:

24 August 2022
Mechanical
59
FUSION WELDING:
Advantages :
➢ (i) Rightward welding is faster by 20 to 25% from and 15 to 25% less acetylene is
needed in comparison to leftward welding.
➢ (ii) The mechanical properties of the weld are better due to the annealing effect of the
flame which is directed on the completed weld.
➢ (iii) The amount of distortion in the work is minimum.
3.9 Gas Welding:

24 August 2022
Mechanical
60
FUSION WELDING:
Note :- The angle at which the torch is inclined to the surface being welded depends
upon the thickness of the metal. Thicker metals require a higher concentration of heat
and cousequently a larger torch angle.
3.9 Gas Welding:

24 August 2022
Mechanical
61
FUSION WELDING:
Types of flames :
Following are the three types of flames of oxygen and acetylene mixture :
➢ 1. Neutral flame
➢ 2. Carburising flame
➢ 3. Oxidising flame.
3.9 Gas Welding:

24 August 2022
Mechanical
62
FUSION WELDING:
Types of flames : 1. Neutral flame
➢When the ratio of oxygen and acetylene is equal, a neutral flame is obtained.
➢This type of flame has a temperature of about 3250°C, is white in colour and has a
sharply defined central cone with a reddish purple envelope.
➢It does not react chemically with the parent metal and protects it (the metal) from
oxidation.
➢The neutral flame is used to weld carbon steels, cast iron, copper, aluminium, etc.
3.9 Gas Welding:

24 August 2022
Mechanical
63
FUSION WELDING:
Types of flames : 1. Neutral flame
3.9 Gas Welding:
Neutral flame (3250°C)

24 August 2022
Mechanical
64
FUSION WELDING:
Types of flames : 2. Carburising flame
➢The ratio of oxygen to acetylene is 0.9 to 1. It consists of the following three zones :
▪ — Luminous zone,
▪ — Feather or intermediate cone of white colour, and
▪ — Outer envelope.
➢It is also called as reducing flame and has a temperature of 3150°C.
3.9 Gas Welding:

24 August 2022
Mechanical
65
FUSION WELDING:
➢ The carburising flame is used for the following purposes :
▪ — To join those materials which are readily oxidised. Thus, it is used to weld
aluminium since it prevents the formation of aluminium oxide at the time of
welding.
▪ — To weld monel metal, high carbon steel and alloy steel.
▪ — To give a hard facing material in some cases.
3.9 Gas Welding:

24 August 2022
Mechanical
66
FUSION WELDING:
➢ The carburising flame is used for the following purposes :
▪ — To join those materials which are readily oxidised. Thus, it is used to weld
aluminium since it prevents the formation of aluminium oxide at the time of
welding.
▪ — To weld monel metal, high carbon steel and alloy steel.
▪ — To give a hard facing material in some cases.
3.9 Gas Welding:

24 August 2022
Mechanical
67
FUSION WELDING:
3.9 Gas Welding:
Carburising flame (3150°C) (Excess acetylene)

24 August 2022
Mechanical
68
FUSION WELDING:
Types of flames : 3. Oxidising flame.
➢ The ratio of oxygen to acetylene varies from about 1.2 to 1.5.
➢ It is used in the following cases :
▪ — To weld copper, brass and bronze and zincbearing alloys.
▪ — For gas cutting.
3.9 Gas Welding:
Oxidising flame (3480°C) (Excess oxygen)

24 August 2022
Mechanical
69
FUSION WELDING:
Other fuel gases:
➢ It may be noted that although, in gas welding, oxygen and acetylene mixture is
popular, other fuel gases like propane, hydrogen and coal gas may also be used, along
oxygen to produce gas flames for welding.
❖ Methyl acetylene propadiene (MAPP) gas is replacing acetylene gas particularly
when portability is important, because :
▪ (i) It is more dense, thus providing more energy for a given volume.
▪ (ii) It can be stored safely in ordinary pressure tanks.
3.9 Gas Welding:

