Process for preparing a pole piece for the rotor of a generator

A process for preparing a pole piece having spiders bent in the axial direction for the rotor of a generator in which a slug is obtained from a round metal bar, said slug is upset to a disc-shaped member, said member is formed with a plurality of radially and outwardly extending spiders on the outer periphery of and a boss on one surface of said member, said spiders are tapered on one surface and an annular bending recess is formed in said one surface of the spiders, said spiders are bent at said annular bending recess until the outer surface of the spiders lie on a plane right angles to the plane of said member to provide a semiprocessed product, and said semiprocessed product is in succession subjected to coining and sizing steps to thereby provide a complete pole piece having spiders bent in the axial direction.

BACKGROUND OF THE INVENTION 
This invention relates to a process for preparing a piece having spiders 
bent in the axial direction of the piece and more particularly, to a 
process for preparing a pole piece for the rotor of a vehicle AC 
generator. 
As more clearly shown in FIG. 9, a pole piece for the rotor of an AC 
generator generally comprises a base having a plurality of radial spiders 
formed on the outer periphery and bent in parallel in the axial direction 
of the base and a center boss formed on one surface of the base. In use, a 
pair of such pole pieces are disposed with their bosses positioned in 
face-to-face relationship and the spiders on one pole piece fitted in the 
valleys defined between the adjacent spiders on the other pole pieces. 
The forging and bending systems have been known as the conventional 
processes for preparing pole pieces of the type referred to hereinabove. 
The former or forging system comprises the steps of cutting a slug having 
a predetermined volume off from a round metal bar of an indefinite length, 
heading the slug, extruding the headed slug to provide a semiprocessed 
product having a base and a plurality of bent radial pieces on the 
periphery of the base and trimming the thus obtained semiprocessed product 
to provide a complete pole piece. Although this system is a high yield 
rate process, the system has the disadvantage that the system requires a 
high capacity press which provides a high processing force and necessiates 
a large scale facility. 
And the latter or bending system comprises the steps of stamping a blank 
having a plurality of radially and outwardly extending spiders out of a 
metal plate material, bending the spiders at right angles to the plane of 
the blank and attaching a boss to one surface of the blank. However, since 
the blank stamped by this system has the radially and outwardly extending 
spiders, this system is disadvantageous with respect to consumption of 
material or this system is a low yield rate and uneconomical process. 
Nevertheless, the bending system has the advantage that the system can be 
performed by the use of a low capacity press which provides a low 
processing force. Thus, the forging and bending pole piece preparing 
systems have their inherent advantages and disadvantages and in 
consequence, a process for the purpose which is easily carried out and 
economical has been long wished for. 
SUMMARY OF THE INVENTION 
Therefore, the present invention is to provide a process for preparing a 
pole piece for the rotor of an AC generator which attains the 
above-mentioned wish, which possesses both the advantage of high yield 
rate inherent in the forging system and that of low processing force 
inherent in the bending system, which consumes material efficiently and 
which can be conducted by the use of a low capacity press. 
The above and other objects and attendant advantages of the present 
invention will be more readily apparent to those skilled in the art from a 
reading of the following detailed description in conjunction with the 
accompanying drawings which show one preferred embodiment of the invention 
for illustration purpose only, but not for limiting the scope of the same 
in any way.

PREFERRED EMBODIMENT OF THE INVENTION 
The process for preparing a pole piece for the rotor of an AC generator 
according to the present invention will be now described referring to the 
accompanying drawings in which various steps of the process are 
illustrated. 
In the first step, a slug 1 having a predetermined volume (as shown in FIG. 
1) is cut off from an indefinite length of round bar material (not shown) 
and the slug 1 is upset to a disc-shaped member 2 (as shown in FIG. 2) in 
the second step. The disc-shaped member 2 is subjected to a first forming 
step to provide a substantially T-shaped cross-section member having a 
base 3, a center boss 4 on one major surface of the base and six equally 
spaced spiders 5 radially and outwardly extending from the outer periphery 
of the base as shown in FIG. 3. After the first forming step, the T-shaped 
cross-section member is subjected to a second forming step in which each 
of the spiders 5 is tapered on one surface which coincides with the 
surface of the base 3 on which the boss 4 is formed and the opposite 
sides, in this step there is produced a thin fin 6 about the associated 
spiders 5 as shown in FIG. 4. Simultaneously, and annular bending recess 
5' is formed on the tapered surface of the spiders 5 as shown in FIG. 4. 
In the fifth step, the T-shaped member is trimmed to remove the fins 6 
therefrom, and thereby obtain a semiprocessed product as shown in FIG. 5. 
The semiprocessed product is then subjected to the sixth or bending step 
in which the spiders 5 of the semiprocessed product are bent toward the 
boss 4 until the non-tapered surface of the spiders 5 lie on a plane at 
right angles to the plane of the base 3 as shown in FIG. 6 and thereafter, 
the semiprocessed product is subjected to a coining step (FIG. 7) to 
eliminate any irregularity which may be present on portions of the 
semi-processed product. Finally, the thus obtained semiprocessed product 
is subjected to a final or sizing step (FIG. 8) to produce a complete 
product or a pole piece 7 for the rotor of an AC generator. 
As mentioned hereinabove, according to the process for preparing a pole 
piece for the rotor of an AC generator of the present invention, the 
forging steps in which a slug cut off from a round metal bar is in 
succession processed are combined with the bending step in which the 
radial spiders formed on the slug and processed in the forging steps so 
that only the advantages of both the forging and bending systems are 
utilized in the process of the invention and therefore, the process of the 
invention has the advantages that the process can be performed with a high 
yield rate and easiness. 
Thus, the process of the invention can be suitably applied to the 
manufacture of various articles having radial portions bent in the axial 
direction with respect to the main body of the article as well as pole 
pieces for the rotors of AC generators. 
While only one embodiment of the invention has been shown and described in 
detail it will be understood tht the same is for illustration purpose only 
and not to be taken as a definition of the invention, reference being had 
for this purpose to the appended claim.