Muri (無理) is a Japanese word meaning "unreasonableness; impossible; beyond one's power; too difficult; by force; perforce; forcibly; compulsorily; excessiveness; immoderation", and is a key concept in the Toyota Production System (TPS) as one of the three types of waste (muda, mura, muri).
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Avoidance of muri in Toyota manufacturing
Muri is one of three types of waste (muda, mura, muri) identified in the Toyota Production System. Waste reduction is an effective way to increase profitability.
Muri can be avoided through standardized work. To achieve this a standard condition or output must be defined to assure effective judgment of quality. Then every process and function must be reduced to its simplest elements for examination and later recombination. The process must then be standardized to achieve the standard condition. This is done by taking simple work elements and combining them, one-by-one into standardized work sequences. In manufacturing, this includes:
When everyone knows the standard condition, and the standardized work sequences, the results observed include:
Implementation
In fact the big contribution of Henry Ford and his manufacturing techniques was the reduction of Muri and not so much the production line itself. In order for the production line to function each station on the line had to achieve standard work because the next station was only equipped to work on standard condition components.
The Ford production line approximates to an implementation of Takt time which gives enough time to perform the standard work.