WELDING
Introduction
Welding is the process for joining different materials.
Welding joins different metals/alloys with the help of number of
processes in which heat is supplied either electrically or by means
of gas torch.
In order to join two or more pieces of metal together by one of the
welding processes, the most essential requirement is heat.
Pressure may be employed but in many processes this is not
essential.
Advantages
1) A good weld is as strong as the base metal.
2) General welding equipment is not very costly.
3) Portable welding equipments are available.
4) Welding permits considerable freedom in design.
5) A large number of metals/alloys both similar and
dissimilar can be joined by welding.
6) Welding is usually the most economical way to join
components.
Disadvantages
1) Welding gives out harmful radiations, light, fumes
and spatter.
2) A skilled welder is required to produce a good
welding job.
3) Welding results in residual stresses and distortion of
the workpiece.
4) A welded joint for many reasons, needs stress-relief
heat treatment.
SHIELDED METAL ARC
WELDING
Gas Welding
• Gas welding is a process in which oxy –fuel flame is used to
weld the work piece. Oxy-fuel welding is fusion welding
process.
• The intensity of the heat generated in the flame depends upon
the oxy-fuel gas mixture and relative pressures of the gases.
• Some times compressed air is also utilised instead of oxygen.
• Generally used fuel gases is C2H2.
• H2,C3H8,C4H10 and Natural gas. But oxy-acetylene mixture
gives more heat intensity compared to other mixtures.
• Oxy –acetylene flame
• The combustion of oxygen and acetylene
results in
• 2C2H2 +5O2 ----- 4CO2+ 2H2O+HEAT
• This combustion takes place in two stages i.e
primary stage of combustion. In primary stage
of combustion inner cone is developed.
• 2C2H2+2O2 ------ 4CO+ 2H2+ 448KJ/Mol
• In secondary stage of combustion CO and H2
ignite and burn at a low temperature than the
primary stage.
• 3O2+ 4CO+2H2 ----- 4CO2+ 2H2O+ 812KJ/Mol
• In gas welding the most commonly used
equipments are welding torch, welding tip,
pressure regulators, gas cylinders, hose and
hose fittings, goggles, spark lighter etc.
• Welding torch is mixing chamber for oxygen
and acetylene.
• Welding tip is that part through which the
mixed gases pass just before ignition.
• Pressure regulator is to reduce the cylinder
pressure and to provide a steady flow of gas.
PRINCIPLE
Disadvantages of Gas Welding
BRAZING
Brazing the joining of two metal pieces by the
addition of a special filler metal is known as
brazing.
During brazing, the base metal of the two pieces
to be joined is not melted.
An important requirement is that the filler metal
must wet the base metal surfaces to which it
is applied.
• Strong joints may be obtained.
• The filler metal having a melting temperature above
427°C but below the melting temperature of base
metal, is distributed between the surface by capillary
attraction.
• In brazing, special fluxes are required to remove
surface oxide and give the filler metal the fluidity to
wet the surfaces.
• Alloys of copper, silver, and aluminium are the most
common brazing filler metals.
• In brazing, generally lap , butt and scarf joints are
used. Out of all three, lap joint is the strongest
because of large contact area.
• Joint clearance is important because sufficient space
must be allowed for capillary attraction.
Application of brazing:
1. Applied to join materials, which is difficult to weld.
2. Possible in dissimilar metals.
3. Thin sections of metals can be joined.
Advantages:
1. Process is rapid
2. Neat appearance of the joint with minimum finishing.
3. Used for assembly of pipes to fitting, carbide tips to
tools, radiators, heat exchangers, electrical parts and
repair of castings.
Soldering
• Similar to brazing but a filler metal introduced into the
joint in a liquid state at a temperature below 427°c and
allowed to solidy to unite with the parent metal.
• Solders are mainly tin-lead alloys having a melting
range of 180°c-370°c.
• The steps involved in making a soldered joint includes
pre cleaning, fitting the parts, Applying flux, heating
the desired section of the parts, applying the solder,
cooling the soldered joint, and post cleaning.
• In a process, a little alloying with the base
metal takes place and additional strength is
obtained by mechanical bonding. The strength
of the joint is largely depends on the adhensive
quality of the alloy, which never reach the
strength of the materials being joined.
• The flux helps clean the base metal to allow
compound to take place.
• Commonly used fluxes with soldering includes
zinc chloride, resin, resin plus alcohol,
ammonium chloride.
• Most metals such as iron, steel, copper alloys,
silver and gold and nickel alloys can be joined
by soldering.
• Applications
• 1. joining automobile radiator core and
plumbing.
• 2. electronic industry including radio, TV and
computers.
• 3. for tight seal joints
• 4. electrical industries for joining wires cables.
• Advantages
• 1. it adds rigidity and improves electrical
conductivity.
• 2. Solders are more ductile in nature.
• 3. used for sealing fabricated joint.
• 4. Low heat input as compared to brazing and
welding.
• 5. It is easy to make a rejoint by soldering.
welding brazing soldering
TEMPERATURE OF JOINING TEMPERATURE OF JOINING TEMPERATURE OF JOINING
IS GREATER THAN MELTING IS MORE THAN 427°C IS LESS THAN 427°C
POINT OF METAL TO BE
JOINED.
STRENGTH OF JOINT IS STRENGTH IS LOW STRENGTH IS POOR
HIGH
USED FOR WELDING OF USED FOR JOINING USED IN ELECTRICAL
MACHINE PARTS AND ALUMINIUM, MAGNESIUM CIRCUITS, DOMESTIC AND
HEAVY STRUCTURAL AND THEIR ALLOYS PLUMBING APPLICATION.
COMPONENTS
IT IS A PROCESS OF IT IS A PROCESS OF JOINING BY MEANS OF
JOINING TWO SIMILAR OR JOINING TWO METAL FUSIBLE ALLY CALLED
DISSIMILAR METALS BY PIECES BY ADDITION OF SOLDER.
APPLICATION OF HEAT, SPECIAL FILLER METAL
PRESSURE OR BOTH AND
WITH OR WITHOUT THE
USE OF FILLER METAL
THE BASE METALS TO BE THE BASE METALS TO BE THE BASE METALS TO BE
JOINED ARE MELTED JOINED ARE NOT MELTED JOINED ARE NOT MELTED