24 August 2022
Mechanical
70
FUSION WELDING:
Other fuel gases: Qualities of welding flame :
The welding flame should possess the following qualities :
➢ (i) Must not burn the metal (oxidise it).
➢ (ii) High temperature to melt the metals.
➢ (iii) Products of combination should not be toxic.
➢ (iv) Very intense concentrated flame so that a spot under the flame becomes molten
and forms a liquid puddle.
➢ (v) Must not add dirt or foreign material to the metal.
3.9 Gas Welding:

24 August 2022
Mechanical
71
FUSION WELDING:
Equipments :
➢ 1. Gas cylinders.
➢ 2. Pressure regulators.
➢ 3. Pressure gauges.
➢ 4. Welding torch.
➢ 5. Hoses and hose fittings.
➢ 6. Safety devices, etc.
3.9 Gas Welding:

24 August 2022
Mechanical
72
FUSION WELDING:
Equipments :
1. Gas cylinders : A. Oxygen cylinder :
➢ — For safety purposes oxygen cylinders are filled at a pressure 12500 to 14000
kN/m2 and cylinder capacity is 6.23 m3.
➢ — The cylinder is provided with a right hand thread valve and is painted black.
➢ — The cylinders are usually provided with fragile disc and fusible plug to relieve the
cylinder of its contents if subjected to overheating or excessive pressure.
3.9 Gas Welding:

24 August 2022
Mechanical
73
FUSION WELDING:
Equipments :
1. Gas cylinders: B. Acetylene cylinder :
➢ — The cylinder is usually filled to pressure of 1600 to 2100 kN/m2.
➢ — The cylinder is provided with left hand threads for accommodating pressure
regulator and is painted maroon.
➢ — Acetylene gas above one atmospheric pressure is highly explosive. Hence, acetylene
is stored with calcium silicate saturated with acetone. Acetone can absorb 25 times
its own volume of acetylene for each atmosphere pressure.
3.9 Gas Welding:

24 August 2022
Mechanical
74
FUSION WELDING:
Equipments :
2. Pressure regulators.
➢ The cylinders are provided with pressure regulators to control the working pressure
of oxygen and acetylene to the welding torch.
➢ The pressure of oxygen and acetylene depends on the thickness of the metal to be
welded/cut.
3.9 Gas Welding:

24 August 2022
Mechanical
75
FUSION WELDING:
Equipments :
3. Pressure gauges.
➢ Two pressure gauges are fitted on each pressure regulator. While one pressure gauge
shows the pressure inside the cylinder, the other one shows the working pressure of
the fuel gas and oxygen.
3.9 Gas Welding:

24 August 2022
Mechanical
76
FUSION WELDING:
Equipments :
4. Welding torch.
➢ It is a device ; for moving oxygen and acetylene in the required volume and igniting it
at the mouth of its tip. Generally, following two types of torches are available :
3.9 Gas Welding:
1. Low pressure blow pipe
(Injector type)
2. High pressure blow pipe

24 August 2022
Mechanical
77
FUSION WELDING:
Equipments :
5. Hoses and hose fittings.
➢ Hoses are the rubber and fabric pipes used to connect gas cylinder to blow pipe and
are painted black or green for oxygen and red or maroon for acetylene.
➢ It should be strong, durable, non-porous and light.
➢ Special fittings are used for connecting hoses to equipment.
3.9 Gas Welding:

24 August 2022
Mechanical
78
FUSION WELDING:
Equipments :
6. Safety devices.
➢ Goggles fitted with coloured glasses should be used to protect the eyes from harmful
heat ultraviolet rays.
➢ Gloves made of leather, canvas and asbestos should be worn to protect hands from
any injury. Gloves should be light so that the manipulation of the torch may be done
easily.
➢ Other requirements include spark-lighter, apron, trolley, wire brush, spindle key,
spanner set, filler rods and fluxes and welding tips.
3.9 Gas Welding:

