2. Joining processes
The metals and non-metals are joining more than one piece with
each other by using various methods . Joints are two types
Temporary joining and Permanent joining
A temporary joint can be dismantled without breaking the assembled parts. A
permanent joint cannot be dismantled without breaking parts. Temporary joinin
g is beneficial where frequent assembly and disassembly are required.
Permanent joining is beneficial where joint is intended to stay fixed for longer
period.
Temporary joining
Nut & Bolts.
Magnetic catches.
Compressions joints as in wheel bearings.
Permanent joining
Welding
Soldering
Brazing
Riveting
5. Arc Welding
Arc welding is a type of welding process using an electric arc to create heat to melt
and join metal. A power supply creates an electric arc between a consumable or
non-consumable electrode and the base material using either direct (DC) or
alternating (AC) currents.
What are the Different Types of Arc Welding?
This process can be categorised into two different types; consumable and non-consumable electro
de methods.
Consumable Electrode Methods
Gas Metal Arc Welding (GMAW)
manual metal arc welding (MMA or MMAW),
Submerged Arc Welding,
Electro-Slage Welding,
Non-consumable Electrode Methods
Gas Tungsten Arc Welding (GTAW)
Plasma Arc Welding
6. MIG
Also known as Gas Metal Arc Welding
(GMAW), uses a shielding gas to protect
the base metals from contamination.
Operation
MIG welding is usually carried out with a handheld gun as a semiautomatic process. The MIG
process can be suited to a variety of job requirements by choosing the correct shielding gas,
electrode (wire) size and welding parameters. Welding parameters include the voltage, travel speed,
arc (stick-out) length and wire feed rate. The arc voltage and wire feed rate will determine the filler
metal transfer method. This application combines the advantages of continuity, speed, comparative
freedom from distortion and the reliability of automatic welding with the versatility and control of
manual welding. The process is also suitable for mechanised set-ups, and its use in this respect is in
creasing. MIG welding can be carried out using solid wire or flux cored wire.
Argon
Carbon dioxide
Argon and carbon dioxide mixtures
Argon mixtures with oxygen or helium mixtures
Each gas or gas mixture has specific advantages and limitations. Other forms of MIG welding
Include using a flux cored continuous wire and carbon dioxide shielding gas, or using self-shielding
flux cored wire, requiring no shielding.
7. TIG
Also known as Gas Tungsten Arc Welding (GTAW), uses a non-consumable tungsten
electrode to create the arc and an inert shielding gas to protect the weld and molten
pool against atmospheric contamination.
Working
Tungsten Inert Gas (TIG) welding uses the heat generated by an electric arc struck between a
non-consumable tungsten electrode and the work piece to fuse metal in the joint area and produce
a molten weld pool. The arc area is shrouded in an inert or reducing gas shield to protect the weld
pool and the non-consumable electrode. The process may be operated autogenously, that is,
without filler, or filler may be added by feeding a consumable wire or rod into the established weld
pool. TIG produces very high quality welds across a wide range of materials with thicknesses up to
about 8 or 10mm. It is particularly well suited to sheet material.
8. Gas Welding
Gas welding is a welding process that melts and joins metals by heating them with a flame caused
by a reaction of fuel gas and oxygen. The flux may be used to deoxidize and cleanse the weld Metal
. • The flux melts, solidifies and forms a slag skin on the resultant weld metal.
Types of Gas Welding:
Oxy-Acetylene Welding
Oxy-Acetylene Welding
Hydrogen Welding.
In this mixing chamber, the ratio of oxygen and fuel gas is mixed according to the type of flame
required. Neutral, oxidizing or carburizing are three types of flame used in welding.
Oxy-acetylene, 3200°C
Oxy-hydrogen, 2800°C
Oxy-butane, 2700°C
Oxy-propane, 2200°C
Oxy-coal gas, 2100°C
Air-acetylene, 2000°C
Air-hydrogen, 1800°C
9. Resistance Welding
Resistance welding is the joining of metals by applying pressure and passing current for a length of ti
me through the metal area which is to be joined. The key advantage of resistance welding is that no ot
her materials are needed to create the bond, which makes this process extremely cost effective.
It is Fusion type welding
Fusion welding process
Resistance welding is a fusion welding process that requires the application of both heat and
pressure to achieve a sound joint. The simplest form of the process is spot welding where the
pressure is provided by clamping two or more overlapping sheets between two electrodes
10. Thermit Welding
Thermit welding is basically a fusion process, the required heat being evolved from a
mixture of powdered aluminium and iron oxide. The ends of the part to be welded are
initially built into a sand or graphite mold, whilst the mixture is poured into a refractory
lined crucible.
Other metal oxides can be used, such as chromium oxide, to generate the given metal in its
elemental form. Copper thermite, using copper oxide, is used for creating electric joints:
3 Cu2O + 2Al ---- 6Cu + Al2O3
In exothermic welding, aluminium dust reduces the oxide of another metal, most commonly iron
oxide, because aluminium is highly reactive. Iron(III) oxide is commonly used:
Fe2 O3 +2Al --------- 2Fe + Al2 O3
11. Soldering & Brazing
Brazing and soldering, in essence, are the same in that they both melt the filler metal (braze or
solder) only, not the base materials. The liquid filler metal wets the base materials through
capillary action. When the liquid filler metal solidifies, it is bonded to the base materials, creating a
joint
Brazing and soldering are classified by the melting temperature of the filler material. Brazing uses
filler materials that have melting temperatures of 450°C or higher; and soldering uses solders (soft
filler materials) that have melting temperatures below 450°C.
12. Applications
Applications of welding
Shipbuilding
Automotive industries
Construction industries
Mechanical industries
Thermit welding is traditionally used for the welding of very thick and heavy plates.
Thermit welding is used in joining rail roads, pipes and thick steel sections.
Thermit welding is also used in repairing heavy castings and gears.
Thermit welding is suitable to weld large sections such as locomotive rails, ship
hulls etc.
13. Advantages
Advantages of Welding:
Welding produces a permanent connection.
Connection weld can be stronger than the initial material when using filler metal and use the
right technique.
In general, the costs incurred for the welding process is connecting the most economical in
terms of the use of material and fabrication costs.
In addition, to using in factories, welding can also be done in the field.
14. Disadvantages
Disadvantages and limitations Of Welding:
Generally, the welding is done manually and requires an expensive charge carrier.
In addition, the welding process requires large energy likely to be dangerous.
Welding results difficult to be dismantled, so that if required the demolition of the product for
repair or maintenance, the welding method will not be used for the process of switching
products.
The defective weld joint may envelop so it is not visible. The flaw can reduce the strength of
the connection.
