The Revolution of Inspection Technology

Constantly changing surface geometries, pin-wheeling shapes and tight, intricate features make turbomachinery components — impellers, blades and blisks — some of the industry's most complex and exacting shapes. Turbocam International specializes in the field of 5-axis machining and 5-axis programming software. 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 coordinate measuring machine (CMM).

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

As 5-axis experts, the Turbocam staff members were quick to see the potential of a revolutionary scanning system from Renishaw that makes possible automated, programmable 5-axis measurement at speeds and accuracies never before possible by CMMs. The Renscan5 scanning system offered the capability for continuous 5-axis interpolated motion, comparable to Turbocam's 5-axis machine tools.

In January 2007, Turbocam became one of the first adopters of the new Renscan5 continuous 5-axis inspection capability. Installed on a new Wenzel LH8.10.7 bridgetype 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, setup time and measurement time by 50%, or more. Besides faster throughput, Renscan5 timesavings allow for taking many more data points, allowing greater measurement precision. In addition, it frees up CMM time for qualifying turned blanks and in-process checks before final machining passes.

Those powerful advantages led Turbocam in early 2008 to become the first company worldwide to add a second Renscan5 CMM, a larger Wenzel LH10.12.8, this time at a new facility in nearby Barrington. In this new facility, Renscan5 is an "essential resource," says Romaine, that is being developed to support higher-throughput production generated by around-the-clock, reduced-staff manufacturing.

XSpect Solutions, now part of Wenzel, did the installation of Renscan5 on both the new CMMs.

Turbocam supplies both production and prototype bladed parts to aerospace, automotive and industrial turbomachinery OEMs. CMM inspection assures that critical parts for turbochargers, jet engines, compressors and gas turbines meet demanding accuracy specifications. Part precision and uniformity are critical in providing dynamic balance, directed airflow and long, reliable service at high rotational speeds.

Renscan5 uses two patented hardware breakthroughs to speed part checking, to generate more data points for analyzing part form, and to increase available CMM run time - an "Active" probe head and lasercorrected probing.

High-speed continuous probing routines are reducing programming time, setup time and measurement time by 50% or more. Besides faster throughput, Renscan5 time-savings allow for taking many more data points, allowing greater measurement precision. In addition, it frees up CMM time for qualifying turned blanks and in-process checks before final machining passes.

Active probe head — Named REVO, a powered head provides infinite positioning capability between simultaneous coordinated motion in vertical and horizontal rotary axes. This allows the low-mass 2-axis head, a 3D 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/deceleration of the larger mass of a CMM structure. Low-mass, lowinertia design allows Renscan5 to measure at up to 500mm/sec vs. conventional CMM scanning, which is typically limited to 5mm/sec to 15mm/sec to avoid dynamic errors.

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

Renscan5 allows the CMM's 3-axis platform to be used primarily to "rapid" 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 accel/decel and inertia.

Laser-corrected probing — REVO employs the industry's first laser-corrected "Tip Sense" probing. A laser mounted within the head sends its beam down a hollow stylus to a reflector at the tip. The return beam is received by a position sensor and any deflection is used to calculate true tip position. This allows REVO 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," Romaine says. Tip Sense probes deliver 1µm accuracy at 250mm from the axis of rotation. Sizes are available providing probe reach to 500mm.

While the previous 3+2 axis CMM at Turbocam provided a 2-axis head, vertical changes in probe angle could only be made in 2.5° 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. Programming, access, stylus change and calibration were incredibly painful," Romaine notes.

Turbocam uses Renscan5 for both pointto- 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's a very simple setup to get more points," Romaine says.

Renscan5 high-speed scanning greatly increases data points. "Previously we might collect 50 points or 100 points spaced over a blade," he says. "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. REVO gives Turbocam up to 4,000pps in scanning mode.

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

Helping to reduce measurement time for higher utilization, 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 small impellers just 2" in diameter to 36" diameter, multi-vane components. Turbocam produces more than 400 different bladed part designs a year for compressor, turbine and pump OEMs.

"Just as important as the inspection advantages," Romaine stresses, "are the programming benefits. This has been exciting. We've been able to apply our 5-axis machine tool programming methods to drastically reduce programming time for 5-axis inspection. This is only possible because of the infinite indexing of REVO and its programmability through the I++ DME protocol."

Renscan5's I++ interface gives the UCC2 controller cross-platform compatibility with measurement software packages and maintains user choice of CMM and software.

On complex parts such as blisks (integral hub and blades machined from a monolithic blank), notes Romaine, "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 5-axis programming expertise makes it much easier and faster to provide programs for part inspection, increasing machine utilization for a wide range of parts, he says. While Renscan5 integration is still evolving, he estimates the CMM utilization has already increased between 30% and 50%.

By automating and simplifying inspection, Renscan5 has changed not only utilization, but also uses and users of CMM inspection, according to Romaine.

First, it greatly reduces need for operator intervention in changing probe orientation. "This has been a big benefit and is definitely one of the selling points of the machine," Romaine says.

Second, the simplicity of Renscan5 in conjunction with the CMM software makes it possible for machinists and operators to directly measure in-process parts without the need for an inspector to run the CMM. "They simply need to put the part on the table and call up the appropriate program," he says. "We do inspections of turned blanks and perform in-process check before final machining passes," he notes.

Turbocam has manufacturing operations in the U.S., England and India, and is certified to ISO 900l:2000, along with other quality standards in those operations. It brings comprehensive partnering resources to prototype and development work, offering world-class capabilities in five-axis machining, metallurgy, aerodynamics, geometric modeling and analysis, and software - and now 5-axis part quality inspection and documentation.

The Barrington Turbocam plant was created for round-the-clock unmanned manufacturing of large numbers of bladed parts for a variety of applications such as air compressors, gas expanders, air cycle machines, jet engines, turbine driven power sources and even artificial hearts. Turbocam specializes in meeting market demand for impellers and blisks machined from wrought aluminum, stainless steel and titanium alloys, enabling higher performance and reliability than cast components.