Quality Assurance On A Massive Scale
In the fast-growing market for wind power systems, quality assurance according to international industrial standards has become an important issue. Wind power plants are no longer a niche playground for environmental proponents, but a serious business where cost efficiency, life cycle costs, reliability, and availability of the components must be considered.
Coordinate measuring machines play a vital role in ensuring the accuracy and quality of components. This article describes how Carl Zeiss IMT has developed its series of MMZ machine measuring centers, which are tailored for the precise, economical measuring of large parts directly in the production environment, and in particular looks at the MMZ G, which has established applications in quality assurance for gearboxes and other parts for large wind turbines.
Gear boxes are a major part of all wind turbines. The quality requirements are high: as the wind blows in gusts, a backlash-free operation is indispensable to ensure a long and beneficial lifespan of the system. Mechanical efficiency is directly related to economic efficiency.
Noise reduction in the gear box is important to ensure the public acceptance of wind turbines, and the industry has to follow these requirements. Not many manufacturers are able to produce such large gear boxes (and with the off-shore systems, the sizes are even larger), and now they have to deal with serial production, having many unknown requirements for quality in very large dimensions.
Gears (ring-gear, sun gear, and planet), bearings, and housings have to be produced with tolerances down to 1/100 mm — on components with 4 m or more in diameter! It is no longer possible to machine these parts without specific measures to ensure the quality because the parts are too expensive to produce rejects. So a reliable control of the manufacturing process has to be installed, in real-time, during machining.
Carl Zeiss has been a manufacturer of precise measuring instruments for 90 years. Since 1973, the company developed into one of the market leaders in 3D-coordinate measurement. For a traditional customer of CMMs, such as the automotive industry, the standard machine size was around 1 m³. But very early on, applications for printing machines, truck diesels, energy, and aircraft parts, made it necessary to develop a series of larger machines.
Today’s larger models are the MMZ series: The MMZ E and B gantry type machines, dedicated for composite parts and machined parts with standard accuracies, the MMZ T bridge type machine with an integrated steel table for the high accuracy “mid-size” class (up to 2000 mm x 3000 mm x 1600 mm), and finally the MMZ-G for large precision components.
Sizes are available from X=2000 mm, Y=3000 mm, Z=2000 mm up to very large systems able to measure gears and bearings up to 5m in diameter and housings or other machined parts up to 11m in length, 5m in width and 3.5m in height.
The machine is designed as a welded steel construction; everything is calculated according to the finite elements method. The machine moves on linear guideways, is driven by a ball screw spindle, is rigid and robust as a machine tool, and has no air consumption. The machine can be equipped with floor integrated rotary tables, holding up to 12,000 kg. Gears can be measured with or without the rotary table. For some helical or bevel gears, a rotary table would help to get full access to gear flanks.
With the standard CALYPSO software, all geometric dimensions can be easily measured, including form and position tolerances. Adding the well-proven GEAR-PRO software allows for measuring of internal and external gears, straight or helical. Bevel gears and worms are measurable.
With the ZEISS VAST probe head, the machine can not only take single points but is optimized for surface scanning. Navigator technology allows scanning using long, flexible styli at high speed rates without losing accuracy. The probe head can hold probes up to 600 g of weight and 800 mm of length in all directions. This makes it possible to reach deep features in housings, making difficult structures accessible.
The typical accuracy varies from 2.8 µm+L/400 for the 2 x 2 m to 8.4 µm+L/180 for the 5 x 3.5 m bridge.
The MMZ G is not a dedicated gear checker. The advantage is that you can measure gears as well as housings, bearings and all kinds of different precision parts on the same machine while the accuracy is best in class. MMZs are in use in the wind energy industry all over the world including North America, South Korea, China, India, and several European Countries. The MMZ helps the wind energy industry to ensure the growing quality standards that have to be achieved – today and in the future.
For more information visit www.zeiss.com.