24 August 2022
Mechanical
79
3.9 Gas Welding:

24 August 2022
Prepared By- Prof. H. N. Patel
GECV Mechanical
80
FUSION WELDING:
General Aspects: Electric Arc Welding
Arc welding is the system in which the metal is melted by the heat of an electric arc. It
can be done with the following methods :
➢ (i) Metallic arc welding.
➢ (ii) Carbon arc welding.
➢ (iii) Atomic hydrogen welding.
➢ (iv) Shielded arc welding.
3.9 Gas Welding:
Advantages :
➢ 1. Portable and relatively inexpensive
equipment.
➢ 2. Very versatile process.
Limitations :
➢ 1. Large heat affected zone.
➢ 2. Weld quality depends upon operator’s skill in
normal operations.
➢ 3. Not suitable for thin sections.

24 August 2022
Prepared By- Prf. H. N. Patel
GECV Mechanical
81
FUSION WELDING:
General Aspects: Electric Arc Welding:
(i) Metallic Arc Welding
➢ Refer to Fig. 7.14. In metallic arc welding an arc is established between work and the
filler metal electrode.
➢ The intense heat of the arc forms a molten pool in the metal being welded, and at the
same time melts the tip of the electrode.
➢ As the arc is maintained, molten filler metal from the electrode tip is transferred
across the arc, where it fuses with the molten base metal.
➢ Arc may be formed with direct or alternating current.
➢ Petrol or diesel driven generators are widely used for welding in open, where a
normal electricity supply may not be available.
➢ D.C. may also be obtained from electricity mains through the instrumentality of a
transformer and rectifier.
3.9 Gas Welding:

24 August 2022
GECV Mechanical
82
FUSION WELDING:
3.9 Gas Welding:

24 August 2022
GECV Mechanical
83
FUSION WELDING:
➢ A simple transformer is, however widely employed for A.C. arc welding.
➢ The transformer sets are cheaper and simple having no maintenance cost as there
are no moving parts.
▪ With Arc system, the covered or coated electrodes are used, whereas with D.C. system
for cast iron and non-ferrous metals, bare electrodes can be used.
▪ In order to strike the arc an open circuit voltage of between 60 to 70 volts is required.
For maintaining the short arc 17 to 25 volts are necessary ; the current required for
welding, however, varies from 10 amp. to 500 amp. depending upon the class of work
to be welded.
3.9 Gas Welding:

24 August 2022
GECV Mechanical
84
FUSION WELDING:
▪ The great disadvantage entailed by D.C. welding is the presence of arc blow
(distortion of arc stream from the intended path owing to magnetic forces of a non-
uniform magnetic field). With A.C. arc blow is considerably reduced and use of higher
currents and large electrodes may be restored to enhance the rate of weld
production.
Applications :
➢ The field of application of metallic arc welding includes mainly low carbon steel and
the high-alloy austenitic stainless steel.
➢ Other steels like low and medium-alloy steels can however be welded by this system
but many precautions need be taken to produce ductile joints.
3.9 Gas Welding:

24 August 2022
GECV Mechanical
85
FUSION WELDING:
➢ Refer to Fig. 7.15. Here the work is connected to negative and the carbon rod or
electrode connected to the positive of the electric circuit.
➢ Arc is formed in the gap, filling metal is supplied by fusing a rod or wire into the arc
by allowing the current to jump over it and it produces a porous and brittle weld
because of inclusion of carbon particles in the molten metal.
➢ It is therefore used for filling blow holes in the castings which are not subjected to
any of the stresses.
▪ The voltage required for striking an arc with carbon electrodes is about 30 volts
(A.C.) and 40 volts (D.C.).
3.9 Gas Welding:

24 August 2022
GECV Mechanical
86
FUSION WELDING:
▪ A disadvantage of carbon arc welding is that approximately twice the current is
required to raise the work to welding temperature as compared with a metal
electrode, while a carbon electrode can only be used economically on D.C. supply.arc
welding.
3.9 Gas Welding:

