From generator shafts to flange bores and fir tree grooves – generator rotors and turbine rotors each pose a number of critical and very different machining challenges. This is why the machining of these complex workpieces usually requires two separate, specialized machine tools. WaldrichSiegen and UnionChemnitz have now developed a universal rotor slotter that allows for the efficient machining of both workpieces on a single machine.
The innovative machine concept is the result of a collaborative effort of the world-leading expert in heavy-duty machine tools for this application, WaldrichSiegen, and its sister company UnionChemnitz, a specialist in manufacturing horizontal boring and milling machines with more than 160 years' experience. The rotor slotter is specifically tailored to the requirements of a large American power plant manufacturer. It is based on UnionChemnitz's most powerful horizontal boring and milling machine PCR 260 with a spindle diameter of 260 mm, a power of 128 kW and a torque of 19,000 Nm, combined with a sophisticated, CNC-controlled set-up system designed by WaldrichSiegen and UnionChemnitz.
The rotor slotter machines rotors with a length of up to 15,500 mm, a diameter of up to 2,400 mm and a maximum weight of 150 t. It is equipped with a FANUC 30i control. Depending on the workpiece, it adapts to the various machining tasks required with a range of boring and milling units. These can weigh up to four tons. Outstanding stability is therefore one of the machine's most vital qualities. The machine bed is made of extremely robust cast iron, reliably absorbing vibrations. A fully hydrostatic guidance system guarantees highest precision and protection from wear even when performing heavy-duty machining. Both the heavily ribbed column and the ram are designed for extra stiffness, as well. Double hydrostatic guideways enclose the ram completely, resulting in excellent damping of vibrations and reliable long-term stability. Thanks to the machine's overall stability, it achieves remarkable performances. When slotting generator shafts, a disk cutter with a diameter of 1,250 mm is mounted. It can mill grooves with a depth of 125 mm in a single cut, applying 111 kW spindle power at a torque of 33,000 Nm, and removal rate of about a ton per hour.
A major challenge in machining rotors is aligning the workpieces in the machine tool, a time-consuming process which often takes up as much as eight hours' valuable machining time. The set-up system automatically adjusts the rotor once it has been placed into a highly precise clamping device, reducing the set-up time to approximately an hour. Based on data gathered by state-of-the-art measuring devices, numerically controlled, hydrostatic steady rests position the rotor in micrometer range – while bearing a weight of up to 80 tons each. Absolute set-up precision is crucial for various demanding machining tasks performed with the rotor slotter – for example when boring flange bores, which form the connection between turbine and generator, to tolerances of 10 µm.
The rotor slotter meets each specific machining challenge with customized spindle units, milling heads and tools and the appropriate NC programming solutions: curved fir tree grooves in turbine rotors, for example, an extremely complex machining task, are pre-machined with a large bell cutter and finished with a finger cutter. An automatic tool changer allows for quick and efficient switching between machining applications.
WaldrichSiegen and UnionChemnitz are specialists in integrating custom solutions. Process integration is the key to success: flexible machining concepts allow for a broad range of applications with a single machine. Solutions specifically tailored to customers' requirements by UnionChemnitz include a boring mill with a high-speed rotary table for turning operations and a boring mill equipped with a grinding unit; WaldrichSiegen recently built a mill turning machine with an integrated grinding unit. By combining their expertise in developing innovative machine concepts, WaldrichSiegen and UnionChemnitz have raised the bar once more in the flexible machining of workpieces for the energy industry: the rotor slotter is unique in its universality, allowing for complete machining of both generator and turbine rotors.