Case Studies: Five-Axis Machining Meets Five-Axis Inspection

October 2, 2008
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Turbocam International supplies both production and prototype bladed parts to aerospace, automotive and industrial turbomachinery OEMs. Part precision and uniformity are critical in providing dynamic balance, directed airflow and long, reliable service at high rotational speeds. However, efficient inspection of ever-increasing numbers of complex parts was frustrated by slow, tedious, stop-and-go measurement inspection on a legacy 3+2 axis CMM.

Turbocam International uses the Renscan5 to inspect the intricacies of impellers, blades and blisks. Source: Renishaw Inc.


Constantly changing surface geometries, pin-wheeling shapes and tight, intricate features make turbomachinery components-impellers, blades and blisks-some of industry’s most complex and exacting shapes. Turbocam International (Barrington, NH) supplies both production and prototype bladed parts to aerospace, automotive and industrial turbomachinery OEMs.

Coordinate measuring machine (CMM) inspection ensures that critical parts for turbochargers, jet engines, compressors and gas turbines meet accuracy specifications. Part precision and uniformity are critical in providing dynamic balance, directed airflow and long, reliable service at high rotational speeds. However, efficient inspection of ever-increasing numbers of complex parts was frustrated by slow, tedious, stop-and-go measurement inspection on a legacy 3+2 axis CMM.

Changing 3-D part geometries required many different probe orientations, plus frequent stylus and tip changes for difficult-to-reach features. “We would have to stop the CMM and calibrate each re-orientation of the probe,” says Dave Romaine, Turbocam’s quality assurance manager. “That was compounded as we inspected multiple blades around a part.”

Streamlining Inspection

The Turbocam staff was quick to see the potential of a scanning system from Renishaw (Hoffman Estates, IL) that makes possible automated, programmable five-axis measurement at high speeds and accuracies. The Renscan5 scanning system offers the capability for continuous five-axis interpolated motion, comparable to Turbocam’s five-axis machine tools.

In January 2007, Turbocam adopted the Renscan5 continuous five-axis inspection capability. Installed on a Wenzel LH8.10.7 bridge-type CMM at the company’s Dover, NH, plant, Renscan5 transformed part measurement and inspection from a bottleneck to an enabler.

High-speed continuous probing routines are reducing programming time, set-up time and measurement time by more than 50%. Besides faster throughput, time saved with the Renscan5 allows more data points to be taken for greater measurement precision and frees CMM time for qualification of turned blanks and in-process checks before final machining passes.

In early 2008, those advantages led Turbocam to add a second Renscan5 CMM at its facility in nearby Barrington. In this facility, Renscan5 is an essential resource, says Romaine, being developed to support higher-throughput production generated by around-the-clock, reduced-staff manufacturing.

The Revo head can produce up to 4,000 points per second in scanning mode. Source: Renishaw Inc.

How It Works

Renscan5 uses two patented hardware developments to speed part checking, generate more data points for analyzing part form and increase available CMM run time.

  • Active probe head. The Revo is a powered head that provides infinite positioning capability between simultaneous coordinated motion in vertical and horizontal rotary axes. This allows the low-mass two-axis head, a 3-D measuring device in its own right, to perform most of the motion during inspection routines. Infinite positioning allows continuous motion, optimizes part access and delivers high-accuracy part measurements. The active head avoids dynamic errors caused in rapid acceleration and deceleration of the larger mass of a CMM structure. Low-mass, low-inertia design allows Renscan5 to measure at up to 500 millimeters per second.

    The Revo head repositions continuously on the fly, simultaneous with measurement, unlike indexing heads, which first must be locked into position, after which the CMM provides the measuring motion. On complex parts, “hundreds of calibrations have now been eliminated, saving us hours of calibration time,” says Romaine.

    Renscan5 allows the CMM’s three-axis platform to be used primarily to rapidly move the Revo head into position for measurement. Where CMM motion is required for a measurement routine, it can usually be limited to a single linear axis and performed at constant velocity, minimizing dynamic effects on accuracy from acceleration, deceleration and inertia.

  • Laser-corrected probing. The Revo head employs laser-corrected, tip-sense probing. A laser mounted within the head sends a beam down a hollow stylus to a reflector at the tip. A position sensor receives the return beam and any deflection used to calculate true tip position. This allows the Revo head to perform a complete part inspection routine in a continuous operation without recalibration or stylus changes.

    “Only one probe is typically used to measure an entire part with no tip change time,” says Romaine. Tip-sense probes deliver 1-micron accuracy at 250 millimeters from the axis of rotation. Sizes are available providing probe reach to 500 millimeters.


  • More Data, Less Work

    While the previous 3+2 CMM at Turbocam provided a two-axis head, vertical changes in probe angle could only be made in 2.5-degree increments, then calibrated and fixed at the position for measuring. “As we inspected more blades around a part, such as a blisk, it would obviously require more and more probe orientations and calibration,” says Romaine. “Programming, access, stylus change and calibration were incredibly painful.”

    Turbocam uses Renscan5 for both point-to-point probing to verify feature location and size and for contact scanning of part surfaces for shape and form data.

    “On point to point we are able to gather more data simply because the head can orient to any angle and it is a very simple setup to get more points,” says Romaine.

    Renscan5 high-speed scanning greatly increases data points. “Previously we might collect 50 or 100 points spaced over a blade,” says Romaine. “Now we can collect hundreds or thousands of points with a scan.” In scanning mode, the probe moves continuously, adjusting to programmed changes in part geometry. The Revo head gives Turbocam up to 4,000 points per second in scanning mode.

    “Increased point data allows us to see a more complete picture of what we are manufacturing,” says Romaine. “We can see deviations better as they increase and decrease along a blade or around a part. This lets us better troubleshoot our manufacturing process.” As an example, he notes that Turbocam has been able to detect tooling breakdowns based on Renscan5 surfacing data.

    The Renscan5 system includes a UCC2 universal CMM controller with patented MoveScan software that synchronizes, smoothes and speeds motion between the CMM and the Revo head. MoveScan drives the probe to the surface of the part in the shortest distance by looking ahead to go-to points and blending moves into smooth, continuous motion.

    Parts inspected on the CMMs range from 2 inches in diameter to 36 inches in diameter. Turbocam produces more than 400 different bladed part designs a year for compressor, turbine and pump OEMs.

    “Just as important as the inspection advantages are the programming benefits,” says Romaine. “We have been able to apply our five-axis machine tool programming methods to drastically reduce programming time for five-axis inspection. This is only possible because of the infinite indexing of Revo and its programmability through the DMIS language.”

    Renscan5’s open DMIS interface gives the UCC2 controller cross-platform compatibility with measurement software packages and maintains operator choice of CMM and software.

    On complex parts such as blisks, Romaine notes that, “What used to take three days to program now takes three hours. The biggest time savings have come in programming and setup, even more than run time.”

    The ability to apply five-axis programming expertise makes it much easier and faster to provide programs for part inspection, increasing machine use for a wide range of parts. While Renscan5 integration is still evolving, Turbocam estimates that CMM use has already increased between 30% and 50%.
      Renishaw Inc.
      (847) 286-9953
      www.renishaw.com


    Benefits

  • With the Renscan5, Turbocam is reducing programming time, set-up time and measurement time by more than 50%.

  • Time savings allow more data points to be taken for greater measurement precision and free CMM time for in-process checks.

  • Turbocam has been able to apply its five-axis machine tool programming methods to reduce programming time for Renscan5 inspection.
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