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High Performance Bonded Neo Magnets using High Density Compaction

High Performance Bonded Neo Magnets using High Density Compaction. J. Herchenroeder, D. Miller, N. K. Sheth, C. Foo, D. Brown and K. Nagarathnam. Introduction.

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High Performance Bonded Neo Magnets using High Density Compaction

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  1. High Performance Bonded Neo Magnets using High Density Compaction J. Herchenroeder, D. Miller, N. K. Sheth, C. Foo, D. Brown and K. Nagarathnam

  2. Introduction • A compression bonded Neo magnet is comprised of NdFeB powder, epoxy and additives conducive to magnet manufacture such as curing agents, coupling agents and lubricants. • Typical magnet densities: 5.8-6.1 g/cm3 • Typical (BH)max of compression molded magnet 8-10 MGOe. • The theoretical density of a compound of magnetic powder and organic binders: 6.9 g/cm3 Higher (BH)max can be obtained if density were increased during molding. • To achieve compact, lighter and efficient products in applications like pumps, power tools, BLDC motors and consumer products a magnet with (BH)max of 11-12 MGOe will help.

  3. Introduction • Magnet (BH)max of 11-12 MGOe  Compact, lighter and efficient end products for applications like pumps, power tools etc. • How to increase density of magnet? • Reduce the percentage of the epoxy binder. • Binder is important to achieve good mechanical strength and magnet integrity. • Increase Compaction pressure. • Frictional forces encountered during pressing put constrain on the magnet geometries (Length of few mm). • Innovative approach to powder compaction called Combustion Driven Compaction (CDC). • Magnet density of 6.5 g/cm3 can be achieved.

  4. What is Combustion Driven Compaction (CDC)? Gas Inlet + • A pressurized mixture of natural gas and air is introduced into the combustion chamber • The mixture is then ignited to drive a piston (ram) • A punch is driven downward by the piston into the metal powder, transferring energy into and compacting the powder • CDC converts chemical energy directly to mechanical energy for high efficiency! • The entire process is smooth and continuous, keeping constant pressure on the part at all times - Electric Ignition US Patent 6,767,505 Natural Gas (CH4) & Air at “High” Pressure One moving part! Powder Die

  5. The CDC Load Cycle can be tailored • Fill gas creates pre-load pushing the piston or ram down, pre-compressing and removing entrapped air from the powder • An ignition stimulus is applied causing combustion and rapid pressure rise, further compressing the metal powder to its final net shape. Peak loads, 30 - 250 tsi Load Significant pre-load from gas fill, 15 –20 tsi The process, although fast and powerful, is smooth and continuous Time

  6. Applied Load (Tsi) 20 40 60 80 100 120 140 160 7.8 98.6 % dense 7.6 7.4 Green Density (g/cm3) 7.2 Typical compaction load with other presses 7.0 6.8 Single press at room temperature with die wall lubricant (Zinc Stearate) 6.6 1103 276 552 827 1379 1655 1931 2206 Applied Load (MPa) CDC Compact Properties Powder metal part density increases with load (without lubricant in powder). Green density versus load for F-0000 powder presses using CDC

  7. CDC benefits • Improved green density • Waste heat can be used for cogeneration heating or cooling the work place. • Energy comes directly from natural gas not from a power plant. • The physical size of a CDC press is only a fraction of a conventional press – a 400 ton press is the size of a phone booth • When operating, CDC makes little or no sound 80 inches tall 50 inches square ~12000 lbs

  8. Results of 15 x 13mm cylindrical magnets • Density = 6.5 g/cm3 • Br = 7.7 kG • (BH)max = 11.7 MGOe

  9. Effect of Different Magnets on Seat Motor Performance • Ring magnets using CDC were made from MQLP-B+™ powder with 1% epoxy, compacted with an average of 20 tonne/cm2 pressure and cured at 160C for 1 hour in argon gas. • Ring magnet dimension Magnet produced using CCM Magnet produced using CDC

  10. Effect of Different Magnets on Seat Motor Performance - Measurement of Magnet Density • Wet-Dry method is used, Magnet produced using CDC has 5.8% higher density.

