Note: Descriptions are shown in the official language in which they were submitted.
J.2~06Z0
OBJECTS OF THE INVENTION
. _ _ . . . . . .
The principal object of the present invention is,
therefore, to provide a new and improved method and means which
enables the economical manufacture of metal parts having sides
extending perpendicular to the plane of the workpiece, which
method permits tl~e holding of extremely close tolerances and
daes not result in stress concentrations which would distort
the workpiece.
Another object of the present invention is to provide
a novel die configuration for use in the said method, which die
configuration may be used for shaping very hard, machineable
materials, such as high speed tool steel.
SUMMARY OF THE INVENTION
Briefly, there is provided in accordance with the
present invention a novel die configuration which may be used
in a metal removal operation which is similar to hobbing and
which is carried out in a punch preSs. In accordance wlth the
novel me~hod of this invention the workpiece is pushed along the
cutting edge o ~he die to remove edge material from the work-
piece and thus provide the desired shape.
In a preferred embodiment of the invention the die has
a three hundred sixty degree cutting edge wherefor the~-entire
external or internal edge of the workpiece i9 formed in a single
operation. In another embodiment of the invention a plurality
of dies are stacked ln mutually spaced relationship and the work-
piece is pushed past the dies which progressively remove material
from the workpiece to provide a finished part in a single punch
press operation.
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'lhe die of the present invention has a facial contour
on the ~ctive side of the die which is mathematically derived
to provide the cutting edge of the die with a substantially
constant shear angle throughout its entire length. The optimum
shear angle is related to the diameter and hardness of the
material being worked and may be chosen on the basis of experi-
ence or in some other suitable manner.
The active side of the die slopes away from the cutting
edge, so that the material which is preferably removed in the
form of chips will move freely away from the workpiece as it
moves past the cutting edge. In the case where the external
edge of the workpiece is being formed, as the workpiece is
pushed ~hrough the die the workpiece is outwardly stressed or
s~retched as the removed material 18 cut and pulled radially
outward. As a result, no stress concentration in the workpiece
results, and no distor~ion of the workpiece occurs. In some
cases it has been found that the flatness of the workpiece is
actually increased when the sides aré~shaped in accordance with
the present invention.
Other inherent advantages of the method of the present
invention as compared to the use of conven~ional dies and punch
press operations are quieter operation and lower maintenance
costs. I have found that the die~ of the present invention need
be sharpened less than one-third as frequently as conventional
punch press dies. Moreover, because of the smooth cutting action
of the die, the temperature of the workpiece is not raised as
much as it would be in a conventional punch press operation.
Also, the close clearances between the pusher member and the die
which would be required to prevent distortion of the workpiece
3~
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in a normal puncl- press operation are unnecessary when using
the method of the present invention.
GENERAL DESCRIPTION OF THE INVENrl`InN
The present invention will be better understood by a
reading of the following detailed description taken in con~
nection with the accompanying drawings wherein:
Fig. 1 is a plan view of an external gear which may be
made by the method of the present invention;
Fig. 2 is a cross-sectionsl view of the gear of Fig. 1
taken along the line 2-2 thereof;
Fig. 3 is a plan view of an internal gear which may be
made by the method o the present invention;
Fig. 4 is a cross-~ectional view of ~ h gear of Fig. 3
taken along the line 3-3 thereof;
Fig. S is a plan view of still another part having a
complex peripheral configuration which may be made by the
method of the present invention;
Fig. 6 is a plan view showing the gear of Fig. 1 being
made by the method of the present invention;
Fig. 7 is a cross-sectional view taken along the line
7-7 of Fig. 6;
Fig. 8 is a cross-sectional view similar to that of
Fig. 7 but showing the gear of Fig. 3 being made by the method
of the present invention; and
Fig. 9 is a framentary, sectional view of a portion
of a die embodying the present invention.
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DETAILED DESCRIPTION OF A PREFERRED
EMBODIME;NT OF THE INVENTION
... ..
The present invention may find application where-
e~er it is desired to form a vertical edge on a part, but it
is particularly suited for cutting vertical side edges on
relatlvely thin, hard metal parts. For example, the invention
has been used to cut both internal and external involute teeth
on thin flat parts sueh as gears and splines formed of high
speed tool steel, and parts having an external diameter of more
than nine inches and a thicknes~ of less than one-eighth inch
have been made in~accordance with the teaching~ of the present
invention. Therefore, although the invention ls described here-
in in connec~ion with th~ manufacture of a few representative
parts, its use i8 not 80 limited.
Referring to Fig~. 1 and 2, there iR shown a thin,
flat member 10 of generally annular shape having a plurality
of external teeth 12. The teeth 12 are iden~ical and equally
spaced, and they have sides 12A in the ~ape of a partial in-
volute. The memb¢r 10 may function as an external gear or
spline and may be seen from an ~nspection of Flg. 2 to be
relatively thin in cross-section. The con~inuous external side
edge of the member 10 i8 identified at 13 and may be seen to be
perpendicular to the principal plane and faces 14 and 15 of
the member 10.
Referring to Figs. 3 and 4, there is shown a thin,
flat member 18 of generally annular shape having a plurality
of equally spaced internal teeth 20 having the sides 20A thereof
each in the shape of a partial involute. As best shown in Fig.
4, the internal side edge of the member is identified at 21 and
is perpendicular to the principal plane and faces 23 and 24 of
the member 18.
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Referring to Fig. S there is shown a thin flat member
26 having an external perpendicular edge 27 of relatively
complex confi~uration in the plane of the member 26. The
external edge 27 may be formed in accordance with the teach-
ings of this invention.
