The Ishikawa Chart is one of seven simple quality management tools. Using this method, you can find bottlenecks in the production process, determine their causes and effects.
From the history
K. Ishikawa was a Japanese researcher in the field of quality. In the mid-twentieth century, he took up the methods of quality management and their active implementation in Japanese enterprises.
He proposed a new graphical method of quality management, called the cause-effect diagram or Ishikawa diagram, which is also called the "fish bone" or "fish skeleton."
This method, which is one of a number of simple quality assurance tools, is known to everyone in Japan - from the student to the president of the company.
Ishikawa originally introduced the “six M” rule for his diagram (all words in English that give rise to production reasons that lead to different results begin with the letter “M”): people (man), material (material), equipment (machine) , method, management, management, measurement.
Today, the Ishikawa cause-effect diagram is used not only for quality analysis, but also in other areas, and therefore the first-order causes may already be different.
Using method
This method can be used to identify the causes of any problems, with the aim of analyzing business processes in the enterprise, if necessary, to evaluate the relationship of cause-effect relationships. As a rule, the Ishikawa diagram is born during a team discussion of a problem conducted by the brainstorming method.
Classification of the reasons that form the "skeleton" of the diagram
The Ishikawa diagram consists of a central vertical arrow, which actually represents the consequence, and large “ribs” that are called the first-order causes. Smaller arrows, called second-order causes, are suitable for these “ribs”, and third-order reasons are even smaller for them. Such “branching” can take a very long time, up to reasons of the nth order.
Applying the brainstorming method in charting
In order to build the Ishikawa diagram, you must first discuss with the team the existing problem and what are the most important factors that affect it.
The brainstorming or brainstorming method assumes that not only employees of a certain enterprise participate in the discussion, but other people can also take part, since they have an “unbroken eye” and approach the problem from an unexpected angle.
If during the first stage of the discussion it is not possible to reach consensus on the reasons causing a certain consequence, then as many stages are carried out as it will be necessary to identify the main factors.
During the discussion, no ideas are discarded; they are all carefully captured and processed.
Build Order
Building a diagram of Ishikawa involves several steps. The first is the correct formulation of the problem:
- It is recorded in the center vertically of the sheet and aligned horizontally to the right. As a rule, the inscription is enclosed in a rectangle.
- First-order causes, which are also predominantly placed in rectangles, lead to the problem-investigation.
- Arrows of the second order are brought to the causes of the first order by arrows, to which, in turn, the reasons of the third order are brought up and so on to the order that was determined during the brainstorming.
As a rule, the diagram should have a name, date of compilation, and object of study. In order to determine which causes belong to the first order, and which ones to the second, etc., it is necessary to carry out their ranking, which can be carried out during a brain attack or using a mathematical apparatus.
Analysis of the causes of defective products
Consider the Ishikawa diagram as an example of an analysis of the causes of defective products.
In this case, production defects are the consequence (problem).
During a brainstorming session, various causes were identified that affect the product’s defect. As a result of consensus among participants in a brain attack, all causes were ranked, minor ones were discarded, and the most important factors were left behind.
The first-order reasons included materials, equipment, components, labor, working conditions and technology.
They are directly influenced by second-order causes: impurities, humidity, delivery, accuracy, control, storage, air, workplace, production culture, machine age, maintenance, discipline, qualifications, experience, instrument, measuring instruments, technological discipline, documentation , snap (its availability).
Second-order causes are affected by third-order causes, which include temperature, storage humidity, acceptance during inspection, illumination and noise at the workplace, and the quality of the equipment.
All these reasons are spaced out to their respective places and a diagram of Ishikawa is built. An example is shown in the figure. It should be understood that the reasons for the other group can be distinguished other.
The main question when plotting
Any diagram of Ishikawa in its analysis should be accompanied by the question "Why?". First we ask this question in relation to the problem: "Why did this problem arise?" Answering this question, it is possible to identify the causes of the first order. Next, ask the question "Why?" in relation to each of the causes of the first order and, thus, we identify the causes of the second order, etc. They also usually don’t distinguish, but in relation to the reasons of the third order and further it is more correct to ask the question “Why?”, but “What?” " or "What exactly?"
By learning to answer these questions with the above examples of the Ishikawa diagram, you will learn how to build it yourself.
Examination of the "Scatter in Details" problem
Consider the Ishikawa diagrams as an example of an enterprise.
An industrial enterprise engaged in the production of any parts often faces the problem of the dispersion of the dimensions of the parts.
To solve this problem, it is necessary to bring together technologists, workers, suppliers, managers, engineers, you can invite other people who will help to find approaches that are not provided by specialists in their field.
With a well-conducted analysis, it is not enough to identify only the factors that cause the problem, they need to be ranked correctly. This can be done in the process of brainstorming, after the process of determining the causes is completed. Each member of the group must give assessments of the significance of individual causes from their point of view, after which the general significance of the causes will be determined.
In the presented Ishikawa diagram, using the example of an enterprise, the following first-order causes were identified: workers, materials, technology, machine tool, measurements, environment and management.
The figure shows the causes of the second and third orders. Asking the questions "Why?" So what?" you can get to the root cause that caused the problem.
The members of the group determined that the most significant indicators affecting the scatter of parts are the measurement period and the accuracy of the instruments.
Thus, the significance does not depend on what order this reason belongs to.
Advantages and disadvantages of the method: continued research
The main advantages of the applied method:
- disclosure of creativity;
- finding interdependencies between causes and effect, determining the significance of causes.
The main disadvantages when using this tool:
- there is no way to check the chart in the reverse order;
- the diagram can be significantly complicated, which will complicate its perception and the possibility of a logical conclusion.
In this regard, the analysis of causes and effects must be continued using other methods, first of all, such as the A. Maslow pyramid, Pareto diagram, stratification method, control charts and others. With a simple solution, it may be sufficient to conduct an analysis using a causal diagram.
Finally
The Ishikawa diagram can be used primarily for product quality management. In addition, it can be used in the design of new products, the modernization of production processes and in other cases. It can be built both by one person and by a group of persons for preliminary discussion. As a result of using this tool in its activities, the enterprise is able to systematize the causes of the problem-consequence in a fairly simple form, while selecting the most important ones and prioritizing them by ranking.