QMT Features: November 2010
Stress-free quality
Portable laser-based measuring technology supports quality improvement and production assembly at Swiss aircraft manufacturer, Pilatus Flugzeugwerke.


Pilatus Flugzeugwerke AG, founded in 1939, is the leading manufacturer of single-engine turboprop aircraft and the only Swiss company to develop and construct aircraft and training systems and sell them on every continent. The highest demands in terms of quality apply globally within the aviation sector. A task that already represents a challenge within series aircraft manufacturing becomes a work of art in itself within customised aircraft manufacturing.

As thousands of individual parts are involved that have to fit together perfectly, the complexity of quality control within production increases, as all of the parts and the modules produced from them must undergo an entire and extremely precise quality control check. In particular, observing the accuracy of fit within the current partial series manufacturing plays a vital role within Pilatus.  The customers' individual challenging requests  can only be taken into consideration and tested with this production process. 

From early in 2009, an API laser tracker has played a major part in the company’s ability to implement these customer requests. Pilatus manufactures the parts of an aircraft, such as the body, cockpit or wings, at different sites. The measuring points are already defined when they are constructed, enabling the jigs for the parts assembly to be checked at a later stage.  Measuring these points guarantees that the jig corresponds with the CAD data. On the basis of these reference points, an aircraft wing, for example, which is made up of thousands of individual parts, can be assembled precisely and be checked at crucial points to ensure that it corresponds with the CAD data. The laser tracker realises the measuring point deviations from the CAD model in real time - a prerequisite for assembling in an efficient and dimensionally accurate manner.

With the ability to measure distances of up to 60 metres, the tracker is also suitable for  body and wing assemblies for large aircraft. However, it is not always the size of a jig itself that can create problems for manufacturing.  Often it is the complexity that can present a metrological challenge - such as in the case of a jig for the construction of a cockpit. Pilatus can only guarantee that the completed cockpit corresponds exactly to the specification on the construction plans due to the large number of measuring points on the jig.

This jig also has tooling holes (drill holes) that accommodate the tooling balls for the laser reflector (SMR) on the tracker.  The measuring process can be initiated by remote control and, in this way, these measurements can be carried out by one person. Each measuring cycle only requires marginally more time than the few seconds required for the sensor to reach the measuring point.  As a result, measurements that previously required days, can now be completed within a few hours.

Drilling holes is not generally considered a challenge or even a time-critical task outside of the oil industry. However, in aircraft construction it is of vital importance. Exact positioning is crucial as the drill holes accommodate the rivets that fasten the aluminium shell of the aircraft to the hull (stringers and ribs). In the past, the drill holes could only be made once the outer skin was fitted onto the hull - the exact position of the drill holes was only determined at this point.

This manufacturing process was extremely time-consuming and complicated - and it had to be completed moving from the interior to the exterior. Laser measuring technology now allows another huge time-saving procedure: using a laser tracker each coordinate can be transferred from the CAD system to the jig. This means that even during the manufacture of the outer skin, all hole positions can be drilled precisely on CNC machines. As Pilatus manufactures a wide range of the most diverse types of aircraft, the efficient and time-saving manufacture of different versions is of particular interest. 

Dynamic measurements
The engineers at Pilatus have already envisaged other fields of application for the API laser measuring system: its ability to measure in real time also enables it to carry out a stress test during a movement sequence. In doing so, the measuring system has the ability to record a 3600 range and +800 to – 600 in the vertial range.   The measuring set-up itself is implemented quickly and setting up close to, or even under the aircraft, poses no problem. The tracker head is only 36 cm high and it weighs only 8.5 kg. The compactness of the whole system also facilitates the measuring of complex jigs with large dimensions, of which there are a large number at Pilatus.

Happy landings
The PC-21 type of aircraft, designed for basic, advanced and mission training, can experience stresses and strains leading to possible or distortion to the structure of the aircraft. Evidence from the inspections that are officially required for such cases was difficult to establish up until now:

  All of the aircraft of this type have over hundreds of measuring points, spread over the entire body of the aircraft, measured precisely during the assembly and also available in the CAD data set. With the help of a laser tracker, it is now possible to measure the position of these points after a specific incident on the aircraft and to compare this with the original structure of the aircraft in the CAD data set. These preventative maintenance and quality control measures significantly contribute to the comparatively low life cycle costs for this trainer.
www.apisensors.com

  
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Rob Tremain Photographer
www.4exposure.co.uk
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