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About the Author

Cliff Holste is Supply Chain Digest's Material Handling Editor. With more than 30 years experience in designing and implementing material handling and order picking systems in distribution, Holste has worked with dozens of large and smaller companies to improve distribution performance.

Logistics News

By Cliff Holste

November 12, 2014



Maximizing DC System Performance

Jams, Backups, & Shutdowns Are All Symptoms of System Deficiencies



Holste Says:

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Because order fulfillment processes are inherently complex and labor intensive, operations managers should examine all DC production areas from time-to-time to determine how they can be simplified and streamlined.
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Previous Columns by Cliff Holste

Sorting It Out: Customized Order Fulfillment Requirements Drives Adoption of Automation Technology

Sorting It Out: The Typical Distribution Center Business Model Is Rapidly Changing

Sorting It Out: The Cause & Effect of Operational Changes on Order Fulfillment System Performance

Sorting It Out: The Case for Industry Standards & Regulations

Sorting It Out: Don't Let Daily Tactical Issues Subvert Strategic Planning

More

 

Maintaining a smooth flow of orders through the DC is key to maximizing system performance. In addition to the annoying equipment problems that popup from time-to-time within a material handling systems, there are system operational issues that can degrade performance. One of the most common is having too many open orders in process on the system at the same time. As an example, let’s look at a typical mechanized batch order picking, sorting, and shipping system commonly found in consumer goods order fulfillment operations.

In this type of system it is critical to maintain proper segregation between batches while balancing the flow between order picking and shipping operations. If not, you can expect the following problems to occur:


 

  • Because order pickers can (and often do) pick next batch orders/cases ahead of the completion of the current batch, stragglers from the current batch can wind-up behind cases belonging to the new batch. Consequently, some of the shipping lanes will not be able to close out the current batch in a timely manner.

 

 

  • System efficiency is degraded when cases belonging to the new batch of orders cannot be sorted and consequently start accumulating on the sorter recirculation loop. Left unattended, the recirculation loop will quickly become overloaded. When this happens, inbound case flow to the sorter is automatically shutdown causing those inbound conveyor lines to backup, which in-turn shuts down picking operations.

 

The congestion caused by the above picking scenario will quickly fill up the available accumulation. Adding more accumulation conveyor will delay the problem, but not fix it. A better approach would be to test different batch picking strategies such as, limiting the pickers to no more than two open batches at a time, and/or inserting end-of-batch totes in each picking zone before starting a new batch. The batch totes are then held at the central merge until the current batch is closed out.

An even better alternative would be to utilize the batch/wave overlap function built into the WMS, which can optimize batch size and go a long way towards eliminating bottlenecks and gridlock. With batch/wave overlap the shipping lanes are divided into two parts (left side & right side). The WMS sorts the current batch cases into the left lane and next batch cases into the right lane. In this way shipping can work on completing the current batch while the next wave is being sorted and accumulated into the adjacent lane.

In addition to picking strategies, you should also review critical path merge logic and conveyor/sorter speeds to determine if they can be adjusted for higher throughput capacity.

In that regard, it’s appropriate for us to note that Dematic (www.dematic.com) has just introduced a newly designed carton singulator (pictured on left) that aligns skewed and “side-by-side” cartons for proper orientation prior to sorting. The singulator improves carton orientation and alignment, thereby optimizing the performance of the downstream sorter. Using this type of carton alignment solution can also improve merge performance and maximize system uptime. This upgrade can be retrofitted into existing convey and sort systems or implemented with new convey and sort systems.


Another good practice is to make sure that the right amount of labor is at the right place at the right time. This may seem elementary but can get out of sync quickly. For example: too many order pickers and not enough shipping personnel will cause system congestion that can reduce throughput and rob system efficiency and productivity. It is better to have a little excess capacity in shipping to insure that order fulfillment efficiency is maintained.

In the typical distribution system, the rate at which cases are introduced into the system from receiving, cross docking, picking, VAS, and staging areas, varies greatly throughout the production cycle. By analyzing each of these inbound production areas it is possible to estimate how much labor is required under various flow scenarios to keep all areas running at their target design rate. Sometimes computer simulations and or emulations can be effective tools for companies to use to better understand system performance, test picking and operational alternatives, identify potential bottlenecks, and understand the likely result of changes to an existing system.


Final Thoughts

 

Because order fulfillment processes are inherently complex and labor intensive, operations managers should examine all DC production areas from time-to-time to determine how they can be simplified and streamlined. Fine tuning slotting, order batching, pick path routing, and workflow paths, can yield productivity improvements with little or no capital expenditure.

 

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