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Bonded Neo Magnetization Guide Dr. Nimit Sheth, Christopher Foo and David Mille

Bonded Neo Magnetization Guide Dr. Nimit Sheth, Christopher Foo and David Miller Magnequench Technology Center, Singapore A Division of Neo Material Technologies Inc. Magnequench -All Rights Reserved Presentation Outline 1. Magnetizing Systems 2. Fixture Design 3. Construction 4. Testing 5. Design Study A Division of Neo Material Technologies Inc. Magnequench -All Rights Reserved Magnetizing Systems •A typical magnetizing system consists of a magnetizer and a fixture. One magnetizer is suitable for many different applications, while a fixture is usually custom made for each application •Magnetizing may be performed at many points in the manufacturing process (magnet, magnetic sub-assembly, or fully assembled product) •Fixture designs range from simple solenoids to very complex multi-pole arrangements •For best results magnetization should be considered when designing an application Magnetizer Magnetizing Fixture Applications requiring magnetization A Division of Neo Material Technologies Inc. Magnequench -All Rights Reserved The Magnetizer is the power supply of a magnetizing circuit. A single magnetizer may be suitable for many different applications. Types of magnetizers include: •Capacitive discharge •Half cycle •Permanent magnet (No Power Required) Capacitive discharge magnetizers are the most common and are specified by: •Maximum operating voltage •Maximum capacitance •Special options Magnetizers which magnetize ferrite sometimes do not have enough energy to fully magnetize bonded Neo. Magnetizing Systems Magnetizer Important A Division of Neo Material Technologies Inc. Magnequench -All Rights Reserved Fixtures are generally application specific and are specified by: •Magnet material •Magnet material orientation •Magnetization orientation •Number of poles •Magnet geometry •Cycle rate (water cooling for faster rates) •Magnet calibration (if desired) Magnetizing Systems Fixture A Division of Neo Material Technologies Inc. Magnequench -All Rights Reserved Outer-diameter Halbach Multi-pole axial Uni-polar radial Inner-diameter Halbach Diametrical Axial Surface magnetization Magnetizing Systems Fixture Fixtures can be designed for many types of pole configurations A Division of Neo Material Technologies Inc. Magnequench -All Rights Reserved Fixtures can be integrated into automated part handling systems. Possibilities include: •Fully automated magnetization •In-line testing (quality check) •Calibration •Safety Features Magnetizing Systems Fixture A Division of Neo Material Technologies Inc. Magnequench -All Rights Reserved Magnetizing Systems RLC Circuit When a magnetizing fixture is coupled to a capacitive discharge magnetizer the system forms an RLC circuit. A Division of Neo Material Technologies Inc. Magnequench -All Rights Reserved 0 5000 10000 15000 20000 25000 30000 0.00 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00 milliseconds Amperes per mm2 Conventional Magnetizing High-Current Ultra High-Current The RLC circuit of the magnetizing system results in a half-sinewave current pulse in the copper wire windings of the fixture. Conventional pulse widths are 2 to 4 milliseconds. Lower impedance systems allow for higher peak currents due to their shorter pulse widths Magnetizing Systems RLC Circuit A Division of Neo Material Technologies Inc. Magnequench -All Rights Reserved Typical Current Pulse Fixture for OD magnetization of 6-pole 40mm diameter ring Magnetizing Systems RLC Circuit A Division of Neo Material Technologies Inc. Magnequench -All Rights Reserved Presentation Outline 1. Magnetizing Systems 2. Fixture Design 3. Construction 4. Testing 5. Design Study A Division of Neo Material Technologies Inc. Magnequench -All Rights Reserved Halbach Radial Straight Radial-flux motor magnets are commonly magnetized with one of three basic orientations 1.Straight – Flux lines are parallel and unconstrained by magnet geometry 2.Radial – Flux enters and exits the ring along a radial vector 3.Halbach – Flux orientation is continuously rotating with respect to the magnet Magnetizing Fixture Design Magnet Orientation A Division of Neo Material Technologies Inc. Magnequench -All Rights Reserved Halbach Radial Halbach and radial magnet orientations are shown on the left. The resulting flux profiles in the air gap are shown in the chart below. Magnetizing Fixture Design Magnet Orientation Magnet Back Iron A Division of Neo Material Technologies Inc. Magnequench -All Rights Reserved Bonded magnets made from HDDR and MQA powders are anisotropic. Sintered ferrite and sintered Neo are also typically anisotropic. Anisotropic magnets have enhanced properties in a specific direction and must be oriented during magnet manufacturing. It is typically not necessary to consider orientation when designing a magnetizing fixture for an anisotropic magnet, because the orientation has already been fixed. Even though the magnetizing field is straight the magnet keeps the radial orientation that it received during the magnet manufacturing process. Magnetizing Fixture Design Anisotropic, or