The three Mu are used in the Toyota Production System (TPS) to describe losses within a production process. The first “M” stands for the Japanese term muda and describes waste within a production process. The second “M” stands for Mura and describes the imbalance of production processes. Muri, the third “M” describes the losses that occur due to overstressing within the production process. The three Mu serve as a starting point for the identification of waste and thus as a basis for corresponding improvements of processes, material, work stations or machines. In this way, the three terms support the continuous improvement process (CIP) or KAIZEN, as potential for improvement is constantly sought here. Through the systematization into the three terms Muda, Mura and Mudi, the employees have a clue what to look for in the processes. This is then the starting point for employee engagement and creativity.
In this blog post, we want to explain these three mu and give you guidance on how digital tools in manufacturing can help identify and then eliminate these types of inefficiencies.
A waste of resources is the most obvious cause of losses and thus inefficiencies in production processes. Resources in manufacturing can be divided into two categories: Value-added resources (e.g., machining times of a product) and, on the other hand, wasted resources (e.g., long setup times). The sum of value-added and wasteful components of a manufacturing process describes the efficiency of that process. Muda — Japanese for waste — describes precisely these non-value-adding components of production processes and systematizes these wastes into eight types of waste. These can be easily remembered by the English term “DOWNTIME”:
Defects are deficiencies that occur during the manufacture of a product. These can be, for example, quality defects that lead to rejects or customer complaints.
Overproduction often occurs when manufacturing is based on the push principle and the individual employees do not have an overview of the overall process. Intermediate warehouses can then quickly fill up and the material stock in work-in-progress increases steadily.
Waiting times can be caused by a lack of material stock or malfunctions at the workstations or machines and are basically not value-adding.
Insufficiently trained or informed employees in manufacturing lead to many defects, a decrease in employee motivation and many other problems. Therefore, inadequate training of employees is also a type of waste.
If transport routes are not well planned, this can lead to employee waiting times and thus inefficiencies. Incorrect conveyors, which can potentially damage products, lead to further types of waste (defect, waiting).
Unnecessarily high material stocks tie up a lot of capital and are therefore fundamentally inefficient. However, it should be noted that a middle ground must be found between low capital commitment and sufficiently high safety stocks!
Motion describes the non-value-adding (i.e. superfluous) movements within the manufacturing process. Unnecessary walking and movement by employees should be avoided, for example, through good workplace design.
Operations should not be duplicated. This includes looking at unnecessary documentation or duplicate process steps at individual workstations. For example, surface damage should only be checked at the last work station and not at each of the stations.
Not all waste can be completely eliminated. However, there are many ways to minimize different types of waste. In our blog post “The eight types of waste”, we look at each type of waste and show you ways to identify and fix them using digital tools.
The Japanese term mura stands for an imbalance. This expresses a lack of harmonization of processes, working methods or capacities in general. One symptom of imbalance is losses due to “queuing” in front of work stations or in the intermediate storage areas between these stations. this results in a high material inventory and thus a high capital commitment in work-in-progress. Machines or equipment that are not optimally utilized, and thus idle time, are also often a symptom of mura.
The imbalance is responsible for some resources being overextended In the case of an assembly line, this can be expressed in the fact that individual assembly stations often remain far below the specified cycle time, while cycle time overruns occur at other work stations. In the case of a line cycle without intermediate storage, this results in waiting times at individual work stations. In a line with station-based takt (i.e. with material storage between the stations), the imbalance can lead to high stock levels.
Mura, i.e. imbalance, can occur in production, but also in the provision of services or in the processing of an operation. The loss due to mura can occur at three levels:
With the number of process steps and variants in a production process, the degree of imbalance increases. The fewer stages or assembly stations a production process has, the easier it is to coordinate them. The more variants of a product are manufactured on the same line, the more complexity increases and it becomes more difficult to coordinate individual processing steps. In principle, therefore, Mura should be countered by reducing complexity. However, it should be noted that a certain degree of imbalance remains in every process. The big goal is to steady manufacturing processes in order to make the best possible use of existing capacities and to avoid waste, especially due to downtimes or waiting times.
Methods such as Heijunka (harmonization of the production flow through quantity-based balancing) or One-Piece-Flow are suitable for this purpose. However, it is first important to uncover the imbalance and identify which of the assembly stations is the bottleneck. This can be achieved through a worker assistance system. This can be used to record the individual work steps and the durations of these steps. In a second step, it is then easy to identify which stations have too much work and which are permanently underloaded. This makes it possible to balance work stations. Another advantage of worker assistance systems is the leveling of employee knowledge. All employees at the workstations have access to comprehensive information on the assembly steps. Digital alerting tools can be used to call for help quickly in the event of ambiguities or impending malfunctions. All these measures lead to a better balance of the manufacturing processes.
Overloading of resources is described in the Toyota Production System as muri (Japanese for overload). This can affect human labor as well as occur on machinery and equipment.
Overloading of personnel results from continuous overuse or misuse. A distinction must be made as to whether the overload arises physiologically (i.e., affecting the body) or whether it is psychological.
Psychological overload can be caused, for example, by excessive time pressure or a lack of knowledge about individual work steps. The consequences of this, in addition to the effect on work results, are a drop in motivation among individual employees and a poor working atmosphere.
Physical overload occurs when employees are exposed to unfavorable environmental conditions. This can be due to noise, vibrations, high or low temperatures, unfavorable lighting conditions, strong odors and much more. Very physically demanding work (e.g. lifting heavy objects) can also lead to physiological overload.
Overload occurs, for example, when people have to absorb the uncoordinated work processes (mura) and the resulting waste due to unfavorable factory design or avoidable transport and long distances (muda). In many cases, this leads to extra work or a faster throughput of work processes. This leads to time and performance pressures. Increased pressure leads to a higher failure rate among those involved and reduces the quality of the results. Ultimately, the result is not only more waste, but also mental and physical stress and overwork. This can lead to fatigue, stress, depression and other sick leave, but it can also affect the work environment.
Machines and equipment can also “suffer” from overload. If they are constantly run at borderline capacity, high wear and tear is to be expected. The quality of the products can also suffer from such a machine. In addition to greater wear and the need for increased maintenance, the life of the machine or system also decreases. Ultimately, the continuous load leads to high downtimes of the machinery and thus to manifold losses.
The most sustainable measure to prevent overloading is good planning of the assembly line. The reason for this is that the workplace design can be optimally adapted to the production and its needs and designed ergonomically. At the same time, many other types of waste (muda) are thus minimized. It is therefore worthwhile to plan ahead in order to improve production processes and other activities in a long-term and sustainable manner.
When optimizing existing processes, it is usually necessary to reduce the number of process steps in order to make the process clearer and simpler. In this way, employees can monitor not only their own actions, but also those of others. This can be supported by other measures to reduce noise and increase staff authority and responsibility. These include, for example
Managers can support the implementation of these measures by training and motivating employees and applying the principles of lean management.