24 August 2022
GECV Mechanical
87
FUSION WELDING:
➢ Refer to Fig. 7.16. In this system heat is obtained from an alternating current arc
drawn between two tungsten electrodes in an atmosphere of hydrogen.
➢ As the hydrogen gas passes through the arc, the hydrogen molecules are broken up
into atoms and they recombine on contact with the cooler base metal generating
intense heat sufficient to melt the surfaces to be welded, together with the filler rod, if
used.
➢ The envelop of hydrogen gas also shields the molten metal from oxygen and nitrogen
and thus prevents weld metal from deterioration.
▪ The welds obtained are homogeneous and smooth in appearance because the
hydrogen keeps the molten pool.
3.9 Gas Welding:

24 August 2022
GECV Mechanical
88
FUSION WELDING:
3.9 Gas Welding:

24 August 2022
GECV Mechanical
89
FUSION WELDING:
Advantages :
➢ 1. No flux or separate shielding gas is used ; hydrogen itself acts as a shielding gas
and avoids weld metal oxidation.
➢ 2. Due to high concentration of heat, welding can be carried out at fast rates
(specially when filler metal is not needed) and with less distortion of the workpiece.
➢ 3. Welding of thin materials is also possible which otherwise may not be successfully
carried out by metallic arc welding.
➢ 4. The job does not form a part of the electrical circuit. The arc remains between two
tungsten electrodes and can be moved to other places easily without getting
extinguished.
3.9 Gas Welding:

24 August 2022
GECV Mechanical
90
FUSION WELDING:
Limitations :
➢ 1. For certain applications, the process becomes uneconomical because of higher
operating cost as compared to that of other welding processes.
➢ 2. The process cannot be used for depositing large quantities of metals.
➢ 3. Welding speed is less as compared to that of metallic arc or MIG welding.
Applications :
➢ Atomic hydrogen welding being expensive is used mainly for high grade work on
stainless steel and most non-ferrous metals.
3.9 Gas Welding:

24 August 2022
GECV Mechanical
91
FUSION WELDING:
(iv) Shielded arc welding
➢ In this system molten weld metal is protected from the action of atmosphere by an
envelope of chemically reducing or inert gas.
➢ As molten steel has an affinity for oxygen and nitrogen, it will, if exposed to the
atmosphere, enter into combination with these gases forming oxides and nitrides.
➢ Due to this injurious chemical combination metal becomes weak, brittle and
corrosion resistant.
➢ Thus, several methods of shielding have been developed.
➢ The simplest (Fig. 7.17) is the use of a flux coating on the electrode which in addition
to producing a slag which floats on the top of the molten metal and protects it from
atmosphere, has organic constituents which turn away and produce an envelope of
inert gas around the arc and the weld.
3.9 Gas Welding:

24 August 2022
GECV Mechanical
92
FUSION WELDING:
(iv) Shielded arc welding
▪ Welds made with a completely shielded arc are more superior to those deposited by
an ordinary arc.
3.9 Gas Welding:

24 August 2022
GECV Mechanical
93
FUSION WELDING:
Arc Blow
▪ Arc blow is the phenomenon of wandering of arc and it occurs in D.C. welding.
▪ When a current flows in any conductor, a magnetic field is formed around the
conductor at right angles to the current.
➢ Since in the case of D.C. arc welding, there is current through the electrode, workpiece
and ground clamp, magnetic field exists around each of these components.
➢ The arc thus lacks control as though it were being blown to and by the influence of
these complex magnetic fields.
➢ This is more common in welding with very high or very low currents, and especially in
welding in corners or other confined spaces.
➢ Usually arc blow results from the interaction of magnetic fields of the electrode
workpiece with that of the arc.
3.9 Gas Welding:

