Hi,
If you do operation subcontracting than in that you can consume the child material which ever are associated with operation .
in that case you can add as co product at the time of next operation confirmation.or create a finish good material code. createbom for the material
create po item category as L issue material to vendor as 541 movment,receive material in 101 agnaist po,same time 543 will happen for raw material.
thanks & regards
sandeep