The mudas: the 7 (or 8) wastes of Lean

In one line

Muda is any expense that adds no value to the product or service from the customer's point of view, and Lean starts by learning to see it.

What it is

Meyers and Stephens define muda (waste) as any expense that does not help produce value, and they propose starting by asking "why" five times about any problem or cost, to get to the original cause (this is the 5 Whys technique). Niebel and Freivalds point out that the seven types popularized by Shingo closely resemble what industrial engineering was already analyzing with process charts and motion study: delays and transports are detected in a flow process chart, and unnecessary motions sum up the work of the Gilbreths.

The seven classic mudas

The Universidad Icesi paper, which follows Ohno, defines them as follows:

Muda	What it is
Overproduction	Producing items the customer did not order: it increases inventory and its storage costs, the risk of obsolescence and the space taken up
Waiting	The operator waits for a part to finish processing or for a station or tool to become available
Transportation	Moving a product from one place to another unnecessarily, including intermediate moves; it wastes time and adds risks for people and cargo
Overprocessing	Putting too much into a product: doing things the customer does not notice
Inventory	Excess anywhere in the process: storage costs, longer lead times and damaged products; it can also hide a quality problem until the good stock is used up
Unnecessary motion	Employee movements, typically caused by disorder or poor sorting
Defects or rework	Product that has to be repaired or scrapped

The eighth, and its cousins

Meyers and Stephens speak of eight classes (they add "poor use of personnel"), and the Ciudad Juárez paper also lists eight wastes: defects, overprocessing, inventories, waiting, motions, transports, overproduction and human talent. That same paper distinguishes two other Japanese words: mura is changes in production planning, and muri is poor manufacturing designs that fail to meet ergonomic requirements and wear people down.

Real example

The Ciudad Juárez case shows waiting in numbers. On a gear-and-chain assembly line, the takt time was 6 seconds, but stations 10 and 20 took more than 7 seconds and stations 30 and 40 less than 5. Every part waited at the slow stations and the operators at the fast ones ended up with idle time: pure waiting, caused by an uneven distribution of work (the first stations assembled 5 components, the last ones only 2). In the test of that cause, rebalancing the line brought the measured lead time down from 26.07 to 20.73 seconds. The full case is in the Lean Six Sigma article.

How to use it

1. Walk through the real process (not the one on paper) with the list of mudas in hand.
2. Note each waste with its location, its frequency and its estimated cost.
3. Attack first the one that costs the most or repeats the most, with the right tool (5S for disorder, spaghetti diagram for transport and motion, SMED for waiting caused by changeovers, poka-yoke for defects).

Benefits

• It provides a common language: the whole team names the wastes the same way.
• It ties loose techniques (5S, SMED, poka-yoke) to a common goal.

Limitations to keep in mind

• The lists vary between authors (seven, eight, with different names): what matters is the way of looking, not memorizing the number.
• Eliminating one muda can move the problem to another if you do not look at the whole system; for example, reducing inventory without cutting changeover times just creates waiting.

In summary

The mudas are the list of things about which you have to ask yourself, "Would the customer pay for this?" They are the starting point of Lean and of the Toyota Production System.