In our business, we’ve discussed some of the typical errors through talking to a number of our customers and simply being around the industry for 25 years. Sometimes process steps may get missed. This may be due to a number of reasons, like familiarity with a process by an individual or some printing issues, or work constructions, or miss-set work pieces. This can be very common for a number of reasons. Again, we’re going to talk about some of the ways that we can eliminate these. All these are the most typical areas that may occur. The bottom line is all of these things will basically cause waste, and we want to eliminate the waste. We’re going to talk about some ways to do that. 

Why implement effective error proofing?  One is the competitive advantage you get. By eliminating error proofing, you're going to improve your quality overall; it’s going to give you a better global competitiveness. Secondly, you're going to reduce your cost because you're preventing errors, and it costs less to prevent an error than it does to correct or catch one later and then have to do the re-work to make the part good. It costs less to prevent errors than it does to catch them later; that’s a key point. 

Obviously, reducing scarp that might be caused by some error in the process is going to reduce your materials cost and it’s going to reduce your labor costs for re-work, and it’s going to improve your delivery.  You can expect less scrap due to less error. With effective error proofing processes you're also going to reduce your work, your raw material and work and process inventories. 

I took kind of informal survey from our own people and some of our customers to ask, ‘what is the scrap rates in the industry today?’  I took a shot with some people that have the experience and I came up with this figure: scrap rates are two to six percent, depending on the flexibility of the part and maturity of the process. 

What we mean by this is that in a low volume environment where you're constantly doing short run parts  and you're doing a lot of first time parts, there's going to be a higher scrap rate than if you're doing a 100,000 parts a year. You go through the prove out and the initial stages of producing a part where you're going to have more errors occurring, but once that higher volume production becomes more mature, the percentage of scrap should go down significantly.

It depends on a lot, but two to six percent, roughly, is what we’re saying might be the scrap rates that are occurring in our industry today. That doesn’t apply to everybody, but it’s very general.  Short term versus long term production has a big impact on that percentage. Again, the scrap rates have a huge impact on your bottom line, which is why we want to talk about error proofing. 

How does error proofing relate to lean?  I mentioned briefly at the beginning that lean is all about eliminating waste and the specific point within lean, for those of you that have gone through the training you know the term, ‘Poka-yoke.’ That’s a Japanese term, as lean really originated in Japan. What we want to accomplish is that any error that does occur needs to be found to deliver a perfect part to that next step in the process. 

Here’s a look at the seven areas of waste as identified in lean manufacturing principles: inventory, processing, correction, overproduction, motion, material movement and waiting.

Error proofing can impact every one of those. For example, for over production there may be a decision in the manufacturing environment to overproduce a part because you have an expected certain scrap rate and have overproduced the parts. Basically, you’ve introduced waste into the process and with effective error proofing, good processes and so on. You can impact and eliminate the need for overproduction, which is one of the seven areas of waste in lean manufacturing. But, certainly, error proofing the manufacturing process can impact every one of these seven areas of waste as identified by lean principles.