Note: Descriptions are shown in the official language in which they were submitted.
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The invention concerns a sintered metal body with at
least one tooth structure formed in a blank, with or without pre-
toothing, by metal forming.
In the DE-PS 26 59 733, a toothed sintered metal body
is described, in which the toothing is formed in the blank by
metal forming. According to this process, toothed gears are manu-
factured with a profile shift which changes continuously and
uniformly from one front face of the toothing to the other front
face with a bevelled enveloped surface of the toothing. For this
purpose a master gear is made by a cutting process, then from the
master gear, using an image-forming manufacturing process, a die
is manufactured, and the toothing of the gear is produced in the
die under heat by a shapinq process, wherein a prescribed final
temperature at the end of the shaping process is strictly adhered
to, and wherein the contraction of and the modular change in -the
toothing upon cooling of the workpiece from the prescribed final
temperature are compensated by corresponding admeasures in the
master gear. Thus the toothed gear produced in the die is cali-
brated to the nominal dimensions usir~g a calibrated die which is
manufactured by an image-forming manufacturing process from a
second master gear made by a cutting process. In the course of
manufacture of the toothed gear by a sintering process, the con-
traction of and the modular change in the toothing during sintering
and cooling of the workpiece are corrected for in the master gear
by the corresponding admeasure. Based on the suggested measures,
by which the toothed gear is forged in a process using an initial
master gear and the manufacture of a die from this master gear,
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wherein the contraction of and the modular change in the toothing
is taken into consideration, and by which the toothed gear is
calibrated in a calibrating die manufactured according to a second
master gear, which deviates from the ini.tial master gear, it is
possible, with good tool-life of the dies, to manu~acture gears
with a very high degree of precision. The process involves very
high costs of production however and is only likely to be applic-
able in special cases.
As is known from the United S-tates Patent 3,772,935, it
is also possible to form the toothing in a blank made of sintered
metal material by metal forming ~see Figures 5, 6 and the corre-
sponding description). In accordance with this/ a type of stamping
tool is used to press the material into a form, in order to pro-
duce the workpiece. The teeth can be subsequently ground or cut,
that is, they require a finish machining process.
According to a procedure described in "Machine Design",
1972, pages 72-76, the final tooth form in a pre-toothed sintered
metal blank is achieved by one or more metal forming processes.
The object of the invention is to produce from a sintered
metal body a toothed gear capable of withstanding high degrees of
stress, to which the strength limitations existing in toothed
gears manufactured by powder-metallurgical processes for example
do not apply, and in which the tooth geometry is not a limiting
factor.
The ~resent invention provides a method of producing a
sintered metal body with at least one tooth formation thereof,
said method comprising the s-teps of: (a) providing a sintered
metal body blank; and (b) roll forming said blank to produce said
final tooth form.
Considering the known properties of too-thed gears manu-
factured by powder-metallurgical processes, the opinion in pro-
fessional circles was that highly-stressed gears, such as those
used in gear boxes of automobiles, could only be manufactured by
conventional processes, for instance by a cu-tting and/or grinding
process, particularly since the cold forminq of gears in solid
blanks had proved to be unsatisfactory.
Surprisingly, however, it was discovered that, starting
from a blank made of sintered material, the desired toothing, for
instance the tooth forms usually used for highly-stressed toothed
gears, such as involutes, cycloids, epicycloids, as used for
example on bevel gears r particularly hypoid or curved-tooth bevel
gears, can be manufactured by rollinq the toothing into the sintered
metal blank. It was discovered surprisingly enough, that because
of the space which can be filled up inside such sintered material
blanks, it is possible to displace the material itself in forming
the toothing into the blank, whereby advantageous work~hardening
occurs in the region of the teeth, a fact that is of great advan-
tage particularly for highly-stressed gears. It has been shown,
for instance, that the strength of the rolled flanks of the teeth
and that of the dedendum of toothed pinions made for automobiles
in accordance with the invention are fully comparable or conform
with those of toothed gears manufactured by conventional gear form-
ing processes. Thus the strength limitations applying to gears
manufactured by powder-metallurgical processes are overcome.
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Further, however, the tooth geometry is not a limitation
in the process of the invention, so that the relevant limitation
applying to gears manufactured by powder-metallurgical processes
is equally no longer present.
The invention has shown that not only can toothed gears,
for example, such as pinions, cylinder gears and bevel gears be
manufactured, but also other bodies with toothings, for instance
splined shafts, and worm gears as used for example for plastics
extruders.
During the forming process, therefore, compression of
the material takes place, which becomes apparent in the region of
the teeth, particularly at the top and on both flanks of the teeth
and the tooth bottom or dedendum, by the high degree of strength
of the rolled flanks of the teeth and the dedendum.
The invention is illustrated - partly schematically - in
the drawings which show an embodiment of the invention given by
way of example only. In the drawings:-
Figure 1 shows a body made of a suitable sintered
material, cylindrically formed on its outer surface.
Figure 2 shows a fixture for rolling, viewed from the
top.
Figure 3 is a front view of Figure 2.
Figure 4 is a sectional representation o-f a sintered
metal body with one toothing, shown on a large scale.
The drawings illustrates the invention as applied to
the manufacture of cylindrical toothed gears which have, for
example, an involute tooth form.
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It was found in all cases, that even under a small load
(roll pressure), the sintered material flows at the highest
possible rate. The effect of the speed of rotation is siqnificant-
ly greater in the case of sintered materials, in comparison with
carbon steels. The reason for this is to be found in the different
structure.
Reference number 1 refers to a blank made of a suitable
sintered material, which in the version shown is of a cylindrical
form. The toothing is to be formed into this cylindrical blank
by a cold forming process.
For this purpose, the blank 1 is mounted between centres
(not shown in the drawing). The longitudinal axis of the blank 1
is, for example, parallel to and in the same plane as the longitu-
dinal axes of the two tools 2 and 3, of which one at least is
driven by a motor.
Both tools 2 and 3 are provided with a suitable profile
corresponding to the desired tooth form. In the constructional
form illustrated, the axis of tool 2 is stationary, while tool 3
can be moved in direction of the arrows. A hydraulic cylinder
(not shown) moves tool 3, which is supported in a carriage, towards
the blank 1 until both tools 2 and 3 penetrate into the blank 1
and the tooth form is produced by cold forming. The blank 1 is
set into rotation by frictional resistance. In this way it is
possible to cold form the toothing in one operation.
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