This article is intended to describe the sequence for Root Cause
analysis, from the point of view of Sensei Shigeo Shingo and is based on my own
experiences as an instructor of TPS continuous Improvement also.
Its not intended to describe how a template must be filled or completed,
the scope is more conceptual, it talks about the interrelation of the tools
Ishikawa diagram, 5 W’ 1 H & the 5 whys?
Write about Zero Defects is not simple, so I have divided in 3 parts and
this is the first one.
The below diagram is basic when determining the root cause of a problem.
This Diagram, was first described by Sensei Shigeo Shingo in his book; Zero Quality Control: Source Inspection and
the Pokayoke System.
Five
Elements of Production and the Five W’s and one H.
Fig.
It is very common for beginners in the method of problem-solving,
wanting to go directly to the solution, without investing a reasonable time
analyzing and finding the true root cause of the problem. Usually when I wonder
what part is the most important for problem-solving over 90% of people answer
Pokayoke, however are in error and without discrediting the importance of
implant a good Pokayoke, the most important thing is to find the root cause
problems, however it is extremely difficult.
In my experience this tools sequence have gave me good results, starting
from Problem definition, 5W & 1 H, followed by Ishikawa Diagram until
answer the 5 Whys that demystify the Root Cause
Five W’s one H.
Fig.
It’s an Information Gathering method; that helps to define the problem,
with data and facts.
5W1H (what, where, when, who, how, why) is a
method of asking questions about a process or a problem taken up for
improvement. Four of the W’s (who, what, where, when) and the one H is used to
comprehend for details, analyze inferences and judgment to get to the
fundamental facts and guide statements to get to the abstraction. The last W
(why) is often asked five times so that one can drill down to get to the core
of a problem.
However many times is not easy to answer
directly and we may get stuck in one question Why?.
In other worlds just after the problem have
defined and the question Why? Is prompted the team may be in blank, not clue at
all; for that situations we should use the Cause and Effect Diagram or Ishikawa
Diagram, to discriminate all the possible causes and find the answer, that
immediately will carry on a new question, Why?... and so on.
Ishikawa diagram.
Fig.
Depict the Causes of a specific event Common uses of
the Ishikawa diagram are Product Design and Quality Defect prevention, to
identify potential factors causing an overall effect. Each cause or reason for
imperfection is a source of variation. Causes are usually grouped into major
categories to identify these sources of variation.
Causes;
Causes in the often categorized, such as to the 5 M's,
described below. Cause-and-effect diagrams can reveal key relationships among
various variables, and the possible causes provide additional insight into
process behavior.
Causes can be derived from brainstorming sessions.
These groups can then be labeled as categories of the fishbone. They will
typically be one of the traditional categories mentioned above but may be
something unique to the application in a specific case. Causes can be traced
back to root causes with the 5 Whys technique.
Typical categories are
The 5 Ms (used in manufacturing industry)
•
Machine (technology)
•
Method (process)
•
Material (Includes Raw Material,
Consumables and Information.)
•
Man Power (physical work)/Mind Power
(brain work):Kaizens, Suggestions
•
Measurement (Inspection)
The original 5 Ms used by the Toyota Production System
have been expanded by some to include the following and are referred to as the
8 Ms. However, this is not globally recognized. It has been suggested to return
to the roots of the tools and to keep the teaching simple while recognizing the
original intent; most programs do not address the 8Ms.
•
Milieu/Mother Nature(Environment)
•
Management/Money Power
•
Maintenance
The categories typically include
• People: Anyone involved with the process
• Methods: How the process is performed and the specific requirements for doing
it, such as policies, procedures, rules, regulations and laws
• Machines: Any equipment, computers, tools, etc. required to accomplish the job
• Materials: Raw materials, parts, pens, paper, etc. used to produce the final
product
• Measurements: Data generated from the process that are used to evaluate its quality
• Environment: The conditions, such as location, time, temperature, and culture in
which the process operates.
5
Why’s
The 5 why’s typically refers to the practice of asking, five times, why
the failure has occurred in order to get to the root cause/causes of the
problem. There can be more than one cause to a problem as well. In an
organizational context, generally, root cause analysis is carried out by a team
of persons related to the problem.
No special technique is required.
Fig.
However in the practice it’s not easy, and like I have mentioned before,
there are situations when the team do not have the answers and they will need
to do an Ishikawa diagram.
Lets see this example.
As you see the Ishikawa Diagram was used at the right moment, to demystify
the answer or answers.
I hope this help you in your next problem-solving event.
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