Method of making an electromagnetic coupling disc

A coupling disc (i.e., the armature or rotor) of an electromagnetic coupling is made by using a punch and die to emboss a plurality of radially spaced rows of angularly spaced grooves in the non-working face of the disc and to cause a plurality of radially spaced rows of angularly spaced projections to be displaced from the working face of the disc. The working face then is machined to remove the projections and, as an incident thereto, circumferentially continuous grooves are formed in the working face in radial alignment with the grooves in the non-working face in order to leave thin webs which establish magnetic flux barriers. To establish even better flux barriers, angularly spaced slots of narrow radial width may be formed through the disc by piercing the disc from the working face thereof and breaking through the thin webs located between the sets of grooves.

BACKGROUND OF THE INVENTION 
This invention relates to multiple pole coupling discs of the type used in 
an electromagnetic coupling such as an electromagnetic clutch or brake. 
The coupling disc may be part of a rotary or non-rotary field or may be a 
rotary or non-rotary armature. 
A typical electromagnetic coupling is disclosed in Silvestrini et al U.S. 
Pat. No. 4,187,939 and, in that particular case, the coupling is an 
electromagnetic clutch having a rotary armature disc made of low 
reluctance material such as steel and having a field with a rotary 
coupling disc or rotor which also is made of low reluctance material. When 
the coil of the field is excited, magnetic flux threads a path between the 
rotor and the axially opposing armature and attracts the armature into 
engagement with the working face of the rotor to couple the two for 
rotation in unison. 
In the coupling disclosed in the Silvestrini et al patent, the armature is 
formed with a ring of angularly spaced "banana" slots while the rotor is 
formed with two concentric rings of angularly spaced banana slots located 
on opposite sides of the ring of slots in the armature. The banana slots 
form high reluctance air gaps causing the rotor and armature to define 
four magnetic poles which increase the torque of a coupling having a coil 
of a given diameter. By forming an additional ring of slots in each of the 
rotor and armature, the coupling may be constructed as a six-pole coupling 
with even higher torque capacity. 
Until just recently, the banana slots conventionally have been stamped in 
the rotor and armature. Presently available stamping techniques dictate 
that, as a general rule, the radial width of the slots cannot be 
substantially less than approximately 3/4 the thickness of the disc. As a 
result, difficulty is encountered in stamping multiple rings of slots in a 
comparatively thick disc which is relatively small in diameter. In 
addition, stamping of the slots leaves burrs at the edges of the slots and 
tends to impose restrictions on the location of the slots in the disc and 
on the shape of the slots. It is difficult to maintain concentricity 
between adjacent rows of slots and it is difficult to keep all portions of 
the disc of a uniform thickness. The design of the disc thus tends to be 
dictated by tooling considerations rather than magnetic characteristics. 
A significant improvement in electromagnetic coupling discs is disclosed in 
Booth et al U.S. Pat. No. 4,951,797. In the coupling disc of that patent, 
the magnetic poles are delineated by closed-end grooves in the non-working 
face of the disc rather than by through slots so as to avoid the 
manufacturing difficulties which arise in the formation of slots by 
stamping or by other techniques such as laser cutting. To form the grooves 
in the disc of the Booth et al patent, the material of the disc is 
displaced by a metal rolling method which requires a rotating die for 
supporting the disc and also requires a traversing roller for pressing the 
disc against the die. Tooling of this type is rather complex and 
specialized and is not compatible with conventional manufacturing 
techniques which assimilate stamping. 
SUMMARY OF THE INVENTION 
The general aim of the present invention is to provide a simplified method 
of manufacturing an electromagnetic coupling disc having a plurality of 
radially spaced rows of angularly spaced grooves formed in its non-working 
face, the method being somewhat analogous to stamping in that it utilizes 
a stationary die and a reciprocating punch. 
