Subtle variations about waste.
Some Japanese words have made their way into the western business language since Lean spread worldwide and inspired all businesses. Three of them are quite well known: Muda, Muri, Mura.
Muda is one of the Japanese words passed in the common language of industry. Muda stands as generic word for any and all of the infamous seven types of waste:
- Waste from overproduction
- Wastes from wait times
- Waste caused by transportation
- Wastage due to unnecessary inventories
- Waste in the manufacturing process
- Unnecessary movements
- Wastage due to defective parts
These seven types of wastes were commonly observed in industrial workshops and proved pretty generic to many other activities, even in administration and services (with a little adaptation).
A later eighth type was identified and now commonly admitted in the list: the waste of human talent(s).
Muda are not the sole type of waste, but they are the most easy to understand and relatively easy to identify by observation. “Muda hunting” has become a regular activity, sometimes even popular activity in some companies.
Muri means unreasonableness, like the use of oversized or excessive means relative to the need or the desired result. Muri can be obvious, like hauling a small light box with a big truck or conversely overloading a smaller truck with large/heavy load.
Other muri may be more subtle like immobilizing large capacity pallet boxes for storing some small lightweight components when the need for storage could be solved with cheaper and easier to handle smaller boxes.
Muri is also about the physical overload, the hardship, exposure to mental stress, which lead to wasting energy, health and ultimately human capital.
Special attention should be paid when working postures include arm extension or leaning forward with the bust, back bent, leaning the head, torso rotations, squat, etc. Repeatedly pushing or pulling strongly, lifting heavy weights, using the fist as a hammer, and so on.
MURA, irregular, variability
Variability can take multiple aspects; different bottle filling levels in a filling line, varying cutting length, or inconsistent color tones in successive batches, etc.
The physical characteristics of a raw material may vary over time or according to different batches supplied; quantity, weight, length, texture, hardness, elasticity, etc. The settings of a machine may vary over time, human practices and actions may vary from one person to another and over one day.
The sources of variability are innumerable and variability generate waste as some of the output must be reworked or even discarded.
Variation in production rhythm often lead to install buffer stocks to smooth irregular flows. Note that acceptance of buffer stocks means creating MURI and MUDA. The Japanese approach seeks to eliminate the causes of irregularities and not hide them with buffers.
By gradually decreasing the size of buffer stocks, causes of irregularities are revealed and it is possible to eliminate / reduce them. The basic idea is that every workflow must flow smoothly like a river. If obstacles are disturbing its course, remove the obstacles, do not add water.
Waste come in three major forms; Mura, Muri and Muda, which are sometimes difficult to distinguish from each other. Indeed, some wastage look like one of the seven types of Muda but could be considered a form of Mura (variability) as well. Others lead to discuss their essence is rather Muri (excess) or Muda, and so on.
Just accept that there are not always clear boundaries between them and it is a mere waste of time to discuss how to consider them.
Lean is relentless about removing waste, which is a way to solve problems and improve processes, not waste hunting per se.