electric resistance welding

1. Geetika K. Gopi

3. Electric Resistance welding
• Type of pressure welding used for joining pieces of sheet metal or wire.
• Resistance welding uses the application of electric current and
mechanical pressure to create a weld between two pieces of metal.
• In this process heat is generated at the interface of contacting work
piece by electrical resistance offered to the flow of electric current for
short duration, low voltage(6-10 volts) high amperage ( 60 - 4000
amperes) electric current.
• When area to be welded is heated, pressure (25-55 MPa) is applied to
joining area by electrodes until weld is solid.

4.  Amount of heat generated at the points of contact
is given by
H = I2 R t
H = Heat generated, in watt-sec.
I = current, in amperes
R = resistance of metal being welded, in ohms
t = time during which the electric current flows, in
seconds

5. ADVANTAGES DISADVANTAGES
• High speed welding
• Easily automated
• Suitable for high rate
production
• Economical
• Initial equipment costs
• Lower tensile and fatigue
strengths
• Lap joints add weight and
material

6. Spot Weld Seam Weld Projection Weld
Upset Weld Flash Weld
After Welding After Welding

7. Spot welding
•It is a RW process, in which two or more
overlapped metal sheets are joined.
•The method uses pointed copper electrodes
providing passage of electric current .
•The electrodes also transmit pressure
required
for formation of strong weld.
•Spot welding machines:
•Single point welding machine (rocker arm
type and press type)
•Multiple point welding machine
•Electrodes:
•Electrode materials in general use are
copper alloys developed to combine high
conductivity and hardness, plus reasonable
resistance to softening at the working
temperature of the tip.

8.  RSW uses the tips of two opposing solid cylindrical electrodes
 Pressure is applied to the lap joint until the current is turned off
in order to obtain a strong weld
Sequence in the resistance spot welding

9.  Surfaces should be clean
 Accurate control of and timing of electric current and of
pressure are essential in resistance welding
Cross-section of a spot
weld,showing the weld
nugget and the
indentation of the
electrode on the sheet
surfaces.This is one of
the most commonly used
process in sheet-metal
fabrication and in
automotive-body
assembly

10. Seam welding
The rollers allow the
workpiece to move through
the welder continously. A
stream of electrical pulses
pass through the rollers and
welds the joint

11.  SW is modification of spot welding
wherein
the electrodes are replaced by rotating wheels
or rollers
 The electrically conducting rollers
produce a spot weld
 SW can produce a continuous seam &
joint that is leakproof
Fig : (a) Seam-Welding Process in which rotating rolls act as electrode (b)Overlapping spots in a seam
weld. (c) Roll spot weld

12.  Spot, seam, and projection welding operations involve a
coordinated application of electric current and mechanical
pressure of the proper magnitudes and durations.
 The welding current must pass from the electrodes through
the work.
 Its continuity is assured by forces applied to the electrodes, or
by projections which are shaped to provide the necessary
current density and pressure.
 The sequence of operation must first develop sufficient heat to
raise a confined volume of metal to the molten state.
 This metal is then allowed to cool while under pressure until
it has adequate strength to hold the parts together.
 The current density and pressure must be such that a nugget
is formed, but not so high that molten metal is expelled from
the weld zone.
 The duration of weld current must be sufficiently short to
prevent excessive heating of the electrode faces.
 Such heating may bond the electrodes to the work and greatly
reduce their life.

13.  The heat required for these resistance welding
processes is produced by the resistance of the
workpiece to an electric current passing
through the material. Due to the short electric
current path in the work and limited weld
time, relatively high welding currents are
required to develop the necessary welding
heat.

14.  Projection welding is a joining
of two sheets to big bodies
like automobile chasis by
making raised portions or
projections on one of the
components. The projections
are made by intersection.
 There are several type of
projections: Round Button or
Dome Type, Ring type,
Elongated Projection,
Shoulder Projection and
Radius Projection.
 PW is developed by
introducing high electrical
resistance at a joint by
embossing one or more
projections on the surface to
be welded
 It is similar to spot welding
Fig: a) Resistance projection Welding b)A welded bracket c) &
d) Projection welding of nuts r threaded hosses and stack

15.  The electrodes exert pressure to compress
the projections
 Nuts and bolts can be welded to sheet and
plate by this process
 Metal baskets, oven grills, and shopping
carts can be made by RPW

16. a) Upset butt welding b) Flash butt
welding
Upset Weld Flash Weld
After Welding After Welding

19.  Recent development
 Welding heat is obtained from arc produced by
rapid discharge of stored electrical energy