A more detailed object of the invention is to achieve the foregoing through 
the provision of a method in which a reciprocating punch having a 
plurality of circular and radially spaced rows of arcuate and angularly 
spaced ribs is impacted against the non-working face of the disc and 
displaces metal from the working face into a plurality of circular and 
radially spaced rows of arcuate and angularly spaced grooves formed in a 
stationary die which underlies and supports the working face during the 
punching operation. In this way, a plurality of circular and radially 
spaced rows of arcuate and angularly spaced grooves is embossed in the 
non-working face of the disc while corresponding projections are formed on 
the working face and are received in the grooves in the die. Subsequently, 
the projections are machined off of the working face so as to leave that 
face substantially flat and planar. As an incident to removing the 
projections, concentric rows of grooves may be machined in the working 
face in radial alignment with the grooves in the non-working face so as to 
reduce further the thickness of the disc in the area of the grooves and 
thereby effect better delineation of the magnetic poles. 
A further object is to take advantage of the reduced thickness of the disc 
in the area of the grooves to enable angularly spaced and substantially 
burr-free slots of extremely narrow radial width to be formed quickly and 
easily through the disc so as to establish flux barriers of even higher 
reluctance between adjacent poles.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
The drawings illustrate the present invention in connection with a coupling 
disc 20 for use in an electromagnetic coupling such as an electromagnetic 
brake or clutch. While the disc could be an armature, it herein is shown 
as forming part of a clutch rotor 21 which may, for example, be of the 
type disclosed in the aforementioned Silvestrini et al patent. In this 
particular instance, the rotor is circular in shape and includes an 
axially extending outer flange 22 and an axially extending inner hub 23 
which preferably are integral with one face 24 of the disc 20. The 
opposite face 25 (FIG. 4) of the disc forms the working face of the rotor 
21 and is adapted to frictionally engage the armature of the clutch. The 
flange 22 and the hub 23 define the outer and inner pole rings, 
respectively, of the rotor 21. 
As is conventional, the rotor 21 is made of low reluctance magnetic 
material such as steel. While the rotor could be cast and then machined, 
it preferably is formed by a stamping and forming operation. 
The specific rotor 21 which has been illustrated forms part of a six-pole 
clutch and thus the disc 20 includes three concentric rings 30 (FIG. 5) 
which carry less magnetic flux than the remaining areas of the disc. One 
magnetic pole is defined by that annular area of the disc located radially 
inwardly of the inner ring, two poles are defined by the annular area 
between the inner ring and the middle ring, two additional poles are 
defined by the annular area between the middle ring and the outer ring, 
and the sixth pole is defined by the annular area located outwardly of the 
outer ring. 
The high reluctance rings 30 are defined at least in part by grooves 32 
which, in accordance with the invention, are embossed in the non-working 
face 24 of the disc 20 by stamping the non-working face with a 
reciprocating embossing punch 34 adapted to coact with a stationary die 36 
that backs the working face 25 of the disc and receives the metal 
displaced therefrom by the punch. By forming the grooves 32 through the 
use of the punch 34 and die 36, the grooves may be formed in a simpler 
manner and with more conventional equipment than has been the case with 
prior grooved coupling discs. 
More specifically, the punch 34 is annular in shape and its working end is 
formed with three radially spaced and generally circular rows of angularly 
spaced and generally arcuate ribs 38 (FIGS. 2 and 7) which project axially 
from the working end of the punch. The ribs are generally V-shaped in 
axial cross-section. 
The die 36 is complementary to the punch 34 and its upper surface is formed 
with three radially spaced and generally circular rows of arcuate grooves 
40 (FIGS. 2 and 8), the grooves 40 of each row preferably being spaced 
angularly from one another. The grooves 40 of the die 36 are aligned 
radially and angularly with the ribs 38 of the punch 34. 
