To reduce transportation costs for products arriving from overseas, cartons are normally hand-stacked in shipping containers. This works well for reducing shipping costs, but if we're not careful, we may give away the savings in storage and handling.

Storing cartons of product would seem, on the surface, to be a relatively simple matter.

Put them on a pallet, stack them on decked rack, put several on a mini-load tray, place them on shelving in the pick face or even put them in carton flow rack. But, which one, and how much?

Most problems have a simple part, and a complicated part. Clearly, when a container arrives with large numbers of cartons for only a few stock keeping units (SKUs), then it seems logical to palletize them for storage. However, each SKU is likely to create several full pallets, and one partial pallet. This partial pallet will underutilize a full pallet storage position. The more SKUs, and the more receipts, the more storage capacity we lose.

Providing some short pallet positions in the rack is a viable approach. However, these positions are less "cube efficient" and it's hard to get the mix of "shorts" and "talls" just right.

A second alternative is to hand-stack the residual cartons on shelving or decked rack. Often, this is done with the cartons two-high per level, or even two-deep.

Standard shelving, with four to five levels, can be served with input and output conveyors, providing the possibility of relatively high throughput capacity.

If the storage mode is decked pallet racking and accessed with order picking trucks in narrow aisles, storage density is very high. But, the efficiency of putaway and retrieval is far less than walking.

Storing cartons in carton flow rack is generally considered to be too expensive, unless the receipts are frequent enough and small enough that the entire inventory can be held in the flow lane. A major grocer, who can control the flow from its suppliers, takes advantage of this opportunity for one-step handling.

Every once in a while, the characteristics of the inventory and activity open the door for higher levels of automation. With today's much faster storage/retrieval machines (approaching 150 dual cycles per hour), cartons may be stored singly on a shelf, or several on a standard tray.

Mini-load storage turned out to be a good solution for an apparel manufacturer, conveying the cartons to the induction stations of a high-speed sortation system. Space is reserved at the front of the storage system for partially filled cartons returning from the sorter so that they may be accessed quickly the next time that SKU is needed.

In choosing which one, or what combination of these storage modes to use, we must consider:

• What is the range of carton sizes and the expected inventory in each?
• How many cartons of each SKU do I have in inventory?
• Do I need to manage inventory on a FIFO basis?
• Do I need to separate inventory by lot code or receipt date?
• How many cartons of an SKU are in a typical receipt?
• How will cartons be drawn from, and perhaps returned to inventory?

Because we can't predict the profile of the inventory very far into the future, it's best to bias the mix of storage modes slightly toward the most flexible alternative.