Thapar Institute of Engineering & Technology –

Patiala

Manufacturing Processes
UTA026

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Manufacturing Processes
UTA026
RESISTANCE WELDING
Lecture - 27

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 Resistance Welding (RW)
• Resistance Welding is a welding process, in which
work pieces are welded due to a combination of a
pressure applied to them and a localized heat
generated by a high electric current flowing through
the contact area of the weld.

• The weld is made by a combination of HEAT,

PRESSURE, and TIME.

• Resistance of the material is used for welding by

current flow which causes a localized heating in the
part.
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Resistance Welding (RW)

*https://www.youtube.com/watch?v=cOAdEIQKZDs
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 Resistance Welding (RW)
• The heat generated in resistance welding
H = I2R t (1)

Hw HL
Heat lost into the
Heat used to
work metal,
form weld
electrodes, and
Nugget
surrounding air
say 60%
say 40%
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 Resistance Welding (RW)
• Therefore the heat generated in resistance welding which
is used to form the weld nugget can be expressed as
H = k I2R t (2)
– H = the total heat generated in the work, J
– I = electric current, A
– t = time for which the electric current is passing through the
joint
– R = the resistance of the joint, ohms
– k= a constant to account for the heat losses from the welded
joint. (if k=0.6, that means 40% of the heat is lost into the
work metal, electrodes, and surrounding air. )
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 4 Major Points of Resistance
• There are 4 major points of resistance in the
work area. They are as follows:
(R1) Resistance of the electrodes.
(R2) The contact resistance between the
electrode and the workpiece.
(R3) The contact resistance between the two
workpiece plates.
(R4) The workpiece resistance.

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 FORCE

R2 R1

R3
R4
WELD
SPOT OR
NUGGET

FORCE

WELDING
TEMPERATURE 8
 Current Voltage
• AC low volt (typically 1 to 30 V ) electric current
(1000–100,000 A) is supplied through copper
electrodes connected to the secondary coil of a
welding transformer.

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https://gfycat.com/tattereddownrightbutterfly
 APPLICATIONS
• Resistance Welding (RW) is used for joining
– vehicle body parts,
– fuel tanks, SHEET
– domestic radiators, METAL
PRODUCTS
– pipes of gas oil and water pipelines,
– wire ends,
– turbine blades etc.

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 Metals Welded
• The following metals may be welded by
Resistance Welding:
– Low carbon steels - the widest application of
Resistance Welding
– Aluminum alloys
– Medium carbon steels, high carbon steels and
Alloy steels

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 ADVANTAGES
• High welding rates
• Low fumes
• Cost effectiveness
• Easy automation
• No filler materials are required
• Low distortions
• Good repeatability and reliability

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Types of Resistance Welding (RW)
The most popular methods of Resistance
Welding are:

1. Spot Welding (RSW)

2. Seam Welding (RSEW)

3. Resistance Projection Welding (RPW)

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 1. Spot Welding (RSW)
• Spot Welding is a Resistance Welding (RW) process, in
which two or more overlapped metal sheets are joined
by spot welds.

• The method uses pointed copper electrodes providing

passage of electric current. The electrodes also
transmit pressure required for formation of strong
weld.

• Diameter of the weld spot is in the range - (3 - 12 mm).

• Spot welding is widely used in automotive industry for

joining vehicle body parts.
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1. Spot Welding (RSW)

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 1. Spot Welding (RSW) - STEPS
• The sequence is as follows:
1. parts inserted between open electrodes,

2. electrodes close and force is applied,

3. weld time— current is switched on,

4. current is turned off but force is maintained or in-

creased (a reduced current is sometimes applied near the
end of this step for stress relief in the weld region), and

5. electrodes are opened, and the welded assembly is

removed. 16
 1. Spot Welding (RSW) - STEPS

(1) parts inserted between electrodes, (2) electrodes close,

force applied, (3) current on, (4) current off, (5) electrodes
opened.
http://www.davidpageassociates.co.uk/spotweld.htm 17
 1. Force, Current vs Time
Welding Current

Postweld Heating
Current

(1) parts inserted between electrodes, (2) electrodes close, force applied,
(3) current on, (4) current off, (5) electrodes opened.
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 1. Spot Welding (RSW) - POSTWELD
• It has been observed that steels containing more
than 0.15% carbon may result into brittle weld
joint during resistance welding.