The first step in the method of forming the high reluctance rings 30 in the 
coupling disc 20 involves placing the working face 25 of the disc against 
the upper surface of the die 36 as shown in FIG. 2. Thereafter, the punch 
34 is shifted downwardly and is impacted against the non-working face 24 
of the disc 20 with such force as to cause the ribs 38 to displace the 
metal of the disc downwardly and thereby emboss three radially spaced and 
generally circular rows of arcuate and angularly spaced grooves 32 in the 
non-working face. The metal displaced by the ribs 38 flows axially 
outwardly from the working face 25 of the disc and forms three radially 
spaced and generally circular rows of arcuate and angularly spaced 
projections 41 (FIG. 2) which are received and confined by the grooves 40 
of the die 36. Thus the punch 34 embosses concentric rows of angularly 
spaced grooves 32 in the non-working face 24 of the disc 20 and coacts 
with the die 36 to cause concentric rows of angularly spaced projections 
41 to protrude from the working face 25 of the disc. Because the grooves 
32 of each row are spaced angularly from one another, adjacent grooves are 
separated from each other by bridges 42 (FIG. 1) which have a thickness 
approximately equal to the original thickness of the disc 20. 
After the grooves 32 and the projections 41 have been formed by the punch 
34 and the die 36, the working face 25 of the disc 20 is machined (e.g., 
by a cutter or a grinder) to remove the projections from the working face 
and to cause the working face to be formed as a substantially flat and 
planar friction surface (see FIG. 3). As part of the machining operation, 
chamfers 43 and 44 are formed at the outer and inner peripheries, 
respectively, of the working face adjacent the flange 22 and the hub 23. 
The cylindrical surfaces of the flange and the hub also may be machined to 
remove material therefrom and establish concentricity. 
Preferably, shallow and circumferentially continuous annular grooves 45 
(FIG. 3) are cut in the working face 25 of the disc 20 as an incident to 
removing the projections 41 or in a subsequent machining operation. The 
grooves 45 in the working face 25 are aligned radially with the grooves 32 
in the non-working face 24 and, by virtue of the grooves 45, only 
relatively thin webs 46 of material are left between the working face 25 
and the non-working face 24 in the region of the grooves 32. As a result 
of the webs 46 being thin, they are resistant to the flow of magnetic flux 
and thus serve to establish flux barriers between the magnetic poles of 
the disc 20. Even though the webs are thin, the disc possesses structural 
integrity by virtue of the bridges 42 between the grooves 32. 
While the disc 20 as described thus far will function satisfactorily in 
many magnetic couplings, the invention further contemplates slotting the 
disc in the regions of the grooves 32 and 45 to further reduce the 
flux-carrying capability of the rings 30 and enable the rotor 21 to be 
used to produce higher torque. For this purpose, provision is made of a 
piercing tool 47 (FIG. 4) having three generally circular and radially 
spaced rows of generally arcuate and angularly spaced piercing elements 
48. The piercing elements are generally "banana" shaped and having a 
radial width just slightly less than the radial width of the grooves 45 in 
the working face 25 of the disc 20. 
When the piercing tool 47 is used, it is oriented such that its piercing 
elements 48 are aligned radially and angularly with the grooves 32 in the 
non-working face 24 of the disc 20. The tool then is moved toward the 
working face 25 to cause the piercing elements to break through the webs 
46 at the bottoms of the grooves 45 and thereby form angularly spaced 
"banana" slots 50 through the disc. Because the webs 46 are very thin in 
the axial direction, the slots 50 may be of relatively narrow radial width 
(e.g., on the order of 0.035") and their edges are virtually free of 
burrs. Very little force is required to break through the webs and form 
the slots. 
From the foregoing, it will be apparent that the present invention makes 
advantageous use of a punch 34 and a die 36 to emboss the non-working face 
24 of a rotor disc 20 and form radially spaced rows of angularly spaced 
grooves 32 in the non-working face. By machining grooves 45 in the working 
face 25, the webs 46 are made thin so as to have only relatively low 
flux-carrying capability. The thin webs 46 defined between the grooves 32 
and 45 enable substantially burr-free slots 50 of narrow radial width to 
be formed in the disc 20 simply by piercing through the webs from the 
working face 25 of the disc with the piercing tool 47.