Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
The present invention relates to a rotating shaft consisting of
at least two parts with a hollow space to be used in machine building,
engine construction and gear assembling, as well as a procedure for the
manufacture thereof.
In machine building, engine construction and gear assembling solid
shafts are normally used. In aircraft-engine construction, in which the
ratio between performance and weight is of great importance, bored hollow
shafts have been used at an early stage of development, for installce in the
well-known Hirt-engines, the bored hollow-shaft parts being assembled by
screw joints. It is obvious, however, that such shaft parts may also be
welded together and in following steps be quenched and tempered.
Moreover it is known that objects shaped symmetrically around an
axis of rotation, e.g. shafts with one open end, may be manufactured by
cold-extrusion, a procedure which not only is very accurate and therefore
requires but little machining allowance, but also is relatively cheap. In
addition it allows for a shaping of the hollow spaces which prevents
dangerous stress concentrations and peaks by appropriate fine transitions
where change in diameter occur.
Particularly in machine building, engine construction and gear
assembling there is a demand for, and it is an object of a broad aspect
of this invention to provide lightweight shafts that can be easily manu-
factured and yet have strength properties guaranteeing safe operation, and
in particular for shafts, the diameters of which become smaller towards their
ends and in which the total material used is not wasted in a substantial
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amount of wasteful turnings or the like.
A hollow shaft for use in machine building, engine construction
and gear assembling~ is provided herein which comprises at least two cold-
extruded parts, the parts being undetachably connected with each other in
at least approximately radial planes.
By one broad aspect of this invention a case-hardenable rotary
drive shaft is provided having a first shaft pin end, a second, opposite
shaft pin end, and a central longitudinal axis extending through the ends,
and being composed of at least two shaft parts being axially aligned and
being joined together in at least one joint plane transverse to the longi-
tudinal axis, the drive shaft having an internal hollow space extending
axially and continuously in the interior of the drive shaft, through all of
the shaft parts present to make up the shaft, each of the two shaft parts
comprising the first shaft pin end and the second shaft pin end containing
a solid wall end portion extending transversely to the longitudinal axis
and closing off the respective end of the hollow space in a substantially
gas tight manner, the configuration of the internal wall of the hollow
space corresponding substantially to the configuration of the outer shaft
surface, at least the shaft end part at the first shaft end comprising a
solid transversely extending wa~l end portion of completely solid cross
sectional area, and axially aligned with the solid shaft pin end constituting
the first end, a larger diameter portion on the side of the first end part
facing away from the solid shaft pin end and having a frontal face located
in such joint plane; each such joint plane present in the drive shaft
intersecting the hollow space, whereby the positions of the hollow space
located in the shaft end part at the first shaft end constitute a cavity
in the frontal face of the larger diameter portion thereof and having a
cavity bottom constituted by -the solid transversely extending internal wall
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portion thereof, the rotary drive shaft having an axially extending outer
shaft surface comprising at least two axially aligned, stepped sections of
different radial diameters, at least two of the sec~ions being each of
constant diameter, at least two of the surface sections belonging to one
and the same shaft part~ one of which sections is nearer one of the shaft
pin ends and is of narrower diameter than the other section, each of
the shaft parts being cold extruded, and all shaft parts being joined
together, in any such transverse joint plane present, by substantially
gas-tight friction welding, as required for subsequent case-hardening of
the composite rotary drive shaft, along the peripheries of the joined
together shaft parts about the hollow space traversed by the joint plane.
By a variant thereof, the shaft end part containing the second
opposite end is of the same configuration as the first end-containing
shaft end part.
By another variant, the hollow space has a region of greatest
internal diameter intermediate the first and second ends of the drive
shaft; and wherein the diameter of the hollow space decreases towards the
first and second ends of the drive shaft, at least one such joint plane
extending through the hollow space region of largest diameter and trans-
verse to the longitudinal axis.
Thus, by a broad aspect, the present invention is characterized
by the fact that the parts are cold-extruded and that they are integrally
connected with each other in at least approximately radial planes.
The method according to another aspect of the invention for the
manufacture of the case-hardenable, rotationally symmetric, hollow shaft,
made from at least two shaft parts each of which parts is produced by the
the method of cold extrusion, which shaft parts are joined with each other
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by welding in regions of constant shaft diameter is provided, comprising
(a) forming the parts destined to be the two oppoSitQ shaft end parts by
cold extrusion, each part having an axial cavity closed at one end there-
of and constituting one of the ends of the hollow space in the shaft;
(b) forming any other, intermediate shaft part likewise by cold extrusion;
at least one of the shaft parts consisting of at least two stepped re-
gions, each being of constant diameter, the diameters of these regions
being stepped down toward a closed shaft end, the configuration of the
internal wall of the hollow space in the hollow shaft corresponding sub-
stantially to the configuration of the outer shaft surface; and (c3
friction-welding the shaft parts together, with the weld between adjacent
shaft parts being located in a joint plane, with the cavities of the
adjacent shaft parts opening in the joint plane, and the cavity of at
least one of the adjacent shaft jparts having its largest diameter in
the joint plane; whereby a finished shaft having a continuous hollow
space in tis interior, sealed at all sides, is obtained.
