Visit Ishikawa diagram, also known as Cause-effect diagram or Fishbone diagram (Fishbone Diagram), is a graphical tool for managing the Quality used to structure the search for potential causes a specific effect or problem.
In-depth definition : Invented by Professor Kaoru Ishikawa, this diagram is a fundamental tool of the Root Cause Analysis (RCA). It organizes the possible causes of a problem into families. This visual structure (hence the name "fishbone") is extremely effective for :
- Make sure you don't forget any causes: Systematic classification prevents bias and hasty judgments.
- Facilitating Brainstorming: It serves as a structured framework for the brainstorming sessions of the’Continuous Improvement (KAIZEN).
- Summarize the analysis: It allows you to quickly visualize the cause-and-effect relationships often used in the D4 (Determine Root Cause) a 8D analysis.
The Classic 5M Model of Industry
The structure of the Ishikawa diagram is traditionally based on a set of categories of potential causes. The model most commonly used in the manufacturing industry is the 5M, sometimes extended to 6M or 8M :
| Category (Main ridge) | Domaine Couvert | Examples of Potential Causes |
|---|---|---|
| Material | Raw materials, consumables, Bill of materials (BOM) | Non-conforming batch quality, non-certified material, reference error, problem with the Supply Chain. |
| Methods | Processes, Manufacturing range, Work Instructions | Incorrect operating sequence, lack of Standardization, using the wrong version of Manufacturing file. |
| Workforce | Personnel, operators, technicians | Lack of training, fatigue, misinterpretation of instructions, lack of self-discipline (Shitsuke of the 5S Method). |
| Resources | Machines, tools, measuring equipment (Poka-Yoke) | Worn tools, incorrect settings, lack of Preventive Maintenance, sensor failure IoT. |
| Environment | Work context, physical conditions | Insufficient lighting, inappropriate temperature and humidity, excessive noise, clutter (Seiri and Seiton of the 5S Method). |
| Measurement (6th M) | Controls, KPI, calibration | Non-calibrated measuring equipment, insufficient inspection frequency, system Machine Vision incorrectly set. |
Application in the Improvement Cycle (PDCA)
The Ishikawa Diagram is the flagship tool of the Plan cycle PDCA (Plan-Do-Check-Act). It allows you to :
- Drawing up an inventory : The Industrial Engineering uses the diagram to identify all the possible causes of the problem (the effect) after having clearly defined it (often using KPI as the TRS or scrap rate).
- Validating assumptions : Once the diagram has been filled in, the team goes beyond ideas and uses data analysis (often the Pareto method) to verify which are the most likely and most critical causes, transforming them into verified root causes.
- Target Action: The resolution then focuses solely on the critical root causes which, if eliminated, will have the greatest impact on the resolution of the problem (principle of the Pareto method).
In conclusion, the Ishikawa diagram is the visual and methodological tool that transforms problem-solving from a disorganized search to a structured, collaborative and rigorous approach. It is indispensable for anchoring the effectiveness of’Operational Excellence in the company.