Note: Descriptions are shown in the official language in which they were submitted.
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Back~round of the Invention
Automotlve vehicles and small vessels use D.C.
electrical power sources for operation of lights and
controls; the traditional power source for these applications
once was a D.C. generator driven from the vehicle engine.
More recently, with ma~or improvements in rectifier
technology, the D.C. generator has been replaced by the
combination of a small alternator and a rectifier. The most
practical and most widely used type of alternator employs a
rotating field, using a field coil mounted in a core formed
by two magnetic steel core members with interleaved
finger-like pole pieces. For these magnetic core members,
precision manufacture is essential.
Traditional processes that have been employed in
the manufacture of maqnetic ro~or core members for
alternators and like dynamoelectric machines include the cold
forging (or cold extrusion) process, the cold forming
stamping process, and the hot forging process. These
manufacturing procedures have each incorporated methods and
techniques that have been developed independently and
separately for each. T~ough significant improvements and
advances in all of these methods have been achieved during
past years, each of the traditional processes nevertheless
still presents drawbacks and disadvantages which have proved
difficult or impossible to overcome. Accordingly, each of
the traditional procedures still leaves much to be desired in
terms of yield rate, productivity, equipment required, etc.
For instance, the cold forging or cold extrusion
method requires a large scale, high capacity press that
affords an extremely high processing force. This presents
substantial problems with respect to operating life and
productivity of the tooling employed in the press. The cold
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forming stamping process presents a distinct disadvantage
with respect to excessive consumption of the material from
which a preliminary core blank is punched and an undesirably
low yield rate. Further, this process cannot create an
integral hub section, as used in many rotor core members, so
that a separate rotor core spacer or hub has to be
manufactured by some other process.
The hot forging process is inherently a higher
yield rate procedure that has the further advantage of
requiring less processing force than cold forging. ~owever,
hot forging alone is inadequate in attaining high dimensional
accuracy and also is poorly adapted to producing a shaft
aperture in the hub of the rotor core member. Consequently,
the basic hot forging process must be followed by a number of
machining steps to achieve the required finished form with
precision controlled dimensional tolerances.
A superior method of manufacturin~ magnetic rotor
core members for dynamoelectric machines is described in the
inventor's earlier United States Patent No. 4,558,511 issued
December 17, 1985; the method disclosed in that patent
employs a combination of hot forging and cold forging
operations that minimizes many of the disadvantages of
traditional processes. In the process disclosed in that
patent, a segment of steel bar stock is first hot forged to
form a prelimlnary core blank having a general approximation
of the external configuration desired for the rotor core
member and is then coined to form a secondary core blank
closer to the final required configuration, after which the
secondary core blank is gradually air cooled. At this stage,
the secondary core blank may be cold punched to form a shaft
aperture through its hub and simultaneously cold compressed
for further shaping; alternatively, the secondary core blank
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may be rough machined on numerous surfaces, the rough
machining also forming a shaft aperture. Finally, one or
more cold compression steps complete the finished rotor core
member, witb no requirement for close tolerance finish
machining.
Although the method of the inventor's earlier
patent No. 4,558,511 affords a marked improvement over
previously known techniques for manufacturing magnetic rotor
core members, further improvement to meet current demands for
higher productivity, improved dimensional açcuracy, and lower
manufacturing costs are highly desirable. The present
invention is intended to and does afford improvements on the
inventor's prior method, affording higher yield rates,
further reduction of manufacturing steps, and more precise
dimensional control.
Summary of the Invention
It is a primary ob~ect of the present invention,
therefore, to provide a new and improved method of
manufacturing magnetic rotor core members for rotating-field
dynamoelectric machines, particularly for alternators, that
effectively minimizes or eliminates any requirement for
close-tolerance machining of the core members, utilizing hot
forging, coining, rough machining, cold punching and ironing,
and cold compression procedures in the production of rotor
core members; the method of the invention completes the
finished rotor core members with minimum wa~te of core
material, minimum energy consumption, and minimal cost at an
improved yield rate and with improved dimensional precision.