In the accompanying drawings, which all are longitudinal sections
through the axes of rotation,
Fig. 1 shows two halves of a stepped hollow shaft tapering
towards the ends on both sides, which are manufactured by cold-extrusion
known per se;
Fig. 2 shows the two hollow shaft parts according to Fig. 1,
after having been welded together by friction welding;
Fig. 3 shows two other shaft parts after cold-extrusion and
before friction welding;
Fig. 4 shows the shaft after joining the two parts according to
Fig. 3 by friction welding;
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~ Fig. 5 shows solid shaft of the prior art corresponding to the
hollow shaft according to Fig. 2 in outer shape, but produced by conven-
tional methods;
Fig. 6 shows a further solid shaft of the prior art, produced by
conventi~nal methods~ the smaller section of which lies between two larger
diameters, C indicating waste material in case the shaft is cold-extruded;
Fig. 7 shows a solid shaft of known design of the prior art with
the largest diameter at one end produced by conventional methods;
Fig. 8 shows a shaft of the same shape as that of Fig. 7, but with
a closed hollow shape;
Figs. 9 and 10 show h~lves of a shaft being cold-extruded as hol-
low bodies and ready for being joined together to form a shat according to
Fig. 8;
Figs. 11 shows a solid shaft of the prior art, produced in a conven-
tional manner, with two stepped sections between larger diameters, C indica-
ting waste material in case the shaft is cold-extruded;
Fig. 12 shows a shaft corresponding to Fig. 11 but with a closed
hollow space;
Figs. 13, 14 and 15 show shaft parts cold-extruded as hollow bodies,
ready ~or being joined together to form a shaft according to Fig. 12;
Fig. 16 shows a conventional solid shaft of the prior art with
different diameters;
Figs. 17 and 1~ show cold-extruded shaft parts of a hollow body
being the constituent parts of the shaft sho~n in Fig. 19;
Fig. 19 shows a shaft according to Fig~ 16 manufactured as hollow-
shaft embodiment according to an aspect of this invention.;
Fig. 20 shows a further solid shaft of the prior art of convention-
al manufacture and design;
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Fig. 21 and 22 show the cold-extruded shaft parts of a hollow body
which are joined together according to an aspect of this invention;
Fig. 23 shows forming the hollow shaft according to an aspect of
this invention which has the sarne outside dimensions as the parts shown in
Figs. 21 and 22;
Fig. 24 shows a solid shaft of the prior art of known manufacture
and shape;
Figs. 25 and 26 show the shaft parts of a hollow body manufactured
according to an aspect of this invention, which are joined together forming
the hollow shaft as shown in Fig. 27; and
Fig. 27 shows a section through the hollow shaft formed from the
shaft parts of Figs. 25 and 26.
In Fig. 1 two hollow-shaft parts 1 and 2 can be seen with hollow
spaces 4 and 5 and axes of rotation 7 and 8. The hollow spaces 4 and 5 are
stepped by shoulders 10 and 11. The two hollow-shaft parts 1 and 2 are
manufactured in a known manner by cold-extrusion. The precision of these
parts is very high and hence the machining allowance required for the
finishing operation is small. The hollow spaces 4 and 5 are very accurately
sy~metrical with respect to the axes of rotation 7 and 8. The two hollow-
shaft parts 1 and 2 are joined together by friction welding - a procedure
which is also well-known,forming a shaft 13O The friction-welding seam 15
is shown in Fig. 2 and due to the total hollow space 16, which is gas-tight
under norrnal operating conditions and liquid-tight, a substantial saving in
material and thus a corresponding reduction in weight is achieved compared
to known shafts of this kind. The wall thickness shoul~
be sufficient to resist the mechanical and thermal stresses and strains.
Another embodiment wherein the two shaft parts 20 and 21 are not
symmetrical is shown in Fig. 3, and Fig. 4 shows the finished shaft 23 with
the friction-welding seam 24.
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Such hollow shafts are up to 50 percent lighter than solid shafts
of corresponding strength.
The present invention in its various aspects is of particular inter-
est due to the fact that cold-extrusion allows for the manufacture of shafts
which, with respect to diameters, taper towards their ends or towards one of
their ends to a large extent which would make the placing of hollow spaces
in the shafts extremely difficult if it had to be undertaken in a different
malmer .
In principle,it is also possible to join together the parts. which
may also be more than two, of such a shaft shaped symmetrically around an
axis of rotation by means of resistance butt welding instead of the cheap
friction welding. Furthermore it is possible to join the individual hollow-
shaft parts through welding by electron beam.
It has been found that these hollow parts of such high precision can
be produced economically in employing the cold-extrusion process and that
for the same reason as just mentioned, namely that the shaft is of rotational
symmetry, no intolerable shifting of weights occur which change the center of
gravity. The inner spaces which are hermetically sealed under normal operat-
ing conditions guarantee that no impurities, e.g. scaling and melting losses
and the like, can get into the machine, or the engine, or the gear during
operation. Neither can the space fill up with oil from the outside, which
is advantageous as far as the amount of oil to be filled in is concerned.
