Order fulfillment is often reported to consume more than 60% of the total direct labor associated with warehouse operation. Consequently, the warehouse picking area usually offers the best opportunities for savings through use of optimization methods. This article focuses on three of those methods.
Slotting is the process of determining where items should be placed in the picking area so that the popular items are stored close together and in close proximity to the starting point of picking so as to minimize walking time. Slotting is often painful since it requires substantial labor to relocate items. Furthermore, picking often must stop while items are being relocated.
A naïve slotting approach would be to simply sort the items by popularity and place them on contiguous picking bays close to the start of picking. The problem with this approach is that the popular zone of the picking area may get congested and pickers will be tripping over each other. A better approach would be to “stripe” the popular items on shelves located at ergonomically beneficial heights. This approach would lengthen the popular picking area but would also reduce congestion, improve picking speed and reduce worker fatigue.
Another important consideration in slotting relates to item size, weight and durability. Fragile items should be picked last and placed on top of durable, heavier items already picked. Similarly, better packing density is generally achieved when larger items are picked before smaller items that can be packed around the larger items. A good slotting algorithm will take all of these factors into consideration when assigning slots to products.