Ask the Manufacturing Specialist: Fishbone Cause & Effect Diagram

 At Acuity, we know how difficult it can be to identify and solve the causes of manufacturing problems. If it were easy, we would never have to fix the same problem more than once.

When I was interviewing for a job a few years back, the interviewer asked me, “Can you fix our ongoing problems with bad parts getting to our customers?”

Tough question, I thought. My answer went something like this, “I don’t know the ins and outs of your operation, your customers, or the problem that made it out the door. What I can tell you is that I have used a tool, the fishbone cause-and-effect diagram, which has helped me find root causes and eliminate single occurrence and recurring manufacturing problems.”

He next asked me, “How so?”

To solve a problem, it helps to understand that a problem is an effect of something else—a cause, such as a change within the process.

One of the easiest ways to identify, fix, and prevent the reoccurrence of problems is through the utilization of the fishbone cause-and-effect diagram, or the Ishikawa diagram.

The Ishikawa diagram is named after Dr. Kaoru Ishikawa who is credited with the development of this root-cause identifying tool. Dr. Ishikawa was an organizational theorist professor at the University of Tokyo. At one point in his career, he was asked by Kawasaki to help solve issues in one of their shipyards. The rest is history.

The fishbone diagram is a simple tool that allows you to document various input factors so you can troubleshoot them for the root cause and develop a permanent solution.

To learn more about how the fishbone diagram works, check out the diagram at the bottom of the page then read the tips below:

• To begin, write the problem, or effect, your operation is facing in a box on the far right side of the diagram. In this example, the problem is that the conveyor goes down with a broken belt once per week.
• Next, draw a horizontal line stretching from the effect box. From the line, draw angled lines above and below the horizontal line. You’ll notice your diagram beginning to look like the skeleton of a fish. On the angled lines, write down any major causes that could be responsible for the problem.
• How many angled lines you draw will depend on the problem you are trying to solve. When trying to solve a manufacturing problem, you should have at least six main cause lines, three above and three below.
• Some of the most common causes of manufacturing problems are material, method, machine, employees, management, and Mother Nature.
• Now you can start adding sub-causes. Check out the example for sub-causes that could be contributing to the conveyor belt problem.

Identifying sub-causes involves brainstorming among your team. While brainstorming,  don’t analyze, critique, or jump to conclusions. Instead, keep brainstorming until you have multiple causes for each category.

By the end of the fishbone exercise, you should have a clear vision of the root of your manufacturing problem and well-developed ideas on how to solve and prevent the problem from recurring.