![]() RCA can progress more quickly and effectively by pairing an Ishikawa diagram with the scientific method in the form of the well-known plan-do-check-act (PDCA) cycle to empirically investigate the failure. Often, failure investigations begin with brainstorming possible causes and listing them in an Ishikawa diagram. This is not necessarily wrong, but often the ideas listed do not clearly contribute to the failure under investigation. Once a problem-solving team has been formed, the first step in an RCA is to create a problem statement. The customer’s description of the failure.The problem statement should include all of the factual details available at the start of the investigation including: Although critical for starting an RCA, the problem statement is often overlooked, too simple or not well thought out. The customer’s description does not need to be correct it should reflect the customer’s words and be clear that it is a quote and not an observation. For example, a problem statement may start as, “ Customer X reports Product A does not work.” The rest of the problem statement would then clarify what “does not work” means in technical terms based upon the available data or evidence. A good problem statement would be: “Customer X reports 2 shafts with part numbers 54635v4 found in customer’s assembly department with length 14.5 +/-2 mm measuring 14.12 mm and 14.11 mm.”Įlements in the Ishikawa diagram should be able to explain how the failure happened. For example, “lighting” is a typical example under “environment” however, it is seldom clear how lighting could lead to the failure. Instead, the result of bad lighting should be listed and then empirically investigated. In this example, lighting could cause an employee to make a mistake resulting in a part not properly installed. Therefore, the part not properly installed would be listed in the Ishikawa diagram. Simply investigating the lighting could take time and resources away from the investigation so the first step would be to see if a part is installed.Ĭauses of a part not being installed can be listed as sub-branches, but the priority should be on determining if the part was installed or not. If a part is not correctly installed, then use the 5 Whys on that part of the Ishikawa diagram for investigation. The lighting may be a contributing cause, but it should not be the first one investigated. The Ishikawa diagram should be expanded each time 5 Whys is used. ![]() For example, the branch may end up as: material → part not installed → employee skipped operation → work environment too dark → poor lighting → light bulbs burned out. In this example, the use of 5 Whys led to the true cause of the failure – the light bulbs burned out. Had the 5 Whys not been used, then the employee may have been retrained, but the same employee or somebody else may have made the same or a different mistake due to the poor lighting. Failing to use the 5 Whys risks a recurrence of the failure – the corrective action may only address symptoms of the failure.įigure 2: Tracking List for Ishikawa Diagram Action Items Each time a cause is identified, the 5 Whys should be used to dig deeper to find the true underling cause of the failure. Here, each hypothesis from the Ishikawa diagram is prioritized and the highest priority hypotheses are assigned actions, a person to carry them out and a due date. This makes it easier for the team leader to track actions and see the results of completed actions. Such a tracking list can also be used to communication the team’s progress to management and customers. New insights may be gained as the investigation progresses. For example, somebody checking the length of a part may have observed damage.
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