Muda (無駄) is a traditional general Japanese term for an activity that is wasteful and doesn’t add value or is unproductive, etymologically none (無)+ trivial or un-useful (駄) in practice or others. It is also a key concept in the Toyota Production System (TPS) and is one of the three types of waste (Muda, Mura, Muri) that it identifies. Waste reduction is an effective way to increase profitability.
A process adds value by producing goods or providing a service that a customer will pay for. A process consumes resources and waste occurs when more resources are consumed than are necessary to produce the goods or provide the service that the customer actually wants. The attitudes and tools of the TPS heighten awareness and give whole new perspectives on identifying waste and therefore the unexploited opportunities.
Muda has been given much greater attention as waste than the other two which means that whilst many Lean practitioners have learned to see muda they fail to see in the same prominence the wastes of mura (unevenness) and muri (overburden). Thus whilst they are focused on getting their process under control they do not give enough time to process improvement by redesign.
Mura (斑 or ムラ) 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.
- The assembly line “makes a request to,” or “pulls from” the Paint Shop, which pulls from Body Weld.
- The Body Weld shop pulls from Stamping.
- At the same time, requests are going out to suppliers for specific parts, for the vehicles that have been ordered by customers.
- 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.
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. This multiple machine handling is called “multi-process handling” in the Toyota Production System.
Avoidance of muri in Toyota manufacturing
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:
- Work Flow, or logical directions to be taken,
- Repeatable Process Steps and Machine Processes, or Rational methods to get there, and
- Takt time, or reasonable lengths of time and endurance allowed for a process.
When everyone knows the standard condition, and the standardized work sequences, the results observed include
- Heightened employee morale (due to close examination of ergonomics and safety),
- higher quality,
- improved productivity, and
- reduced costs.
One 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.
The Seven Wastes
One of the key steps in Lean and TPS is the identification of which steps add value and which do not. By classifying all the process activities into these two categories it is then possible to start actions for improving the former and eliminating the latter. Some of these definitions may seem rather ‘idealist’ but this tough definition is seen as important to the effectiveness of this key step. Once value-adding work has been separated from waste then waste can be subdivided into ‘needs to be done but non-value adding’ waste and pure waste. The clear identification of ‘non-value adding work’, as distinct from waste or work, is critical to identifying the assumptions and beliefs behind the current work process and to challenging them in due course. Breakthroughs in SMED and other process changing techniques rely upon clear identification of where untapped opportunities may lie if the processing assumptions and beliefs are challenged.
The expression “Learning to see” comes from an ever developing ability to see waste where it was not perceived before. Many have sought to develop this ability by ‘trips to Japan’ to visit Toyota to see the difference between their operation and one that has been under continuous improvement for thirty years under the TPS. Shigeo Shingo, a co-developer of TPS, observed that it’s only the last turn of a bolt that tightens it – the rest is just movement. This level of refined ‘seeing’ of waste has enabled him to cut car body die changeover time to less than 3% of its duration in the 1950s. Note that this period has allowed all the supporting services to adapt to this new capability and for the changeover time to undergo multiple improvements. These multiple improvements were in new technologies, refining value required by ‘downstream’ processes and by internal process redesigns.
One More Waste
Any failure to fully utilize the time and talents of people is a waste of talent.