Decreased Variability in Bottlenecks

There are cases where a suitable process control can even increase the overall performance of the process, especially in production processes working with bottlenecks. Such is the case of a factory that makes cereal bars where the product labels indicate a fiber content of 4 %. Given that the machines at the factory are not well controlled, the addition of fiber has a variability of 2 %. In fact, the machines, programmed to add 4 % fiber, deliver a product that has between 2 and 6 % fiber. Therefore, to ensure that the products comply with the information on the label, 6 % fiber must be added and all bars are expected to have between 4 and 8 % fiber. 

Suppose that, due to supplier constraints, the plant only has 100 kg of fiber a day and each cereal bar weight 100 g. Whereupon, under current conditions, the processing plant will be able to produce 16,667 cereal bars day. The situation would be very different if we could improve the control of the machines so that the error in the added amount of fiber were 1 % instead of 2 %, as shown in the center of Fig. 9.6. In this case, you could add 5 % fiber and expect the bars to have between 4 and 6 % fiber. It is easy to calculate that in this new scenario, the plant could produce 20,000 cereal bars daily. Although not conclusive, it seems attractive to invest in improving the control system. 

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