Design Guide
Manufacturing
Methods
Permanent
magnets are manufactured by one of the following methods:
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Sintering,
(Rare Earths, Ceramics, and Alnicos)
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Pressure
Bonding or Injection Molding, (Rare Earths and
Ceramics)
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Casting,
(Alnicos)
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Extruding,
(Bonded Neodymium and Ceramics)
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Calendering
(Neodymium and Ceramics)
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The
sintering process involves compacting fine powders at
high pressure in an aligning magnetic field, then sintering
to fuse into a solid shape. After sintering, the magnet
shape is rough, and will need to be machined to achieve
close tolerances. The intricacy of shapes that can be
thus pressed is limited.
Rare
Earth magnets may be die pressed (with pressure being
applied in one direction) or isostatically pressed (with
equal pressure being applied in all directions). Isostatically
pressed magnets achieve higher magnetic properties than
die pressed magnets. The aligning magnetic field for
die pressed magnets can be either parallel or perpendicular
to the pressing direction. Magnets pressed with the
aligning field perpendicular to the pressing direction
achieve higher magnetic properties than the parallel
pressed form.

Both
Rare Earth and Ceramic magnets can also be manufactured
by pressure bonding or injection molding the magnet
powders in a carrier matrix. The density of magnet material
in this form is lower than the pure sintered form, yielding
lower magnetic properties. However, bonded or injection
molded magnets may be made with close tolerances "off-tool"
and in relatively intricate shapes.
Alnico
is manufactured in a cast or sintered form. Alnicos
may be cast in large or complex shapes (such as the
common horseshoe), while sintered Alnico magnets are
made in relatively small sizes (normally one ounce or
less) and in simple shapes.
Flexible
Rare Earth or Ceramic magnets are made by calendering
or extruding magnet powders in a flexible carrier matrix
such as vinyl. Magnet powder densities and therefore
magnetic properties in this form of manufacture are
even lower than the bonded or injection molded form.
Flexible magnets are easily cut or punched to shape.
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