UNIT 2 RESISTANCE WELDING PROCESSES

PR 8592 WELDING TECHNOLOGY UNIT -2
P.VENGALA KUMAR ME.,MBA
TF/MECHANICAL ENGG.,
UNIVERSITY VOC COLLEGE OF ENGINEERING
VENGALAKUMAR ME,MBA., 1

UNIT II - RESISTANCE WELDING PROCESSES:
• Resistance Spot welding,
• Seam welding,
• Projection welding,
• Resistance Butt welding,
• Flash Butt welding,
• Percussion welding
• High frequency resistance welding

RESISTANCE WELDING
• Resistance welding is a group of welding processes wherein
coalescence is produced by the heat obtained from
resistance of the work to the flow of electric current in a
circuit of which the work is a part and by the application of
pressure.
• No filler metal is needed. Fundamentals of Electric
Resistance Welding the two factors or variables mainly
responsible for resistance welding are the generation of
Heat at the place where two pieces are to be joined.
• The application of pressure at the place where a weld joint
is to be formed.

Principle
• When electric current flows through a material, it offers resistance to
the flow of current resulting in heating of the material.
• The heat generated is used to make a weld between two or more
workpieces.
• Resistance welding is based on the above principle.The heat
generated in the material is given by Joules law:HαI2RTor H = k I2
RTwhere H = heat generated in the material in Joules,I = Flow of
current through the material in AmperesR = Electrical resistance of
the material in OhmsT = time for which the electric current flows
through the material in seconds,k = a constant, usually < 1 to
account for heat loss through conduction and radiation.High current
is the primary requirement to produce a resistance weld.
• A step down transformer that converts the high voltage, low current
power line to a high current (upto 100,000 A) and low voltage ( V)
power is used for the purpose.

Resistance Spot Welding (RSW)
• Spot welding is a resistance welding process in which
the two overlapping workpieces held under pressure
are joined together in one soot (location) by the heat
generated due to the resistance of the workpieces to
the flow of electric current through.

Resistance Spot Welding (RSW) Description
• The two workpieces to be joined are cleaned to
remove dirt, grease and other oxides either chemically
or mechanically to obtain a sound weld.The workpieces
are then overlapped and placed firmly between two
water cooled cylindrically shaped copper alloy
electrodes, which in turn are connected to a secondary
circuit of a step-down transformer.
• The electrodes carry high currents and also transmit
the force/pressure to the workpieces to complete the
weldOperationThe welding current is switched ON.

• Spot Welding ( Continued….)
As the current passes through the electrodes, to the
workpiece, heat is generated in the air gap at the point
of contact of the two workpieces.
• The heat at this contact point is maximum with
temperature varying from °C, and as a result melts the
workpieces locally at the contact point to form a spot
weld.
• In order to obtain a strong bond, external pressure is
applied to the workpiece, through the electrode, by
means of a piston-cylinder arrangement.
• The current is switched OFF.In some cases, external
pressure is not required and the holding pressure of the
two electrodes is just sufficient to create a good joint.
• Heat dissipates throughout the workpiece which cools
the spot weld causing the metal to solidify.

.
Spot Welding ( Continued….)
The pressure is released and the workpiece is moved
to the next location to make another spot weld.In
some spot welding machines, the workpiece remains
stationary while the electrode moves to the next
location to make a weld.
The duration of current flow varies from a fraction
of second to a few seconds.Both the current and the
duration of current flow form the important
parameters in spot welding and depend on the
thickness and type of the workpieces being welded.
The shape and the surface condition of the electrode
is another parameter in obtaining a good weld

Advantages of Resistance Spot Welding
• Comparatively Low cost
• Resistance Spot Welding (RSW)
method doesn't need highly skilled worker.
• Distortion or warping of parts is eliminated
though it leaves some depressions or indentation.
• The joint made is highly uniform.
• Automatic or semi-automatic operation both can
be done.
• There is no need for edge preparation.
• Welding can be done in quick succession. It just
needs a few seconds to make the joint.

Disadvantages of RSW
• The equipment cost is high so it can has an
effect on the initial cost.
• Skilled welders or technicians are needed for
the maintenance and controlling.
• Some metals need special surface preparation
for making the RSW a success.
• The thick jobs are not easy to weld.

