Our company is trying to move into powder coating in the jewelry business. We are also trying to get a 6-sigma program going. I copied an editorial article called “Powder Reject Rates." The question was by a S.J. and asked about internal and external rejection rates in powder coats. The responder calls out numbers like 10-25% for high rates and 0.025-1% for low visual standards.
Because we are in the high end of the market and can control most, if not all, of our processes, I feel powder coating is the way of the future.
This is the main argument to keep powder coating out of our plants, as it is obvious from this article that powder coat will never be capable of six-sigma. D. Z.
Well, since I was the one who wrote the article you refer to, I won’t refute it, but I can clarify the issues you are dealing with. In fact, since I wrote that article, I have been at your plant and seen the method you use to powder coat your jewelry products. As a result, I can tell you, your situation is special for numerous reasons.
My original article talks about mainstream powder coating systems where products are processed in batch quantities or hung from a moving conveyor with little, or no, in-process inspections or corrective actions. In this case, the process has many opportunities to fall short in providing a perfect part and, since it is inspected once at the end of the process, defects are normally within the ranges I originally specified.
Your situation is much different from this. You process your products individually in a batch process using manual application of the powder to the entire part and then remove the coating manually from the areas where the coating is not required before curing the powder. This process is performed under high magnification using well-trained “artists” where great care is exercised on each part to produce the desired results. If a defect is created during this arduous coating method, the part is quickly cleaned and reprocessed before the coating is cured. Defects are only noted after the part has been painstakingly processed through numerous manual activities with close inspection occurring at each stage. In fact, to my recollection, there are close to two-dozen manual stations where these activities occur in series to each other, and close examination of the part occurs at each station. Under these conditions, it would be a rarity if a part were rejected at the end of this process.
Therefore, I have no doubt that your six-sigma principles will be met using this process. However, most powder coaters are not in the jewelry business and do not have as many inspections throughout their process and therefore can have some difficulty in achieving the same results.