Design and Manufacture of a Composite Flywheel Press-Fit Multi-Rim Rotor

Abstract

The pre-compression that develops in a press-fit multi-rim rotor suppresses tensile stresses caused by the curing process and high speed rotational centrifugal forces, increasing the overall performance of the flywheel rotor. In this study, the interferences and the rim thickness of up to five rims of graphite/Ep and glass/Ep are analyzed to maximize the specific energy density (SED) of a multi-rim composite flywheel rotor. Three states are considered: (a) cured rims with residual stress prior to press-fitting; (b) a stationary press-fitted rotor; (c) a rotor at maximum rotational speed. Two methods of press-fitting rims are presented. One method has each rim machined with tapered inner and outer rim surfaces. The other method uses a guiding rim to expand the outer rim and guide the inner rim into the expanded outer rim. An optimized multi-rim rotor, composed of one glass/Ep rim and one graphite/Ep rim, is scaled to have energy storage capability of 5 kWh, and is successfully manufactured by machining tapered rims and hydraulic pressing.