24 August 2022
GECV Mechanical
94
FUSION WELDING:
Arc Blow
➢ The movement of arc blow causes atmospheric gases to be pulled into the arc,
resulting in porosity or other defects.
▪ The severity of arc blow problem can be reduced by taking the following corrective
measures :
❖ 1. Change to A.C. welding, if possible (since due to change in the polarity, the effect of magnetic field is
nullified).
❖ 2. Reduce the current used so that the strength of magnetic field is reduced.
❖ 3. Use a short arc length so that filler metal would not be deflected but carried easily to the arc crater.
❖ 4. Place more than one ground lead from the base metal (preferably on each from the ends of the base
metal plate).
❖ 5. The ground cable may be wrapped around the workpieces such that the current flowing in it sets up
a magnetic field in a direction which will counteract the arc blow.
3.9 Gas Welding:

24 August 2022
GECV Mechanical
95
FUSION WELDING:
General Aspects: Electric Arc Welding (Comparison between A.C. and D.C. Arc Welding)
3.9 Gas Welding:

24 August 2022
GECV Mechanical
96
FUSION WELDING:
General Aspects: Electric Arc Welding
▪ A.C. transformer :
➢ Step down, oil cooled = 3 phase, 50 Hz
➢ Current range = 50 to 400 A
➢ Open circuit voltage = 50 to 90 V
➢ Energy consumption = 4 kWh per kg of
metal deposit
➢ Power factor = 0.4
➢ Efficiency = 85%
▪ D.C. generator :
➢ Motor generator—3 phase, 50 Hz
➢ Current range = 125 to 600 A
➢ Open circuit voltage = 30 to 80 V
➢ Arc voltage = 20 to 40 V
➢ Energy consumption = 6 to 10 kWh/kg of
deposit
➢ Power factor = 0.4
➢ Efficiency = 60%
3.9 Gas Welding:
Specifications of A.C. Transformer/D.C. generator :

24 August 2022
GECV Mechanical
97
FUSION WELDING:
General Aspects: Electric Arc Welding: Electrodes
▪ 1. Consumable electrode :
➢ (i) Base electrode
➢ (ii) Flux coated electrode.
▪ 2. Non-consumable electrode :
3.9 Gas Welding:

24 August 2022
GECV Mechanical
98
FUSION WELDING:
1. Consumable electrode :
▪ (i) Bare electrode :
➢ These electrodes do not prevent oxidation of the weld and hence the joint is weak.
➢ They are used for minor repairs where strength of the joint is weak.
➢ Employed in automatic and semi-automatic welding.
• (ii) Flux-coated electrode :
➢ The flux is provided to serve the following purposes :
o — To prevent oxidation of the weld bead by creating a gaseous shield around the arc.
o — To make the formation of the slag easy.
o — To facilitate the stability of the arc.
3.9 Gas Welding:

24 August 2022
GECV Mechanical
99
FUSION WELDING:
2. Non-consumable electrode :
➢ These electrodes are 12 mm in diameter and 450 mm long.
➢ These are not consumed during the welding process.
➢ Examples of these electrodes are : Carbon, graphite and tungsten.
3.9 Gas Welding:

24 August 2022
GECV Mechanical
100
FUSION WELDING:
General Aspects: Electric Arc Welding: Types of Welded Joints
The type of joint is determined by the relative positions of the two pieces being joined.
▪ The following are the five basic types of commonly used joints :
➢ 1. Lap joint
➢ 2. Butt joint
➢ 3. Corner joint
➢ 4. Edge joint
➢ 5. T-joint.
3.9 Gas Welding:

24 August 2022
GECV Mechanical
101
FUSION WELDING:
1. Lap joint:-
➢ Refer to Fig. 7.18. Plates Plates
➢ The lap joint is obtained by overlapping the plates and then welding the edges of the
plates.
➢ The lap joints may be single traverse, double traverse and parallel lap joints.
➢ These joints are employed on plates having thickness less than 3 mm.
3.9 Gas Welding:

