“Task interleaving” – a distribution term I’ll define more clearly in a second - might be a bit low level for some of our supply chain readers, but this is the “Logistics Edition” of SCDigest, and for those that worry at all about distribution operations it’s worth a few moments of time.

Interleaving is a concept arising out of the early days of the warehouse management software industry that involves system-directed linking of discrete task types. Commonly, this might mean an operator performing a pallet putaway is then asked to pick a nearby pallet for replenishment of a forward pick site. The idea is to reduce “deadheading,” or driving empty material handling equipment around the DC. (Click here for illustrative diagram.)

The promise is dramatically increased operator productivity. In fact, you will rarely find a seminar presentation on WMS that doesn’t tout task interleaving as one of the key ROI generators of a WMS. But I have a secret – interleaving isn’t used nearly as much in the real world as these presentations would have you believe.

It’s definitely being used – just not nearly with the frequency that many pundits and vendors would have you believe. A few years ago, I spoke with the CEO of one medium-sized WMS vendor (but which had several very large corporate clients), who asked me straightforwardly if anyone was actually using true task interleaving.

The answer is definitely yes, but as with most things you have to peel back some layers. For example, almost everyone using Very Narrow Aisle storage with specialized equipment in those aisles will have to employ some form of drop and pick-up using more traditional equipment to deliver and take product away from the aisles - and most advanced warehouse systems can support this kind of task linking (e.g., a pallet drop at the end of an aisle triggers a task for the VNA vehicle). It’s also pretty easy to link a non-movement activity, like a cycle count, to a traditional task (such as forcing an immediate cycle count if there is a picking discrepancy or the location is picked clean).

But beyond that there are real challenges. It clearly works best for full pallet movements, and changing order profiles and other dynamics are in many cases reducing the opportunities to link putaway with picking or replenishment tasks. Second, it can simply be hard to implement, adding complexity into operations and the jobs an operator performs that some companies find just isn’t worth it. It adds a lot more WMS set-up, for example, and may involve substantial training and change management issues for workers used to performing mostly one job. Last year, I was in a DC that was sending workers far across a large warehouse for the next task because the system configuration was just not right.

For many companies, though, the results are worth the effort. One very large consumer products company (where pallet moves are the rule) that had not yet adopted interleaving estimated potential annual savings in the tens of millions of dollars. I’ve talked to a number of companies that have saved 5-15 percent in labor costs after introducing interleaving techniques.

We’ll end in three quick thoughts. First, remember the four attributes of interleaving: permission, proximity, priority and time (age of the task). Your system needs to be able to accommodate those factors in making interleaving decisions. Second, the evidence seems to be that in most cases, the best decision is to turn a new WMS system on without including interleaving. First get users acclimated to the new environment and system before adding this additional element of change. Third, WMS vendors and consultants need to develop better tools to really understand the flow and real labor savings expected from interleaving – the estimates I’ve seen often are too much guesswork.

Are you using task interleaving in the DC. If so, what were the challenges and benefits? If not, why not? 

We'd really like to know your thoughts.