Holste Says: |
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| A system sorting strategy that eliminates segregated batches and allows for overlapping is the best solution. |
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What Do You Say?
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Previous Columns by
Cliff Holste |
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There are several operational factors that contribute to shipping delays. However, frequent shutdowns of the order fulfillment operation, in addition to being annoying, can be a major contribution factor. The key question then is – what’s causing the system to shutdown and how can this be resolved.
Because there is a great deal of volume fluctuation in the typical distribution system operation it’s very difficult to estimate just how much buffer, i.e., accumulation conveyor, is needed between operations to keep all operations running smoothly. Picking and shipping are both labor intensive and therefore can easily become out of sync – too many pickers or not enough loaders.
As an example, let’s look at a typical batch-order picking, sorting, and palletizing system operation. In this type of operation it is critical to maintain proper balance between the picking and palletizing/loading. If not, you can expect the following problems to occur:
• When order pickers pick ahead of the palletizing operation (start the next batch before the current batch is completed), cases belonging to large orders from the current batch will frequently end up accumulating on the sorter recirculation loop behind cases belonging to the next batch of orders. Consequently, some of the after-sort palletizing/shipping lanes will not be available for the next batch.
• Inbound cases belonging to the next batch will begin accumulating on the sorter recirculation loop until it becomes full. At this point a condition known as “system gridlock” occurs leading to a total system shutdown.
• Shipping operation are idle waiting for the system to sort through cases belonging to the current batch thus reducing system throughput and potentially resulting in overtime hours and shipping delays.
The congestion caused by the above pick ahead strategy left unchecked will quickly fill up the available accumulation capacity. In this case, adding more accumulation conveyor will delay the problem, but not solve it. It may be better, and certainly less expensive, to test different batch picking strategies like limiting the pickers to no more than two batches at a time. You may also want to review critical path conveyor speeds to determine if they can and should be increased. And, adjust labor deployment making sure that the right amount of labor is at the right place at the right time.
A system sorting strategy that eliminates segregated batches and allows for overlapping is the best solution. There are various strategies to implement this capability. You can establish more than one palletizing station for each after-sort lane. This allows the next order to be started while waiting for the last few cases from the current batch to be sorted.
If you don’t have the room for more than one palletizing station, consider dividing half the after-sort lanes into one batch and the second half into the second batch. Although this reduces the size of the batch, which ultimately can increase the man-hours required to pick, the overall time to complete batches is reduced because you have eliminated the idle time (time between batches). Maintaining sorter capacity during batch transitions can improve overall throughput by 10-25% depending on the severity of the batch overlap problem.
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