A system and method for reducing the cost of producing a brushless DC
motor (58) is presented. The brushless DC motor (58) provides higher
power density and efficiency with an increased tool run time. The
brushless DC motor (58) includes a rotor assembly (72) that has an
unmagnetized permanent magnet (74) affixed to a shaft. The permanent
magnet (74) remains unmagnetized until the motor is partially assembled.
A plurality of coils (94) for producing a magnetic field are wound about
the rotor assembly (72). The coils (94) include end turns that enclose
the rotor assembly (72) such that the rotor assembly (72) is not
removable. Since the windings (94) are wound with the rotor assembly (72)
already enclosed, the windings (94) do not require large end coils to
allow subsequent insertion of the rotor (72). Minimizing the end coils
reduces the length of wire required per turn, thereby reducing the
resistance of the winding (94). Also, since the permanent magnet (74) is
unmagnetized when the coils (94) are wound around the rotor assembly (72)
the winding process is simplified by not coupling energy into the wire
which would influence the winder operation. The wound assembly is
inserted into a stator stack (96) comprised of magnetic material that
provides a magnetic flux return path for the magnetic flux generated by
the permanent magnet (74). Using an unmagnetized permanent magnet (74)
facilitates easy insertion of the wound assembly into the stator stack
(96), reduces the accumulation of magnetic debris during the
manufacturing process, and permits the motor assembly to be sealed prior
to magnetizing the permanent magnet (74).