How to Implement Poka-Yoke (Mistake-Proofing) Effectively

You’ve probably heard of Poka-Yoke before, the concept that's designed to minimize or eliminate errors in work done, but getting it right can be challenging. Here's how to implement it properly.

Kenneth Stem

Written by Kenneth Stem

If you are at all familiar with Lean Manufacturing, you’ll almost certainly have heard of Poka-Yoke. Most books and guides you’ll read about lean manufacturing will include a section about it. And there are also over 2 billion search results for poka-yoke on Google alone, many explaining the concept in-depth.

It’s safe to say that there’s a wealth of information out there on what it is and the tools associated with it. So I thought it would be better to focus on something different: Why Poka-Yoke? And how do you implement it properly? 

Where organizations get Poka-Yoke wrong

Engineers inspecting petroleum equipment

Poka-Yoke is a simple idea that is designed to minimize or eliminate errors made in work done. Yet this simple concept is almost always lost at many organizations. 

This is because many tend to see errors as someone’s fault — whether it be the supplier, subordinate, designer, etc. To fully implement Poka-Yoke correctly, we need to begin to see errors and failures of ours, not someone else’s processes. Only then, will we begin to understand the concept of Poka-Yoke. 

Once we start to look at perfecting our processes, we can then begin to understand and look at using Poka-Yoke correctly. 

What is Poka-Yoke, really?

Let’s go back to basics first. The simple definition of Poka-Yoke is error-proofing or inadvertent mistake-proofing. Essentially, a Poka-Yoke is any method in any process that makes errors unlikely or impossible. 

The specific method you use in your situation will depend on many factors. Within each system, you’ll need to look at:

  1. The risk of error
  2. The cost of implementing your error-proofing method
  3. How effective the method is. 

I fear very often that organizations will see an article about Poka-Yoke or visit a factory that has some in use, and simply copy what they saw. This is a mistake for almost any tool, but it’s an especially big mistake here

How should I implement Poka-Yoke?

Instead of repeating the exact method you read about or saw at another factory, you should focus on what you are trying to accomplish and why you want to accomplish it. Ask yourself questions like:

  • How expensive is the thing you are making?
  • What is the risk to the safety of the associates making the product 
  • What is the safety risk to the end-user?

For example, if the risk is quite low (like if you’re manufacturing drinking straws), then you’ll likely not need to employ a very sophisticated Poka-Yoke device (unless it is very inexpensive). The relative cost of one straw is quite low and the risk to the user is minimal to none.

However, let’s take a look at a more complex example, where eliminating errors becomes more critical and complicated. 

Welder working at a manufacturing workshop

Real Life Poka-Yoke Example

Formerly, I worked at a company that made flatbed trailers. During production, a critical component was the attachment and welding of the axles to the trailer — it was critical that no welds were ever missed. 

Our problem was that in a low volume operation, it wasn’t feasible to invest in an automatic system of detection (cost was too high). Instead, we came up with a method that was practical (although not fail-safe). Here’s what we did:

  1. The welder that did the first welding pass was required to market the weld with a paint pencil immediately after finishing. 
  2. The next welder will then use a second color paint pencil to mark the same welds, as well as his own. 
  3. Finally, a supervisor would then mark each weld with another color. 

This way, it would be impossible to mark the weld if the weld was not there. The only way to miss the weld would be to purposely fail either the weld or inspection. Additionally, the other welder and supervisor would have to make the same mistake. So for this particular operation, we made it difficult to carry it out wrong. 

What can we learn from Poka-Yoke? 

Not every situation can be like ours though, you may find that your situation calls for much more high-tech operations — such as automated visual systems, process design that makes it impossible to orient a part the wrong way. 

Other examples might include limit switches to make sure a part has been inserted correctly. The list of examples would be almost endless. But all-in-all, the tech level does not matter; just the solution. 

The most important takeaway is that we must treat every mistake in our operation as a failure of systems and not of our people. Every error that occurs is a result of a process that was designed in such a way that this mistake could happen. 

As long as we think in terms of who was to blame, instead of how the process failed — we will not be creative enough to generate the solutions we need. So, make sure you’re focused on perfecting processes since it is impossible to perfect our people.

Manufacturing Transformation Group (MTG)’s goal is to assist North American factories in overcoming all sorts of manufacturing challenges – including mistake-proofing. Talk to one of our experts to learn how we can help you build systems for long-lasting competitiveness.

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This article was originally posted on the China Manufacturing Consultants (CMC) blog on January 23, 2020.

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