Danfoss Motor – Aeromotor Overall Leaf Ring Structure: Research Progress


       The high thrust-to-weight ratio is an important indicator of the performance of advanced aeromotors in the future. While improving motor reliability and maintainability, reducing motor structural weight, improving motor structural efficiency and gas temperature are important ways to increase the thrust-to-weight ratio. To this end, in addition to improving the motor design method, the development and adoption of advanced lightweight high-performance materials and high structural efficiency of the overall, lightweight structure is currently the main development trend. Foreign countries (such as the United States and Europe in accordance with IHPTET, UEET, ACME, etc.) have successively developed a series of advanced manufacturing technologies for aero-motors. The new fan and compressor structure developed mainly includes titanium alloy whole leaf disc (BLISC) and integral leaf ring (BLING). And continuous fiber reinforced titanium-based composite hollow blades and the like. The continuous fiber-reinforced titanium matrix composite monolithic ring structure has obvious advantages in weight reduction and bearing hoop load, and will surely become the development direction of advanced motors in the future.     Danfoss Motor     discusses the composition, material selection and processing and manufacturing process of the whole leaf ring structure, and hopes to provide reference value for the study of the whole leaf ring in China.

  Aeromotor overall leaf ring structure

  The overall leaf ring was developed on the basis of the whole leaf disc. The integral leaf disc structure is an integrated joining process that manufactures the blade and the disc into one body, eliminating the need for a conventional blade-jointed hoe and gutter. This structure eliminates the weight of the blade boring and gutter connection and the structure required to support these qualities, thereby greatly reducing the quality of the fan and compressor rotor; there is no gutter leakage channel to ensure uninterrupted flow at the blade root And reduce the windage loss in the recess between the stages, thereby improving the performance; no groove leakage, the compressor rotor temperature is lower, thereby increasing the life of the rotor; eliminating the mounting side and the bolts, nuts, locking pieces and the like, thereby The number of parts is greatly reduced; there is no gutter, which avoids potential troubles such as gutter damage and breakage, thereby greatly improving reliability. For the damage caused by the use of the whole leaf disc, the linear friction welding technology can be used to cut the damaged blade and then weld the new blade to realize the repair of the damaged blade. At present, the overall leaf disc technology is already a mature general technology, but the overall weight reduction effect is the overall leaf ring technology.

  Removing the wheel part of the whole leaf disc becomes the integral leaf ring; due to the lack of the load-bearing wheel, the integral leaf ring can not withstand the centrifugal load of the blade, therefore, the overall leaf ring can only use the composite material with less density. To manufacture. At present, the whole leaf ring being developed is made of continuous single silicon carbide (SiC) long fiber reinforced titanium matrix composite (TiMMC) [5~7], which has high strength, high temperature and fatigue and creep properties. Good advantage.

  The TiMMC integral leaf ring replaces the compressor disc, which not only expands the design range of the compressor, but also greatly reduces the weight. Compared with the conventional wheel and blade structure, the overall leaf disc can reduce the weight by 30%, while the overall leaf ring can Reduce the weight by 70% [4~8].

  Application of integral leaf ring structure

  The continuous fiber-reinforced MMC integral leaf ring structure has received great attention and development from the world’s aero motor design and manufacturer.

  The application of American continuous fiber reinforced MMC to the overall leaf ring of the compressor began in the 1980s. The US Air Force, Garrett, AADC, GEAE, and P·W have done a great deal of work in feasibility studies, manufacturing processes, and test validation. In the early 1990s, under the IHPTET research program, AADC designed and tested the third and fourth stages of the XTC-16 series core machine 4-stage compressor with a silicon carbide-reinforced TiMMC integral leaf ring. The mass of the integral leaf ring rotor is greatly reduced, for example, the mass of the third stage integral leaf ring rotor is only about 4.5 kg, and the actual mass of the same rotor made of the conventional nickel base alloy is 25 kg. In the mid-1990s, under the IHPTET research program, GEAE developed and validated the overall leaf ring of the TiMMC compressor. The ATEGG verification machine XTC76/2 core machine 5-stage high-pressure compressor developed by the company and AADC company uses the outer ring-enhanced MMC compressor rotor to meet the requirements of high speed and high temperature, which reduces the quality of the disk and reduces the manufacturing. Cost, improved maintainability. The second phase of the IHPTET program uses TMC integral leaf ring technology on the verification machine high pressure compressor. The blade material of the whole leaf ring to be verified in the third stage of the IHPTET plan is a γ-titanium-aluminum intermetallic compound, and the drum is a SiC-reinforced reinforced titanium-based composite material, which is made by a bonding process, and its weight is only a conventional metal material drum. 30% of the structure.

