Concept of constraint:

The manufacturing system can be considered to be analogous to the chain with different links. The chain is as tough as, its weakest link. It is significant to improve the strength of the weakest link for improving the strength of chain. Similar is true for any system. In the context of a manufacturing system, the concept of constraint, and the analogy of chain provides following insights:

• Throughput of system is restricted by the critical (or, weakest) link in the system, which is the constraint of the system.
• This is of no great significance where the weakest link or constraint is located. As soon as this link fails, the whole system will fail.
• Manufacturing system, as the chain, must be considered as a whole.
• Because of bottleneck (or, constraint) :

        a. Production upstream shall produce excess inventory and generate queues. Any queue is a sign of inefficiency, which should be removed.

        b. Production (or operation) downstream shall remain starved. This shall cause the under utilization of manufacturing/human resources. The under-utilization is again a sign of inefficiency, which must be removed.

• Due to above reasons, the thrust should be on continuous identification and removal of constraints. This gives rise to the Theory of Constraints.