What Is … Resistance Spot Welding?


Resistance spot welding is one of the most cost effective joining processes. This welding process has been being used in industrial manufacturing since around 1930 to join plates made from different metals. Resistance spot welding is mainly used in the auto industry for bodywork and vehicle construction. It is also used in the electronics industry, such as in the construction of switch cabinets or to produce EMC shields (electromagnetic compatibility).

The welding process is simple, energy efficient, and does not require the use of a shielding gas or filler metals. With certain restrictions, it is also possible to join materials that would otherwise be very complicated to weld – such as aluminum. This makes resistance spot welding particularly interesting for lightweight auto construction and in the aerospace sector.

Spot-by-Spot for the Perfect Result

The principle of resistance spot welding is based on guiding a current to the component via an electrode with high electrical conductivity and low thermal resistance. The parts that are to be joined are laid one on top of the other and mechanically fixed in place under high pressure by two electrodes. Current is passed between these two electrodes, forming contact resistance in the workpieces themselves. This causes the plates being joined to heat up at the point of contact and liquefy until the desired welding spot diameter is achieved and the two workpieces fuse together.

The biggest challenge with this process is achieving the right balance of a sufficiently high welding force and the lowest possible welding current. If the mechanical force of the electrodes is too high, the contact resistance between the plates is reduced, resulting in significantly higher power requirements. If the force is too low, it is often not possible to keep the molten mass at the desired location, creating spatter. The right balance of force and current ensures perfect results and keeps both wear and energy consumption low, thus reducing costs.

It is also essential for the success of the welding process that the guns that hold the electrodes are sufficiently rigid. If they are not, this can result in what is known as “electrode sliding”: the action of the force causes the electrodes to slide forwards during welding. Electrode sliding can cause nugget-shaped welding spots to develop, rather than round ones. This is an undesirable outcome in manufacturing operations. Spot welding guns with a robust design avoid this effect and make high quality spot welding processes possible.

Qualitative spot welds without spatter with DeltaCon, the gun for conventional spot welding.

Advantages of Resistance Spot Welding:

  • Cost effective
  • Easy to automate
  • High productivity
  • Suitable for joining different materials
  • Multi-sheet joints possible

Disadvantages of Resistance Spot Welding:

  • Good workpiece surface quality required
  • Variable welding parameters due to electrode wear

The Fronius product range contains different spot welding systems suitable for different requirements: the conventional DeltaCon spot welding guns and the revolutionary DeltaSpot welding process with continuous process tape. Find out more about these solutions on our website and on our blog in the near future.