Accordingly, the invention relates to an improved
method of manufacture of a maqnetic rotor core member for a
dynamoelectric machine of the rotating-field type, the rotor
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core member including a cylindrical hub section mountable on
a rotor shaft, an integral disc section extending radially
outwardly from one end of the hub section, and a plurality of
annularly spaced integral pole pieces pro~ecting from the
outer edge of the disc section in a direction parallel to the
hub axis. The method comprises the following steps:
A. Hot forging a metal segment of given volume to
form a preliminary core blank having a general approximation
of the external configuration desired for the rotor core
member, including a central hub section, an integral disc
section extending radially outwardly from one end of the hub
section and a plurality of pole piece fingers equally spaced
around the outer edge of the disc section and projecting
therefrom in a direction parallel to the axis of the hub
section;
B. Coining the preliminary core blank to form a
secondary core blank more closely approximating the desired
external configuration for the rotor core member;
C. Gradually cooling the secondary core blank;
D. Rough machining the open end surface of the hub
section and the outer surface of the disc section of the
secondary core blank to adjust the volume of metal to suit
subsequent cold forming operations;
E. Cold punching a shaft aperture through the
central portion of the hub section and simultaneously ironing
the fingers to shape them to a form and dimensions closely
approximating those required for the pole pieces of a
finished rotor core member; and
F. Cold compressing the secondary core blank to
final form and dimensions to complete a finished rotor core
member.
Brief Description of the Drawings
.
Fig. 1 is a simplified, partially ~chematlc
half-sectional elevation view of a rotating-field alternator
incorporating magnetic rotor core members manufactured by the
method of the present invention;
Fig. 2 i8 a flow chart illustrating the steps for
the method of the invention;
Figs. 3 through 8 are elevation views of a rotor
core member at various stages in the method of manufacture of
the present invention, Figs. 3-5 taken from the pole-piece
side of the core member and Figs. 6-8 taken from the opposite
side; and
Figs. 3A through 8A are simplified sectional views
taken approximately as indicated in Figs. 3 through 8.
Description of the Preferred Embodiment
Fig. 1 illustrates a small alternator or other
rotary dynamoelectric machine 10 of the rotating-field type;
alternators having the construction generally illustrated for
machine 10 are in common use in vehicles, small vessels, and
other like applications. Alternator 10 includes a rotary
magnetic core formed by two core members 11 which are usually
essentially identical to each other. Each rotor core member
11 includes a cylindrical hub section 12, an integral disc
section 14 extending radially outwardly from one end of the
hub section, and a plurality of integral, finger-like pole
pieces 13, angularly spaced from each other, that project
from the outer edge of the disc section 14 in a direction
parallel to the axis X of hub section 12.
In alternator tO, the two rotor core members 11 are
mounted on a shaft 16 that extends through their hub sections
t2, the orientations of the two core members being such that
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their pole pieces 13 are interleaved with each other. A
field coil 15 is mounted in encompas~ing relation to the hub
sections 12 of the two core members 11 to complete the rotor
for alternator 10. An annular stator core 17 is disposed in
encompassing relation to the rotor of alternator 10 and
supports the usual stator coils 18 from which the output of
the alternator is derived. In Fig. 1, the stator 17,18 has
been shown in simplified form because it is not relevant to
the present invention.
Fig. 2 affords a flow chart of the steps involved
in the method of manufacture of a rotor core member, such as
one of the core members 11 of Fig. 1, according to the
present invention. A number of intermediate stageq of the
process of Fig. 2 are illustrated in Figs. 3-7 and Figs.
3A-7A, culminating in a finished magnetic rotor core member
11 as shown in Figs. 8 and 8A.
At the outset, in the first step 21 of the
procedure illustrated in Fig. 2, a segment of round steel bar
stock (not shown) that is to be shaped into a rotor core
member is cut from a length of steel bar. Care should be
exercized so that the segment will have a given volume. A
conventional cutting press can be utilized for step 21. The
segment of steel bar stock should have relatively closely
controlled dimensions to avoid excessive waste and to assure
adequate performance of succeeding steps in the manufacturing
procedure. The bar stock employed may vary considerably; it
usually con9titutes a low carbon steel and must afford
adequate magnetic properties for the core of an alternator or
other small dynamoelectric machine.
In the second step 22 of the manufacturing method
illustrated in Fig. 2, the bar stock segment from step 21 is
hot forged to form a preliminary core blank 31, shown in
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Figs. 3 and 3A. The shape of the preliminary core blank 31
is a general approximation of the desired external
configuration for the finished rotor core member 11 (Figs. 1,
7 and 7A) with the exception of the pole piece fingers as
explained hereinafter.
