Cause Analysis of Failures: Fishbone Diagram or 5 Whys?

Reducing Downtime with the Ishikawa Diagram and the 5 Whys

When a breakdown occurs in a production line or an industrial system, it is crucial to understand its root causes to prevent any recurrence. Two popular methods for this analysis are the Ishikawa diagram, often referred to as the Fishbone diagram, and the 5 Whys method. These tools are cornerstones in the realm of Industry 4.0, playing a vital role in minimizing downtime and promoting continuous improvement. But which one should you choose? In this article, we will explore these two methods, their respective advantages, and when they are most effective.

What is the Fishbone Diagram?

You have likely seen a diagram shaped like a fish with main branches leading to a central backbone. This is what is known as a Fishbone diagram. This diagram helps identify, explore, and illustrate all potential causes of a complex problem.

Structure of the Fishbone Diagram

1. The Main Problem: It is located at the right end of the diagram, like the head of the fish.
2. Main Categories: Typically, these include People (workforce), Machines (equipment), Materials, Methods (processes), Measurements, and Environment, but they can be adjusted based on the context.
3. Secondary Causes: Each branch can contain sub-branches detailing specific causes that contribute to the main categories.

This clear visual structure helps teams organize and examine each aspect that could be the source of the problem, which is essential for comprehensive resolution.

Advantages of the Fishbone Diagram

• Overall Visualization: Allows viewing all potential causes at a glance.
• Encourages Collaboration: Teams can work together to identify possible causes.
• Flexibility: It can be adapted to any type of problem.

The 5 Whys Method

On the other hand, you may wonder how a simple series of questions can compete with a detailed diagram. This is where the 5 Whys method comes into play. Created by engineer Taiichi Ohno for Toyota, this method involves asking the question "Why?" five times in succession to dig deep into the root causes of a problem. Sometimes, five questions are sufficient, but it may take more or less depending on the problem's complexity.

Implementing the 5 Whys

1. Describe the problem: Start by clearly stating the issue encountered.
2. Ask the first "Why": Identify why this problem occurred.
3. Continue to ask "Why": For each answer, ask again "Why?" until reaching the root cause.

Let’s take a fictional example to illustrate:

• Problem: The machine stopped.
• Why? The motor overheated.
• Why? There was a lack of lubricant.
• Why? The lubrication pump was not functioning correctly.
• Why? One of the pump components was defective.
• Why? The component was not replaced during the last maintenance.

Advantages of the 5 Whys

• Simplicity: Easy to understand and use without needing extensive training.
• Speed: Can often be conducted very quickly.
• Focus on the Root Cause: Helps to avoid superficial solutions.

Comparison and Choice

One might think that one of these methods is necessarily better than the other, but it really depends on the context and the nature of the problem.

When to Use the Fishbone Diagram?

• Complex Problems with Multiple Possible Causes: This method is ideal for problems where causes are not immediately evident and can be numerous and varied.
• Collaborative Analyses: Useful when a diverse team works together to identify potential causes.

When to Use the 5 Whys?

• Relatively Simple Problems: When the problem is clearly caused by a simple chain of events.
• Quick Analyses: Perfect for situations requiring a rapid solution without losing analytical depth.

Mixed Perspective

It often happens that both methods are combined for even more effective analysis. For instance, first using the 5 Whys to quickly identify a potential cause, then delving deeper into that cause with a Fishbone diagram to explore all its ramifications. This hybrid approach allows for the best of both worlds, offering both clarity and depth.

Conclusion

In industrial production, determining the cause of a breakdown is crucial for maintaining efficiency and continuity in the production line. There is no one-size-fits-all answer to whether the Fishbone diagram or the 5 Whys method should be prioritized. The choice depends on the complexity of the problem and the context of your analysis. For complex and multidimensional issues, the Fishbone diagram is often the most suitable. For more straightforward and direct questions, the 5 Whys can serve in a quick and effective manner.

I bet that by using these tools strategically and complementarily, you will be able to identify and resolve breakdowns more effectively. So, which approach will you try today in your breakdown analysis?