Advanced manufacturing resources, techniques and lower prices portend further growth.

Neodymium-iron-boron processing

The market for permanent magnet motors such as DC brushless and induction motors has grown significantly, especially in the last 40 years. This market growth, coupled with price decreases in electronics and permanent magnet materials, have presented designers with an increased demand for a motor that is more cost effective. Yet many designers continue to view permanent magnets as a commodity item, and are not aware of the benefits of certain high-energy magnets that can help motor applications maintain high torque and a low profile while reducing the total system cost.

Permanent magnets have steadily become an indispensable component in products such as DC brushless and induction motors for household appliance and portable power tools; spindle motors for computer storage devices; small motors in copiers, printers and fax machines; and electric fuel pumps, sensors, and generators in automobiles. No other magnetic material possesses higher energy density than magnets made from neodymium-iron-boron (NdFeB or Neo for short), which enable motors to have smaller size, greater torque and greater efficiency. This characteristic has revolutionized an engineer’s ability to improve designs across nearly all industries. Such advances helped spur the Neo market into an exponential growth mode since its introduction almost 15 years ago, with expected levels reaching just short of $2 billion worldwide in 1999. Increases of more than 16 percent annually are expected until 2005.

The benefits of smaller, lighter motors in high-tech products have outweighed the component cost considerations. A total system value approach enabled the innovative designs of many small motor applications, and gave companies such as Matsushita, Toshiba, Sony, and Canon an additional technological edge in their respected markets. With the enabling technology of Neo magnets, computer disk drives, fax machines, flatbed scanners, copiers and laser printers became indispensable products. The growth of these applications and the accompanying productivity and process improvements has driven magnet costs substantially lower.

Neo magnets continue to play an essential role in technological advances in an increasing range of industries by offering diverse magnet manufacturing processes. The rare-earth magnet can be processed by powder metallurgy (crushing, pressing and sintering), gas atomization or rapid quenching and pressing. Sumitomo Special Metals Co., Ltd., Osaka, Japan, holds the patents for the powder metallurgy process and Magnequench, Inc., Anderson, Ind., holds the patents for the gas atomization and rapid quenching process.

In the rapid quenching process, molten NdFeB alloy is ejected onto a chilled, rotating metallic wheel. The alloy cools or quenches as it hits the wheel, rapidly solidifying into ribbon-like flakes, which are crushed to form NdFeB powder. Compared to the powder produced by the metallurgy process, the rapidly quenched powder is considerably coarser and has an ideal microstructure for making a magnet. The powder is used to produce bonded or hot-pressed magnets that are used in various motion control applications.

Bonded magnets are produced by combining the powdered alloy with an epoxy or thermoset resin and molded through either compression or injection molding techniques. Hot-pressed magnets are produced by cold pressing the powdered alloy to a form and then hot pressing at around 750ºC to increase density. This process is remarkably different from sintering because it uses fewer steps in the production process and does not use an orienting magnetic field, yet still achieves similar magnetic properties. In either case, bonded or metal magnets can be made to the net final shape without expensive grinding, unlike sintered magnets.

Injection molding high-energy Neo magnets is the most recent development within the magnet industry. Injection molding capabilities allow manufacturers to create intricate magnet subassemblies that are custom made for each individual application. Injection molding enables design applications to be more flexible by allowing the engineer to specify varied, complex shapes and tight tolerances not easily achieved by other manufacturing processes. The injection molding process of Neo magnets has enabled custom, innovative designs in power hand tools, servo devices and automotive applications that have higher power and efficiencies at a total cost low enough to use in new applications and even justify redesigning existing applications.

Manufacturing low total cost

Using Neo magnets gives design engineers more freedom and creativity to define a more robust design for new applications and redesigns of existing applications. In general, Neo magnet motors are smaller and have greater torque, providing enough benefits to justify the redesign of existing motor platforms. Designers are now using the materials to achieve a competitive advantage in their particular market. A prime example illustrating this is the partnership of Magnequench with a large international appliance manufacturer.

The company had an existing 24V DC motor using ferrite arcs in a typical 2-pole configuration, and wanted proof of the benefits of substituting Neo for ferrite. The goal was to improve the power density of the motor: more power for the same frame size; or a smaller frame size for the same power. The motor had a maximum operating temperature ranging from 150░C to 160░C, so a bonded Neo magnet would need a suitable binder and use a Neo powder with inherent temperature resistance.

In pursuing more power for the same frame size, Magnequench evaluated three different designs using injection molded and compression molded magnets. In each case, the magnet outer diameter (OD) dimension was optimized to maximize the air-gap field, the rotor teeth were slightly widened to accommodate the extra flux, and the slots were also slightly reshaped to retain the winding area. In this case, the optimum design was an injection molded ring magnet that yielded at maximum torque a 15 percent improvement in speed, efficiency and output power. Injection molded and magnetized in the stator housing, the bonded Neo provided a reduction in manufacturing and assembly cost over the multiple steps for magnetizing, gluing and curing the ferrite arcs, providing higher output power for the similar total cost.

As the cost of materials continues to drop and applications of Neo magnets in all types of motor-design applications continues to soar, the projections for NdFeB market growth will continue at exponential levels.