Task interleaving is an advanced productivity practice enabled by leading warehouse management systems (WMS) with task management engines. Task interleaving is designed to reduce deadheading—i.e., when a worker, for example, picks products and drops them off at a dock and then returns to the picking area without performing any useful tasks along the way. In most operations, some workers are dedicated to picking, while others are dedicated to put-away. Task interleaving is most common in operations with workers that have permission to do both. So instead of a selector returning all the way across a warehouse to a pick zone, they may stop at a nearby receiving dock, pick up a pallet for put-away, and then store it in a location near where their next pick occurs.
I spoke with a warehouse project manager recently whose company started using interleaving across its network of warehouses and distribution centers in 2007. The company has standardized on RedPrairie (an ARC client) as its WMS solution at both the warehouses they operate and the mixing centers managed by its 3PL partners. (A mixing center is a DC that gets products from different factories or divisions so that customers can receive truckload shipments of all the products they want, instead of having to receive multiple less-than-truckload shipments to complete an order). Two days before turning interleaving on, the company moved about 470 stacks of pallets at one of its DCs. The day it started interleaving, the company moved over 700 stacks.
These types of productivity gains are not that unusual. What is unusual, in this instance, is how quickly the gains were achieved. This manager mentioned that when the company first turned on interleaving at its other facilities, productivity typically dropped for a period of time before rising to a level that would have been unachievable without interleaving. This also happened when the company first introduced WMS with more basic task management to existing warehouses. However, in this manager’s experience, the “valley of despair” (the period when productivity falls) lasts longer for task interleaving, but the productivity gains also exceed what is usually achieved with more basic WMS task management functionality. In short, more pain, more gain. You need to set expectations properly or the warehouse manager may want to turn interleaving off before it has had a chance to prove itself.
What was different about this warehouse, and the reason the company was able to achieve instant productivity gains, was that this was a ‘greenfield’ facility—i.e., workers had not yet learned behaviors that needed to be unlearned.
Task interleaving does not just change the way floor-level employees do their job, it also changes things for managers, particularly shipping coordinators. Task interleaving works best at larger facilities where more tasks can queue up in the task management rules engine. This project manager explained to me that prior to interleaving the guys at the dock knew that once a truck was loaded they needed to bring their paperwork to a manager and get new work to do. Now, however, if the task queue is empty, workers tend to slip outside to smoke or talk. Shipping coordinators need to monitor the docks more proactively than they did in the past.
Further, task interleaving may require changes in scheduling, layout, and flow to maximize the productivity gains possible.
If your warehouse does put-away during the day, and picks and ships at night, your productivity gains are apt to be more limited. You might still interleave cycle counting with put-away, or picking with value-added services, but your ‘bang for the buck’ won’t be the same.
Also, a warehouse layout that has receiving docks on one side and shipping docks on the other is not as conducive to productivity gains from interleaving as a layout that has a few dedicated receiving docks next to a few dedicated shipping docks. Actually, some of the warehouses operated by the manager I spoke with have an even a better layout for interleaving. The company’s newer DCs have dock doors only on one side of the warehouse, and any dock can be used for receiving or shipping. To use a statistics term, the company has built in more degrees of freedom into its layout.
In conclusion, pundits have talked about task interleaving for more than a decade, but only in the past few years have I started to come across warehouses that have actually implemented it . Task interleaving can be a great way to improve productivity, particularly for pallet moves, but change management must be addressed carefully.