Fortunately, there are several ways to reduce and/or eliminate the inefficiencies between waves and improve overall throughput.

Many Distribution Centers have implemented waving within their order fulfillment process to control and manage the requirements for the day into smaller groups. The term waving simply means grouping a set of order fulfillment requirements (normally a group of orders) for picking, packing and shipping purposes. The wave planning process determines which orders are placed into each wave. The wave release process provides the work to the floor in terms of releasing picks regardless of pick method (Paper, Label, RF, Voice, etc.). The completed picks are normally placed onto a conveyor and transported to a sortation system to segregate the picked containers (full cases, or split case picks) by some other attribute (by ship to location, by order, by carrier, etc.) based on the facilities requirements.

Grouping picks into waves provides many benefits over traditional order picking processes. When order picking, the picker must travel the entire pick path to complete the picks for the order. Incremental improvements over order picking include batching or grouping a set of orders together to complete all of the picks for the batch while only traveling the warehouse pick path once. Other variations include breaking order picking requirements by zone or area within the warehouse. All of these variations are intended to reduce the amount of man-hours required to complete the picks. Variations like zone picking can reduce congestion.

The Problems with Waving

If you pick in waves, you likely have some sort of conveyor sortation process to separate out the picks in order to prepare the shipments for delivery to your customers. Full pallet picks are normally picked separately and moved to staging locations awaiting the full case and split case picks. Full case picks are likely sorted to divert lanes assigned to a carrier or customer (ship to location or order depending on requirements).

The assignment process of requirements to divert lanes implies that the divert lanes are resource constrained, meaning you can only include into the wave a number of containers (full cases or split case picks) that match the number and size of the divert lanes. So you need a WMS or WCS to build the wave for you in a manner that controls these resources. 

The diverts lanes will either be directed to a destination (palletization station or direct load lane) that may or may not require separation. For example, orders shipped by a parcel carrier, like UPS Ground, or Fed Ex Next day do not require separation other than only one carrier/service per divert lane. LTL and TL shipments normally must be palletized by order or ship to location.

This need to manage the fixed number of sortation resources available in the facility can be the problem.  You may only have the ability to sort one order at a time to many of these sortation divert destinations. This means the person at the end of the divert lane is working to palletize the products presented by the sorter but cannot finish the pallet until all of the waves requirements have been sorted. This requirement for a fixed segregation between waves is the problem.

Many facilities employing fixed segregation between waves may see productivity on their sorter decrease near the end of the current wave and go to near zero until the next wave is released to the sorter.

Solutions to the Problems

Sortation that eliminates segregated waves is the solution. There are various strategies to implement this capability. You can establish more than one palletization station for each sortation divert lane. This allows the next pallet to be started while waiting for the last carton for the pallet from the previous wave to be completed. 

If you don’t have the room for more than one palletization station per divert lane, consider only including half the divert lanes into one wave and the second half into the second wave.  Although this reduces the size of the wave, which ultimately can increase the man-hours required to pick, the overall time to complete waves is reduced because you have eliminated the time of low efficiency on your sortation system.

Maintaining sorter capacity during wave transitions can improve your overall throughput by 10-25% depending on the severity of your wave overlap problem. Although it is best to implement these strategies while designing new order fulfillment facilities, these strategies can be implemented within existing facility layouts. Your business requirements and rules will determine the best way to implement overlapping waves. 
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