Wind power: a fresh wind for tool technology
The facts make things quite clear: while in the year 2000 there were 9,325 wind power installations in Germany, by 2009 the figure had reached 19,870 wind turbines, together providing a total power of 23,044 megawatts. The boom continues, and presents particular performance challenges to tool technology. The components are relatively large. Bearings, live rings and gearboxes must be machined to the highest quality if they are to withstand the large and varying loads created by the wind while reducing noise emissions to a minimum. LMT Fette has assembled a range of tools particularly tailored to the special requirements of wind power.
Modern wind power installations need to master a number of challenges: the gears of a wind turbine are subject to significantly greater stress than other gears. Whereas a typical car engine is designed to run for between 4000 and 6000 hours, a wind generator will operate for 120,000 hours. This takes about 20 years. Taking 15 rpm as the average speed of the rotor, the rotor shaft of a wind generator must turn 144 million times, while the generator shaft must manage 15 billion rotations. In addition, unsteady winds put the rotor blades under additional stress, and minimal noise emissions are expected from the machines.
Tools as the key to profitabilityIf we are to satisfy the world's hunger for energy in the future, the question of whether the installations are in fact profitable is crucial. The parts that transmit the kinetic energy extracted from the wind – the gears, the toothed wheels and the shafts – play a key role here. The lower the friction, in a quite literal sense, between the individual engineering components, the more efficient the installation is. As a specialist in gear-cutting tools, LMT Fette offers a range of tools particularly tailored to match these requirements. Innovative gear hobs and involute gear cutters permit high productivity in the manufacture of large-modulus live rings and gearboxes. Tap drills and tap formers guarantee the highest quality to the threads. Turning tools with indexable inserts from group partner Boehlerit for the fabrication of shafts and flanges, along with drills and cutting tools, handle other phases of the manufacturing process.
- Hochleistungsgewindeformer von LMT Fette.
The right tool for every application:
• Cutting large gear teeth: involute gear cutters are used in the manufacture of the large gear teeth on live rings. They are fitted with carbide indexable inserts whose substrates and coatings are matched to the particular requirements. Small cutting forces allow low-vibration running, resulting in optimum workpiece surfaces and long tool lives. These tools are also available with internal cooling. The ecologically beneficial dry machining process, cooled predominantly with air, has a favorable effect on the generation of flying chips, thereby avoiding adhesion of the chips to the workpiece. At the same time, the current of air emerging from the chip space significantly reduces heating of the tool and the workpiece, and this helps achieve the long life that is wanted from these components. The segment gear hobs fitted with indexable inserts also make a significant contribution to the economical manufacture of large gears. LMT Fette has recently introduced a double-start segment gear hob whose particular advantages consist firstly in the improved surface quality of the workpieces, and secondly in halving the machining time through correspondingly increased feed rates.
• Thread manufacture: the wind exerts large forces on the equipment. The internal threads of the components therefore not only need to be made to high precision, but also need to be particularly tough. High-performance tap drills are used for the larger thread dimensions, as well as high-performance tap formers from the HPF (High Performance Forming) product family for the smaller threads. Process reliability demands that the sensitive cutting edges of the tap drills can withstand the stresses – particularly when backing the tap drill out – without being deformed or fracturing. The toughness of the cutting material in the tool is therefore particularly important. For this reason, something like 90 percent of all tap drills still consist of high-speed cutting steel. The powder-metallurgical version is capable of providing enormous improvements in performance. Thanks to the development of carbide substrates comprising finer and finer carbides (ultra-fine-grained carbides), tap drills and formers made from this cutting material continue to find new applications.
A massive shield for the tool
Innovative coatings are the key to further improvements in the performance of cutting processes. Coatings such as TiCN, TiAlN or AlCrN with nano-structured layers allow longer service lives and greater cutting or feed rates. In combination with HSS or carbide base materials, they protect the micro-geometry of the tool from being damaged by the extreme thermal and mechanical stresses.
The new Nanotherm coating provides an example of the performance of this technology. The carbide indexable insert gear hobs from LMT Fette coated with this material are already in use with a company in the wind power business in the south of Germany. In dry machining, the tool operates at a cutting speed of 158 meters per minute with a feed rate of 300 millimeters per minute. The tool life is increased by 100 per cent. The Nanotherm structure, with a layer thickness of 6 µm, is critical for this improved performance, providing significantly increased productivity in comparison with the titanium-aluminum-nitride coatings used formerly.
Gear cutting tools in the wind power industry