Theory of Constraints Handbook - James Cox Iii [135]
Step 3: Subordinate Everything Else to the above Decision
Once the bottleneck or capacity constraint has been identified, policies to ensure full productive utilization is put in place, the resource properly buffered, and the planned flow through this resource is identified, then Step 2 is complete. The next step, Subordinate, is to make sure that all other resources focus on performing tasks in such a way that the planned flow through the constraint is supported.
All activities from the release of material to how they are processed upstream and downstream of the bottleneck should be done in a manner that best supports the decisions made in Step 2. It is important to realize that while the discussion on the constraint is powerful and interesting, the task of execution falls mostly on Step 3 and the management of non-constraints. This is a simple consequence of the fact that most resources (95 to 100 percent) are non-bottleneck resources and to control execution means controlling what is happening at these resources.
The subordination required by Step 3 is made challenging because the mentality fostered by traditional cost world management is not consistent with subordination. This is the point at which the third principle of flow management (efficiencies must be abolished) needs to be implemented. The case in Fig. 8-4 illustrates this point. Resource R2 is the constraint and can process 100 units per day. Resource R1 is a non-constraint and can process 120 units per day. Subordination requires that R1 only process 100 units per day, but traditional mindset would encourage R1 to work to its full potential and thus produce in excess of 100 units per day. In almost every implementation of DBR that the author has done, the task of subordinating (or holding back production) non-constrained resources has been the most challenging and difficult task.
FIGURE 8-4 PFD for a one-product flow line indicating the production capacity of the different resources.
An alternate way to look at Step 3 is as follows. Steps 1 and 2 have established the total flow that must be achieved—product mix, volumes, etc. In accordance with the section on managing flow, we must now implement the four principles of flow. In particular, recognizing that improving flow is the primary objective, we must establish how to implement Principle 2—a mechanism to prevent overproduction. This overproduction (Sugimori et al., 1977) is the first and most important waste that is explicitly identified in TPS as well as in JIT, Lean, and other offshoots of TPS.
The process by which subordination is enforced in the DBR system is the rope and is discussed in a later section.
Steps 4 and 5
At the completion of Step 3 (subordination) we have a system that is operating at full potential—we are getting the maximum Throughput by what has been done at the constraint and waste is minimized by subordination at all other resources. In order to improve the performance of the system further yet, we must raise the performance of the constraint itself. However, when the performance capability of the current constraint is elevated, it may no longer remain the constraint. Its new potential may be larger than the capability of another resource in the system. Steps 4 and 5 are designed to deal with this possibility. Since our focus is managing a plant that has a current constraint, we will not discuss ramifications of Steps 4 and 5. Rather, we proceed to the