24 August 2022
GECV Mechanical
102
FUSION WELDING:
2. Butt joint :
➢ The butt joint is obtained by placing the plates edge to edge as shown in Fig. 7.19.
➢ In this type of joints, if the plate thickness is less than 5 mm, bevelling is not required.
➢ When the thickness of the plates ranges between 5 mm to 12.5 mm, the edge is
required to be bevelled to V or U-groove, while the plates having thickness above 12.5
mm should have a V or U-groove on both sides.
➢ The various types of butt joints are shown in Fig. 7.20.
3.9 Gas Welding:

24 August 2022
GECV Mechanical
103
FUSION WELDING:
2. Butt joint :
3.9 Gas Welding:

24 August 2022
GECV Mechanical
104
FUSION WELDING:
3. Corner joint:-
➢A corner joint is obtained by joining the edges of two plates whose surfaces are at an
angle of 90° to each other.
➢In some cases corner joint can be welded, without any filler metal, by melting off the
edges of the parent metal.
➢This joint is used for both light and heavy gauge sheet metal.
3.9 Gas Welding:

24 August 2022
GECV Mechanical
105
FUSION WELDING:
4. Edge joint:-
➢ This joint is obtained by joining two parallel plates.
➢ It is economical for plates having thickness less than 6 mm.
➢ It is unsuitable for members subjected to direct tension or bending.
3.9 Gas Welding:

24 August 2022
GECV Mechanical
106
FUSION WELDING:
5. T-joint:-
➢ It is obtained by joining two plates whose surfaces are approximately at right angles
to each other.
➢ These joints are suitable up to 3 mm thickness.
➢ T-joint is widely used to weld siffeners in aircraft and other thin walled structures.
3.9 Gas Welding:

24 August 2022
GECV Mechanical
107
FUSION WELDING:
Note : The lap joints, corner joints and T-joints are known as fillet weld joints. The fillet
crosssection is approximately triangular. Fig. 7.24 shows the three types of fillet welds.
3.9 Gas Welding:

24 August 2022
GECV Mechanical
108
FUSION WELDING:
General Aspects: Electric Arc Welding: Welding positions
It is easiest to make welds in flat positions, i.e., both the parent metal pieces lying in
horizontal plane over a flat surface. But, several times it becomes unavoidable to weld
the workpieces in some other positions also. The common welding positions are :
➢ 1. Flat position
➢ 2. Horizontal position
➢ 3. Vertical position
➢ 4. Overhead position.
▪ 1. Flat position:
➢ In this welding position, the welding is done from the upper side of the joint and the
welding material is normally applied in the downward direction.
➢ On account of the downward direction of application of welding material this position
is also sometimes called as downward position.
3.9 Gas Welding:
Flat position

24 August 2022
GECV Mechanical
109
FUSION WELDING:
▪ 2. Horizontal position:
➢ In this case, the weld is deposited upon the side of a horizontal and against a vertical
surface.
3.9 Gas Welding:
Horizontal position

24 August 2022
GECV Mechanical
110
FUSION WELDING:
3. Vertical position:
➢In this position, the axis of the weld remains either vertical or at an inclination of less
than 45° with the vertical plane.
➢The welding commences at the bottom and proceeds upwards.
➢The tip of the torch is kept pointing upwards so that the pressure of the outcoming gas
mixture forces the molten metal towards the base metal and prevents it from falling
down.
3.9 Gas Welding:
Vertical position

24 August 2022
GECV Mechanical
111
FUSION WELDING:
4. Overhead position:
➢ In this case, the welding is performed from the underside of the joint. The workpieces
remain over the head of the welder.
➢ The workpieces as well as axis of the weld all remain in approximately horizontal
plane.
➢ It is reverse of flat welding.
3.9 Gas Welding:
Overhead position

24 August 2022
GECV Mechanical
112
FUSION WELDING:
General Aspects: Tungsten Inert-gas (TIG) Welding
➢ In this process the heat necessary to melt the metal is provided by a very intense
electric arc which is struck between a virtually non-consumable tungsten electrode
and metal workpiece.
➢ The electrode does not melt and become a part of the weld.
➢ On joints where filler metal is required, a welding rod is fed into the weld zone and
melted with base metal in the same manner as that used with oxyacetylene welding.
➢ The weld zone is shielded from the atmosphere by an inert-gas (a gas which does not
combine chemically with the metal being welded) which is ducted directly to the weld
zone where it surrounds the tungsten.
➢ The major inert gases that are used are argon and helium.
3.9 Gas Welding:

