Task Interleaving

I hear more people asking about task interleaving, so I thought a quick post to describe a scenario and some things to think about would be helpful to interested people.

Task interleaving adds efficiency to a warehousing operation by getting rid of useless travel time.

It's the same principle that freight companies use when they try to eliminate the "empty backhaul". You don't want people and equipment driving around empty.

I will describe a common scenario to help you visualize this.  

Wholesale Distribution - Mixed Inbound and Outbound

In this scenario, an inbound and outbound truck are at the dock and close to each-other. A lift driver is unloading the inbound, and loading the outbound at the same time. The user will start by unloading a pallet from the inbound truck, put it away, and pull a pallet for the outbound truck to take to the dock to make the round trip. These could be staged loads or direct loads. ie: The inbound could just be a put-away of previously unloaded pallets. And the outbound could be staging a load near the dock.  

What Makes Interleaving Work:

• This can work with either direct load / unload, or staged loads.
• Inbound and outbound work is active at the same time.
• Inbound and outbound dock locations are near each-other.
• The same drivers and equipment can handle both types of work.

When Interleaving Isn’t The Answer

• Inbound and outbound is not active at the same time. Sometimes, for example, the inbounds come early in the day and outbounds are scheduled for later in the day. This doesn't work well for interleaving, for obvious reasons.
• Inbound and outbound docks are on opposite sides of the building. In this scenario, when you complete the outbound load task, you will have to drive all the way back to the receiving dock for the next inbound. This defeats the purpose.
• Different equipment needed for inbound vs outbound.
• A lot of mixed case order picking. Interleaving is the most effective when drivers are handling full pallets in and out, and not building mixed case orders.

Other Considerations

• Outbound load sequencing - the more stringent the sequencing requirements for outbound pallets, the less efficient the interleaving will be. This is because the outbound pallet should ideally be selected based upon what is the closest to the user. But if the sequencing is strict, then the next pallet to pull will probably not be the one closest to the user. This means you either have to pull the closest pallet and re-sequence before loading the truck (double handling), or drive further to get the next pallet to load.

Since most of a warehouse's expense is labor, and the biggest component of labor is travel time, any method to reduce total travel will increase efficiency. Interleaving is tool that can help.

Other tasks such as replenishments can also be interleaved with picking and receiving.

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Cheers,
Nate