Returnable packaging

Dear Experts,

I want to configure the returnable packing scenario. in that i want the system to automatically calculate the packing materials required for packable materials while doing delivery as sub item. also this sub item should not be billed and there is no handling unit management.

for Eg:1 Carton=8 pieces(Sales order Qty)

2 Carton=16 pieces(Sales order Qty)

Regards

Ramesh