Questions related to Work Definition involving Phantom parts

Summary:

Questions related to Work Definition involving Make and Phantom parts ( for Hi Tech Industry)

(a) Can we create a Work Definition for a Phantom Part number? I dont think we should, but what exactly will determine whether we can create a Work Definition for (is it the 'Make' flag at Item level)?

(b) My Make Part (say A), has to undergo Operation Welding. It undergoes this process itself and comes out as a welded part (same Part #). How can we represent the same in Work Definition? (can we represent the Item as part A and Operation As Welding and the Operation Items as Part A itself?