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What's the Criteria for Slotting?

This is a guest post by UNEX distributor Cisco-Eagle


In the warehouse or distribution center, where speed and precision play an important role in end-user satisfaction, ensuring proper product flow is critical to improving supply chain efficiency.

In fact, most warehouses and DCs of significant size incorporate a thoughtful mix of static storage, carton flow, and goods-to-person automation to increase pick productivity and maximize their operations’ throughput rate.

At Cisco-Eagle, we help a lot of operations figure out what kind of storage equipment is ideal for their product mix and operational needs. Obviously, there are a whole host of options to choose from (even within the simplest, least automated solutions), so it’s important to first determine whether a product or group of products is best slotted into shelving and bins or better suited for carton flow solutions.

Our friends at UNEX Manufacturing have also developed a tool that will analyze your product mix and help identify what storage medium best suits your SKUs. 

Carton Flow vs. Shelving: Which Storage System Fits Your Product?

Carton flow can be used for full cases, but is more effectively used for piece picks. Its main attributes are that it helps reinforce organization and the order in which a product is picked. It has better product density, although that isn't the main argument for using it. It is also easier to re-stock than shelving. But when you are trying to decide whether an item is appropriate for carton flow, what are the decision points?

The following is a look at some of the criteria for slotting inventory into carton flow:

How Often Is the Item Picked or Accessed?

For each-pick applications, target the fastest-moving SKU's in your product mix by a unique number of picks and not total stock numbers. If the item has a large number of picks, it's a good candidate for carton flow. If you must re-stock during working shifts, the case for flow storage gets stronger. Because flow rack is likely the most costly of static storage options (based on cubic feet analysis), it's usually reserved for the highest velocity SKU's, which have the most average picks per day. If you have a limited amount of flow storage space, you should frequently analyze order picking activity and move slower movers to shelving or racks for newer, or faster movers. Don't do this so infrequently that it becomes a tangled mess – you should not allow it to get to the stage that it is major undertaking.

But what about case picks? For case picking, carton flow is a mid-range solution. If the item is picked at least once every week, it's a candidate for flow storage. If more than half a pallet (of cases) of it is picked in a week, you may want to look at other alternatives. Fast-moving cases are better picked from pallets, and slow movers from static shelving. There are good situations for carton or case level picking from flow storage. It can also be used to reduce refill time for slow-moving cases (less than five times a day). You don't want to restock during a picking shift, and carton flow is a very good solution for that time frame.

Other Factors to Consider

  • Vertical shelf openings: The height of your shelf openings in flow rack should be evaluated, and re-evaluated. Companies often install flow rack beams at consistent heights, so that all beam levels have the same distance between them. It looks nice and neat! This might work for pallet rack, but unless all your cartons or SKU's are the same, it's not optimum. If some cases are taller than others, it causes difficulty for pickers reaching into them. In the meantime, lower profile cartons have copious amounts of wasted space between them and the next level. To maximize your system's capacity, consider grouping cartons of similar sizes together, or regularly reconfiguring your carton flow beam spacing to fit the current inventory profile.
  • Does your load and rack layout fit the restocking situation?If you can get through a full pick face of it in less than a week, carton flow is more than justified for that SKU. You'll do this to minimize replenishment efforts and costs. Since you can stock from the back side of a flow rack, it can be done during a pick shift, which can't be done with a shelving or rack storage solution.
  • Mix static and dynamic storage: One solution that isn't uncommon is to have an SKU in both a static and a flow storage setup. Static for certain shifts or low activity times, and flow storage for rush orders or high priority customers. This requires some process and organizational work, but can be done effectively.
  • Does the SKU picking scheme cause excess travel time? One of carton flow's chief advantages is that it is a manual goods-to-picker solution that helps reduce walking and travel time. Since labor makes up so much of your cost structure, moving items to flow storage is ideal when it comes to reducing wasted "walk" time. Carton flow slashes walking time by three-quarters, so it is ideal for these situations.
  • Can you pick an entire lane in one week? This requires a bit of evaluation, but the outcome is worth it. If you can pick a full lane's worth of product in a week, the product is an ideal carton flow candidate. This reduces replenishment burdens and ensures that the product has the ideal picking velocity for a carton flow application.

Final Thoughts

While the cost of carton flow implementation is less than that of automated systems, it’s significantly more expensive than static storage.  That said, a flow system can cut labor costs dramatically and make efficient use of floor space, so it’s important to weigh the investment with the many advantages of carton flow.

The above list outlines some of the criteria to use for slotting inventory into carton flow.  What factors does your organization take into account to determine how to increase productivity and maximize their operations’ throughput rate in the most cost-effective way?