Content area
Full text
The new regime deploys technology for current business conditions.
The quiet revolution that has been underway in in-process gaging for more than a decade has been one of the many changes wrought by Six Sigma manufacturing. As the philosophy gained popularity, its adherents built gages that could take finer measurements, report the results instantaneously and work inside production machinery. These gages contributed, heavily to an unprecedented level of repeatability, encouraged the movement toward 100% inspection, and expedited the migration of measurement and inspection from the lab into the manufacturing processes themselves.
At the heart of this change have been radically tighter tolerances. "Years ago, manufacturers used to talk about tolerances in thousandths of an inch," says Chris Koehn, president, Stotz Gaging Co. (Freeport, IL). "Then they went to ten-thousandths of an inch, and now tolerances are in the millionths."
He points out that the greater expectations have been putting pressure on manufacturers of in-process gages to improve the repeatability and reproducibility (R&R) of their products. Users typically want their gages to have an R&R that is an order of magnitude better than their tolerances. Consequently, those confronted with tolerances of 20 millionths of an inch look for gages with R&Rs of 2 millionths.
Although gage manufacturers have responded with technology that can meet these expectations, such gage R&Rs are not always achievable in practice, especially when people are part of the process. If the parts are small enough to hold, for example, just the heat from the operator's hand can cause enough thermal expansion to affect the measurement. Removing people from the process can help, but does not guarantee a 10% gage R&R when tolerances are very small. Careful engineering and innovation are required.
A good match
Such is the case for producing match sets of bearings and other assemblies that require the pieces to fit together perfectly. Stotz, for example, is working with an automotive supplier to tighten the 8 millionths of an inch R&R that Stotz is already guaranteeing for some of the air gages on the grinders that the supplier is using to produce components for such an assembly. Given the progress to date in the engineering project, Koehn expects the R&R to be 4 millionths within a few months.
The...