If you have gone beyond the title you probably have an interest in this and have some knowledge of what a poka-yoke is. For the sake of focus I will state in my words what a poka-yoke is.
Also, there have been two types of poka-yokes generally accepted. The first and the one you want to use is the poka-yoke that aids the operator from making the mistake in the first place. Examples: Configure the assembly nest so the product can only be installed one way before it is assembled; Color code stops that can be put in place for the different products made off the same equipment; Barcode scan and build off the barcode requirement. The second method, and the one you want to use least, is to check at the end of the process step and to contain the product if it is non-conforming.
I bring this topic up because I see issues how people perceive poka-yoke. In automotive everyone believes that 100% poka-yoke is the golden rule, the cure all, to build in quality. However those who believe this lack the comprehension it is not free, that there are still risks. When there are risks, there are associated costs.
Specifically in automotive I have seen a defect product repeatedly make it to the next process step from a fully poka-yoked previous step. Every time you ask them why this occurred the response was “the machine allowed it”. So the poka-yoke failed and made the defect. WRONG. The Help to the operator failed and the Operator made the defect. Quality at the source please . . .
This fully poka-yoke system was not robust. It had a 50% Type II (false negative) failure rate. Production rate out of this cell was 50% because of this. So the operator had to work even faster to make up for the loss in defects, creating a higher chance of defects. Nobody tracked OEE (overall equipment effectiveness – a topic for some other day), however the OEE would have brought you right to the problem which was machine downtime. The company’s solution was to add higher cost poka-yokes. The problem persisted.
My solution was to turn off the poka-yoke, which I did without the boss’ approval. Most reading this already know what happened. The defects went away. I mean went away to zero. The operator took the responsibility to build quality. After turning off the poka-yoke the operator “owned” this cell, not allowing supervisors to remove them from it. Why? The operator did not have to wait for the poka-yoke to pass the part. The assembly was uninterrupted by the process (no machine failure), allowing for more time to build in quality. There were zero machine adjustments needed, allowing time for maintenance to work on other now higher risks within the plant. You see the picture . . . costs dropped dramatically.
Once the boss found out I turned off the poka-yoke he was not happy, though he could not argue the facts. He had been taught you poka-yoke everything. Here I come along and say you do not. You only poka-yoke what the operator has difficulty with, and even then material presentation can make a greater positive impact than a poka-yoke. He still wanted a solution. So I stripped off the $20k poka-yoke system and threw it in the trash. With the help of the people who add value (the operators) we found a feature we could poka-yoke for $1.2k. We implemented it and began having 3% Type I (false positive) errors. Much better than a Type II, but you wonder why we would even have them if we had zero without the poka-yoke. Answer: People can become complacent with fully poka-yoked equipment. If the poka-yoke fails they will not notice. The flip side is, if the machine and poka-yoke fail often, nobody will have faith in the equipment, so when the equipment Does build it right the operator says “it’s wrong, I know I made it correctly”, and pass on a defective product. Hmmm, the Hawthorne Study comes to mind all of a sudden (when I ran without a poka-yoke).
Then, and this is true, a month later my boss had to be at another plant because Toyota was coming to visit. The team there proudly displayed their masterpiece poka-yoke that was ingenious (and it was). After they explained it to Toyota, the response from Toyota was, “You were having problems maintaining quality?” The answer was, “No.” So Toyota was very dissatisfied. All of this additional cost (cost of engineering, making the poka-yoke, maintenance, added equipment down time when the poka-yoke fails) and added machine cycle time for something the operator was not having a problem with.
To poka-yoke, or not to poka-yoke, that is the question. Whether ‘tis nobler in the mind to suffer the defects of outrageous poka-yokes, Or to take arms against the sea of problems, And by making the operator accountable end them?
Poka-yoke is a Japanese term that basically means “fail safing” or “mistake proofing”. The intent is to Help the equipment operator from making a mistake. This is not to be confused with Jadoka (sometimes referred to as autonomation). This is another Japanese term for detecting when an error occurred and automatically stopping the machine or operator until the error is fixed.
Also, there have been two types of poka-yokes generally accepted. The first and the one you want to use is the poka-yoke that aids the operator from making the mistake in the first place. Examples: Configure the assembly nest so the product can only be installed one way before it is assembled; Color code stops that can be put in place for the different products made off the same equipment; Barcode scan and build off the barcode requirement. The second method, and the one you want to use least, is to check at the end of the process step and to contain the product if it is non-conforming.
I bring this topic up because I see issues how people perceive poka-yoke. In automotive everyone believes that 100% poka-yoke is the golden rule, the cure all, to build in quality. However those who believe this lack the comprehension it is not free, that there are still risks. When there are risks, there are associated costs.
Specifically in automotive I have seen a defect product repeatedly make it to the next process step from a fully poka-yoked previous step. Every time you ask them why this occurred the response was “the machine allowed it”. So the poka-yoke failed and made the defect. WRONG. The Help to the operator failed and the Operator made the defect. Quality at the source please . . .
This fully poka-yoke system was not robust. It had a 50% Type II (false negative) failure rate. Production rate out of this cell was 50% because of this. So the operator had to work even faster to make up for the loss in defects, creating a higher chance of defects. Nobody tracked OEE (overall equipment effectiveness – a topic for some other day), however the OEE would have brought you right to the problem which was machine downtime. The company’s solution was to add higher cost poka-yokes. The problem persisted.
My solution was to turn off the poka-yoke, which I did without the boss’ approval. Most reading this already know what happened. The defects went away. I mean went away to zero. The operator took the responsibility to build quality. After turning off the poka-yoke the operator “owned” this cell, not allowing supervisors to remove them from it. Why? The operator did not have to wait for the poka-yoke to pass the part. The assembly was uninterrupted by the process (no machine failure), allowing for more time to build in quality. There were zero machine adjustments needed, allowing time for maintenance to work on other now higher risks within the plant. You see the picture . . . costs dropped dramatically.
Once the boss found out I turned off the poka-yoke he was not happy, though he could not argue the facts. He had been taught you poka-yoke everything. Here I come along and say you do not. You only poka-yoke what the operator has difficulty with, and even then material presentation can make a greater positive impact than a poka-yoke. He still wanted a solution. So I stripped off the $20k poka-yoke system and threw it in the trash. With the help of the people who add value (the operators) we found a feature we could poka-yoke for $1.2k. We implemented it and began having 3% Type I (false positive) errors. Much better than a Type II, but you wonder why we would even have them if we had zero without the poka-yoke. Answer: People can become complacent with fully poka-yoked equipment. If the poka-yoke fails they will not notice. The flip side is, if the machine and poka-yoke fail often, nobody will have faith in the equipment, so when the equipment Does build it right the operator says “it’s wrong, I know I made it correctly”, and pass on a defective product. Hmmm, the Hawthorne Study comes to mind all of a sudden (when I ran without a poka-yoke).
Then, and this is true, a month later my boss had to be at another plant because Toyota was coming to visit. The team there proudly displayed their masterpiece poka-yoke that was ingenious (and it was). After they explained it to Toyota, the response from Toyota was, “You were having problems maintaining quality?” The answer was, “No.” So Toyota was very dissatisfied. All of this additional cost (cost of engineering, making the poka-yoke, maintenance, added equipment down time when the poka-yoke fails) and added machine cycle time for something the operator was not having a problem with.
To poka-yoke, or not to poka-yoke, that is the question. Whether ‘tis nobler in the mind to suffer the defects of outrageous poka-yokes, Or to take arms against the sea of problems, And by making the operator accountable end them?
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