  11. Effect of Different Magnets on Seat Motor Performance - Magnetization of the Isotropic Bonded NdFeB Magnets Magnet Laminated back iron Magnetic Fixture Hall sensor or probe Motor housing Magnetizing current pulse Center iron piece Magnet Magnetization of the Magnets in presence of laminated back iron Closed Magnetic Circuit for Mid Airgap Flux Measurement

  12. Effect of Different Magnets on Seat Motor Performance - Magnetization of the Isotropic Bonded NdFeB Magnets Magnet Saturation analysis during magnetization Mid airgap Flux Density for the Closed Magnetic Circuit

  13. Effect of Different Magnets on Seat Motor Performance - Motor Testing • Magnets were assembled in a seat motor. • The motors with following three types of magnets were tested to achieve the performance including back-emf constant, and the performance was compared at room temperature before and after thermal aging in which motors were kept (un-operational) in an oven at 120 C for 24 hours. • Anisotropic Neo (Original magnet in the motor) • Isotropic bonded neo made using CCM • Isotropic bonded neo made using CDC

  14. Effect of Different Magnets on Seat Motor Performance - Test Setup for Motor Testing Measurement of back-emf constant Dynamometer Test Setup for Motor Characteristics Measurement

  15. Effect of Different Magnets on Seat Motor Performance - Motor Performance before Thermal Aging Motor efficiency and output power at various load torques before thermal aging of the magnets Motor current and speed at various load torques before thermal aging of the magnets

  16. Effect of Different Magnets on Seat Motor Performance - Back-emf Constant before/After Thermal Aging at 120 C for 24 hrs. • The motor with anisotropic neo magnet has 11.9% higher back-emf constant compared to the isotropic magnet produced by CCM. • The use of isotropic magnet produced by CDC reduces the difference to 6.0%. This is due to the improved magnet density for CDC compared to CCM.

  17. Effect of Different Magnets on Seat Motor Performance - Back-emf Constant before/After Thermal Aging at 120 C for 24 hrs • To study the effect of thermal aging on various magnets and then on the motor performance, the test motors were kept in an oven at 120 C for 24 hrs and then again the Back-emf constant (kb) and motor performance was evaluated. • Reduction in Back-emf constant (kb) is the highest at 2.65% for the anisotropic Neo magnet compared to 1.26% and 2.12% for isotropic bonded Neo magnets produced using CCM and CDC method respectively. • Thermal aging reduces the difference in performance for anisotropic Neo and isotropic bonded Neo from CDC method.

  18. Effect of Different Magnets on Seat Motor Performance - Motor Performance after Thermal Aging at 120 C for 24 hrs Motor efficiency and output power at various load torques before thermal aging of the magnets at 120 C for 24 hrs. Motor current and speed at various load torques after thermal aging of the magnets at 120 C for 24 hrs.

  19. Conclusions • The net shaped and thin walled ring magnet produced using CDC technology has much higher density, 6.22 g/cm3, compared to the isotropic bonded Neo magnets produced commercially by CCM, 5.88 g/cm3, an increase of 5.8%. • The airgap flux for the magnet produced by the proposed method is 6% more compared to the commercial isotropic bonded Neo magnet. • At room temperature the performance of the motor with the anisotropic magnet is comparable to the motor with the isotropic bonded Neo magnet produced by proposed CDC method, but after exposure to high temperature the difference is further reduced.

  20. Conclusions • Bonded Neo magnets using CDC exhibits superior thermal aging stability compared to anisotropic neo magnets. • Isotropic bonded Neo magnets produced by CDC will be the ideal choice for applications where good thermal stability is required and where slightly higher magnetic property is needed compared to conventional bonded Neo

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