24 August 2022
GECV Mechanical
113
FUSION WELDING:
3.9 Gas Welding:
Tungsten inert-gas (TIG) welding

24 August 2022
GECV Mechanical
114
FUSION WELDING:
TIG process offers the following advantages :
➢ 1. TIG welds are stronger, more ductile and more corrosion resistant than welds
made with ordinary shield arc welding.
➢ 2. Since no granular flux is required, it is possible to use a wide variety of joint
designs than in conventional shield arc welding or stick electrode welding.
➢ 3. There is little weld metal splatter or weld sparks that damage the surface of the
base metal as in traditional shield arc welding.
Applications :
➢ (i) The TIG process lends itself ably to the fusion welding of aluminium and its alloys,
stainless steel, magnesium alloys, nickel base alloys, copper base alloys, carbon steel
and low alloy steels.
➢ (ii) TIG welding can also be used for the combining of dissimilar metals, hard facing,
and the surfacing of metals.
3.9 Gas Welding:

24 August 2022
GECV Mechanical
115
FUSION WELDING:
General Aspects: Metal Inert-gas (MIG) Welding
TIG process offers the following advantages :
➢ The inert-gas consumable electrode process, or the MIG process is a refinement of the
TIG process, however, in this process, the tungsten electrode has been replaced with a
consumable electrode.
➢ The electrode is driven through the same type of collet that holds a tungsten
electrode by a set of drive wheels.
➢ The consumable electrode in MIG process acts as a source for the arc column as well
as the supply for the filler material.
➢ MIG welding employs the following three basic processes.
▪ 1. Bare-wire electrode process
▪ 2. Magnetic flux process
▪ 3. Flux-cored electrode process.
3.9 Gas Welding:

24 August 2022
GECV Mechanical
116
FUSION WELDING:
3.9 Gas Welding:
Metal inert-gas welding (MIG)

24 August 2022
GECV Mechanical
117
FUSION WELDING:
Advantages :
➢ 1. It provides higher deposition rate.
➢ 2. It is faster than shielded metal-arc welding due to continuous feeding of filler
metal.
➢ 3. Welds produced arc of better quality.
➢ 4. There is no slag formation.
➢ 5. Deeper penetration is possible.
➢ 6. The weld metal carries low hydrogen content.
➢ 7. More suitable for welding of thin sheets.
3.9 Gas Welding:

24 August 2022
GECV Mechanical
118
FUSION WELDING:
Limitations :
➢ 1. Less adaptable for welding in difficult to reach portions.
➢ 2. Equipment used is costlier and less portable.
➢ 3. Less suitable for outdoor work because strong wind may blow away the gas shield.
Applications :
➢ Practically all commercially available metals can be welded by this method.
➢ It can be used for deep groove welding of plates and castings, just as the submerged
arc process can, but it is more advantageous on light gauge metals where high speeds
are possible.
3.9 Gas Welding:

24 August 2022
GECV Mechanical
119
FUSION WELDING: Difference between TIG and MIG Welding Processes
3.9 Gas Welding:

25 August 2022
GECV Mechanical
120
References
R.K. Rajput, “A textbook of manufacturing technology (manufacturing processes)” Laxmi publications (p) Ltd, 2nd Edition.

Chapter 3.0.1 All Welding Part 1.pdf

Recommended

Recommended

More Related Content

Similar to Chapter 3.0.1 All Welding Part 1.pdf

Similar to Chapter 3.0.1 All Welding Part 1.pdf (20)

Recently uploaded

Recently uploaded (20)

Chapter 3.0.1 All Welding Part 1.pdf