Theory of Constraints Handbook - James Cox Iii [157]
A status of red means less than one-third of the original buffer remains and thus it is now priority one to flow the order to its destination (either the CCR or shipping).
Thus, the decision rules for the execution phase are based on the status of the buffers. BM imposes one clear set of priorities and does not tolerate any others. Thus the buffer status of any order can be checked and according to the resulting priorities every resource is able to decide what to do next. Following the BM priorities yields the highest probability that we will ship everything on time and utilize the CCR to its planned exploitation level.
The viewpoint of minimum planning requires the extra emphasis on a priority scheme for the execution phase. It fully supports the move from the excessive planning in OPT® to the leaner planning of DBR, but with the addition of BM as the execution aid to achieve the objective of reliable due date performance coupled with good exploitation of the CCR. Later in this chapter, it will be shown how this view also supports S-DBR.
Concentrating on the Flow
The third viewpoint on operations comes from Goldratt’s (2009) article, “Standing on the Shoulders of Giants.” The flow concepts are attributed to both Henry Ford and Dr. Taiichi Ohno and highlight the TOC approach to planning and execution in manufacturing.
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Goldratt7 (2009, 3) has verbalized the four concepts that lie behind the work and achievements of both Ford and Ohno:
1. Improving flow (or, equivalently, lead time) is a primary objective of operations.
2. This primary objective should be translated into a practical mechanism that guides the operation when not to produce (prevents overproduction).
3. Local efficiencies must be abolished.
4. A focusing process to balance flow must be in place.
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Certainly, the four concepts for flow link the Lean concept with TOC and particularly DBR (actually, it is more attuned to S-DBR as will be explained later in this chapter). We certainly do like to get faster flow throughout the shop floor. Moreover, the rope is just another tool to prevent any overproduction. Of course, the main point is how to distinguish between overproduction and what should be produced.
The fourth concept is interesting as it can be interpreted as applying both to the immediate state as well as to longer periods. For the immediate situation, it fully supports the idea of giving higher priority to orders that seem “almost late,” thus enabling faster flow for the urgent orders. We still need to develop a more global view on how to focus the efforts on improving the flow in the longer-term period of time.
Challenging the Traditional DBR Methodology
When DBR first appeared in 1984 (The Goal), it signalled a departure from the very detailed production planning process like OPT® as well as a contrast to MRP. It was much later that we learned that when planning is minimal then execution gets more responsibility and it needs better guidelines for decisions. BM was mentioned first in Goldratt and Fox (1986), The Race. It took additional time for Goldratt himself and other researchers to define clearly the linkages of BM to DBR and additional time for practitioners to understand it fully. BM is a necessary condition for DBR to work effectively.
The three viewpoints poses various questions regarding the central role of an internalcapacity constraint. Let’s first summarize the claims and then inquire into each of them more deeply.
1. From the 5FS perspective, there are some questions that are at the core of the challenge:
a. Is the proper strategic constraint an internal resource? Should the capacity of an internal resource be the constraint of the whole organization?
b. Suppose we do have a real capacity constraint in the