• Therefore post-weld heating is sometimes

applied to eliminate possible brittleness.

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 2. Resistance Projection Welding
(RPW)
• When increased strength is required, multiple welds are
often needed, and this means multiple operations.

• Dimples are embossed into one of the workpieces at the

location where a weld is desired.

• The two workpieces are then placed between large-area

electrodes in a press machine, and pressure and current
are applied as in spot welding.

• Since the current must flow through the points of contact

(i.e., the dimples), the heating is concentrated where the
weld is desired.
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• Resistance projection welding (RPW): (1) start of operation, contact
between parts is at projections; (2) when current is applied, weld
nuggets similar to spot welding are formed at the projections.
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 3. Seam Welding (RSEW)
• Seam Welding is a Resistance Welding (RW)
process of continuous joining of overlapping
sheets by passing them between two rotating
electrode wheels.
• Heat generated by the electric current flowing
through the contact area and pressure provided
by the wheels are sufficient to produce a leak-
tight weld.
• Resistance seam welds (RSEW) can be made by
two distinctly different processes.
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 3. Seam Welding (RSEW)

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https://gfycat.com/gifs/search/resistance+welding
3. Seam Welding (RSEW)

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 3. Seam Welding (RSEW)
• Seam Welding is high speed and clean
process, which is used when continuous tight
weld is required .
• Can produce air-tight joints
• Applications:
– Gasoline tanks
– Automobile mufflers
– Various other sheet metal containers

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 Resistance Welding Numerical (RW)
• The heat generated in resistance welding
H = I2R t (1)

Hw HL
Heat lost into the
Heat used to
work metal,
form weld
electrodes, and
Nugget
surrounding air
say 60%
say 40%
26
 Resistance Welding (RW)
• Therefore the heat generated in resistance welding which
is used to form the weld nugget can be expressed as
H = k I2R t (2)
– H = the total heat generated in the work, J
– I = electric current, A
– t = time for which the electric current is passing through the
joint
– R = the resistance of the joint, ohms
– k= a constant to account for the heat losses from the welded
joint. (if k=0.6, that means 40% of the heat is lost into the
work metal, electrodes, and surrounding air. )
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 NUMERICAL- Q
• A resistance spot-welding operation is performed on
two pieces of 3.5-mm-thick sheet steel using
12,000A for a 0.20 s duration. The electrodes are 7
mm in diameter at the contacting surfaces.
Resistance is assumed to be 0.0001 Ω , and the
resulting weld nugget is a sphere of 6 mm in
diameter. The unit melting energy for the metal
U=12.0 J/ mm3. What portion of the heat
generated was used to form the weld nugget, and
what portion was dissipated into the work metal,
electrodes, and surrounding air?
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 NUMERICAL- Ans
Electrode

Weld Nugget
Work piece

Work piece

Electrode

Volume = 4 π R3/3
Sphere nugget 29
 NUMERICAL- Ans

• The heat generated in the operation (H)

H = I2R t
H = (12000)2× 0.0001× 0.20
H = 2880 J

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 NUMERICAL- Ans

• Volume of weld nugget = vol of sphere with a

diameter of 6 mm

4 π R3
= 3
= 4/3 × 3.14 × (3)3
= 113.04 mm3
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 NUMERICAL- Ans

• Heat required to weld the nugget (HW ) = vol X U

= 113.04 × 12
= 1356.48 J

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 NUMERICAL- Ans

• Heat Lost (HL ) = (H ) - (HW )

= 2880 - 1356.48
= 1523.52 J

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 NUMERICAL-
Electrode

Weld Nugget
Work piece

Work piece

Electrode

Cylindrical Nugget Volume = πR2h

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 References:
• M. P. Groover, Fundamentals Of Modern Manufacturing:
Materials, Processes, and Systems, Wiley (2016), 5th edition.
• Degarmo, E. P., Kohser, Ronald A. and Black, J. T., Materials and
Processes in Manufacturing, Prentice Hall of India (2008) 8th ed.
• Kalpakjian, S. and Schmid, S. R., Manufacturing Processes for
Engineering Materials, Dorling Kingsley (2006) 4th ed.
• https://www.youtube.com/watch?v=cOAdEIQKZDs
• https://gfycat.com/tattereddownrightbutterfly
• http://www.davidpageassociates.co.uk/spotweld.htm
• https://gfycat.com/gifs/search/resistance+welding

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Thanks!!

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