Mura – what does it mean?

Mura – we define something as unevenness, variability or irregularity. Mura can refer to variations in production, demand or process. Mura is also one of the three wastes defined in the Lean Manufacturing “3M concept”. We wrote more about 3M in this article.

The occurrence of mura has a negative impact on the other wastes, namely muda and muri. Mura is associated with the occurrence of descrete variability in various aspects of the company’s operations.

Taiichi Ohno – founder of the Toyota Production System – said that a company works properly when it produces according to schedule and accepted standards. Responding dynamically to changing conditions and making sudden changes causes instability and generates takeoffs in various areas. Perhaps this seems to contradict the concept of Just in Time – that is, producing exactly on time, as much as the customer wants, when the customer wants, where the customer wants, and with the right quality parameters – nothing could be further from the truth!

Variability in processes and flexibility in the manufacturing system

The vast majority of manufacturing companies would like to have a system that allows flexible manufacturing without waste of downtime, changeovers or other modifications. Is this possible? The production system in a “lean enterprise” such as Toyota is undoubtedly based on production in large batches under the Just in Time system. Toyota strives for flexible manufacturing and focuses on improving the ability to adapt lines, production or assembly cells to a “smoothed” production schedule (Heijunka).

Changing customer demand may make it necessary to change production plans, and thus change the supply of raw materials, the use of human resources and machinery. However, these changes should not be so radical and sudden. Let’s test this with an example.

Example of unevenness in processes

Let’s imagine a company “X”, which produces according to a schedule, determined from day to day based on customer orders. For the first 4 days, they increase production, and thus it is necessary to:

• Start overtime for workers in production,
• Change machine parameters to increase production speed,
• Utilize non-standard locations in the production and storage space – storage fields for increased work-in-progress,
• Order more raw materials and auxiliary materials.

On the fifth day, the production schedule is “empty” – no scheduled production, zero orders. This causes all sorts of waste – overloaded and then unused human resources, machine and production line downtime, etc.

The situation described above or other similar situations (e.g., no production on the first day of the week), unfortunately, are often repeated in different manufacturing companies. Variability in this case will be the main destabilizing factor. During the first 4 days there will be overloading – that is, muri, as well as waste – that is, muda, and on the last day there will be mura, in which case there will be an uneven workload of people and machines. Excessive repetition of this type of situation consequently leads to employee dissatisfaction and production downtime – which is bad for both people and machines.

How to prevent the mura waste?

The previously mentioned Heijunka is a concept that is part of the Toyota Production System, literally meaning “leveling”. Heijunka helps in planning and managing labor in a company. The use of this concept influences the reduction or even complete elimination of mura and muri.

However, balancing all workstations and setting exactly the same cycle time may prove difficult to implement in practice. However, one should strive to “smooth” cycle times and run production in One Piece Flow. This solution will work especially well in continuous and high-volume production. On the other hand it also has some limitations – it makes it difficult to adapt to changing conditions.