SPOT
WELDING
Spot
welding as the name implies, is carried out in which two or more metal sheets
are welded by holding them between metal electrodes.
Spot
welding is "the welding of overlapping pieces of metal at small points by
application of pressure and electric current."
Spot
welding basically joins two pieces of metal using the heat from an electric
current. The two pieces of metal are pressed together with electrodes on either
side.
“It
is a welding process that involves the generation of heat by passing current
through the resistance induced by the contact between the surfaces of two or
more metals. Small pools of molten metal are made at the weld area as high
current passes through the metal”.
PROCESS
1.
Spot Welding works by holding sheets of metal together with two copper alloy
electrodes.
2.
The welding current depends upon the thickness and the composition of the
plates. It varies from 1,000 to 10,000 amperes and this current may be flow
from a fraction of a second to several seconds.
3.
Clamping (hold tightly to something else) two or more pieces of sheet metals
between two copper or copper-alloy welding electrodes.
4.
A large electric current flows through the electrodes and melts the metal into
a “spot”, and welds the two pieces together.
5.
The current and the heat generation are localized by the form of the
electrodes.
6.
The sheet metal's material type and thickness, along with the type of
electrodes used, will help to determine the right amount of current required to
create a spot weld.
7.
As the current passes through one electrode and the job to the other electrode,
the area in contact of the electrodes gets heated to 800 to 900 degree
centigrade.
8.
When the temperature is reached the welding current cut off.
9.
Then mechanical pressure is then applied by the electrodes to forge the weld.
Finally the electrodes open.
10.
The weld nugget size is usually defined by the electrode tip contact area.
ADVANTAGES
1.
Spot welding is quick and easy.
2.
There is no need to use any fluxes or filler metal to create a joint by spot
welding, and there is no dangerous open flame.
3.
This process does not require skilled labours.
4.
Spot welding can be used to join many different metals, and can join different
types to each other.
5.
Sheets as thin as 1/4 inch can be spot welded, and multiple sheets may be
joined together at the same time.
DISADVANTAGES
1.
If the current is not strong enough, hot enough or the metal is not held
together with enough force, the spot weld may be small or weak.
2.
Warping and a loss of fatigue strength can occur around the point where metal
has been spot welded.
3.
The appearance of the join is often rather ugly, and there can be cracks. The
metal may also become less resistant to corrosion.
APPLICATIONS
1.
Steel, brass, copper and light alloys can be joined by this method, which forms
a cheap satisfactory substitute for riveting.
2.
Spot welding is the predominant joining process in automotive industry for
assembling the automobile bodies and large components.
3.
It is also widely used for manufacturing of furniture and domestic equipment
etc.
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