When product is stored in convenient locations, then it is easy to retrieve when requested by a customer. But what is meant by “convenience” depends on models of labor and of space. These models are simplest for pallets, because they have some standard dimensions and are, in many cases, handled one at a time. The concept of“convenience” becomes progressively harder to pin down as we discuss smaller units of storage and handling, such as cartons and pieces.
Layout of a unit-load area
The simplest type of warehouse is a unit-load warehouse, which means that only a single, common “unit” of material is handled at a time. The typical unit-load is a pallet. Because pallets are (mostly) standardized and are (mostly) handled one-at-a time, both space and labor requirements scale: It takes about n times the space to store n pallets as for one; and it takes about n times the labor to handle n pallets as for one.
An example of unit-load is a 3rd party transshipment warehouse that receives, stores, and forwards pallets. The 3rd party warehouse is a subcontractor to others for warehouse services. A 3rd party warehouse typically charges its customers for each pallet handled (received and later shipped); and rent for space occupied. In this chapter we study unit-load issues in the context of such a warehouse; but many warehouses have some portion of their activity devoted to moving unit-loads, as in Figure 6.1.
Figure 6.1: Flow of unit-loads through a typical warehouse
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