There are two basic strategies for assigning items to bin locations in a warehouse. In a fixed slotting system, every SKU has a set location and new replenishments of that item go to the same bin. In a random slotting system, items are placed in any open bin into which they fit. The decision in that case is made on the fly by a system or a warehouse worker. In either case, the replenishment is recorded so that the inventory system knows the quantity in stock in every location.
Which approach is better? Partisans on both sides are equally convinced of the merits of their strategy.
Fixed Slotting System
Those on the “fixed” side of the debate argue that by optimizing the slotting of a pick line, an operation can increase picking productivity and ensure a particular sequence (e.g., one that avoids crushing in a case-to-pallet environment). They also argue that pickers work faster after learning products’ set locations.
Random Slotting System
Over on the “random” side, supporters would argue that their approach optimizes put away. Storing items is faster because products are assigned to whichever location is most efficient at that particular moment. Furthermore, this strategy avoids the overhead of maintaining an optimally assigned pick line, thereby saving the time of both analysts and line workers who would have to re-bin products periodically. Finally, they would say that there is not much penalty on picking efficiency, particularly if most SKUs tend to move at the same speed.
The Right System for the Right Situation
I think people are partial to whichever slotting system they have become accustomed to. It’s hard to imagine the other system working well if you haven’t experienced it. But slotting strategy isn’t just a matter of comfort or opinion. Neither system is inherently better; they just fit different situations depending on the dynamics of an operation. Consider the following scenarios:
- Fast fashion” or flash sales. Operations like these involve thousands of SKUs, the constant reception of new ones, and a short lifespan for each SKU. It wouldn’t make sense to establish fixed bin locations with such a high SKU turnover. Random slotting is the better solution in this situation.
- Fast movers section of a grocery DC, where you constantly pick SKUs in high volumes. Here, a well designed pick face with fixed bins is more likely to provide maximum picking efficiency and ensure sequencing from heavy to light.
- Slow movers section of a grocery DC, where you have a long tail of slow movers, each with only a few units on hand. It’s not worth the overhead of maintaining set locations, as it won’t make your picking that much more efficient. Random slotting would therefore be a valid option in this case.
Final Thoughts
In the end, choosing the right strategy will depend on various aspects of your operations: what is the nature of your product? How many SKUs do you hold? How much inventory do you have on hand, and how fast do items move? What kind of container are you picking from: pallets, boxes, etc.?
But remember: regardless of which binning strategy you pick, you’ll need a well-maintained WMS to ensure your warehouse is managed efficiently.