Applications of Resistance Spot Welding
• Spot welding of thick steel plates has been done
and it has replaced the need for riveting.
• The welding of two or more sheet metals can be
joined by mechanical means more economically
by using the spot welding methods. We don't need
gas tight joints.
• Spot welding can be used for attaching braces,
pads or clips with cases, bases and covers which
are mainly product of sheet metal forming.
• Automobile and aircraft industries relies greatly
of spot welding these days.VENGALAKUMAR ME,MBA., 13

Resistance SeamWelding (RSEW) Working Principles :
• The Resistance Seam Welding (RSEW) is very much
similar to the Spot Welding (RSW) but
here circular rotating electrodes are used. And here we
get continuous weld which is air-tight (If the process is
perfect).
• The seam-welding form of the resistance process is a
series of overlapping welds. Two or more sheets
of base metal are usually passed between electrode
rollers, as shown in following Figure, which transmit
the current and also the mechanical pressure required
for producing a welded seam which is normally gas-
tight or liquid-tight.

Resistance Seam Welding (RSEW)

Resistance SeamWelding (RSEW) Advantages
• Gas tight as well as liquid tight joints can be
made.
• The Overlap is less than spot or projection
welding.
• The production of single seam weld and
parallel seams can be got simultaneously.

Resistance Seam Welding (RSEW) Disadvantages
• The welding process is restricted to a straight
line or uniformly curved line.
• The metals sheets having thickness more than
3mm can cause problems while welding.
• The design of the electrodes may be needed to
change to weld metal sheets having
obstructions.

Applications of RSEW
• Girth weld is possible in rectangular or square
or even in circular shapes.
• Most of the metals can be welded (Except
copper and some high percentage
copper alloys)
• Butt welding can be done.

Working Principle of Resistance Projection Welding (RPW)
• In resistance projection welding (RPW), small
projections are formed on one or both pieces of
the base metal to obtain contact at a point which
localize the current flow and concentrate the heat.
• Under pressure, the heated and softened
projections collapse and a weld is formed.
Projection on the upper component is pressed
against the lower component by electrode force.
• The projection collapses and a fused weld nugget
are formed with the application of current. This
technique is of special value in mounting
attachments to surfaces of which the back side is
inaccessible to a welding operator.

Projection Welding (RPW)

Advantages of resistance projection welding
• Simultaneous operation can be done i.e. more than one welds can be
made.
• Projection welding has this advantage that it can weld metals of
thickness which is not suitable for spot welding.
• Projection welding electrodes have a longer life when compared to
spot welding electrodes. Its because projection welding electrodes
have to withstand less wear and less heating.
• Resistance projection welding is not limited to sheet to sheet joints.
• Projection welding can be done in specific points which are desired
to be welded.
• In difficult welding work projection welding gives a better
heat balance.
• Projection welding saves electricity because it needs less current to
produce heat. So it reduces the shrinkage and distortion defects.

DISAdvantages of resistance projection welding
• All types of metals cannot be welded using
projection method. Metal thickness and
composition.
• All the metals are not strong enough to support
the projections. Some brasses and coppers
cannot be welded satisfactorily using
projection welding.
•

Applications
Resistance Projection welding is used
in Automobile sector.
Projection welding is used in refrigeration works
( mass production of condensers, gratings, racks
etc.)

RESISTANCE BUTT WEIDING
1.UPSET BUTT WELDING
2.FLASH BUTT WELDING

UPSET BUTT WELDING
• For making upset welding , edges of the
workpiece should be cleaned perfectly and
flatten. The parts to be welded are clamped in
copper jaws as shown in figure.
• The jaws act as electrodes. Both workpieces
edges are prepared and butted together. There
may be some gap between parts but it should
be such that no arcing takes place.

UPSET BUTT WELDING (CONT)
• Then the jaws are brought together in a solid
contact when the current flows through the
point of contact of jaws to from a locality of
high electric resistance.
• At this point, the applied pressure upsets or
forges the parts together

ADVANTAGES
• Upset butt welding is more suitable for
welding many alloys which are difficult to
weld using fusion welding.
• The metal retains base metal characteristics
because the base metal does not melt during
welding.

APPLICATIONS
• Upset welding is used to make closure of
capsules , small vessels and containers.
• Its applied in welding steel rails.

Flash Butt welding
Introduction
The welding process in which the
end of rods are heated and fused by an arc struck
between them and forged to produce a weld is
called flash butt welding.

Flash Butt welding

Working Principle
In this process the parts to be welded are
clamped in upper jaws of the welding machine.
One of the jaw is stationary and another one is
made as movable.
They act as electrodes the jaws are water
cooled when they are connected to heavy current
electric power supply.
The workpiece are brought together in a
slight contact.
When the current flow through the
workpieces an electric arc or flash is produced.

