Error Proofing / Poka Yoke / Fool Proofing / Mistake Proofing
“The best approach is to dig out and eliminate problems where they are assumed not to exist”: Shigeo Shingo
How many times, you could insert your flash Drive in a USB port in reverse direction?
How many times you could insert your car keys in reverse direction?
How many times you could unlock your mobile phone by putting the wrong password?
While traveling by Aircraft, how many times you could insert the seat belt in reverse direction?
The answer for this and many more such questions is NO. In this fast-paced & competitive world, everyone wants everything to be perfect. No one wants any mistake to happen as it costs heavily to the individual and organization. The only objective of error proofing is to ensure that either mistake is identified or the defect is not produced.
Poka-yoke is a Japanese term coined by Shigeo Shingo as part of the Toyota Production System in the 1960s that means “mistake-proofing” or “inadvertent error prevention”. Its purpose is to eliminate product defects by preventing, correcting, or drawing attention to human errors as they occur. It is based on the principle that it is the process which is flawed and not the operator. It helps to eliminate the blame game.
As per IATF 16949 (Clause 3.1), the definition of Error proofing:
Product and manufacturing process design and development to prevent the manufacture of nonconforming products.
Following are the 6 clauses of IATF 16949 where the reference of error proofing has been made
· Clause 3.1 (Definition) Challenge Parts (Master Sample)
· 8.3.3.2 Manufacturing process design input: To inbuilt error-proofing during process design.
· 8.3.5. 1 Design and development outputs-supplemental: Fool Proofing defined in the design documents.
· 8.3.5.2 Manufacturing process design output: Error proofing in the processes are implemented.
· 8.5.6.1.1 Temporary change of process controls: How to manage the alternate process using poka-yoke?
· Annexure A-Control Plan: Where to document mistake-proofing?
As per Clause 10.2.4 of IATF 16949, following are the important points to understand and implement
1. Documented Process: It is a requirement to have documented procedure (process), how to identify, implement and verify the error-proofing in the organization.
2. Risk Analysis:
· CFT (Cross-Functional Team) to identify where mistake proofing is needed.
· Some of the common methodologies include DFMEA (Design Failure Mode & Effect Analysis), PFMEA (Process Failure Mode & Effect Analysis).
3. Control Plan:
· Identified poka-yoke to be specified in the control plan.
· The frequency of fool proofing verification to be defined (hourly, once in a shift, once in 15 days, etc.).
· The frequency will depend upon the criticality of the process and customer-specific requirement (CSR).
4. Master Sample (Challenge Parts):
· Samples to be properly identified with a unique number or code.
· Samples to be prepared to simulate a condition to verify if mistake proofing is actually working or not?
· Example: If a fool proofing is to ensure the load between 100 to 150. Samples to be prepared for 95 and 155 to check, whether fool proofing will work when the load will be less or more?
· The master samples to be periodically revalidated (calibrated, if possible), whether they are actually producing the right results or not (by independent process owner)?
5. Records:
· Records of poka-yoke verification to be maintained.
· In case of mistake-proofing failure, actions to correct it and components produced so far to be recorded.
· Retention of records to be defined based on the organization or customer-specific requirement (CSR).
6. Reaction Plan:
· Proposed contingency plan when error proofing fails (to quarantine manufactured products and how to restart the process).
· It has to be specified in the control plan.
Should mistake proofing to be applied every-where?
It is not important to apply fool proofing in all the processes. It has to be implemented based on the criticality of the process. Sometimes the cost of implementing mistake proofing is very high. Following steps to be followed before deciding about poka-yoke.
· Eliminate the mistake-prone process during the development process
· Make it easy to do the right thing
· Build-in self-checks
If above processes do not work, then do apply Mistake Proofing
How to identify where fool proofing is needed?
There are 4 steps:
· Map the process
· Identify the Risk
· Apply Mistake proofing techniques
· Check effectiveness
In FMEA, there is 2 type of controls: Prevention and Detection. Fool Proofing (even a Foolcan not make mistake) is applied for prevention of any mistake to occur or to identify in case any defect has been produced.
Benefits of Poka-Yoke Implementation:
Productivity: Detecting mistakes as they occur, Elimination of defects before they occur
Quality: Reduced number of rejects, Prevention of defective products from reaching customers
Cost: Elimination of many operations related to Quality Control
Delivery: Less time spent to train workers, Immediate action when a problem occurs
Safety: Reduced accidents
Morale: Unburdening of operators, Promotion of the improvement-oriented approach
Challenges with Error Proofing:
1. Sometimes machine efficiency goes down
2. Difficult for the operator to understand and implement
3. The tedious process to check the effectiveness of mistake proofing
4. The high cost of production (Customer may not pay for it!)
Some question to ponder
1. How many organizations actually verify Poka-Yoke?
2. How many operators actually know how to check Error Proofing?
3. How many organizations have documented fool proofing in their control plans?
4. How many organizations have documented Reaction plan in case of the mistake-proofing failure?
This is the 17th article of this Automotive series. Every weekend, you will find useful information which will make your Management System journey Productive. Please share it with your colleagues too.
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