Making the Most of the Wind
How much electricity can a turbine construction more than 328' (110-m) tall generate? How can you ensure the assembly of any wind turbine runs smoothly when there is only one chance to put it together? Vestas Nacelles (Lem, Denmark) answers those questions with a strict quality policy enabled by high-capacity portable measuring systems.
No small object has ever left the Vestas Nacelles factory. Hubs, housings and other steel-made structural elements for wind turbine nacelles can be over 11' (3.5-m) high, weighing up to 16 tons (14.5 t). For such enormous parts, Vestas Nacelles relies on valid data enabling the monitoring of process performance. “This means we will be alerted if a process gets out of control by showing evidence of systematic variation,” said Ingo Boysen, production quality manager. “By reacting fast in these situations, we have been able to expand our knowledge. Our testing phase led to the conclusion that laser trackers were still the ideal solution for Vestas Nacelles’ measurement challenges due to their mobility, their measurement range and high accuracy under difficult shop-floor conditions.
“Our developers define a certain number of points per object that are critical to quality, the so-called CTQs. So we measure the CTQs on each part, and a big number of additional characteristics such as the position of holes or other features on a hub. Subsequently, we make sure all single components of the nacelle fit together before the wind turbine is assembled. It is very difficult to correct any mistakes once a part has left the factory, and in the case of a hub, scrap would cost us over $27,000 per piece for just the material. Measurement pays off, but not only for us. We are using the measurement data actively to reduce cost to the benefit of our customers,” said Boysen.
Laser Trackers Add Precision Edge
The quality team at Vestas Nacelles has a long history in metrology. Besides a large stationary CMM, they have used two Leica laser trackers—a LTD300 and LTD500—for many years. “The time had come to look for new measurement systems,” said Jeppe Nielsen, head of the measuring department. “The old laser trackers still worked perfectly, however, we wanted to see if there was something faster. A new tool should help us with saving time and effort.”
Nielsen and his team utilize two Leica Absolute Tracker AT901s from Hexagon Metrology (North Kingstown, RI). These high-performance, next-generation metrology tools have made verifying large parts considerably more efficient for Vestas. The laser tracker relies on a laser beam to measure and inspect objects in a spherical volume up to 525' (160 m). The AT901 was engineered with an overall focus on portability—lean construction, compact dimensions, and long-life battery power. Inspection of large wind components can be performed without repositioning the instrument due to its long measurement range. The entire package can be transported by one person and fits into an average-size station wagon, giving quality control departments the ability to follow wind power components from factory to field.
The Leica Absolute Tracker line introduced an important technological advance called the Absolute Interferometer (AIFM), which provided the ability to instantly re-establish an interrupted laser beam and immediately start measuring a moving target. The “dynamic lock-on” capability was a very significant improvement for user productivity. The system’s PowerLock feature enables the tracker to automatically lock the laser back onto the reflector or probe. Previous generation laser trackers used laser interferometers (IFM) and absolute distance meters (ADM) in combination. The Absolute laser tracker leverages the strengths from both technologies and combined them to produce the AIFM, which can measure absolute distances to a moving target with the instantaneous update rate and the dynamic performance of a laser interferometer.
“Besides gathering data in real-time, the laser tracker’s PowerLock function impressed us,” said Nielsen. “Because of PowerLock alone, we save two hours of work time per object—in some cases, that means we cut the measurement time in half. Before, every time the laser beam was interrupted, it was a long procedure to re-establish the connection—it could even mean we had to climb down the ladder from which we measure some points, recover the beam, and continue the measurement. With PowerLock and a remote control, we can now measure our parts with only one operator compared to before when it was a two-man task.”
Tailwind for the Measuring Arm
Vestas Nacelles also produces bearing housings, 100% of which undergo a measurement procedure in terms of process and items. This practice has provided the opportunity to reduce process variation, and in doing so, improved process robustness while lowering the cost of poor quality. Every single part the factory produces is also measured. “We understand measurement is not just part inspection,” said Boysen. “For us, it is an integral part of the production. You could say that our production relies on measurement.”
“We used to have these parts measured by an external supplier before, which meant transport and lead time. That was too expensive for us, so we looked for our own tool to carry out these measurements. It had to be an additional one, since our two laser trackers are already in constant use. We developed a business case and found out that the Romer Absolute Arm from Hexagon Metrology would be the best tool for this application,” Nielsen said.
The department’s ability to quickly inspect parts can help to minimize production wait times and reduce both scrap and rework. The measuring arm essentially moves dimensional inspection to the point of shop-floor production. Parts and assemblies that are too large or difficult to move can be measured in place with the portable CMM, well known for its ease-of-use factor. The articulating arm operates much like a human arm and floats in the operator’s hands due to its pneumatic Zero-G counterbalance, which offsets its weight and minimizes user fatigue. The arm’s patented infinite rotation in the principal axes allows access to difficult to reach areas, while avoiding damage to the arm against rotational hard stops. The instrument can also operate wirelessly with its WI-FI capability and high-capacity rechargeable batteries.
“Ordering the measurement, sending the part and getting it back eventually took us days before. Now we have the results in 10 minutes. The measuring arm paid for itself in less than half a year. In addition, wireless data transmission, the fact that no setup time is necessary and the strong carbon fiber construction make it a very convenient and reliable measurement solution,” said Nielsen.
Five measurement specialists in Nielsen’s team use the two Leica Absolute Trackers and the Romer Absolute Arm every day. Without the metrology equipment, production stops at Vestas Nacelles—and that makes reliable metrology systems essential to their manufacturing success.
This article first appeared in Motorized Vehicle Manufacturing 2013-2014. It was edited by Yearbook Editor James D. Sawyer from material provided by Hexagon Metrology.
Published Date : 6/4/2014