Action: Replace the damaged screen. This will prevent additional metal shavings from getting into the coolant. But, even with the new screen, the seal remains damaged and leaking will continue. Therefore, the corrective action is to replace the damaged screen and the damaged seal, to stop the coolant from leaking.  

However, the screen likely will become damaged again, which in turn will lead to the seal being damaged and more leaking coolant. So, the permanent corrective action: Redesign the machine or add a guard to cover the screen and prevent damage from occurring.

This simple approach proves useful for employees in all levels of responsibility. A disadvantage to using this method is that it depends on the knowledge and experience of the team members participating in the exercise. Creating a multifunctional team incorporating people with differing backgrounds likely will prove beneficial. Each may offer different answers as to the cause of the same problem, but this ensures consideration of viable alternative theories.
For technical issues, be sure to include an SME on the team to ensure contemplation of facts rather than tribal knowledge.

Create a Fishbone Diagram

A fishbone diagram (above), also known as an Ishikawa diagram (after the person who first developed the concept), is a brainstorming tool that helps identify potential causes of a specific defect. The head of the fish shows the defect on the right, with potential causes extending to the left as fishbones.  Ribs branching from the backbone show major contributing factors, with sub-branches used to identify root-causes, to as many levels as required to answer why the defect might have occurred. The five-whys technique helps to drill down to deeper layers.

For manufacturing, the largest branches highlighting the major contributing factors likely fall into a category beginning with the letter M—these are known as the 4Ms, 5Ms, etc.  Examples:

• Manpower: Is the workforce sufficiently trained and motivated? Is employee fatigue or distraction a concern? Are there employee shortages?
• Machines: Are the machines working properly with all signals correctly reported? Were the correct tools, settings and setups used? Are the tools worn or otherwise nonconforming?
• Metals: Were the materials used appropriate for the application, within specification, and available in sufficient quantities?
• Methods:  Were process instructions clear and followed? 
• Measurements: Were the correct measurement tools used, and were they properly calibrated and employed? Are the measurement outputs easy to read and interpret?
• Mother nature: Does the work area have ample space, with ergonomically favorable conditions and sufficient lighting? Is the work area clean enough to support quality production?
• Management: Does leadership create and enforce appropriate practices, policies and procedures to achieve a cost-effective, high-quality product? Does leadership create a safe and collaborative environment with clearly stated goals and objectives?
• Maintenance: Are preventive-maintenance plans sufficient and followed? Is there a focus on safety? Is there an appropriate inventory level of spare parts?

These major areas are just examples; use those most pertinent to your organization or industry. Some ideas may appear in multiple places. For example, list calibration under “Methods” as it relates to an analytical procedure, and under “Measurement” as a cause of lab error. 

Disadvantages to using fishbone diagrams for root-cause analysis include mixing irrelevant potential causes with pertinent key ones, leading to digressions of time and resources. When representing complex issues with multiple factors, a simple diagram may obscure the interrelated nature of many variables.

When and How

Although using these techniques is a common approach to determine the root cause of an existing defect, it’s also useful to apply the methodologies at the design stage during quality planning where it will be possible to avoid a problem rather than correct it. Some companies use failure modes and effects analysis (FMEA) as a tool to provide a detailed risk assessment associated with a potential defect.

For either the five-why or the Ishikawa fishbone approach, be sure to focus on eliminating the problem’s root cause, rather than just deploying effective but temporary solutions. MF

See also: Engineering Quality Solutions, Inc., 4M Partners, LLC

Technologies: Management

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