mrp multi level panning

i want run mrp for multilevel by exploding the bom.

i have already created bom with piece parts and created all necessary data in mrp.(mrp type:manual reorder point level,lot size and safety stock)

when i run md02, and the planning is happening for finished part no only and not for piece parts. i am not able to see any piece parts no, quantity in md04.

can anybody tell why this problem is, what should i do for bom explosion and planning.

the material type for finished part is fert and piece parts are halb(semi finished)

regards

partha