Counting on quality

Counting on quality
Counting on quality

Historically seen as a cause of bottlenecks and delays, the world of quality and inspection is changing. Ed Hill hears how Hexagon Metrology is employing the latest technology to overcome the challenges

. In such a tightly regulated industry as aerospace manufacturing the quality of parts is paramount. However, components range from large aerostructures such as the fuselage, right down to the smallest aero engine part. How do quality and metrology providers meet the demands of such a wide range of components and not create delays in production?
Brett Green, director of sales and marketing at Hexagon Metrology, believes making inspection an integral part of the production process is partly the answer.

“Final inspection remains an important quality assurance step, but the focus for high-value manufacturers, as well as for metrology companies such as Hexagon, is obtaining and providing ‘actionable information' throughout the entire manufacturing process. The aim is to capture the issue at each major step and take action before the manufactured part moves to its next process.

“We have launched a new series of shopfloor CMMs able to operate at the production floor. They don't offer the same level of performance as some of our ultra-high accuracy machines, but they do enable our customers to validate their parts at the point of production.

“Likewise, our solutions for ‘on machine' gauging allow the part to be inspected whilst it's still in the machine tool, meaning set-up times and workflows are reduced. For many customers, particularly in the aerospace sector, it is not practical to take a large machined assembly out of the machine itself. We have to bring the metrology to the part.
“Similarly, in the airframe sector, where assemblies are sizeable, our large-volume portable metrology solutions such as Leica laser trackers are widely utilised.”

Touchless metrology

Newer methods of non-contact measurement such as Lasers, X-ray and ultrasonic are speeding up inspection but Green believes it's important to make the right choice for a cost effective solution.

“The general rule when determining what is appropriate is to assess the manufacturing tolerances. Even if a given sensor is suitable for the location or for the environment, its absolute capability may not be. Hexagon's Romer Absolute portable measuring arms are ideally suited to the production environment, but if you have a sub-micron accuracy requirement then we have to consider alternative technologies.

“Laser scanning in particular is in the ascendancy. Our sensors such as the T-Scan 5 coupled with the new AT960 Leica laser tracker can measure up to 210,000 points per second throughout a volume up to 40m. This technology is set up on the line.

“With our latest HP-L-20.8 laser scanner, the Romer Absolute arm offers first-class performance even on complex surfaces and workpieces made of the most challenging materials. Setting the laser according to surface colour or reflectivity is not required: the laser control of the scanner automatically adapts to the surface conditions.

“Another consideration for production line inspection is vibration. It's important to ensure you measure the part and not environmental noise. One non-contact technology suited to these environments is Hexagon's White Light System (WLS). WLS projects a random pattern on the measuring object and analyses surface, features and edge lines using stereo vision. Because the average optical exposure time is typically around 20msec, the system is almost impervious to vibration. One aerospace customer is measuring countersink and fastener flushness whilst other operations are simultaneously taking place on the airframe.”

Green believes there is still a role for CMMs for very high levels of accuracy if combined with the latest censors.
“Tactile measurements may often be perceived as ‘slow' but it can still capture data in the sub-micron range. We have also launched the HP-O sensor for the Leitz Ultra-High Accuracy CMM. This fibre optic sensor features an accuracy and reliability compared to tactile standards but with higher scanning speeds, increased measurement range and the generic optical advantage of touch-free measurements. For applications such as those on blisks and blades, this technology provides game-changing performance.”

Flexibility is also seen as desirable particularly in aerospace manufacturing where batch runs can vary and certification requirements continually evolve.

“Commercial considerations such as return-on-investment are also important,” Green adds. The sensors we have developed are used across all of our hardware platforms. Our laser scanners operate on Romer arms with Leica laser trackers and on our CMMs. Automatic tool change on our CMMs means that the machine can select, in process, the most appropriate sensor for the measurement task in front of it. A suite of sensors on one machine can offer greater value than a suite of different machines. Similarly, our Optiv machines incorporate both tactile and non-contact probing in the same machine.”

The big stuff

So how does Hexagon tackle the large structures found in aerospace?

“Challenges with large aero structures can be overcome with portable metrology. The Leica laser tracker AT960 offers a measurement volume up to 120m. Even when enabled with the Leica T-Probe, whereby the laser tracker becomes a walk-around CMM, the measurement volume is impressive at 40m. This solution is well proven in the airframe sector and widely used.

“However, our laser tracker still requires line-of-sight, even with our patented PowerLock which recognises that the laser beam is broken and automatically re-acquires the target. Increasingly we support our aerospace customers in the design phase so that measurement plans are created and included as part of the overall manufacturing solution. Tracker reflectors and targets are designed into the jig and fixture locations and positions of the trackers themselves are clearly set out. Our AT960 laser tracker has variable mounting positions, meaning the tracker can be suspended in an inverted position or even wall mounted.

“As we move towards automated measurement on large structures, our T-Probe and T-Scan units are robot mountable and provide the additional benefit of on line robot guidance for improved accuracy.”

What effect are newer materials such as composites and exotic alloys having on inspection?

“New materials create more challenges. Hexagon is overcoming some of these by considering what we call ‘multi-physics sensors'. The exotic alloy may behave differently to traditional steel and, consequently, we may have to consider additional material properties when analysing the inspection – material hardness, temperature, micro-form, stress, roughness, etc. By combining multiple sensors in one machine, in one measurement routine, we believe we can capture many of the additional requirements.

“Nowadays, our sensors can automatically adapt to both light-reflecting and light-absorbing surfaces and are far less susceptible to colour or shade variations. Also, the software becomes more powerful and intuitive.”

Finally, what impact does Green believe Additive Manufacturing (AM) will have on inspection where increasingly complex parts can be produced by designers?

“Ultimately measurement and inspection technologies will be an intrinsic part of the AM machine, although I can't tell you what these technologies will be yet! The movement, in some sectors, away from monitoring pure geometric tolerances towards assessing form and functional performance of the parts will also underpin the thinking behind the measurement technologies. Multi-sensor machines with absolute control of the AM process may be the answer, but it's going to be an interesting journey.”

www.hexagonmetrology.com

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