Gap Welding (aka Series Welding) is utilized when only one side of the weldment is accessible with electrodes. Weld current flows from one electrode through the top part and partially into the bottom part before returning to the power supply via the second electrode (see figure).
This form of welding has the advantage of making two weld nuggets at one time. However, series welding is generally less controllable because of the many shunt paths available to the welding current.
Typical Parallel Gap Welding applications include battery packs, medical or automotive sensor wire to PCB, solar cells, hybrid or microwave circuitry, thin or thick film substrate, potentiometers and other miniature components, semi-rigid substrates and fine line printed circuit trace repair.
For more information, read our 'Fundamentals of Resistance Welding'