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

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: g/cm 3  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/cm 3  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 MGOe will help.

Introduction  Magnet (BH) max of 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/cm 3 can be achieved.

What is Combustion Driven Compaction (CDC)? + - Gas Inlet Electric Ignition PowderDie One moving part! Natural Gas (CH 4 ) & Air at “High” Pressure 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 US Patent 6,767,505

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. The process, although fast and powerful, is smooth and continuous Load Significant pre-load from gas fill, 15 –20 tsi Peak loads, tsi Time

CDC Compact Properties Powder metal part density increases with load (without lubricant in powder). Applied Load (MPa) Green Density (g/cm 3 ) Single press at room temperature with die wall lubricant (Zinc Stearate) 98.6 % dense Typical compaction load with other presses Applied Load (Tsi) Green density versus load for F-0000 powder presses using CDC

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

Results of  15 x 13mm cylindrical magnets Pressure tonne/cm 2 Density g/cm 3 (BH) max MGOe H ci kOe  Density = 6.5 g/cm3  B r = 7.7 kG  (BH) max = 11.7 MGOe

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/cm 2 pressure and cured at 160  C for 1 hour in argon gas.  Ring magnet dimension Outer DiameterThicknessLength mm1.50 mm25.30 mm Magnet produced using CDC Magnet produced using CCM

Effect of Different Magnets on Seat Motor Performance - Measurement of Magnet Density  Wet-Dry method is used, Process Density g/cm 3 (BH) max MGOe B r kG CCM CDC Magnet produced using CDC has 5.8% higher density.

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

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

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. 1.Anisotropic Neo (Original magnet in the motor) 2.Isotropic bonded neo made using CCM 3.Isotropic bonded neo made using CDC

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

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

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. Type of Magnet Anisotropic Neo (Original Magnet in Motor) Isotropic Neo using CCM Isotropic Neo using CDC k b (mV/rpm) before thermal aging k b (mV/rpm) after thermal aging at 120 

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 (k b ) and motor performance was evaluated.  Reduction in Back-emf constant (k b ) 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.

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

Conclusions  The net shaped and thin walled ring magnet produced using CDC technology has much higher density, 6.22 g/cm 3, compared to the isotropic bonded Neo magnets produced commercially by CCM, 5.88 g/cm 3, 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.

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