Many people today will tell you that "Six Sigma" and associated programs are the cat's meow in product quality. While I can use the tools well, I've got my doubts, as I'm using things my grandfather purchased, but throwing away quite a few things I purchased for myself. Seems to me that our grandfathers knew a bit about quality and reliability that we've forgotten today.
Perhaps a couple of stories might make clear what's going on.
First, the standard example of Six Sigma quality is the failure rate airlines have of getting you off the plane alive; about four per million, or 4.5 Sigma. Our grandfathers would have hesitated at such a bait & switch, don't you think? Something about the 9th Commandment being the real start to quality?
Next, a wonderful quality success story told me had to do with an eight factor (variable) designed experiment done to figure out what caused high failure rates in transmission chains. After a lot of wonderful quality work, they found out what any competent machinist could have told them; they were using the assembly tools long after they were worn out.
In other words, they ended up fixing a problem they'd likely caused by extending the replacement intervals to save money, and at a massive cost to the company. Somehow (9th Commandment again?), my instructor didn't see fit to share that side of the story.
Don't get me wrong; statistical methods have a lot to offer. However, my experience is that too often, they're used to replace the expertise of craftsmen and high quality materials with unskilled labor and plastics. If you wonder why you're making good use of a lot of product warranties, you might find that your difficulties ironically have a lot to do with the manufacturer's quality program.
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