Referring now to Figs. 6 and 7 there is shown a die
30 for removing metal from the external side 32 of a flat metal
plate or workpiece 33 as the plate 33 is pushed past the cutting
edge 35 of the die through the center opening 36 therein by
mesns of a pusher member 38 The side 39 of the pusher member
38 is complimentary to the cutting edge 35 of the die 30 although
a substantial clearance of a few thousandths of an inch or
more may be provided between the pusher member and the die. The
lower face 40 of the pusher ~ember i8 complimentary to the upper
face of the workpiece 33. The die 30 and the pusher member 38
are preferably mounted to the base and upper platen respectively
of a conventional punch press whereby the pùsher member 38 i9
driven down toward the die 30 to pus4 the workpiece 33 there-
through as in a conventional punch pressoperation. Preferably
the workpiece 33 is a blank having its outer edge more or less
conforming to the external shape of the final part thereby
to facilitate removal and dlsposition of the metal from the
workpiece in the form of 8mall chips.
In accordance wlth an important aspect of the present
invention the die 30 has a particular facial contour 42 on the
working si~e of the die, which contour, in associaiton with the
vertical side 36, provides a cutting edge 35 having a sub-
stantially constant shear angle throughout its entire length.
The optimum shear angle will vary with the hardness and thick-
3~ ness of the part being made, but whatever shear angle is selected,
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it is sul~stantially the same along the entire cutting edge of
the die. I`or example, for most applications where high speed
tool steel is to be worked, a shear angle between six degrees
and fifteen degrees will generally be used. The facial contour
of the die can, as more fully described hereinafter, be math-
ematically computed when the planar shape of the part to be
formed is given mathematically, and the computation necessary
for developing this facial contour can best be made using a
general purpose computer. However, since the facial contour
42 is uniform for all radii of the die the contour can be
shaped in any preci~e metal working process such as turning or
milling.
The working contour of the die 30 extends from the
innermos~ portions of the edge 35, identi~ied in Fig. 6 as
Rl, to a location a short distance outward of the maximum
external radius of the cutting edge 35. The reference character
Ro ln~icates the latter location or radius. The upper face of~
the die between the locations RI and Ro has a cross-sectional profi
which in combina~ion with the involute tooth configuration shown
in Fig 6 provides the cutting edge 35 with a constant shear
angle throughout it~ entire 360 length. The shape of the con-
tour between the radii RI and Ro can be mathematically computed
as described hereinafter. I have found, however, that for
some applications the contour between the radii RI and Ro can
be a portion of a cone closely approximating the actual contour
as mathematically computed and still maintain the shear angle
substantially constant throughout the entire length of the
cutting edge.
The portion of the die which is exterior to the radius
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Ro does not have a critical facial contour, but it preferably
slopes downwar~lly s~ that the removed chips will fall by
gravity away from the workpiece and away from the die itself.
Referring to Fig. 8 there lS shown a novel die 46 for
cutting the internal edge of the part 18 shown in Figs. 3 and 4.
In Fig. 8, a blank 48 rests on ~he upper face 50 of an annular
support piece 52 adapted to rest on the base platen of a punch
press. The support piece 52 has an internal vertical wall 54
which is similar in horizontal cross-section to the internal
edge of the part to be formed. The lower face of the die 46 is
the working face thereof and is contoured to provide a cutting
edge 56 having ~ constant shear angle throughout its entire 360
length. The edge 56 lies in a horizontal plane and correspondR
to the internal edge of the part lB as shown in Fig. 3.
When forming the internal edge of a part in accordance
with this aspect of the invention, a flat, annular blank 48 is
placed on the support member 52 in a punch press and the die 46
ls fixedly mounted to the upper platen~ The press i8 then
operated to push the die 46 into the central opening ln the
support member 52 thereby to cut the metal from the interior
edge of the blank 48 to precisely form the internal edge of the
finished part. The metal is removed in the form of chips
and falls by gravity into the central opening in the support
member 52.
The optimum speed at which the die is moved past the
workpiece during the cut~ing operation will vary with the
hardness and thickness of the workpiece, but I have produced
acceptable parts at the rate of thirty-five per minute.
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Wi L1- re fer~?nce to Fig . 9, the facial contour of the work-
ing area of the die for cutting radial teeth of involute config-
-` uration may be computed using the following formula:
A = Arc Tan _ _ Tan B
~ Rl Co s 1 ~ 2 + (~ + INV01 - INV02 )
wherein
A - angle of contour at radius R2
B = shear angle of cutting edge
~ Rl - pltch radius
- R2 ~ radius at each point in the die
Tl = arc thickness of tooth at Rl
T2 = arc thickness of tooth at R2
01 = pressure angle at Rl
This equation can best be solved for a plurality of
incremental values R2 by means of a digital computer. The
angular values A can be plotted in the associated computer
printer to provide the plot shown in Fig. 9, which contour
is a radial section taken at all circumferential points of
the die. It will be apparent that for the parts 10 and 18
, ~
the contour profile i8 the same even though one die is for
cutting radial involute teeth on the external edge of the
workpiece and the other die is for cutting identical involute
teeth in the internal edge of the workpiece.
It will be understood that other equations ~ay be used
for determining the contours necessary for providing constant
~: :
shear angles for cutting edges of other shapes such, for example,
as those shaped to form a complex configuration such as the ex-
ternal profile of the part 26 shown in Fig. 5 or of square
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~eeth (not shown) or of any other configuration.
Whi le the present invention has been described in
connection with particular embodiments thereof, it will be
understood by those skilled in the art that many changes and
modifications may be made without departing from the true
spirit and scope of the present invention. Therefore, it is
intended by the appended claims to cover all such changeQ
modifications which come within the true spirit and scope
of this lnvention.
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