11.2: Points Made in the Case Study

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Some benefits of using simulation to enhance lean manufacturing techniques are illustrated. The effect of random variation in raw material (part) arrival times as well as worker walking times is taken into account. Performance of the cell, in terms of the maximum work-in-process and throughput, is predicted. The simulation model and experiment are used to validate the cell design generated by traditional cellular manufacturing computations. Operating rules to co- ordinate part arrivals and the movement of the cell operators are tested.

The movement of both a part through the operations of the cell and a worker from workstation to workstation within a cell must be included in the model. The movement of workers is used as the perspective for model building. The number of parts in each area of each cell is counted. Part movement results in changes in the counts. The average part cycle time in the cell can be estimated from the average number of parts in the cell using Little's Law. This approach is based on a technique developed by Hyden, Roeder and Schruben (2001).

Random variation in worker walking time may be significant since waiting while a worker walks between machines may cause a delay in the start of an operation. Such delays could effectively reduce the capacity of the cell. Thus, the cell could fail to meet its throughput target.

The work done at a workstation must be modeled as multiple tasks: initiating an operation, the operation itself, and removing the part from the machine after the operation is completed. Different resource combinations, machines and workers, are required for each task. Thus, the joint allocation of machine and worker resources must be accomplished.

More than one worker is required to staff the cell. The effectiveness of alternate assigments of workers to workstations can be determined using simulation experiments.

A trace of worker activities can be generated to aid in model validation. The trace is used to provide evidence that the worker moves through the cell as was intended.