Joining process

1. Joining Processes
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2. Introduction
• Joining process is where two or more pieces of parts are
joined together to produce a single product of required
shape and size.
• The joining process can be classified as
a. Permanent joining process
It is done by fusing the metal together. The metal is
heated to its melting state and then it is fused to become
one unit.
Ex. Welding, soldering and brazing
b. Semi – permanent or temporary joining process
In this the metal is not heated. Process is carried out
at room temperature. Temporary joining process can be
done using nuts, bolts, screws and adhesives.
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3. WeldingProcess
• Simple definition of welding -
"joining metals through heating them to a
molten state and fusing them together.“
• Technical definition of Welding -
“a localized coalescence of metals, wherein coalescence is
obtained by heating to suitable temperature, with or
without the application of pressure and with or without the
use of filler material. This filler material has the melting
point same as the base material.”
It is also know as a metallurgical joining process of two
metal pieces, to produce a single piece of product.
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4. Welding Terminologies
• Base Metal – Work pieces that are needed to be joined
• Weld Bead - A weld bead is a weld deposit produced by a
single pass of the welding processes. It is also known as
bead
• Puddle – The molten base metal at the joint during the
welding operation
• Weld pass – Movement of weld torch from one end of the
joint to the other end.
• Tack Weld – it is the temporary joint done before welding
to keep the work pieces to be welded in place during
welding. The joints are done at the ends of the work
piece.
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5. Classification of Welding Process
The welding process can be
classified based on the source of
energy to heat the metal and the
state of metal at the joint.
•Pressure Welding
•Fusion Welding
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6. Pressure Welding
• The surfaces of the joint to be welded is heated to a
plastic state and forced together with external pressure to
finish the joint.
• Depends on the application of pressures and temperature
• ISO – 857 defines “Welding in which sufficient outer force
is applied to cause more or less plastic deformation of
both the facing surfaces, generally without the addition of
filler metal. Usually, but not necessarily, the facing
surfaces are heated in order to permit or to facilitate
bonding”
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8. Fusion Welding
• Heating in to molten state and allowed to solidify
to form joint with or without the addition of
filler material.
• The process is carried out with out the
application of pressure.
• ISO – 857 defines “Welding without application
of outer force in which the facing surface must
be melted. Usually, but not necessarily, molten
filler metal is added”.
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10. Advantages
• It is a high temperature process where the base
metals are heated above their melting temp.
• Strength of the joint obtained in welding is much
stronger than the parent metal
• Welding produces stronger joints.Hence this
process is used for fabrication and structural
applications
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11. Disadvantages
• Requires certain finishing operations like
grinding , filing etc
• Since welding is carried out at high temp,
the metal adjacent to the weld portion
called the heat affected zone which is
affected to a large extent
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12. Applications
It can be employed in industry as a tool for,
Fabrication of automobile cars , Air- craft,
Refrigerators, Pressure vessels , Furnaces
etc
Repair and maintenance work
Joining broken parts
Rebuilding worn out components etc
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13. Brazing
• it is a method of joining two similar or dissimilar metals using a
special fusible alloy called as “Spelters”.which is non ferrous
metal or alloy
• The base metals do not melt; they are heated above 450 deg
C but below their melting temperatures of base metal.
• Some diffusion of the filler metal with base metal takes place.
• There are two types of spelters used:
• Copper and Copper base alloys
• Silver and silver base alloys
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Butt Joint
When two metals are positioned in a head-to-head
arrangement for brazing, it will result in a Butt joint.
Lap Joints
Lap joint is the type of joint that have a larger surface area
because it is formed by overlapping of two metals.
Butt-Lap Joint
It is a combination of both butt and lap type of joint and offers
the advantages of both. Butt-lap joint give the profitable
features of single thickness as well as of maximum strength

15. Advantages
• Dissimilar metals and parts having thin
sections can be joined easily.
• Brazing may avoid the metallurgical
damage to the base metals.
• Strong joint can be obtained by brazing.
• It is economical and quick process
• Less heating is required than for welding.
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16. Soldering
• Soldering is a method of uniting two thin metal pieces
using a dissimilar metal or an alloy by application of
heat.
• The alloy is called as solder.
• Two types of solder are:
• Soft solder
• Hard solder
• Usually the base metal is heated upto around 350 deg
C.
• Soldering is usually used for electrical & electronic
works and some low end sheet metal work.
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Soft soldering is characterized by having a melting point of the
filler metal below approximately 400 °C (752 °F). Soft solder
filler metals are typically alloys (often containing lead) that have
liquidius temperatures below 350°C. Soft soldering can be done
with a heated iron whereas the other methods require a higher
temperature to melt the solder than can be achieved with a heated
iron.
Hard soldering use higher temperatures, typically requiring a
flame or carbon arc torch to achieve the melting of the filler. Hard
soldering, as used by jewelers, machinists and in some plumbing
applications, requires the use of a torch or other high temperature
source and is much stronger than soft soldering.

18. ADVANTAGES
• It is simple and economical process
• Since it done at relatively low temperature, no
metallurgical damage to the base metal.
• The soft soldered joints can easily be dismantled by
simple heating
• Operator fatigue is less compared to welding process.
• DISADVANTAGES
• 1. The process is limited to minimum thickness (3mm)
• 2. Skilled operator is required.
• 3. Strength of joint when compared to welding is low.
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19. DifferencebetweenSoldering and Brazing
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Sl no Brazing Soldering
1 Melting point of the filler
material is about 600 degree.
Melting point of the filler material
is below 450 degree.
2 Dissimilar metals can be
joined easily.
Only similar metals can be joined.
3 Good surface finish. Does not yield a good surface
finish
4 Stronger joints. Less stronger joint.
5 It is used for production of
heat exchangers and
radiators.
It is used for electrical and
electronic applications.

20. DifferencebetweenWelding,Brazing andSoldering
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Sl no Parameter welding brazing soldering
1 Temperature Very high, about
more than 5000
degree c
Melting point of the
filler metal is above
600 degree c
Melting point of
the filler metal is
below 450
degree
2 Type of metal
to be joined
Only similar metals Dissimilar metals Only similar
metals
3 Surface finish moderate good poor
4 strength Very high high weak