Making the Right Order Picking Choices: Static Storage, Automated Systems, and Gravity Flow Alternatives

The question is this: how quickly do your order-picking employees need access to stored items? You have quite a few alternatives, and virtually all of them can play a role in picking operations, depending on your circumstances.

Many DC's -- in fact, most of them -- find reasons to utilize static storage, carton flow, and automation in their operation.  There are three basic choices, listed below. But within each method can exist hundreds of alternatives.

Static Shelving, Pallet Racks, & Bulk Racks: The "Primitive" Solution that Works in Modern Operations

Conventional static shelving or bulk rack is relatively inexpensive and basically maintenance free. It is the best choice for very slow moving merchandise, and can be coupled with gravity flow and automated systems as the picking method for slower items. 

It works just as well for each-pick or case-pick applications, provided it can provide sufficient space for the stored items.

Static storage is sometimes maligned as "primitive" but primitive solutions are that way because they have worked for a long time. You don't need to be high-tech to pick an item that is called for only a few times a shift. The key is to understand when the money you save by throwing a slow-mover into racks or shelving is costing you in productivity.

Direct productivity comparison: gravity flow vs. static shelving. While it may take longer to pick items from static storage, if the sku is a very slow mover that isn't accessed often, and space in the facility isn't compromised by the presence of shelving or racks, static storage can be a perfectly viable order picking method.

THE HYBRID: Pallet racks can be used to store palletized loads of slower-moving product in some order picking applications. In fact, pallet racks that utilize Span-Track carton flow rails in some of the bays are a good way to mix slow and fast-moving items in the same storage unit, or to store bulk quantities that are easily transferred to active operation later. This provides you with a mixture of pallet storage and carton flow within the same space. (see drawing above).

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Gravity Flow & Carton Flow Solutions: The "Middle Ground" Solution that Blends Automation and Static Storage

Gravity Flow or Carton Flow systems, such as gravity flow racks offer many of the best features of both other methods. (Direct productivity comparison: gravity flow vs. static shelving.)

You can consider flow storage to be a "middle-ground" method. They are faster and more efficient than static storage, but cost more. Gravity flow isn't typically as fast, accurate, or secure as automation, but it is less expensive to implement and requires little maintenance. Flow racks are far less costly than automated systems, and more efficient than static shelving. They are virtually maintenance free and allow you to rotate merchandise on a first-in, first-out basis.

Space is conserved to a degree, since carton flow units can offer more dense storage than static shelving -- although often less than automated systems. Placed along a line of conveyors, flow racks can provide a solid wall of picking faces that an operator can access quickly to add to incoming orders with less operator "travel time" than static storage, at a higher cost per position--but at an implementation cost significantly less than that of automated systems.

Carton flow can also be enhanced with CAPS systems. Computer & Light Assisted picking systems can be installed with many kinds of gravity flow racks to increase accuracy. Flush-mount pick modules are easy to read, soft on the eyes, and tough on the rigors of the warehouse environment. This helps gravity flow take on some of the information-trail advantages incumbent in automated systems.

Automated Systems & Carousels: Fast Movers, High Efficiency for Palletized or Mini Loads

Automated systems such as carousels and AS/RS systems work well if you're storing extremely fast-moving goods in full case quantities.

You can certainly reduce personnel needs with automation, but it may be a case of using a shotgun to kill a fly -- do you need to?

The answer is: sometimes. Automated systems tend to be more costly than static picking or gravity flow, but in the right application, at the right spot, carousels, mini-load, and unit load picking systems are the best picking solution, and can save you money despite a higher cost of implementation vs. the other two broad methods.

Automated systems provide very high storage density. Operators do not have to walk to find things in most automated systems, as items to be picked are delivered to pickers by the system. They tend to be very accurate.

If the items being picked are fast movers, or space is at a premium in your facilities, or accuracy and a more comprehensive audit trail are factors, AS/RS and carousels emerge as the best choice.

Security is another factor: Because automated systems are typically driven by WMS and other external intelligence, it can deliver information quickly on what was picked and when. It also removes access to stored items for most everyone except the operator or designated pickers, denying access to unauthorized personnel.

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