Flash Butt welding (CONT)
The end reach fusing temperature and power is
switched off .
Now the ends are forced together by applying
mechanical force to complete the weld.
In this welding the small projection is produced
around the weld.
That projection is finished by grinding. The welded
parts are after annealed to improve the toughness of
weld.
This process is used for the part having larger
cross-section.
This process is suitable for welding steel and
ferrous alloy other then cast iron.VENGALAKUMAR ME,MBA., 34

Advantages
Many dissimilar metals with different welding
temperature can be flash welded.
Flash butt welding allows fast joining of larger
and complex part.
Power consumption is less.
Clean welds can be made.
Application
Butt welding is used in automobile construction
of the axle,
body, wheel etc. Non-ferrous alloys such as lead, tin,
zinc, antimony, bismuth and alloys.

Percussion Welding
 Introduction
 It is one type of resistance butt welding
process.
 The part to be welded are clamped in copper
jaws of the welding machine in which are
clamp is fixed and the other one is movable.

Percussion Welding

Working principle
The movable clamp is backend up against the
pressure from the heavy spring .The jaws are act as a
electrode heavy current is connected to workpiece.
Now the movable clamp is released rapidly and it
moves forward at high velocity.
When the two parts are approximately 1.6mm apart
a sudden discharge of electrical energy is released
there by causing an intense are between two surfaces.
The arc is extinguished by the percussion blow of
the two path coming together with sufficient force to
complete in 0.1 second. No upset or flash occurs at the
weld.

This method is primary employed to join
dissimilar metals .this method is limited to
small area about 150 to 300𝑚𝑚2
.
Working Energy E=
1
2
C𝑉2
Where,
E= energy in watts-seconds(joules)
C= capacitance in farads
V= voltage
Amount of energy required to make joint
depends on the following factors.

Advantage
Time cycle involved very short .
Shortness of arc limit melting and heating.
Heat-treated and cold worked materials can be welded
annealing.
No filler metal is required.
No cast structure is produced at interface.
Charging rate is low and controlled.

Disadvantages
The welding process is limited to butt
joints.
Total area is limited.
Similar metal can usually be joined
more economically by other process.
Welding is typically dirtier and less
smooth than resistance welding.
The workpieces must be free of oil
or drit.

Applications
It is used for fine wire leads to filaments
such as an in lamps and electrical components.
The method is also used to weld pins, stud,
bolts and so on.

HIGH FREQUENCY RESISTNCE WELDING
High frequency resistance welding describes a
group of process that uses high frequency
electric current to concentrate the welding heat
at the needed location.
 The process is similar to seam welding but it
uses high frequency current.
 The require frequency is upto 450khz.

WORKING PROCESS:
In high frequency welding the phenomenon of skin
effect by which the current flows near the surface of
conductor and not through its entire thickness.
The required frequency is passed between electrodes in
contact with the edge of strip forming a tube when it
passes though forming pressure rolls.
 It shows schematic of high frequency resistance weld
used for making pipes.
 The pressurerolls apply the required welding pressure.
The required welding heat is governed by thecurrent
passing through work and speed of tube movement.

HIGH FREQUENCY RESISTNCE WELDING (CONT)
Due to this,only a small amount of metal is heatedat the welding
interface.
 The processes produce welds at high speeds at very highenergy
efficiency.
They are generally prepared for welding in a continuous roll
forming stripmill where the flat strip is gradually shaped to a round
form.
In the weld area, open edges ofthe formed strip are brought
together by pressure rolls to form a vee shape with the open at weld
point.
 The preferred vee angle for roll forming is between 4° to 7°
The welding current usually ranges between 200 to 5000amps.
Using ,50 kw power unit,tube of material 0 to 5mm thick can be
welded at up to 100m/min

Advantages:
High-Frequency resistance welding is more efficient because the
distance between point of weld and sliding contacts is shorter and
there are no induction losses.
It is suitable for long production runs where coils of strip are butt
welded which isan end to end welding process to avoid the need to
stop and restart the line.
 It needs less energy efficient than contact welding.
 Weld quality is not sensitive to the presence of air around the
weld.
Limitations:
The contact wear requires maintenance and replacements.
It cannot be used at slow speeds or as a manual process.
 The stop and restart will cause visual objectionable
discontinuities.

APPLICATIONS:
The predominant application of this type of
welding is continuous manufacturingof pipe and
tubing
It is more suitable for high speed welding of a
large range of sizes and materialsSteels, stainless
steels, aluminum, copper, brass and titanium
areSuccessfullywelded by High-Frequency
resistance welding processes.
It is used in making tubing I-beams and wheel
rims.

UNIT 2 RESISTANCE WELDING PROCESSES

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UNIT 2 RESISTANCE WELDING PROCESSES