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Use of 5 Why's

KZK Solutions /kzoli62/
Published by Z. Kovács in Quality · 21 April 2021
Tags: QA5W
With my entry today, we will continue our trip to the field of quality assurance.

Those who have children, we all know the kids, "BUT WHY" era. This is the time when the questions correctly they can go to their parents nerves. This period is based on the experience of the process is shown below.

In my following training material I deal the 5W (5Why) method often used in quality assurance, projects implementation.
The 5W, or 5 Why method, is one of the problem-solving tools used primarily in lean companies. Not to be confused with the 5W + 2H method. You can use it to discover basic causal relationships and find the real cause of the problem (root cause). This device comes from Toyota founder Tojoda Sakics. Sometimes we get to the solution with less than 5 questions starting with "why ...", but in more complicated cases, more questions starting with "why ..." may be needed.

The material contains a case study that will help shed light on the essence of the process.
This method is based on the innate people "curiosity", the answers to questions.

1. Root Cause Analysis

In order for a company to find problems while the production, to survive in this material, or fame caused the loss caused by the problems, you need to find the root cause of the problems.


The emergence of problems often leads to frustration in the areas affected, the derivation of which is often pointing at each other. Obviously, the goal is not to 5 Why? technique should be reduced to the level of 5 charges.
For example, we can get rid of the trap of accusation by convening all those involved when analyzing the problem.

2. Why and How of Root Cause Analysis

How caused the problem?

It helps to have the proper CORRECTIVE ACTION can be determined.

Why the problem occurred?

It helps in the INITIAL diagnosis of the problem, so you can prevent the problem from occurring again.

3. Symptom - Cause Analysis


Indicates that something is wrong, but it does not show why.

Genuine cause:

It shows exactly why something bad and which is the right direction in which you must go to prevent the problem from occurring again.

4. A Case Study

In this case, I show the operation of the process through an electronic production failures.

What is the problem?

The control found more bad soldering after wave soldering process during the examination of the panel. The fault is discovered on panels later too.

Using the 5 "Why" in the case study

Description of the problem:

More bad soldering on the PCB were found in the post-wave control.

1. Why - there are bad solder joints in the panel?

Because the wave soldering is not working properly (the raw panel error-free and complies with the specification).

2. Why - the machine is not working properly?

Because the profile of the machine is incorrect.

3. Why - the Profile is incorrect?

The conveyor speed is to slow based to the specification.


4. Why - the band running too slowly?

Because the belt engine running unevenly, and the rate does not correspond to the actual setting.

5. Why - the conveyor belt engine work unevenly?

Because the internal brushes of the motor are worn.


5. Tools

The answers to 5 whys does not always give a clear answer, so the process can also be used with other tools:


- every opportunity has to be formulated.

Cause and effect

- (Or fishbone) diagram.

Always refer to the original cause of the improvement process. However, the degree of improvement is determined by the number of factors.


  • Cost - benefit.
  • Impact on business (+ value added / - value addition).
  • The feasibility of change.

The simple stability problems, the method of solution are already known.

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