October 1, 2004
By Darren Dolcemascolo
Mistake proofing is a powerful tool for creating more stable processes by reducing defects and ensuring that they are never passed down to the next downstream customer. Processes with high defect rates are very problematic for the lean producer: such processes are not conducive to a lean value stream because they require overproduction to ensure that demand is met. This article talks about seven keys to implementing an effective mistake proofing system:
Key #1: Create a team and always include those people that work on process in question. Organizations still have the tendency to turn to “technical experts” working in isolation to implement poka-yoke systems. Involving operators in a team setting will dramatically increase the likelihood of success. A kaizen blitz event is one very effective team activity for implementing mistake proofing.
Key #2: Use Value Stream Mapping to determine where process stability must improve. (If you are not familiar with value stream mapping, go back and read our series of articles on the subject.) This will allow you to focus on areas that will impact continuous flow.
Key #3: Use process mapping within the area selected. If you are implementing mistake proofing as a part of a kaizen blitz event, then this step should be done as a matter of course. However, if you are not using this methodology, you still need to map the current state process in detail. This will clearly identify each process step.
Key #4: Use a simple problem solving methodology like a fishbone diagram to determine root causes of problems within the process. This will identify those specific steps in the process that need mistake proofing.
Key #5: Use the simplest technology that will work when implementing a poka-yoke. Many times, low-tech solutions like guide pins and limit switches will work effectively. However, there are times when more complicated systems are necessary.
Key #6: Use control systems instead of warning systems wherever practical because control systems are not operator-dependent. (Control systems stop equipment when an irregularity happens, while a warning system signals the operator to take action).
Key #7: Have a standard form for every “Poka-Yoke” that indicates the:
Problem being addressed
Emergency alarm that will sound
Action to be taken in an emergency
Method and frequency of confirming it is operating correctly
Method to perform a quality check in case of breakdown
Mistake proofing systems are critical to the success of a lean organization simply because process stability is so critical. Using the above seven keys will improve the likelihood of implementing a successful mistake proofing program.
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