Preparation And Machining Precision Control Of CFRP Retaining Ring For Electric Generator

Along with the increase of total electric quantity that was consumed in our country, we expected to manufacture the high-capacity generator autonomously.Retaining ring was one of the most important parts of electric generators.When the electric generator was running,the retaining ring suffered a radial press caused by the rotor and a tensile stress caused by the rotation of itself. Therefore the requirements from the retaining ring to mechanical properties became very demanding.The traditional anti-magnet steel retaining ring was one of the most important factors to restrict manufacturing high-capacity generators autonomously in our country,because of the difficulties in processing,the high cost and the limits of raw materials et al.Also,the traditional anti-magnet steel retaining ring could not meet the demand of high-capacity generators because of its mechanical properties.So using the CFRP retaining ring to replace the anti-magnet steel retaining ring was imperative.Carbon fiber reinforced composite (CFRP) was widely used in engineering because of its high specific strength and high specific modulus.With increase of the properties of fibers, the performance of fiber reinforced composites made a further improvement.Therefore, using CFRP to manufacture high-performance rotor became feasible.In this paper, a composite retaining ring of600MWe electric generator was designed and manufactured.Firstly,a fiber-epoxy system was confirmed, a composite laminate was designed. Secondly,the reliability of the retaining ring was analysed by finite element method from force analysis and thermal expansion. Thirdly,molding technology and manufacturing equipments were confirmed.And the mould used in the chosen molding process was designed and manufactured.Finally, the preparation and machining of the retaining ring was completed.Also,the finite element method was used to research the cutting characteristic of composites in this paper.(1)Through the simulation of cutting process,the thermal deformation of the retaining ring was got to research the machining precision.Simulation results:when machining the composite retaining ring of600MWe electric generator,in order to ensure the precision after cutting,the changed cutting depth was0.210mm in the radial direction and0.243mm in the axial direction.(2)A model based in finite element was developed. The mechanisms of chip formation of CFRP were analyzed. Stress-strain fields of the workpiece and tool were obtained by transforming fiber orientation of the composite.Combining with the cutting theory of Composite materials,the influence of cutting composites which had different fiber orientation was discussed. Simulation results:1)Simulation results were accord with the composite cutting theory.When cutting FRP, the Cutting force was mainly transmitted by fibers and the fiber orientation of the composite influenced the performance of cutting composites in significant measure.2)When the fiber orientation was0°, the cutting force in composite workpiece was minimum. With the increase of fiber orientation, cutting force was increased on the horizontal direction and vertical direction. Especially when it was135°, cutting force was maximum and fluctuated sharply.3)When the fiber orientation was30°, the contact stress suffered by composites was maximum. When it was far away from90°, in other words, fiber direction and cutting direction approached to be more parallel, the contact stress became less.4)Comparing with the cutting force and the contact stress, simulation results of friction had no particular tendency, however, when the fiber orientation was135°, the friction was found to be maximum.And when it was0°the cutting performance was optimal as previously mentioned.