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First Thoughts

By Dan Gilmore


June 8 , 2006


Warehouse Management: To Wave or not to Wave?


It’s been a long time since I got this granular with distribution issues (see Task Interleaving in the DC – Reality of Myth?), but some recent discussions with a couple of companies and some smart distribution experts got me on the track of a basic but very important distribution question: when does it make sense to use “waves” to process order batches and release picks to the floor, and when not?

To get everyone on the same page, a “wave” is basically an automated grouping of orders by some criteria that is released to the floor for processing as a set. Grouping attributes might be a set of carriers, a group of stores in retail, high priority orders, orders requiring a specific type of value-added services, or even a specific customer or three if they order in large enough quantities. In general, a wave should consist of something like 45 minutes to 2 hours worth of work.

Let’s dismiss for a second distribution models like flow through or cross dock where waving just doesn’t apply. What’s the alternative to wave processing? Some form of straight order release, where orders flow right to a work queue, with high priority orders and/or those deemed important by a supervisor (e.g., the truck is here!) bubbled to the top. And are their maybe some alternatives in between?

At a high level, wave processing does allow creating of a manageable block of work, can allow the picks to be sequenced in logical groups that meet any number of operational and shipping requirements, and (depending on the scope of the supporting WMS technology) enable order batches to be released that balance work across areas.

In these recent conversations, however, I’ve heard some shippers wonder whether some of the expected efficiency of wave processing is lost in terms of labor workforce downtime at the end of waves. It also seems that in today’s increasingly complex DCs and distribution channels, what is often really needed is an intelligent release of different batches to different processing areas, in effect a series of waves that is different than the traditional model.

I asked SCDigest friend Noah Dixon, VP of Product Management for Catalyst, where he thought the use of wave processing made the most sense.

“One thing that is different today than a few years ago is how orders come down to the DC,” Dixon noted. “Before, almost everyone got a batch download of orders in the morning, and that big batch lends itself to wave thinking. Now, while big one time downloads are still frequently found, many more companies get orders in near real-time all day, which changes your operating model.”

Wave processing is the “moment of truth” when the WMS looks for consolidation opportunities to reduce travel time and transportation costs, Dixon added.  “In addition, when the work force moves through the facility with the work or where the material handling control systems need it, wave processing is really the only way to go.”  However, he added that “most warehouses run better if the work is released when needed rather than in bigger groups.  Exceptions will be fewer and less expensive.” He also added that in facilities that are mostly pallet picks for truckload and multi-stop TL shipments, such as food and consumer packaged goods companies, it is generally easier and faster to release orders based upon appointment times rather than waves. 

Brian Hudock, a principle at Tompkins Associates, offered some similar thoughts. He’s seen waves used to facilitate a group of workers first completing picks in one area for the wave of orders, then moving to another area for the next wave, etc., in addition to the traditional retail model where a wave is released for a group of store replenishment picks, followed by the next, etc. But he noted with the growing complexity of DCs, the order release process is one where there is still often a lot of customization in WMS implementations to meet the unique needs of each company.

“I’m not sure you could or would want to build those specific rules into a base WMS product,” Hudock added, noting that the end effect may use some wave principles, but does not involve a “master wave” across areas, but rather an interleaved series of smaller ones.

Finally, Jim Barnes of enVista thinks there may be a hybrid model, even in retail. “Too often waves are used trying to optimize picking efficiency, when for highly automated environments we should be trying to optimize equipment utilization,” Barnes told me. For many environments, this would better be done by “waveless” picking that still gains consolidation efficiencies through local area batching, using “dynamic” inventory allocation.

By the way, if you are at all interested in Warehouse Management Systems, you really benefit from our How to Select a WMS 2006 Videocast (where I am joined by Jim Barnes and SCDigest’s Mark Fralick). We have a similar one for Transportation Management Systems as well, both in two weeks, though you can watch on-demand later if you can’t make the original dates.

We’re out of space. I am still pondering. More in a few weeks. We’d love your thoughts.

Where does use of pick waves makes sense and where not? Is this changing based on changing DC and order dynamics? Are there alternatives between a full wave orientation and straight order release to the floor? Let us know your thoughts.


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