Resistance Spot Welding

Resistance Spot Welding is a thermo-electric process where heat is generated at the interface of the parts to be joined by passing an electrical current through them or a precisely controlled time and under a controlled pressure (also called force). The name “resistance” spot welding derives from the fact that the resistance of the workpieces and electrodes are used in combination or contrast to generate the heat at their interface.

Key advantages of the resistance spot welding process include:

  • Very short process time
  • No consumables, such as brazing materials, solder, or welding rods
  • Operator safety because of low voltage
  • Clean and environmentally friendly
  • A reliable electro-mechanical joint is formed

Resistance spot welding is a fairly simple heat generation process: the passage of current through a resistance generates heat. This is the same principle used in the operation of heating coils. In addition to the bulk resistances, the contact resistances also play a major role. The contact resistances are influenced by the surface condition (surface roughness, cleanliness, oxidation, and platings).

The general heat generation formula for resistance welding is:

Heat = I2 x R x t x K

Where “I” is the weld current through the workpieces, “R” is the electrical resistance (in ohms) of the workpieces, “t” is the weld time (in hertz, milliseconds or microseconds), and “K” is a thermal constant. The weld current (I) and duration of current (t) are controlled by the resistance welding power supply. The resistance of the workpieces (R) is a function of the weld force and the materials used. The thermal constant “K” can be affected by part geometry, fixturing and weld force.

The bulk and contact resistance values of the workpieces, electrodes, and their interfaces both cause and affect the amount of heat generated.  The diagram (above right) illustrates three contact and four bulk resistance values, which, combined, help determine the heat generated.

See Spot Welding for more information

And for more information about the resistance welding process read Fundamentals of Resistance Welding

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