The preliminary core blank 31 consi~ts of a central
hub section 32, still solid rather than cylindrical, an
integral disc section 34 extending radially outwardly from
one end of the hub section, and a plurality of integral
fingers 33 that are equally spaced along the outer edge of
the disc section and project therefrom in a direction
parallel to the axis of the hub section. The fingers 33,
however, are formed to have a length L1 that is somewhat
shorter than the length L2 ~Fig. 8A) required for the pole
pieces 13 of a finished rotor core member 11, while all other
elements are formed to as close an approximation as possible
of their required final forms.
At this stage, any excess material in the original
segment of steel bar stock may produce a forging burr 38
around the periphery of the preliminary core blank 31 and ?
between its fingers 33. The next step 23 in the
manufacturing procedure illustrated in Fig. 2 is de-burring
of the preliminary core blank formed in the preceding step
22. No sophisticaed process is involved. Conventional
punching procedures are utilized to eliminate the forging
fringe or burr 38 from core blank 31 ~Figs. 3 and 3A).
De-burring produces the cleaned-up version of the preliminary
core blank 31 that is illustrated in Figs. 4 and 4A.
The fourth step 24 in the manufacturing process,
Fig. 2, is coining of the preliminary core blank formed in
the preceding steps to produce a seconaary core blank more
; closely approximating the desired external configuration for
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one of the rotor core members 11. This coining operation
also facilitates the subse~uent rough machining operation
of step 26. Again, no ~ophisticated or special equipment i5
required. A conventional coining press i8 utilized, further
shaping the core blank to the configuration illu~trated for
the secondary core blank 41 shown in Figs. 5 and 5A. In core
blank 41, the central hub section 42 is still solid. The
disc section 44 has been flattened to a closer approxi~ation
of the required final form. The fingers 43 that are to form
the pole pieces of the rotor core member are still shorter
than required for their final form.
In the fifth step 25 of the manufacturing
procedure, Fig. 2, the secondary core blank 41 from step 24
(see Figs. 5 and 5A), which has been hot since step 22, is
gradually air cooled. Most simply and effectively, the
secondary core blanks are left to cool from the red-hot
condition in which they emerge from the coining press ~step
24) until they cool off naturally. The combination of the
hot forging operation of step 22 and the gradual air cooling
24 operation of step 25 affords, without the expense of special
heat treatment procedures, an effect which is comparable to
an annealing treatment that tends to homogenize the magnetic
steel being worked, with the result that subsequent cold
forging processes require less force and energy than if cold
proceasing were used throughout the manufacturing procedure
and with the further result that the final product affords
improved electrical performance.
The ~ixth step 26 in the manufacturing procedure is
rough machining of the outer surface 44A of disc section 44
and the open-end surface 42A of hub section 42 as indicated
in Fig. 6A. That is, only these two portions of the core
blank 41 are rough machined as compared with the
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.` rough machining of numerous surfaces effected in Patent No.
4,558,511.
By comparison with the machining operations which
~ollow hot forging in the traditional hot forging process to
provide a rotor core member, the rough machining step 26 as
discussed herein, is employed to remove a much smaller
quantity of metal from the core blank. Step 26 is a much
simpler, much less time-consuming, and much less
sophisticated sort of machining than in the traditional
process it is principally intended to adjust the volume of
metal in the secondary core blanks 41 to suit subsequent cold
forging in steps 27 and 28.
In any forging operation, it is highly desirable to
make certain that a uniform quantity of metal is contained
within the forging dies; this is particularly important in
cold forging operations. Generally, the uniformity in
quantity of metal of the secondary core blanks 41, after step
26, provides such benefits as ease of cold forging (requiring
less force and energy), prolonged life for the cold forging
dies, reduction of product spoilage and of dimensional
variations, etc., with the result that improved productivity
and higher yield rate are achieved.
