Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
2001-12-13
2004-06-08
Trinh, Minh (Department: 3729)
Metal working
Method of mechanical manufacture
Electrical device making
C029S596000, C029S598000, C029S732000, C029S738000, C310S216006, C310S216055
Reexamination Certificate
active
06745458
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to laminated parts. More particularly, the present invention relates to lamina stacks, and especially long, slender lamina stacks, formed by stamping a plurality of lamina layers from a sheet or strip of stock material and the methods and apparatuses, i.e., progressive dies, used in the manufacture of such laminated parts.
2. Description of the Related Art
The manufacture of parts, e.g., stators and rotors for electric motors, employing stacked laminae is well known in the art. Typically, the laminae are blanked from a continuous strip stock and then stacked and bound together to form the completed part. Progressive die assemblies for producing laminated stacks, wherein a strip of lamina material is fed through a sequence of punching steps to progressively form the laminae to the desired end configuration, are also well known.
It is also known to form, in the laminae, interlock tabs which extend below the generally planar lamina surface and engage slots formed in the next lower lamina. In this manner, a plurality of laminae may be stamped from a single sheet of strip stock and formed into an interconnected lamina stack in the die by means of interlocking tabs and slots. More specifically, to form an interconnected lamina stack each lamina, except the bottom lamina of the stack, may have a plurality of arcuately spaced interlock tabs (typically ranging from 3 to 8 circumferentially disposed tabs) depressed from the lamina lower surface adjacent to slots formed in the next lower lamina. Each interlock tab engages a corresponding slot in the next lower lamina of the stack, generally by the entire thickness of the tab. The bottom lamina of the stack may have the interlock tabs blanked and removed to avoid interlocking the bottom lamina with the next lower lamina which forms the top lamina of the previous stack. In rare instances the tab may lock as deeply as two lamina thicknesses, in which case two end laminae must be blanked.
Rotor laminae generally include a plurality of skewed conductor slots which are formed around the periphery of the rotor stack in arcuately spaced relation to one another. The conductor slots are arcuately spaced in an individual lamina in a fixed relationship to one another and, in a rotor stack, are skewed relative to an adjacent lamina by rotationally indexing the partially completed rotor stack with respect to the last produced lamina being attached thereto. Indexing involves rotating the rotor stack and the last produced lamina relative to each other by a predetermined rotational increment so that, when the laminae are combined in a stack, the rotor conductor bar slot defined by adjacent conductor slots are skewed or slanted relative to the stack axis. Stator stacks, on the other hand, include winding slots around the inner periphery of the stack which extend parallel to the stack axis, without skew, and are shaped to receive the stator windings. In some circumstances, however, it may be desired to build an “inside-out” motor wherein the outer lamina stack forms the rotor and would, thus, require skewed slots.
Another system of forming a stack involves loosely stacking the laminae as they are formed and blanked from the stock material in a progressive die assembly. After all the laminae for a given stack are collected, they are shuttled to a pressing station and the laminae are pressed together to engage the interlock tabs and thereby form the lamina stack. Loosely stacking the laminae after they are blanked from strip stock has several disadvantages; loose stacking and subsequent pressing does not as consistently lock adjacent laminae together; the required handling slows production times; and the system lacks a means for automatically correcting thickness inconsistencies of the stock material or creating a desired skew angle for the conductor slots. A similar process can be employed without the use of interlocking features on the laminae. Assembly of the non-interlocked laminae requires the welding, keying or riveting (or pinning) of the laminae to interconnect the laminae in a stack.
In response to these problems, an autorotation system for compensating for the nonuniform stock thickness was developed which both rotates and interlocks the stacked laminae. This system compensates for variations in lamina thickness while still properly skewing the conductor slots of rotor laminae, as described in U.S. Pat. Nos. 4,619,028; 4,738,020; 5,087,849 and 5,123,155, all assigned to the assignee of the present invention and the disclosures of which are incorporated herein by reference. In the system disclosed in the aforementioned patents, the choke barrel or passageway holding the lamina stack may be automatically rotated before each lamina is blanked from the strip stock and the lamina's circumferentially disposed tabs are interlocked with the slots of the uppermost lamina of the incomplete lamina stack within the barrel. Alternatively, the choke may be automatically rotated with every other press cycle, every third press cycle, and so on.
In the apparatus and method disclosed in the aforementioned patents, the individual laminae are typically rotated through an angle of 180°. Although the laminae may be rotated through other angles, the angle must be at least 360°/(number of interlock tabs) so that the interlocking tabs and slots are properly aligned.
The above described improvements have been implemented with rotor laminae and stator laminae which have identical outer perimeters which enables their insertion into a choke barrel designed to hold a lamina having the outer perimeter configuration of the laminae being stacked. Many of these improvements require the use of interlock tabs in combination with autorotation of a partially formed lamina stack.
Autorotation requires the use of a rotating choke barrel which firmly holds the partially formed lamina stack in position as blanked laminae are forced into engagement with the uppermost lamina of the stack. The choke barrel is typically configured to match the outer perimeter of the blanked lamina and may be slightly undersized, e.g., by 0.001 inch, so that the laminae will be firmly held and accurately positioned within the choke barrel. The laminae, after they are located in the choke barrel with an interference fit thereby provide back pressure or resistance which facilitates the entry of the interlock tabs of the next lamina when it is pressed into the choke barrel.
In certain applications, however, it is desirable to have a lamina stack, typically a stator core but also rotor cores in some situations, wherein some of the laminae have an outside perimeter which differs in shape and/or size from the remainder of the stack of laminae, i.e., the laminae in the stack have a plurality of distinguishable configurations. For example, the stator core may incorporate a fastening feature, such as a projecting flange, to provide a mounting surface which is integral with the stator core, or the stator may incorporate a sealing feature to provide a seal between the housing of the motor and the stator core for motors to be used in environments which include flammable vapors. To incorporate such features, a fraction of the laminae in a stack are manufactured with integral portions which provide such features.
Traditionally, the manner in which stator cores having a plurality of outer perimeter configurations have been produced is to stamp the differently configured laminae in separate dies, i.e., each die provides only a single lamina configuration. The plurality of dies produce loose laminae having the desired plurality of outer perimeter configurations. The laminae must then be manually assembled at a station where laminae of the different outer perimeter configurations are placed in the proper vertical stack arrangement and are pressed together to interlock the laminae. Instead of using interlocking tabs, the laminae may also be secured together in some other conventional fashion such as by the use of clamps, pins, rive
L.H. Carbide Corporation
Trinh Minh
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