Staggered Procurement of Raw Material

Hi,
I'm am currently finding it difficult to cope with the ordering cycles that we have for materials. The lead time for our main component is around 2 months, I have however staggered it to set it up in such a way that I have shipments coming in every 2 weeks. I really am not sure if this is the best way of doing things. Do you know of any method that is available to ensure that the material coming in, is in line with the demand prediction. When the demand is static, what you order is the average consumption over the lead time + safety stock. now when I have broken up the shipments in this fashion, I really can't seem to use a formula!