Author: Pavel Ryvola | Updated:
What is a Fishbone Diagram (Ishikawa) and how does it help?
The Fishbone diagram (often called the Ishikawa diagram) is one of the seven basic tools of quality. It is used for visual Root Cause Analysis (RCA). By graphically breaking down a problem into the main 6M categories, it makes it easier for teams to uncover the true origin of a nonconformity rather than stopping at superficial symptoms.
When should you use a Fishbone diagram in practice?
- When analyzing customer claims and compiling 8D reports (typically in the D4 phase) in the automotive industry.
- As a necessary prerequisite for the 5-Why method. You select the most likely causes from the Fishbone diagram and apply deeper questioning to them.
- During brainstorming and process audits to uncover hidden risks, whether you are addressing a process drop-off or investigating why a visual inspection failed to catch a planted test piece (e.g., a Red Rabbit).
Practical Example: Ishikawa Diagram for Gearbox Oil Leak
Imagine a typical situation in automotive manufacturing: at the end of the assembly line, a tester detects an oil leak from a gearbox. If the team simply repairs the defect on the part and does not secure corrective actions, the situation will repeat tomorrow. Instead, you call a brainstorming session with production staff, maintenance, and engineers and start populating the fishbone diagram:
- Man: A new operator was not trained on the correct sealant application procedure.
- Machine: The sealant dispenser has a clogged nozzle due to skipped preventive maintenance.
- Material: The sealant paste was stored outside the recommended temperature and its viscosity changed.
- Method: The Standard Operating Procedure (SOP) does not clearly define the required amount of applied paste.
- Measurement: The pressure sensor at the leak test station did not have a valid calibration.
- Environment: Fluctuating humidity and temperature in the hall slow down the paste curing before testing.
From this list, the team then selects the most likely root causes (e.g., missing specifications in SOP and skipped maintenance) and subjects them to detailed analysis using the 5-Why method.
How to create a Fishbone diagram online (6M method)
Instead of drawing on a whiteboard or complex formatting in Excel, use our online tool. Write the specific problem (e.g., "Oil Leak") in the "head" of the fishbone. During the team brainstorming session, visually place ideas directly onto the corresponding bones: Man, Machine, Material, Method, Measurement, and Environment. Our generator allows you to confirm the true root causes and download a professional PDF report with a single click.
What's next?
While the Ishikawa diagram helps you visualize all potential causes, to reveal the true Root Cause we recommend seamlessly following up with a 5-Why analysis. If you are not sure which problem to tackle first, take a step back and create a Pareto Diagram. Do not forget to report all corrective actions to the customer using a standardized 8D Report.