The seventh step 27 in the manufacturing procedure
of Fig. 2 is cold punching of the central portion of hub
section 42 to cut a shaft aperture 46, illustrated in Figs. 7
and 7A. At the same time, the press employed for the cold
; punching operation is utilized for ironing the fingers 43 to
shape them to a form, a length and dimensions very closely
approximating those required for the pole pieces 13 of a
finished rotor core member. Thus, at this stage, Fig. 7A,
the length L3 of fingers 43 is appreciably greater than the
initial finger length L1, Fig. 3A; L3 may still be very
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slightly shorter or longer than the required fini~hed pole
piece length L2 (Fig. 8A). The dimensions of the shaft
aperture 46 are still inadequate and inaccurate, particularly
in the portion of the aperture close to the open end 46A of
the hub section, Fig. 7A.
A section or a part of a hot forged workpiece which
is long yet slender in contour, like a pole piece of a rotor
core member, is the trickiest of all sections, and can at
times emerge from the hot forging dies with an inadequate or
incomplete shape, particularly in length, rendering the hot
forged blank a reject. To minimize the risks of having such
a defective forging, manufacturers utilizing traditional hot
forging processes have had to start with a metal segment
having a substantially greater volume than theoretically
required in order to insure that these tricky, intricate
sections acquire a desired, complete shape with an adequate
volume of metal. This is one of the reasons the pole piece
fingers 33 are formed to a lesser length Ll in the initial
hot forging stage 22 and then ironed to a very close
approximation L3 of their required final length L2 in the
subsequent cold forging and ironing procedure of step 27.
By comparison with the inventor's earlier method,
Patent No. 4,558,511, in which the pole piece fingers are
formed in an initial hot forging step to a relatively close
approximation of the external configuration desired for the
pole pieces of a finished rotor core member, the method of
the present invention, which starts with the fingers haYing a
length shorter than finally required and irons them, in the
later stage 27, to a close approximation of their required
final form, affords an appreciable reduction of spoilage of
forgings as well as substantial saving in starting material.
The ironing procedure for pole piece fingers 43, Fig. 7A, is
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so effectual and adequate in providing them with a form and
dimensions closely approximating those required for pole
pieces 13 that it eliminates any need for rough machining the
periphery o~ the core blank and the tips of the flngers,
which are among the most critical surfaces in the pole pieces
of a rotor core member and which, according to the inventor's
earlier method, were rough-machined to a closer approximation
of their required, final configuration. The ironing
procedure also permits the concluding, finishing step 28 to
be performed in just one cold compression.
The final step 28 in the manufacturing process,
Fig. 2, is a cold compression procedure, carried out in a
conventional cold forging press, to achieve the final,
finished shape for a rotor core member 11, illustrated in
Figs. 8 and 8A. As stated in connection with the preceding
step 27, a single cold compression is adequate. This
concluding cold forming procedure provides the final,
finished configuration for all elements of rotor core member
11, including the hub section 12 with its finished shaft
aperture 56, the disc section 14 that joins the pole pieces
13 to hub 12, and all edges, transition surfaces and
corners.
The initial hot forging step 22 produces a
relatively close approximation of the desired external
configuration for the rotor core member directly from a metal
segment, whereas the traditional cold forging ~cold
extrusion) and cold forming stamping methods require
additional steps to shape a starting piece of material into a
general approximation of its required final configuration.
The combination of steps 22 and 25, hot forging and gradual
air-cooling, affords a favorable effect on subsequent steps
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of metal working, without the expense of special heat
treatment procedure. The uniformity in quantity of metal in
secondary core blanks 41 that results from limited rough
machining in step 26 affords such benefits as ease of
subse~uent cold forging requiring less force and energy, a
prolonged life of the cold forging dies, reduction of
, spoilage of cold forged blanks, and reduction of dimensional
! variations, with resulting higher yield rate and higher
dimensional precision.
The initial hot forging of the pole piece fingers
33 (step 22, Fig. 3A) to lengths less than required for the
pole pieces of a finished rotor core member, and subsequent
ironing of the fingers to a close approximation of their
final length, form and dimensions in step 27 also contributes
much toward saving in starting material, reduction of
spoilage of hot forged blanks, curtailment of manufacturing
procedures and attainment of higher dimensional precision.
The method of manufacture of the present invention, combining
the steps of hot forging, coining, gradual air cooling,
limited rough machining, cold punching of a shaft aperture
I simultaneously with ironing of the fingers, and cold
compressing, makes it possible to complete a rotor core
member of high dimensional accuracy with high productivity,
with minimum waste of material and minimal energy
consumption, and at minimum cost.
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