Sridhar,
I hope when you are talking about SFGs at 3 operations W,X and Y they are different material codes and You want to receive the stock after each operation.
In this case you need to define 4 different BOMs and 4 Routings for each BOM level and Operations level.
Example if you take first level SFG lets say material A Base quantity is 10 in BOM and component quantity is 1 and Routing consist one operation called W.
Same way you need to define BOM and Routing for other 3 levels.
BR
KK