Copyright © 2005, TWI Ltd World Centre for Materials Joining Technology RESISTANCE WELDING TWI Training & Examination Services EWF/IIW Diploma Course.
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Copyright © 2005, TWI Ltd World Centre for Materials Joining Technology
RESISTANCE WELDING
TWI Training & Examination TWI Training & Examination ServicesServices
EWF/IIW Diploma CourseEWF/IIW Diploma Course
Copyright © 2005, TWI Ltd World Centre for Materials Joining Technology
Resistance spot welding principle
Copyright © 2005, TWI Ltd World Centre for Materials Joining Technology
Resistance seam welding principle
Copyright © 2005, TWI Ltd World Centre for Materials Joining Technology
Projection welding principle
Copyright © 2005, TWI Ltd World Centre for Materials Joining Technology
Spot welding - heat generation
• a & g - electrode a & g - electrode material resistancematerial resistance
• b & f - contact b & f - contact resistance resistance electrode to base electrode to base metalmetal
• c & e - base metal c & e - base metal resistanceresistance
• d - base metal d - base metal interface interface resistanceresistance
Electrical Electrical resistance in the resistance in the welding circuitwelding circuit
Copyright © 2005, TWI Ltd World Centre for Materials Joining Technology
Spot welding equipment
• Pedestal Pedestal welding machinewelding machine
• Portable welding Portable welding machinemachine
Copyright © 2005, TWI Ltd World Centre for Materials Joining Technology
Spot welding equipment
Resistance electrodes Resistance electrodes functionsfunctions
• conduct the welding conduct the welding current to the work current to the work made from Cu alloysmade from Cu alloys
• transmit force to the transmit force to the workpiece workpiece Cr, Mo or Cr, Mo or W additionsW additions
• dissipate heat from dissipate heat from the weld zonethe weld zone
Base metal thickness
Metal to be welded
• fix the current fix the current density in the weld density in the weld zone zone size size depends on base depends on base metal thicknessmetal thickness
Copyright © 2005, TWI Ltd World Centre for Materials Joining Technology
Welding cycles• squeeze - assure squeeze - assure
proper contact proper contact before welding before welding current is appliedcurrent is applied
• hold - weld nugget hold - weld nugget solidifies and coolssolidifies and cools
• upslope - avoid upslope - avoid overheating and overheating and expulsion at the expulsion at the beginning of weldbeginning of weld
• downslope - downslope - control weld control weld nugget nugget solidificationsolidification
Copyright © 2005, TWI Ltd World Centre for Materials Joining Technology
Welding cycles• gradually build up gradually build up
the heat at the the heat at the interface while interface while welding thick welding thick steel sheetsteel sheet
• forging force - to forging force - to consolidate weld consolidate weld nugget, reduce nugget, reduce porosity and hot porosity and hot crackingcracking
Copyright © 2005, TWI Ltd World Centre for Materials Joining Technology
Resistance welding parameters
Welding currentWelding current
• Q=IQ=I22Rt Rt the most the most important parameterimportant parameter
• can be AC (most of the can be AC (most of the applications) or DCapplications) or DC
• DC normally produced from DC normally produced from stored electrical energystored electrical energy
• affected by impedance affected by impedance variations caused by variations caused by magnetic metals magnetic metals introduced into the introduced into the secondary loop of the secondary loop of the machinemachine
• excessive current result in excessive current result in deep indentationdeep indentation
Copyright © 2005, TWI Ltd World Centre for Materials Joining Technology
Resistance welding parameters
Weld timeWeld time
• depends upon the rate of heat depends upon the rate of heat generation/dissipationgeneration/dissipation
• excessive time lead to exceeding the excessive time lead to exceeding the melting temperaturemelting temperature
Welding pressureWelding pressure• affects the contact resistanceaffects the contact resistance• as the pressure increase, the heat as the pressure increase, the heat
generated decreasegenerated decrease• if pressure is increased, current and/or if pressure is increased, current and/or
time must increase tootime must increase too
Copyright © 2005, TWI Ltd World Centre for Materials Joining Technology
Spot weld testing
Peel testPeel test
Tensile shear testTensile shear test
Copyright © 2005, TWI Ltd World Centre for Materials Joining Technology
Spot weld testing
Tension testTension test
Copyright © 2005, TWI Ltd World Centre for Materials Joining Technology
Projection welding
Projection welding Projection welding machinemachine
Projection weldsProjection welds
Copyright © 2005, TWI Ltd World Centre for Materials Joining Technology
Advantages:Advantages:
1) High speed1) High speed
2) Less skill 2) Less skill requiredrequired3) Adaptable to 3) Adaptable to automationautomation
5) Leak tight 5) Leak tight welds (seam welds (seam welding!)welding!)
DisadvantagesDisadvantages::
1) Disassembly is difficult1) Disassembly is difficult
2) Lap joints add weight; also 2) Lap joints add weight; also eccentric load!eccentric load!
3) Equipment cost higher than 3) Equipment cost higher than arc welding equipmentarc welding equipment
4) Unfavorable line power 4) Unfavorable line power demandsdemands
Resistance welding advantages/disadvantages
5) Abrupt changes in joint 5) Abrupt changes in joint contour cannot be leak tight contour cannot be leak tight (seam welding)(seam welding)6) Built-in notch gives poor 6) Built-in notch gives poor fatigue resistancefatigue resistance
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