oriented material Radial material orientation denoted by black arrows Magnetizing field is relatively straight Orientation is radial in the motor A Division of Neo Material Technologies Inc. Magnequench -All Rights Reserved Magnets made from MQP are Isotropic. Isotropic magnets have uniform properties in all directions, so there is no need to orient them during magnet manufacturing. It is highly important to consider orientation when designing a magnetizing fixture for an isotropic magnet, because the orientation will be determined during the magnetization process. Fixtures designed for anisotropic magnets typically will not properly magnetize isotropic magnets. In the isotropic magnet a straight magnetizing field results in a straight magnet orientation. Magnetizing Fixture Design Isotropic, or non-oriented material The orientation denoted by the black arrows is identical to the orientation of the magnetizing field Magnetizing field is relatively straight Orientation in the motor is straight, as it was determined by the magnetizing field. Important A Division of Neo Material Technologies Inc. Magnequench -All Rights Reserved Magnetized magnet without skew magnetized Magnetized magnet with skew magnetized Straight pole transition zone Shifted pole transition zone Magnetizing Fixture Design Skewed Magnetization A magnetizing fixture can be designed to skew the transition zone. This is typically done to reduce cogging or noise in a motor. A Division of Neo Material Technologies Inc. Magnequench -All Rights Reserved Skewed magnetization on the magnet helps in reducing the cogging torque. Skewing the magnet is simpler than skewing the armature. Magnetized magnet with and without skewing Normalized Cogging Torque for skewed and non-skewed magnetization Magnetizing Fixture Design Skewed Magnetization A Division of Neo Material Technologies Inc. Magnequench -All Rights Reserved Magnetizing Fixture Design Skewed Magnetization The proper skew angle is determined by the number of slots on the armature. Typically a skew angle is [360°/ # of slots] or [180° / # of slots]. The second formula results in a smaller angle and is more commonly used, since larger skew angles result in greater reduction in the output torque of a motor. The proper measure of the skew angle is defined in the figure on the left. Important Proper skew angle is important, and improper skew angle will result in poor motor performance. A Division of Neo Material Technologies Inc. Magnequench -All Rights Reserved Magnetizing Fixture Design Applied Field Required for Full Magnetization Note that a magnetizing system designed to magnetize ferrite will likely not be capable of full magnetization of bonded Neo. Important Intrinsic flux density vs Magnetizing Field (cylindrical magnet 9.7mm diameter x 6.3mm length) A Division of Neo Material Technologies Inc. Magnequench -All Rights Reserved 3 to 4 Tesla is required for full magnetization of bonded Neo. Therefore steel in a bonded Neo fixture becomes partially or fully saturated during the current pulse and will not focus flux the way that it tends to do in ferrite magnetizing fixtures – saturated steel has the same permeability as air. Fixtures designed for ferrite often will not give proper orientation to bonded Neo magnets. For this reason the shape of a steel pole in a bonded Neo fixture is relatively unimportant. Magnetizing Fixture Design Steel is saturated in bonded Neo fixtures In the regions near the red conductors flux lines can be seen to exit the blue steel regions at non-orthogonal angles. This is due to the steel’s being saturated and having the same permeability as air. Important Important The most important considerations when designing a bonded neo fixture are: •Location of conductor •Shape of conductor •Current density of conductor These items should be considered first in the design process. A Division of Neo Material Technologies Inc. Magnequench -All Rights Reserved Due to B-fields well above 3 Tesla the steel in a bonded neo fixture is saturated and has only three purposes: 1.Decrease the amount of current required to produce a given B-field. 2.Improve the mechanical strength of the fixture. 3.Improve the cooling efficiency of the fixture. Steel is often very useful for all of the above purposes. Therefore, steel is often used in bonded neo fixtures. Magnetizing Fixture Design Steel is useful even though it is saturated Even though the steel above is saturated it reduces the conductor current necessary for magnetization, enhances the fixture’s mechanical strength, and improves cooling efficiency. A Division of Neo Material Technologies Inc. Magnequench -All Rights Reserved If steel is used it should be laminated and not solid. With solid steel there may be significant eddy current losses. Magnetizing Fixture Design Steel should be laminated The effect of eddy currents is seen in the comparison of these two pictures. The same fixture design is shown at the time of peak field in the magnet using an identical color scale. The fixture on the right has a solid steel outer pole piece, while the fixture on the left has a laminated steel uploads/Management/ magnetizing-guide.pdf