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Optimising Turbo-Spindle Efficiency for Machining at Ultra-High Speed

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New turbine technology to boost micromachining efficiency

The development of miniature radial turbines looks set to make high speed manufacturing spindles – from micromachining to paint spraying machines – much more energy efficient.

Industrial Technologies

In a world where competing resources and increasing pollution are making our lives more challenging, industry is looking at how to make equipment and machinery more energy efficient and cost effective. The EU-funded OpTEMUS (Optimising turbo-spindle efficiency for machining at ultra-high speed) project researched how to improve the energy efficiency of ultra-high-speed spindles used in precision machine tools. The early investigations of the OpTEMUS project revealed that the energy efficiency of existing commercial turbine spindles ('turbo-spindles') is typically less than 20 %. Aiming to increase spindle efficiency and power-to-weight while lowering costs, the project team proposed a new 90-degree radial-inflow type turbine for micromachining spindles. To improve spindle performance, the OpTEMUS team articulated a low reaction and highly loaded radial turbine stage design that achieves high turbine efficiency whilst minimising inertia, weight and size. Computational fluid dynamic simulations were used to determine key design parameters such as blade thickness, number of blades, rotor outlet blade angle, and the radial gap between rotor and stator. The new design also boasts low turbine thrust forces to reduce the axial load on the spindle bearings, as well as low blade speed that helps in manufacturing the rotor using a magnesium alloy for further inertia savings. The new prototype turbine rotor, which has an outer diameter of 25 mm and inlet blade span of 1.9 mm, was built using an aluminium alloy. The prototype spindle weighs less than 300 g and has a static radial stiffness (at toolholder) of 0.66 N/µm. The newly developed turbo-spindle has been operated successfully up to 100 000 rpm and has clocked over 24 hours of running time. To measure torque and power output, the prototype turbo-spindle was attached to a high-speed electric motor/generator and loaded with a range of resistors. A Maximum turbine power output of approximately 100W and efficiency of over 50% have been achieved to date, thus demonstrating the performance improvements possible. Armed with these positive results, the OpTEMUS team joined forces with industrial partners to submit two funding proposals for further research projects. In addition, the team has been investigating commercialisation options for the new technology, including its potential benefit for power tools, paint spraying equipment and medical/dental devices. Once the project’s outcomes are fully exploited, industry is poised to benefit from much more efficient manufacturing equipment.

Keywords

Micromachining, machinery, OPTEMUS, turbo-spindle, turbine, efficiency

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