Ishikawa Diagram, 5 Why Method, Fishbone Diagram by qmBase

The Ishikawa Diagram and the 5 Why Method

History and application of the Ishikawa Diagram

The Ishikawa Diagram was developed in the '40s of the last century by the Japanese scientist Kaoru Ishikawa and named after him. Other names for the diagram are: Cause and Effect Diagram, Fishbone Diagram
The Ishikawa diagram is used for the systematic development and presentation of error causes. For example, the Ishikawa diagram can be used in the context of an 8D report in step 4 "Determining the cause(s) of the error". The graphical representation provides a good basis for jointly deriving and discussing the causes of errors. Creating an Ishikawa diagram can be divided into 5 steps.

1. Drawing the Ishikawa diagram and entering the main influencing variables

First draw the bones of the Ishikawa diagram and add the problem or fault to be solved to the right of it. Then add the main influencing variables. Usual are here: Man, machine, process, environment, material, equipment.

2. Identify main and secondary causes

In the second step, you collect and document the main and secondary causes in the Ishikawa diagram. At this point, it is useful to use methods like 5-Whys (see below). Secondary causes are represented graphically by further ramifications.

3. Check for completeness

Question whether you have actually identified all influences. The graphical representation often makes this easier and stimulates the creativity of the problem solver.

4. Selecting the potentially most influential causes

Analyze the identified causes in terms of their significance to the problem and try to weight them. The aim is to identify the most influential causes, to test them and, if necessary, to define measures for dealing with them afterwards.

5. Checking the potentially most influential causes for accuracy

After identifying the most influential causes, check them for correctness. For example, consult other experts or use statistical methods to validate your assumptions.
To make it easier for you to start working with the Ishikawa Diagram, we have created a template for you to download. You can find it at the end of the blog article.

History and application of the 5-Why method

Developed in the 30's of the last century by the Japanese quality management mastermind Sakichi Toyoda, the 5-Why method (or 5-Why method) is a simple way to determine the causes of defects. This method is to be used when dealing with problems, improving processes and quality as well as identifying the causes of errors. However, the method is best suited for problems with low to moderate complexity. Especially in combination with other tools the 5-Why method often leads to success. For example, it is suitable for creating Ishikawa diagrams.

The procedure

The procedure is simple, just ask yourself why five times to identify the root cause of the problem. The goal is to keep asking until you have identified the actual root cause and measures to deal with the cause become obvious. The procedure should become clear in the following example.

Example of the 5-Why method

Here is a simple example of the 5-Why Mehtode that can easily be transferred to other situations:

Situation: The workpiece has surface defects

1. Why does the workpiece have surface defects?

Answer: Because it has fallen to the floor.

2. Why did the workpiece fall?

Answer: Because it has slipped out of the holder.

3. Why did it slip out of the holder?

Answer: The operator has chosen the wrong fixture.

4. Why did the operator choose the wrong support?

Answer: The brackets were not labeled.

5. Why were the brackets not labeled?

Answer: It is not specified in the current work instructions that the brackets must be labeled.

In the example shown, the core cause of the error was identified as the non-existent instruction for labeling the workpiece holders. With this finding, it should be easy to take measures to avoid the error in the future. The 5-Why methodology does not force you to settle for a simple answer, but to get to the bottom of the cause.

Download our Ishikawa Diagram Template now!

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