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Root cause analysis (Part 1)

KZK Solutions /kzoli62/
Published by Z. Kovács in Quality · 25 May 2021
Tags: QSRootcause
In today’s article, I continue my quality assurance series that I have already started.
In the first two parts, I wrote about filling in 8D reports, followed by a presentation of the 5W2H procedure. Today, I write about root cause detection in failure processing.
If we search the internet for “root cause analysis,” we get millions of results. Today, I will try to narrow down this topic, which I will also bring to a real-life footprint.

Root cause analysis

The 5W2H method, which I recently wrote about, can help to fully describe the problem. This ensures understanding of events through answering a few simple questions.

Another, also simple mode of analysis is 5 Why use analysis. I have already covered this topic in an older newsletter.
To do this again, just keep the following in mind:

  • In the “5 Why” analysis, ask the Why as a question until we get to a poorly, not properly functioning process. Responses such as “lack of time”, “lack of people”, “little money”, “inadequate management expectations”, “supplier error” are not acceptable.
  • Once we have found the roots, formulate at least two actions. The first action should be for a short-term solution (firefighting) and the second action should be to ensure that the problem never occurs again.

Let's look at a practical example:


What is it ?

  • To make the analysis with facts and data
  • The analysis PDCA / 8D includes Factor Tree Analysis and 5 Whys
  • Basic comparison between Good, Bad and standard

What is it for ?

  • To find the factor that can reproduce the phenomenon
  • To find out the root cause
  • Then the solution will be easy to identify

Symptoms on BAD PART -> 5W2H

- Result or outcome of the problem.
- What you see as a problem?(Obvious)


- Gap from standard

Cause -> 5Whys

- “The roots” – system below the surface, bringing about the problem (Not obvious)


- What are the factors that explain the defect:

  • Based on 4M: Material, Machine, Method, Men.
  • No brain-storming but study of the reality
  • San Gen Shugi. (Shortly I will wrire about it too.)

Two activities:

- Occurrence / work on the creation of the defect
- Non detection / work on the fact that defect was not stopped internally. (easier to start with)

FTA / 4M

Material:Factors related to the Material or components used for the manufacturing of the defective part.Method:Factors related to the process and the way the product is manufactured and delivered. It can include also the conditions of process. In this way, “Method” can also include Environment and Measurement. If it is really necessary, a 5th or 6th “M” can be added separately.Man:Factors related to Human ability to do properly the work :Training, Communication conditions for example.Machine:Factors related to the machine capabilities, Poka Yoke and software  


  • Based on experience and observation, define most obvious factors that could potentially generate the problem. Ask Operators and Experts.
  • For physical issues, drawing the issue helps to identify relevant factors.
  • or administrative issues (ex: products delivered to wrong plant), factors are the process steps related to the issue. Then, you might draw the issue using physical factors.
  • If no anomaly found, use Control plan, Process/Product/ Design FMEA’s to go deeper, by adding less obvious factors.

Example 4M


-Training(Manual dexterity, Competence,…)
- Capability of people (Eye sight,…)
- Test or material handling equipment, Production tools(PM)
- Poka-Yoke
- Software(Ex: Revision(A,B,C,…))
- Jigs & Fixtures
- Work station (Layout, Red box,…..)
- Chemical part: Viscosity , Hardness, Color,
- Electronic part: Dimension, Color, Electronic value
 (Resistance, Voltage, ….)
- Mechanical part: Dimension, Color
- Condition as Machine parameter (Air pressure, Voltage, Current, Resistance, Distance, Duration of product transformation, Position,…)
- Environment
- Method of work(Working instruction, Visual aids)
- Measurement method  

1. Master sample for set up is available?            1. Master sample for set up is available?
2. Is master sample within right dimensions?     2. Is workinstruct. clear, doable, quantified?
3. Are set up parameters respected?                 3. Is the Operator trained (deployment)?


  • Where and how the factor is measured or checked, and how often
  • Going to the control point allows to quickly find standard values and history/traceability on the factor. It is also a place where a measurement method for the factor exists.
  • In case there is no control point, indicate the method to use to measure the factor.
  • The control point can be at supplier, at incoming inspection, in process control stations or final test. It can be 100% test, sampling or done at initial sample and then periodically.
  • When a characteristics is critical, it must be verified at several control points during the process.


  • What is the applicable standard?
  • Answer with specific values when the factor is measurable. Do not enter only drawing reference excepted if the standard is a set of measures. In that case, attach the drawing with highlighted measured characteristics.
  • Check if the standard is clear and updated.

Next, we will continue from here and get acquainted with the other points of FTA (Factor Tree Analysis).

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