What Are the Differences in How Bottleneck and Non-Bottleneck Work Centers Are Scheduled Under Toc?

What are the differences in how bottleneck and non-bottleneck work centers are scheduled under TOC? Why are these differences desirable?

Ans:

The reason TOC focuses on bottlenecks is that these determine output for the entire production process. For example, if machine A produces parts at the rate of fifty per hour and feeds them to machine B, which runs only twenty per hour, the final output through these two machines will be only twenty per hour. In this example, machine B is the bottleneck, and machine A is a non-bottleneck. Theory of constraints scheduling involves the preparation of an exact schedule of jobs for bottleneck work centers, and sequencing the non-bottleneck work centers by a priority sequencing rule. Any resource whose capacity is equal to or less than the required demand is referred to as a bottleneck. As a consequence the fundamental principle of TOC systems is that only those work centers that are bottlenecks are of critical concern in scheduling.

This is because the bottleneck work centers limit the overall production output of a plant. Further output beyond the constraint of the bottleneck can be achieved only by improved utilization of the bottleneck facilities, using approaches such as reduced downtime, improved productivity, and reduced changeover times. The objective of TOC scheduling is to maximize throughput. Because throughput is limited by the bottleneck resources, all efforts are devoted to maximizing capacity utilization in these work centers. Therefore, TOC scheduling systems focus on the identification of bottleneck work centers, and the scheduling of these work centers.

The goal is always to break a constraint, or bottleneck condition, and thereafter identify the next constraint. Continuous improvement is an integral part of the theory of constraints philosophy. Moreover, the path for the improvement is directed by the theory, always following the constraints. A fundamental tenet in TOC is that an hour lost in a bottleneck resource is an hour lost to the entire factory's output, while an hour lost in a non-bottleneck resource has no real cost. This means capacity utilization of bottleneck resources is important. TOC increases utilization by using WIP buffers in front of bottlenecks, and where output from a bottleneck joins with some other parts. TOC also runs large batch sizes at bottleneck operations, thereby reducing relative time spent in setup downtime. All non-bottleneck resources should be scheduled to be sure that the bottleneck is not starved for materials and can keep busy processing orders needed for sale. Also, a queue should be formed in front of the bottleneck resource to ensure that it stays busy.

Non-bottleneck resources don't need to operate at full capacity provided they process enough to keep the bottleneck busy. Thus, some of the non-bottleneck work centers may have idle time in their