Stopping a machine to measure a workpiece is a waste of time. Not only is a high-priced piece of CNC equipment being taken out of production, but the measurements obtained when a machinist leans into a machine with a micrometer or bore gage can’t compare in accuracy to those generated by a coordinate measuring machine or inline probe. Yet shops do just that every day, increasing downtime and jeopardizing part quality. Fortunately, there’s a better way.
Metrology equipment providers have been busier than hummingbirds on a warm spring day, rapidly developing in- situ gaging systems that may eliminate the inspection status quo, common in many shops, of taking it to QC and waiting for someone to check it. Not only do these new systems reduce the cost of inspection and improve machine uptime, they also open the door to unattended machining.
There’s more to this than uptime, however. As part tolerances grow tighter and geometries become increasingly complex, pulling a part out of the machine for measurement makes about as much sense as giving U.S. politicians more paid vacation. When the CMM indicates a bore is undersize by a few tenths, what are the chances of positioning that part in the machine accurately enough to rework it? It’s far better to have this information before the first clamp is ever loosened.
Machine-mounted probing has been around since the early 1980s. Aimed primarily at setup time reduction and broken tool detection, these devices have evolved into systems as accurate and repeatable as top-caliber machine tools, making it possible to measure a large percentage of part features and all but the tightest part tolerances without ever setting foot in the inspection room.
Intelligence is just as important as accuracy. Adrian Johnson, in-process business manager for Hexagon Metrology Inc., North Kingstown, R.I., said the key development in today’s probing systems is the ability to do in-situ measurement of complex parts.
“In the past, the primary limitation with machine probes was the CNC software driving them,” he said. “Probes could measure basic things like diameter or length, but they weren’t smart enough to do any sort of detailed dimensional analyses.”
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