I was asked by a student to explain constraint management and flexible processes, with simple examples. Here is my response.
Very briefly, the theory of constraints (TOC) is based on the premise that in any sequence of process steps, or on a larger scale any sequence of processes in a value stream, there is one step or one process that limits the throughput of the entire process or value stream. (For simplicity I will use the term “process” for both multi-step processes and multi-process value streams.) This “bottleneck” requires special treatment. In addition, the way in which constraints are handled has an impact on the choice of Six Sigma projects, as described in this article.
Flexible processes are arrangements of inputs (space, equipment, people and materials) that can be quickly reconfigured to produce a variety of different outputs (products or services) and quantities in response to changing customer demand. Ideally a flexible process will use only a limited amount of specialized equipment and the personnel will possess the skill sets needed to adapt to the different process configurations. Flexible process design is at the heart of Lean production. Compared with mass production processes, flexible processes use less capital, fewer employees and a smaller area to produce a given amount of output.
The coming together of TOC and flexible process design occurs when TOC principles are applied to the management of flexible processes. That is, once a set of inputs is configured to form a given process, the process designer considers the 5 steps of TOC and prepares a process management plan that incorporates this. The 5 steps are:
- Identify the system’s constraint(s).
- Decide how to exploit the system’s constraint(s).
- Subordinate everything else to the decision made in step 2.
- Elevate the system’s constraint(s).
- If, in the previous steps, a constraint has been broken, go back to step 1.
I.e., each process configuration is a new system and the constraint will likely be different for each configuration. Process improvement and Six Sigma project selection depends on knowing which process step is the constraint and managing the constraint as well as process steps prior to and subsequent to the constraint properly, as discussed here. This article shows a simple example of a process with a constraint and describes how knowing which step is the constraint impacts process management and process improvement activities.