A fishbone diagram (Ishikawa diagram) is a visual tool that organizes the potential causes of a specific problem into structured categories branching out from a central axis. Its purpose in Lean is to facilitate a systematic root cause analysis, enabling teams to look beyond superficial symptoms and identify the actual source of process waste or defects. By mapping out factors such as equipment, methods, and people, it ensures a thorough exploration of all variables before a solution is implemented.

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We investigate where causes tend to concentrate within a process. A process = People who, following a specific method, use machines to process materials.