Ok so it may not be a lightsaber factory BUT that doesn’t exclude this from the fact that it’s still potentially terrifying albeit  extremely cool. It’s actually from a Polish steel factory and well this rather helpful YouTube commentator gives the breakdown of why this actually occurs:

[info_box]

This is cobble in Rolling mill. Temperature of the steel on this point is about 1000′C. So the steel is plastic but no liquid. This particular cobble happened because material did not enter to the next rolls inside stand x. Because material did not enter to the stand number x and stand number x-1 is giving material. Stand x-1 can not stop becasu stand x-2 is giving material and so on.

Is is common phenomena in rolling mills around the word.[/info_box]