  In the 1990s, aero-motors in European countries began to study high-strength, high-rigidity, low-density SiC fiber-reinforced titanium alloy-based composite monolithic rotor rings. The silicon carbide fiber reinforced TiMMC integral leaf ring rotor developed by MTU of Germany [9] has completed the low cycle fatigue rotation test and is planned to be applied to the first two stage high pressure compressor of the EJ200 modified motor with a weight ratio of 15~20. The overall leaf disc structure of the lift fan studied by the Luo Luo Company for the F136 motor will eventually be replaced by the integral leaf ring structure. SNECMA of France also used the method of coating the fibers on the substrate to manufacture the SiC fiber reinforced titanium alloy matrix composite compressor integral leaf ring insert.

  In the development plan of Advanced Material Gas Generator (AMG) launched in Japan in 1993, the high-pressure compressor titanium-based composite integral leaf ring was processed by hot pressing and hot isostatic pressing method [10], and the fracture test was successfully completed. And the cycle life spin pit test, verifying its burst strength and target life. Japan developed and validated the silicon carbide fiber (SCS-6) reinforced titanium base (SP-700) processed by the substrate-coated single ribbon process under the launch of the next-generation supersonic transporter environmental propulsion system development (ESPR) program in 1999. Composite fan integral leaf ring rotor.

  In the international cooperation research project between China and India, there is a single-stage fan test with a hoop. The design parameters of the fan are: boost ratio 3.0, tip tangential speed 470m/s, 17 blades, outer diameter 0.4m, using a composite overall leaf ring structure with an outer hoop, India has successfully manufactured the test piece, and is in a leading position internationally.

  Selection of integral leaf ring structure materials

  The silicon carbide continuous fiber reinforced titanium matrix composite combines the plasticity and formability of the base titanium alloy with the superior load carrying capacity and rigidity of the reinforcement SiC fiber, and has excellent comprehensive properties not found in a single alloy, and has high specific strength and specific stiffness. High, good high temperature resistance, creep resistance, fatigue performance, etc. It is ideal for lightweight high temperature resistant structural materials for aero motors with high thrust-to-weight ratio (15~20) medium and high temperature (600~800°C) [13- 14].

  Due to the high specific strength and specific stiffness along the fiber direction at high temperatures, the single filament reinforced composite has the advantage of being applied to components of an aviation turbofan motor. Continuous single SiC filament reinforced TiMMC is manufactured as a whole leaf. The ideal material for the ring. Typically, low temperature components of the motor, such as shafts and casings, and low pressure rotors are manufactured using single filament reinforced TiMMC, while high temperature turbine components are fabricated from single filament reinforced intermetallic matrix composites. At present, the main reason for hindering the large-scale entry of fiber-titanium alloy into the space technology market is that the material manufacturing process is complicated and expensive. In its development process, the emergence of high-strength and high-modulus continuous silicon carbide crude fiber has played a big role in promoting.

  1 Selection of reinforcing fibers

  The mechanical properties of TiMMC are closely related to the properties and content of SiC fibers, the properties of the matrix titanium alloy, the preparation process and the interface state of the fiber/matrix.

  Generally, the volume content of the fibers in the composite is in the range of 25% to 45%, and preferably about 35% [16-17]. Compared with titanium alloys, TiMMC has extremely high strength and stiffness in the fiber arrangement direction, while the lateral stiffness does not change, but the lateral strength decreases. And as the fiber volume ratio increases, the longitudinal tensile strength and elastic modulus of the composite increase, but decrease or change little in the transverse direction.

  In the case of a given fiber content, the coarse fiber can increase the distance therebetween, which is beneficial to reduce the tendency of the fiber to generate radial cracks in the high temperature composite consolidation process and to fully exert the toughness effect of the titanium matrix. At present, the crude fiber prepared by the chemical vapor deposition method (CVD) has a certain residual stress, and in consideration of economy, the continuous fiber diameter of the reinforced titanium alloy is preferably 0.12 to 0.15 mm.

  SCS-6 fiber produced by Textron Company of the United States has high antioxidant capacity and good structural stability, and is the most ideal reinforcement of titanium matrix composites [19]. The performance parameters are shown in Table 1. It is a continuous silicon carbide fiber (carbon core) with a diameter of about 140 μm, and a carbon-rich layer (about 3 μm thick) on the outer surface, in which SiC exhibits non-stoichiometric composition and amorphous state. And the silicon content peaked at about 1.5 μm from the outer surface. This structural feature of the surface layer makes the SCS-6 fiber not only have good compatibility with the titanium matrix, but also has no significant change in strength after high temperature composite consolidation treatment.

  SCS-6 fiber has high strength properties, tensile strength at room temperature of about 4,500 MPa, and elastic modulus of 400 to 415 GPa. Compared with general CVD-prepared SiC fibers, the tensile strength of SCS-6 fibers after exposure to air at 1100 ° C for 15 min in Ar or N 2 atmosphere; tensile strength at 600-1400 ° C (for 15 min) in O 2 atmosphere It is also relatively high. This indicates that SCS-6 fiber has high resistance to oxygen attack and good structural stability.

