Exactly what it says in the subject title really,

I'm used to, in reenactment simply having the wings attached to the socket using a Mig welder but, clearly they didnt have those in the viking age.
So do we have any clue from original finds how they were attached, obviously fire welded in some way but how was the steel for the wings given enough purchase to weld it to the socket

(if it was attached seperately and not perhaps formed integral to the socket using various forging methods)

I have seen one way to do it where the socket was forge-welded together in two halves. Then separate pieces for the wings was inserted in the seams when the two pieces where welded.

To complete forge-welding of two rather long seams like that requires great skill but it seems like a valid method (bet there is more ways to do it)