Machine Design

Retrofitting a CMM with a Renishaw Contact-Probing System Let the Machine Analyze Complex Impellers

Renishaw Inc.,

GE Oil and Gas,

Retrofitting a large coordinate-measuring machine (CMM) with a Renscan5 contact-probing system from Renishaw, Hoffman Estates, Ill., let a company collect data fast enough to analyze complex impellers. This was previously not practical due to the lengthy inspection times involved. Renishaw engineers replaced the original head of a DEA Global CMM from Hexagon, touch-trigger probe, controller, and software with Renishaw’s Renscan5’s Revo head and integrated probe, UCC2 controller, and Modus software. The DEA Global measures components up to 1,000 mm in diameter.

“The retrofit slashed our dimension-inspection time on a standard impeller by 40%,” says Claudio Bartali, manufacturing technology project leader for GE Oil and Gas, Florence, Italy. “In addition, collecting the massive amount of measurement data lets us easily compare the form of inspected surfaces with 3D CAD models.”

The Revo has two built-in measuring axes. Along with the three axes of the CMM, this gives users five-axis measuring capabilities. According to GE, the system provides a completely different method of checking impeller dimensions. For example, the top of the part is measured with what Renishaw calls a “gasket scan,” a rapid sweep of the top machined face that takes about 2 sec and gathers thousands of points. The previous method involved four touch-trigger points and took close to 30 sec.

A best-fit calculation of the scanned data plots a plane through all the points, verifying the position of the face and its relation to other surfaces. This data is also used to calculate where a surface might be deformed. A comparison shows exactly which parts of the face deviate from the CAD model.

GE tested the accuracy of the retrofit by comparing the touch-trigger method with the Revo. “The accuracy of measured points from the Revo was at least as good, but the device traveled considerably faster and captured many more points,” says Paolo Trallori, calibration and metrology leader for the plant. The Revo is so fast because it maintains constant contact with the surface in one smooth rapid move, instead of taking single points, he says.

The Modus software executes inspection moves as directed by the CAD/CAM package. Modus works closely with PC-DMIS software, important because it provides measurement routines for all kinds of parts. The software tracks each component by serial number, with a full record of every stage of production. The software also lets the company add extra quality data to the record.

Edited by Leslie Gordon

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