  2 Selection of base titanium alloy

  The density of titanium is 4.5g/cm3, which is only 56% of steel, which meets the light material requirements of aviation products. The tensile strength of titanium alloy is 500~1400MPa, which is much higher than that of Al and Mg alloys; Excellent high-temperature performance, can maintain long-term performance at 550 °C high temperature and maintain the same performance, titanium deposit is 10 times that of copper, is the “third metal” after iron and aluminum. It is rich in resources, but its industrial production has only been more than 60 years. It is aptly called “baby metal” compared with aluminum and magnesium with a history of 100 years. Titanium alloy has low density, high specific strength, high specific stiffness, good corrosion resistance, high temperature mechanical properties, fatigue resistance and creep resistance. It has excellent comprehensive performance and is a new type with great development potential and application prospects. Structural material.

  In theory, α-type, α+β-type and β-type titanium alloys can be used as the composite matrix. However, continuous fiber reinforced composite materials often take into account the requirements of the manufacturing process and take into account factors such as performance and cost, and pay more attention to the α+β type and metastable β type titanium alloy which are easy to process into foil and can be aged. The titanium alloy foil currently used as a matrix of a composite material is generally 0.08 to 0.38 mm thick, preferably about 0.13 mm.

  Since different titanium alloys will show their best performance in different temperature ranges [22], in the design of the motor, the appropriate titanium alloy should be selected according to the operating temperature of the motor parts to ensure the safe operation of the motor. The commonly used Ti-6Al-4V can work at 350 °C for a long time. Therefore, Ti-6Al-4V alloy can be used in the motor fan and low pressure compressor. TC11 can work at 500 °C for a long time. It can be used in the high pressure compressor part of the motor. An alloy such as TC11 is used.

  SCS-6 fiber [20] has high strength properties, tensile strength at room temperature of about 4,500 MPa, and modulus of elasticity of 400 to 415 GPa. Compared with general CVD-prepared SiC fibers, the tensile strength of SCS-6 fibers after exposure to air at 1100 ° C for 15 min in Ar or N 2 atmosphere; tensile strength at 600-1400 ° C (for 15 min) in O 2 atmosphere It is also relatively high. This indicates that SCS-6 fiber has high resistance to oxygen attack and good structural stability.

  2 Preparation of composite rings

  There are still considerable difficulties in the manufacturing process of fiber reinforced titanium matrix composites. The key issue is how to make the active titanium matrix and fiber have a short duration of action, ie how to expose the fiber to a high temperature titanium matrix for a short period of time. The main processes for preparing a fiber-reinforced titanium-based composite ring are generally: a foil-fiber-foil (FFF), a substrate-coated pre-formed tape (MCM), and a substrate-coated fiber (MCF). However, the high cost of the manufacturing process is the biggest obstacle encountered in the above process.

  The Oxford Advanced Materials and Composites Center (OCAMAC) study [26] used a plasma spray method to fabricate a composite unidirectional tape, and sprayed the Ti-6Al-4V alloy onto a wound single-layer SiC fiber, which was then cut, layered and Hot pressed into a test piece under vacuum. In the sprayed state, titanium has no interfacial reaction with the fiber, and the fiber has only a small amount of shrinkage during consolidation, and the interfacial reaction after consolidation is equivalent to some existing layup and consolidation methods. Based on this research, the OCAMAC Center developed a filament winding and spray parallel process that can form a multilayer SiC reinforced ring with a density of 95% at a time. When spraying, the drive unit is sealed in a steel shell that is installed in the spray booth to prevent the filament winding system from being attacked by hot gases and dirt. After obtaining a given number of layers, cutting the fibers, and depositing the outermost layer, the desired ring is obtained.

  Japan’s A. Kono et al. have developed a relatively economical manufacturing process with a filament winding and spraying process and a substrate-coated single ribbon process to produce a silicon-based fiber (SCS-6) reinforced titanium-based (Ti-4.5Al-3V). -2Fe-2Mo) composite ring, and successfully completed the tensile test and the over-rotation test to compare the performance of the composite ring produced by the two processes, and found that the composite material produced by the fiber spray/winding method The reinforcing effect of the fiber in the ring on the matrix is ​​not significant; the composite ring made by the single-coating process of the substrate has made significant progress in tensile strength and deformability. Therefore, the substrate coated single ribbon process is used to manufacture the composite material. Ring preform.

  At present, the immature manufacturing process of the whole leaf ring, the high manufacturing cost of silicon carbide fiber and the difficulty in repairing the blade after damage are the main factors hindering the development of the overall leaf ring structure, but with the continuous development of material technology, the continuous advancement of technology Novel lightweight structures such as integral leaf rings are expected to be widely used in future aero motors. Foreign countries have carried out research work on the whole leaf ring, and have been applied in low pressure compressors; the research work of China’s overall leaf ring has just begun, and there is a big gap with foreign countries. We must adopt phased plan and step by step. The research method implemented is a systematic study combining parts design, material development and applied technology research