Interleaving makes logical sense – but does interleaving make business sense?
Having wrung savings out of many areas of the warehouse, distribution-center managers are looking at interleaving as the next big improvement. But will it pay out?
Interleaving makes logical sense…. none of us leave home on a Saturday morning and go to the bank and then go home only to leave again and go to the dry cleaners. No, we plan ahead that includes both the bank and the dry cleaners. This is the essence of interleaving – sequencing tasks that logically fit together…retrieving product from deep storage and taking it to the dock will be matched up with unloading a truck and putting it back into deep storage. The hope is that productivity (traveling with something on the forks) might be much higher. And there is plenty of room for improvement. Forklift productivity, in a large plant warehouse we studied, showed the forklift trucks operating loaded about 20% of the time. Logic tells us that interleaving should improve productivity – but will it?
The jury is still out! While WMS suppliers tout the functionality that not many companies have successfully implemented interleaving, even fewer have improved productivity – many have tried and failed.
What conditions allow interleaving to work and where will it fail? I don’t know – there are hard and fast rules, but here are some thoughts. To work, interleaving must:
- Be structured to maintain accountability for, for example, loading a customer order.
- Provide enough information about how the task is to be performed. For example, a truck loading sequence must be detailed down to the exact location in which to put each pallet using a product like AutoLoaderT3 from warehouseoptimization.com Even when just staging product, unless there is a lot of space, sequencing must be observed. In both cases – truck loading and staging – the timing of each activity must be carefully choreographed. If the product for row 3 arrives before the material for row 4, all is well…but if the reverse sequence applies, then there is trouble. The places we’ve seen it work are when product is being staged both inbound and outbound. That of-course adds time as lift trucks must both deposit and pick up the product. This traditionally adds about 33% more labor so how much is gained in total?
- The workload must be balanced. In a manufacturing plant, for example, line-take-away is unbalanced – normally raw materials are brought to the line in a very different place. And palletizers require attention. Similarly, shipping volume is often not balanced with receiving volume. Month-end peaks drive an-all-hands-on-deck approach to shipping driving the unbalance.
- Get staff confidence. Remember that the loaders are generally the most skilled material handlers. Asking them to convert from planning their own work to being told what to do, is a significant cultural shift. And as soon as the system makes a “dumb” mistake (and during start-up-it will), staff can hold up an example. A million successes can be undermined by one failure.
- Have management support. The previous bullet makes this need abundantly clear.
The summary is that the conditions must be right to make interleaving work. Think long and hard before you sign up for this technology.
- Tom Moore
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