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Quick Sortation Line Analysis

How a simple FlexSim model allowed Ghafari Associates to extract some valuable information

Initial Objectives

  • Test the value of FlexSim on a small scale.
  • Quickly model a section of the warehouse to evaluate throughput and utilization.

New Objectives

  • Stress test system to validate throughput and identify opportunities.
  • Measure operator utilization levels to establish appropriate work pace.
  • Highlight potential bottlenecks through experimentation with system inputs.


  • System can meet a “worst case” theoretical maximum throughput rate.
  • Operators are unlikely to be pressured (utilization rate under 30%).
  • Found that two pallet loading stations are needed for each sortation operator.

Did you know that simulation is extremely useful, not just in large and complex scenarios, but in smaller ones as well? The model you see here was developed in just a day and a half by Ghafari Associates, and it was created by an engineer who had only just picked up FlexSim weeks prior. The initial goal was simple: model a section of a warehouse from one of Ghafari’s clients just to see what the model would tell them.

In this system, totes are fed into two sortation lines, where they are sorted onto pallets and then placed into racks. The first item of business was to stress test the system to its max capacity to see if it could keep up. The simulation showed that, under a “worst case” theoretical maximum throughput rate, the sortation line conveyors would need to be moving at 40 feet per minute to keep up. The conveyor speed was originally planned for 20 feet per minute, but since they are variable speed conveyors, this speed increase can happen in order to meet demand.

This system seems fairly straightforward, but it also has a unique element – the sorters are volunteers, so it’s important not to stress them as they pick totes from the conveyors. Ghafari used utilization as a key metric to make sure this wasn’t happening. The model showed that volunteers were unlikely to be pressured, since their utilization hovered under 30%. The operator at the head of the sortation line was utilized 70% of the time, but this individual is a paid employee – further experiments on the model could see if a second operator at the head of the line might make sense.

As far as the forklifts are concerned, they found that one forklift was generally enough to feed the sortation lines with totes as well as to take the pallets of sorted totes and place them into racks. The simulation showed that at times a little help might be needed when things get backed up. But the bigger revelation came in the individual sortation stations – when a full pallet of sorted totes is taken away, there is sometimes a delay before a fresh pallet arrives and the volunteer can’t place any new totes down. This happens often enough that two pallet loading stations are needed for each volunteer sortation operator so there is always a place to put a tote.

Ghafari was able to quickly create a model that allowed them to explore their client’s process and extract some valuable information. Contact us today to see how FlexSim can fit in with your operations.

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