6.1 CAUSE AND EFFECT DIAGRAMS

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Consider a production team about to launch a new product. They must anticipate factors that will affect the final product

APPROACH - Use a Cause and Effect Diagram

The cause and effect diagram was developed by Kaoru Ishikawa in 1943.

- Commonly called - Cause and Effect (CE), Ishikawa Diagram or Fishbone diagram

In quality we use these to find factors that have some role in a good/bad quality.

For manufacturing there are some more standard causes to consider.

How can a CE diagram be made up?

- use a team for more ideas

- use brainstorming techniques

Brainstorming is a two stage process

Step 1: As a group, have each team member contribute ideas. If an idea is not good it doesn't matter. Add ideas to the diagram. Exhaust all ideas! NO CRITICISM!!!

Step 2: Review the diagram critically as a group. Voting will help to narrow down what are the most important factors.

What use is a CE diagram?

- Post it in visible spots for common reference by all the workgroups.

- Use it to anticipate, or find the cause of problems.

- Keeps workers involved and informed.

Advantages of CE diagram

- Analysis - allows tracking of errors, efficient use of resources, lower costs.

- Elimination of unwanted causes.

- Standardization of existing and proposed operations.

- Education and training to allow personnel to make decisions and correct problems autonomously.

6.1.1 Process Diagrams

Another type of CE diagram is the Process-Analysis diagram. This is used when there are a number of operations or factors involved.

When considering CAUSES, there are two main types, assignable and chance.

chance - normal, or natural variations that occur in a system (e.g. dice)

assignable - controllable parameters such as material, process parameters, operator skill, etc.