Metalworker's union
(Other definitions for weld that I've seen before include "Join using fusion" , "Bond" , "Solder" , "Join together by heating" , "Fused metal joint" .)
(Other definitions for solder that I've seen before include "Join or fuse metal, using an alloy" , "Join two metals with a melted alloy" , "Metal bond" , "Soft alloy used to cement metals" , "Join two metal surfaces together" .)