In my previous post, I defined recurring problems, explained why they occur, and how to counteract them. I also explored common problem-solving traps and explained how they foil manufacturing personnel. To review, the six traps are as follows:
- Erroneous information, facts, or data supplied by another involved party.
- Defective replacement parts from the supplier.
- Defective measurement tools or gauges.
- Defective input material.
- Incorrect drawings or schematics.
- Incorrect logic on the part of the problem solver.
In today’s post, I will describe two critical problem-solving tools: cause-and-effect diagrams and causal chains. Both tools are indispensable for cutting through to the root of a problem with high efficacy. As I have stated in previous posts, much of what I’m presenting in this series of posts is taken directly from my first book written in 2001,  Process Problem Solving—A Guide for Maintenance and Operation’s Teams.
Cause and Effect Diagrams
One of the most popular and widely used problem-solving tools available is the Cause and Effect (C & E) Diagram. C & E Diagrams were developed by Dr. Kaoru Ishikawa, a noted Japanese consultant and author of A Guide to Quality Control (2). They have been used successfully by teams around the world. In honor of Dr. Ishikawa, this tool is sometimes referred to as an Ishikawa Diagram, but it is also referred to as a “fishbone diagram” because its basic structure resembles the skeleton of a fish. Whatever you wish to tall it, a C & E Diagram is a useful tool that must be part of the problem-solver’s tool kit.
The figure below is the basic structure of the Cause and Effect Diagram which is used to develop and organize potential causes of a problem. The potential causes are listed on the fishbones driving toward the problem (i.e. the effect). The effect or problem statement is stated to the right while the potential causes are listed as “fishbones” to the left under the appropriate category headings. By arranging lists in this manner, there is often a greater understanding of the problem and possible contributing factors.
Typical C & E Diagrams are constructed with four major categories of potential causes (4 M’s: Man, Method, Materials and Machines), but the C & E Diagram should be customized to the needs of the user. In other words, other categories can be added to further organize the potential causes. In our example, two other categories, Environment and Measurement have been added.
The following are the steps used to create a C & E Diagram:
- Develop a statement of the problem which describes the problem in terms of what it is, where it is occurring, when it is occurring, and how extensive it is. This statement is the effect and is listed to the right on the C & E Diagram.
- Brainstorm and create a list of causal categories that will be used to develop the possible causes of the problem on the C & E Diagram. For example, if the problem being studied was equipment related, our categories might be listed as Electrical, Mechanical, Pneumatic, Man, Methods, and Materials. The team must be creative when selecting the causal categories.
- Construct the C & E Diagram by:
- Placing the problem statement to the right of the fishbones.
- Listing the causal categories above and below the centerline or “spine” of the fishbone diagram.
- Brainstorm and list possible causes on the fishbones under the appropriate causal category heading.
- Interpret the C & E Diagram by:
- Looking for causes listed in the individual fishbones and testing the potential causes to determine if they have an impact on the effect.
- Gather additional data and information to validate the potential causes.
Let’s now look at an example of a real C & E Diagram. In our example, a team was attempting to solve a pinhole problem on a fiberglass part. Although the team had developed a more comprehensive problem statement, they simply stated the problem as Pinholes in Gelcoat, and then brainstormed to develop a list of potential causes. The figure below is the final C & E Diagram that the team had completed. One-by-one they tested the list of potential causes and narrowed it down to two possibilities, either contaminated gelcoat or contaminated catalyst. The replace both ingredients and the problem was solved. Remember, like all problem-solving tools, the C & E Diagram will only identify potential causes. Only data and other information about the other causes will lead you to the actual root cause(s).
In the next post, I will discuss another problem-solving tool referred to as the Causal Chain. As always, if you have any questions or comments about any of my posts, leave me a message and I will respond.
Until next time.
 Bob Sproull - Process Problem Solving – A Guide for Maintenance and Operation’s Teams, 2001, Productivity Press
 Ishikawa, Kaoru, Guide to Quality Control (Asia Productivity Organization, 1986)
Don't miss out!
Stay on top of the latest business acumen by subscribing to the Manufacturing Breakthrough blog.