The volume of material saved by cold-extrusion (due to the hollow
space) leads to a substantial reduction of the entire material used and for
that reason to a corresponding cost reduction of the whole workpart.
37~a 19~
As shown in Figures 3 and 4 the described procedure also allows for
the manufacture of shafts which have two sections of larger diameters and
a mid-section of a smaller diameter. This relatively frequent type of shaft
can be manufactured by way of cold-extrusion only if substantial am.ounts of
material are accumulated at the tapering sections. The new
procedure eliminates this disadvantage.
Figures 5 to 2, show further embodiments of solid shafts and hollow
shafts, which need not be described in great detail herein.
The shafts according to aspects of this invention have the follow-
ing advantages:
1. Reduction in weight ~hrough placing a hollow space closed initself within the interior of up to now solid shaf-ts.
2. Production methods bv
(a) cold-extrusion of two or more parts with hollow spaces at
one end,
(b) joining of the parts according to (a) by friction welding.
3. The posibility of economical shaping of the hollow space in the
course of the cold-extrusion process with the following ad-
vantages:
The shape of the hollow space follows the outer shape and
thus results in an optimum reduction of weight and optimum
geometrical shapes for polar and axi~l moments of inertia, as
well as for the smallest optimum possible losses in torsional
and bending strength.
Ideal transitions at changing diameters whereby a notch effect
is avoided.
Uninterrupted grain flow along the workpart irrespective of
all shoulders.
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The use of hollow par~s instec3d of solid oncs, in particular of
shafts and axles in the driving systems of vehicles, allows for a substan-
tial quantitative reduction of the weisht of the entire vehicle, and yet the
resistance of these parts against the mechanical stresses and strains
through bending and torsion is not substantially lessened.
Most of the mentioned parts present journals of much reduced
diameters at both ends. Even in cases where the design would still allow
cutting of the hollow spaces, this method is out of question for reason of
economy. This procedure according to an aspect of this invention, however,
makes the economical production of these parts possible and offers the
following advantages:
1. The individua] hollow parts open at one end or at both ends
can be economically produced by cold-extrusion or similar
procedures before welding.
2. I'he shape of the hollow space can be adapted to the outer
shape without any difficulties in employing the cold-ex-
trusion process. Thus optimum stress ratios are achieved
at sections of changing diameters.
3. In manufacturing the individual parts for a hollow shaft it
is possible - thanks to the proposed cold-extrusion process -
to extend the hollow spaces into the relatively long shaft
sections, while the production process still remains econo~
mical. Thus an optimum reduction of weight can be achieved.
4. Employing the cold-extrusion process the shoulders at the
transitions of different diameters can be designed with
respect to the flow lines in such a way that no significant
stress concentration occ~rs, which could impair the fatique
strength of the part.
5. Throug}l cold--extrusion the difference in concen~ricity be-
tween hollow space and outside shape can be kept so small
that no disturbing unbalanced forces will occur. Thanks to
the obtainable small difference in the wall thickness no
intolerable distortions result through auenching due to the
fo~lowins case hardening.
6. The quantitative reduction of material thallks to the hollow
space results in a sub~stantial reduction of costs for raw
material, which fully r compensates for the additional ex-
penses that may arise in certain cases when employing the
procedure according to the invention.
7. Up to now parts with nec~s as for instance the back gear shaft
according to Fig. 6 and ~ig. 11 could not be produced economi-
cally by cold-extrusion even as solid parts, because this
would have required a die partible in two planes, or because
expensive raw material in excess at the aress A and ~ in Fig.
6 and Fig. 11 would have to be cut off.
8. Up to now journals of relatively much reduced diameters at one
end or at both ends of the shaft could be manufactured as one-
piece solid shafts only with additional costs for shaping and
cutting. This problem is easily solved by manufacturing these
shafts out of two or more hollow parts without any additional
costs accruing-
9. If parts of complicated shapes are to be manufactured, e.g.shafts with small shanks and large flanges, problems arise in
shaping because of the flow of material to very small and
very large diameters. In extreme cases these problems cannot
be solved at al~ or onlv a~ sub~tantially higher costs. These
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difficulties ar substantlally e~iminated by the procedure
according to asl~ects cf this invention, since by way of manu-
facturing two or more inc'ividual parts which are joined to-
gether later tile critical cross-sectional transitions are
avoided.
10. If solid shafts are cold-extruded the material-quantity
tolerance of tlle slug flows into the smaller end of the shaft.
Since the diameter of this section is relativ~ly small, this
flow results in an unacceptable length-tolerance in the finished
1~ extruded part, which requires the additional operation of
trimming. IE the procedure according to aspects of this in-
vention is employed the mentioned tolerance occurs at the point
of weld and can be reduced to the required extent bv appropri-
ate control of the welding-process according to an aspect of
the invention without any additional costs accrueing.
11. The liquid-tight and gas-tight hollow space produced by weld-
ing together the respective shaft parts is hermetically sealed
towards the outside. Thus, any further treatment or cleaning
after the welding process in order to remove scale and residues
is not required.
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