To enhance knowledge in error proofing or mistake proofing, it is important to understand the difference between a defect and an error.

We can use the cause and effect diagram to identify the errors that cause defects to occur.
An error is any deviation from a specified production process. Errors can be made by machines or people and can be caused by errors that occurred previously.

All defects are created by errors.
This means that if errors can be prevented, no defects will be created.
By using Error Proofing, the errors that cause defects are located and eliminated.
Error Proofing should be continuously used to locate and prevent new errors.
The 10 most common types of errors:
Error proofing can only affect the errors which potentially cause defects - not all errors cause defects!
Here is a list of the 10 most common errors which Error Proofing is designed to correct or eliminate:

Error - 01
Processing omissions: Leaving out one or more process steps.

Error - 02
Processing errors: Process operation not performed according to the standard work procedures.

Error - 03
Error in setting up the work piece: Using the wrong tooling or setting machine adjustments incorrectly for the current product.

Error - 04
Missing parts: Not all parts are included in the assembly, welding, or other processes.

Error - 05
Improper part/ item: Wrong part installed in assembly.

Error - 06
Processing wrong work piece: Wrong part machined.

Error - 07
Operations errors: Carrying out an operation incorrectly; having the incorrect revision of a standard process or specification sheet.

Error - 08
Adjustment, measurement, dimension errors: Errors in machine adjustments, testing measurements or dimensions of a part coming in from a supplier.

Error - 09
Errors in equipment maintenance or repair: Defects caused by incorrect repairs or component replacement.

Error - 10
Error in preparation of blades, jigs, or tools: Damaged blades, poorly designed jigs, or wrong tools.

How to use Poka-Yoke

1. Identify the operation or process that needs to be mistake proofed (target areas where there are high numbers of errors or where even single errors are very costly).
2. Use the 5 Whys or cause and effect analysis to get to the root of the problem.
3. Decide which type of poka-yoke devices are to be used
4. Design an appropriate poka yoke.
5. Test it to see if it works (try to avoid large expense before you have completed this step - use mock ups or make-dos).
6. Once you have a working method then ensure you have the right tools/checklists/software, etc for it to work consistently and correctly.
7. Train everyone to use it.
8. After it has been in operation for a while (the time period will depend on the frequency of the activity) review performance to ensure errors have been eliminated.
Take whatever steps are needed to improve on what you have done. The next article will discuss what types of poka-yoke devices are available to use in business processes.