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Innovative probe upgrades CMM.

Shafer Valve, Orville, OH, is making its CMM inspections and machine operations more productive through the use of an innovative probe head from Renishaw Inc, Dayton, OH. The manually indexable head (MIH) speeds inspection runs on the company's Numerex ring-bridge 4048-24 MD ceramic coordinate measuring machine to get "first part" results back to machine-tool operators faster.

As an example of the time savings, Dennis Massie, shop floor supervisor, cites a large transfer-case housing which originally took six hours to inspect on a layout table. The Numerex CMM, as originally fitted with a Renishaw PH1 probe head, cut inspection time to 1 1/2 hours. Switching to the MIH sliced the inspection run to just half an hour. "We've cut hold time for the machine tool by 5 1/2 hours--most of a shift," stresses Mr Massie.

Between the Numerex CMM and the Renishaw MIH, Shafer's plant has reduced machine tool waiting time for first parts results as much as 90% over previous layout table checks--from hours to minutes in most cases.

Shafer has found that the MIH gives it much of the speed, ease, and efficiency of a motorized head and the economies of a manual unit. A self-contained unit, the battery powered MIH clamps into the CMM's probe shaft. No extra electrical connections or special software are required. The simplicity of the MIH allowed it to be installed and running inspection routines at Shafer in less than half a day.

Pointing the way

Built-in memory and LCD displays allow programming and predatuming of up to 19 angular probe positions (out of 720 combined A and B axes possibilities). So far, Shafer has programmed the MIH for nine different probe angle positions out of 19 memory slots available.

"Actually, we do most of our inspections with only five positions and a Renishaw TP2 five-way probe," says Mr Massie. "We predatum all the tips at the start. Then we can use any probe position or tip we need to run that inspection routine with no more datuming, no delays."

A head-mounted LCD shows directional arrows to guide the CMM operator in hand-indexing the MIH to a programmed probe angle. Displays of A and B axes aid precise positioning, while an error indicator warns when the head is accidentally locked in an incorrect, non-programmed position. A simple thumb wheel unlocks/locks both axes on changes.

Solution for complex parts

The MIH lets a probe angle change be made in 15 seconds, while eliminating previous delays for redatuming. This yielded major time savings for Shafer on complex parts that require a great deal of probe reorientation, says Mr Massie. Shafer is a leading maker of automated, hydraulic actuators for oilfield production control valves. Actuator components are machined in complex shapes and can range up to several feet in all dimensions and hundreds of pounds in weight.

Because of part complexity, Shafer's CMM part routines demand high levels of probe angle and tip changes. Recalibration of the original PH1 probe head meant taking the part off the table, putting the master on, calibrating the probe, then putting the part back on. Further complicating inspection routines is that many critical features are located internally. Accessing and accurately measuring the complex internal geometries with the PH1 probe head require lots of changes in probe tips and angle positions, even long probe extensions for deep recesses. The changes and redatuming put a heavy drag on CMM productivity.

Probing for improvements

The two-axis positioning capability of the MIH probe head effectively turns the CMM into a five-axis machine. This lets Shafer measure five sides and often internal features of a part in a single setup, notes Mr Massie. Previously, with layout table measurement, a part would have to be turned and fixtured for each side. The process was not only slow and laborious, but inherently less accurate and repeatable. Internal features were particularly difficult for layout inspection. The indexable probe head offers 2 micron (2 sigma) repeatability and the robustness to accept 300 mm maximum probe extensions for deep reaches.

Single setup inspection offers another benefit: "With parts the size and value of many that we run, you want to eliminate part moves and handling wherever possible," Mr Massie says. "We do as much as possible in one operation."

Shafer uses just about every geometric function of the CMM in measuring its complex parts--"everything so far but the sphere function," says Mr Massie. The company is producing to standard tolerances of |+ or -~ 0.0002".

The MIH offered much of the time savings and versatility of a motorized head at one-third the cost. "A motorized head would let us run parts a bit faster," says Mr Massie, "but the small differential wasn't enough to justify the additional cost and the extended payback."

A motorized head would have eliminated all need for manual probe settings, but not really saved Shafer on labor since a CMM operator would still be required for loading and unloading of parts onto the Numerex machine. The whole inspection system needs to be automated to realize full benefits from a motorized head, he feels. The nature of Shafer's production--large, complex parts at fairly low production levels--makes such automation harder to amortize and justify than in high-throughput and high-volume operations.

For more information on probes from Renishaw Inc, Schaumburg, IL, circle 299.
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Title Annotation:Quality Solutions; Shafer Valve Co. installs Renishaw Inc.'s probe in coordinate measuring machines
Publication:Tooling & Production
Date:Dec 1, 1992
Words:886
Previous Article:Casting process gaining ground.
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