Like most complex machines, manufacturing a modern wind turbine is the story of materials, processes, and trends. The material story is mostly of composites. For instance, blades in particular are manufactured from fiberglass in an infusion process that excludes air. For other tasks, interest has been on a tooling resin and closed molding because the two deliver substantial commercial and environmental savings. A lot of manufacturing effort is going into making blades lighter and longer.
The advanced technology in wind turbines depends a lot on conventional manufacturing techniques, such as welding. One welding-machine manufacturer recently called on a linear motion and assemblytechnology company to help build a new generation of custom welding machines for the wind industry. Such welding equipment is used to build turbine towers up to 100-m high. Engineering taller tower may have to put conventional thinking on hold. For example, one engineering firm proposes a wide concrete base, 35-ft tall, cast and built on the site to keep tower costs down.
Conventional towers are manufactured by first rolling a plate into a cylinder, or “can”, measuring about 9-ft long by 8 to 15-ft dia. Another machine then welds along longitudinal seams to complete the can and then circumferentially to join cans. The welder is suspended from a guide rail for outside welding. In each case, most of the machine is stationary while the weld head moves short distances on two and three axes, both along and across the seam. A linear control actuator at the end of a horizontal arm determines the motion of the weld head.
A manufacturer of equipment that quickly places composite material and a quick-cure-molding system for wind blades, says the combination cuts labor by two thirds, doubles throughput, and produces a consistently high-quality blade.
The machine can produce both halves of a large turbine blade in about 15% of the time needed by manual lay-up. As fabric pays out onto the mold, two articulating powered brushes smooth the fabric onto the tool surface. Lay-ups repeat to ±2 mm with and application tolerance of ±5 mm.
The automated blade molding facility is capable of spraying in-mold coatings, dispensing and lay-up of glass and carbon-fiber materials, and applying adhesives. It places material at 3 m/sec (lay-up speed) on blade skins, spar caps, and sheer-web molds, with laser and vision-based wrinkle detection in cross or longitudinal directions. Depending on a laminate schedule, the manufacturer says the system can cut up to 85% off the lay-up time of a 45-m blade.
The CNC-controlled system consists of a gantry with multi-axis spray heads and adhesive applicators, along with tooling for spooling and placing materials. After spraying on a gel-coat, a ply-generator with a ten-roll magazine of material cuts and dispenses plies to the layup end effector on the gantry. The lay-up end effector spools out material supplied by the ply generator.
Two such gantries adjacent one another can each produce a 45-m blade-shell half in less than two hours, with half the manual labor of conventional methods. The gantry rides on rails flush with the floor. It also carries bulk supply systems for gel-coat and adhesive. Offline programming software developed by the company creates the CNC code from imported CAD data. However, at least one machine in development aims to produce a blade in one piece–without seams, a weak point in conventional designs.
Another manufacturing challenge has been to true-up a tower’s flange bottom with the tower centerline. Tower sections are huge and heavy. One solution, a portable mill, can machine wind towers that now have from 10 to 14-ft dia. The mill is said to produce a surface-flatness tolerance of 0.002 in. The mill creates a 60-rms micro finish, exceeding the current requirements of the windpower industry and, in particular, tower fabricators.
Thanks to its modular design, the portable mill can store in a fabrication shop until needed and reassemble in 60 min, moved into position by an overhead crane. Its in-situ machining eliminates the time and work required to build subassemblies at a machine shop for re-machining, and the cost of subcontracting with field service companies.
Filed Under: Components, Turbines