A custom machining system from Mag Industrial Automation Systems (Hebron, Kentucky) recently demonstrated the ability to simultaneously machine all three blade faces of one of the industry’s largest wind turbine hubs in record time, the company says.
Known as the Megaflex, the system is installed at Astraeus Wind Energy, an Eaton Rapids, Michigan-based partnership formed by Dowding Industries and MAG that works to develop new technologies for wind-component manufacturing. It consists of three FTR 5000 floor-type boring mills surrounding a B-axis rotary table, a configuration similar to systems used for high-volume automotive components and smaller parts. “This is automotive machining technology scaled up an order of magnitude,” explains Pete Beyer, MAG director of product development. “We are using multiple spindles, specialized tools and clever process technology to finish a part in one setup, in the shortest time possible, while maintaining the flexibility to process a family of different hubs.”
The spherical turbine hub, a Clipper Windpower C96, weighs 40,000 pounds (18,144 kg) and measured approximately 12 by 12 ft (3.6 by 3.6 m) in size, with a blade bolt-circle measuring about 8.2 ft (2.5 m). The machining completed in record time—less than one shift—by the Megaflex consists of a specific set of processes known as “Operation 20.” Operation 20 processes include milling the blade faces, drilling and tapping or counter-boring more than 60 1.5-inch (39-mm) holes per face, boring and drilling the blade-pitch gear-mounting surfaces, and more. Tolerances include 0.002-inch (0.05 mm) true position on holes and ±1 degree on angles. Now that the system is operational, Astraeus is forecasting a capacity of approximately 1,800 hubs per year.
Conceived by MAG in 2009, the MEGAFLEX system's development was funded in part with grants from the Michigan Economic Development Corporation (MEDC), which audited and approved the progress of Astraeus in meeting its performance requirements. Concepts borrowed from the automotive industry include offline setup and quick part loading, using a fixture interface plate and a lifting bracket for the workpiece. The interface plate is bolted offline to a locating feature on one side of the casting; the plate then mates with a locating feature on the worktable for fast part setup. The lifting bracket attaches to the top of the part to allow a single crane to transfer the part in and out of the workzone safely and quickly. This enables setting up the next part offline on an interface plate for quick exchange with a completed part. MQL, another automotive machining technology rarely used elsewhere, eliminates the need to control splashing and misting coolant in the shop.
The boring mills themselves include a specialized tooling package utilizing numerous extension tools and a servo-controlled tilting A-axis on the W-axis ram. The tilting A axis can position the ram for a normal approach angle to the work face. This is required because the blade face of the hub is not always perpendicular to the hub's axis of rotation, but may be two to three degrees off, depending on the manufacturer. Mr. Beyer explains that the tilting ram is also stiffer than other solutions, such as a multi-axis A/C head, and it eliminates the need to interpolate axies. Each machine also has a latch-plate interface to accept head-changing attachment, although the system currently uses only one rack that can be moved for use by any of the machines.