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Mura (斑 or ムラ)[1] is traditional general Japanese term for unevenness, inconsistency in physical matter or human spiritual condition. It is also a key concept in the Toyota Production System and is one of the three types of waste (Muda, Mura, Muri) it identifies. Waste reduction is an effective way to increase profitability. Toyota merely picked up these three words with prefix mu-, which every Japanese know, as product improvement program or campaign.

Mura is avoided through Just In Time systems which are based on little or no inventory, by supplying the production process with the right part, at the right time, in the right amount, and first-in, first out component flow. Just in Time systems create a “pull system” in which each sub-process withdraws its needs from the preceding sub-processes, and ultimately from an outside supplier. When a preceding process does not receive a request or withdrawal it does not make more parts. This type of system is designed to maximize productivity by minimizing storage overhead.

For example:

  1. The assembly line “makes a request to,” or “pulls from” the Paint Shop, which pulls from Body Weld.
  2. The Body Weld shop pulls from Stamping.
  3. At the same time, requests are going out to suppliers for specific parts, for the vehicles that have been ordered by customers.
  4. Small buffers accommodate minor fluctuations, yet allow continuous flow.

If parts or material defects are found in one process, the Just-in-Time approach requires that the problem be quickly identified and corrected.

Implementation

Production leveling and frequent deliveries to customer are key to identifying and eliminating Mura. The use of different types of Kanban to control inventory at different stages in the process are key to ensuring that "pull" is happening between sub-processes. The use of Heijunka will aid in scheduling work in a standard way that encourages lower costs.

It is also possible to smooth the workflow by having one operator work across several machines in a process rather than have different operators; in a sense merging several sub-processes under one operator. The fact that there is one operator will force a smoothness across the operations because the workpiece flows with the operator. There is no reason why the several operators cannot all work across these several machines following each other and carrying their workpiece with them[2]. This multiple machine handling is called "multi-process handling" in the Toyota Production System.

References

  1. ^ Mura, 斑 translation to English on Sanseido "EXCEED Japanese-English dictionary".
  2. ^ A study of the Toyota Production System, Shigeo Shingo, Productivity Press, 1989 , p 157
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