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).