Transcript RESISTANCE WELDING - stanzen TOYOTETSU India Worker Union

RESISTANCE WELDING
TWI Training & Examination
Services
EWF/IIW Diploma Course
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World Centre for Materials Joining Technology
Resistance spot welding principle
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World Centre for Materials Joining Technology
Resistance seam welding principle
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World Centre for Materials Joining Technology
Projection welding principle
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World Centre for Materials Joining Technology
Spot welding - heat generation
Electrical resistance
in the welding circuit
• a & g - electrode
material resistance
• b & f - contact
resistance
electrode to base
metal
• c & e - base metal
resistance
• d - base metal
interface resistance
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Spot welding equipment
• Pedestal welding
machine
• Portable welding
machine
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Spot welding equipment
Resistance electrodes
functions
• conduct the welding
current to the work 
made from Cu alloys
• transmit force to the
workpiece  Cr, Mo or
W additions
• dissipate heat from
the weld zone
• fix the current density
in the weld zone 
size depends on base
metal thickness
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Base metal
thickness
Metal to
be welded
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Welding cycles
• squeeze - assure
proper contact
before welding
current is applied
• hold - weld nugget
solidifies and cools
• upslope - avoid
overheating and
expulsion at the
beginning of weld
• downslope - control
weld nugget
solidification
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Welding cycles
• gradually build up
the heat at the
interface while
welding thick steel
sheet
• forging force - to
consolidate weld
nugget, reduce
porosity and hot
cracking
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Resistance welding parameters
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Welding current
Q=I2Rt  the most
important parameter
can be AC (most of the
applications) or DC
DC normally produced from
stored electrical energy
affected by impedance
variations caused by
magnetic metals introduced
into the secondary loop of
the machine
excessive current result in
deep indentation
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Resistance welding parameters
Weld time
• depends upon the rate of heat
generation/dissipation
• excessive time lead to exceeding the melting
temperature
Welding pressure
• affects the contact resistance
• as the pressure increase, the heat generated
decrease
• if pressure is increased, current and/or time
must increase too
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Spot weld testing
Peel test
Tensile shear test
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Spot weld testing
Tension test
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Projection welding
Projection welding
machine
Projection welds
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Resistance welding
advantages/disadvantages
Advantages:
Disadvantages:
1) High speed
1) Disassembly is difficult
2) Less skill required
2) Lap joints add weight; also
eccentric load!
3) Adaptable to
automation
3) Equipment cost higher than arc
welding equipment
5) Leak tight welds
(seam welding!)
4) Unfavorable line power demands
5) Abrupt changes in joint contour
cannot be leak tight (seam welding)
6) Built-in notch gives poor fatigue
resistance
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World Centre for Materials Joining Technology