What is Flash Welding?

Flash welding is a type of Butt welding that fuses metal surfaces together via electrical current.

Due to the conductive properties of metal, an electric current can pass through while there is a small gap between work pieces. This in turn creates localised sparks or “arcing,” which rapidly heats up the metal.

The worker then forces the pieces together to create a bond between the metal surfaces.

How does flash welding work?

Flash welding works by applying a current through the necessary metals to form a bond. The metal itself acts as a conductor, allowing the current to flow; this process generates a significant amount of heat. The resulting heat is enough to fuse the metals together to form a weld.

Flash welding is unique in its application because it requires you to pass a current through the metal pieces while there is still a small gap between them. The gap is small enough to allow the current to arc between the gap, which creates heat in both metal pieces. The amount of heat generated is enough to soften and often melt the surface of the metals being joined.

It is at this point that the worker forces the two metals together, creating a strong and secure bond.

Once a suitable temperature is reached, the current is switched off and the worker waits for the weld to cool down.

Why do we see a “flash”? The small contacts made between the two metal pieces during the flash welding process produce localised areas of high current density. As the electrical current heats, melts and burns off impurities within the metal, the characteristic flash appears.

What are the advantages of this process?

Typically, you’d use flash welding on anything that can be clamped and slowly brought together. This allows joins to be made on parts with a wide range of shapes and sizes. Railway rails and car rims are common applications for this process.

This method requires no filler, and workers don’t need to prepare surfaces beforehand, which reduces the overall complexity.

While arcing is occurring and heat is being generated, any impurities at the weld site are burnt off in the flash, creating a strong and reliable join.

Finally, it is possible to join dissimilar metals, including ferrous and non-ferrous metals.

What are the limitations?

The most obvious drawback is the arcing and flashing that’s produced during the process. This is a potential fire hazard waiting to happen that needs to be diligently managed with every weld.

Every flash produced is hot metal – metal that is lost during the welding process. This metal ends up as flash product on the weld site, which necessitates manual cleaning.

And finally, flash welding requires welding machines that are bulky and heavy; this limits work to dedicated workshops or to specially designed equipment.