Case Study in Hypothesis Prioritization with Ishikawa Diagrams

The objective of this paper is to explore a multidisciplinary problem-solving team investigating a customer-reported failure using an Ishikawa diagram with a spreadsheet for prioritizing and tracking investigation actions in a manufacturing organization. A case study methodology is used with the actions taken to investigate a customer-reported failure explained. The highest priority failure hypothesis was found to be unrelated to the failure. Two medium-rated hypotheses were found to be causing the problem; leakage was occurring at the connection between two components due to a diameter deviation of one of the components. Identifying and prioritizing hypotheses from the Ishikawa diagram provided structure to the investigation and gave the investigation team leader a tool for tracking the investigation actions. This approach is suitable for all types of failure investigations in which an Ishikawa diagram is used to list hypotheses.