Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
1325883
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PROCESS FOR PRODUCING A CONNECTION
Descriptlon
The Inventlon relates to a process for produclng a connect-
tlon between a hollow shaft and deslgn eiementsslId on to
the shaft and havlng anaperture whlch corresponds to the
outer dlameter of the hollow shaft, especlally for pro-
duclng assembled camshafts, crankshafts or tranmlsslon shafts
by hydraulically expandlng the hollow shaft , a process whlch
results In plastlc deformatlon and permanent elastlc pre-
tenslon In the surface layer of the aperture of the slId-
on deslgn ele~ents, as well as to deslgn elements sultable
for thls process.
The process of the above type for connectlng deslgn elements
wlth hollow shafts has been found to be partlcularly sucess-
ful In the fleld of camshafts. As compared to so-called
shrlnk connectlons It Is advantageous In respect of the
transmlsslon of torque as the achlevable tenslon Is not
r~strlcted by temperature llmlt values for the materlals
whlch must not be exceeded when Jolnts are produced. As
compared to soldered connectlons, the advantage essentlally
conslsts In the fact that the process Is slmplIfled; In
prlnclple It can be carrled out under cold condltlons and
Is therefore more cost-effectlve. Furthermore, the Indl-
vldual components may be manufactured wlth smaller tolerances.
It Is the object of the present Inventlon to Improve
the process of the above-mentloned type even further
In respect of the torques transferable between the deslgn
1325883
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elements and the hollow shaft, therebY extendlng the range
of application to components such as assembled crankshafts
subject to highest loads wlthout having to do wlthout the
baslc process-related advantages In producTng the connectlon.
The obJective of the Invention Is achieved by provlding a
process which ts characterlsed in that the hydraulic ex-
panslon of the hollow shaft results In a materlal-locking
connectlon between the materlal of the surface layer of
the aperture of the deslgn element and the materlal of the
plastlcally deformed hollow shaft.
The process in accordance wlth the Invention ensures that
the percentage of surface area whlch Is directly contacted
and at which the adheslon effect causlng the materlal-lock-
lng connectlon occurs Is Increased considerably. In this
way, the transferable torque dependent on the product of
area fit and frlctlon coefficient Is Increased considerably
~Mt = ~z x Fr). Whereas In the case of purely force-locklng
co~nnections the journal friction coefficients~z were empriric-
ally determined as being in the region of 0.1 to 0.65, the
journal frlction coefflclent ~z of connections produced
in accordance wlth the Inventlon Increases to values In
excess of 1 and may reach up to a multiple of 1. The per-
centage of mechanlcal toothing effects between surface
Irregularities as otherwise utulIsed In press-fittlng
connectlons may be regarded as relatlvely inslgntficant
because even if the counter faces are machined with the
utmost accuracy, only a small percentage of the theoretical
surfaces Is In direct contact. By Increasing the pressure
on the faces to be connected up to the point of plastic
deformation of the material, as proposed by the invention,
the area percen~ages In contact with each other Increase
to an optlmum value.
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Wlth thls process, the compressive force during the applic-
atlon of pressure, which Is decisive for the remalnlng
frlctlon coefflclent, Is greater than the compresslve force
remalnlng after completion of the expanslon process. In
prlnclple, the moments achlevable wlth such a pressure
connectlon are greater than those of a shrink connectlon
In the case of whlch the maxTmum compresslve force is at
the same tlme the remalnlng compressive force.
In the case of the process In accordance with the Inventlon,
In addition to the plastic deformation of the hollow shaft
It Is also possible to achleve a plastlc deformatlon at
least tn the surface layer of the aperture of the desTgn
elements by applying hTgher hydraulic pressures. The de-
sired effect depends on metalllc particles of both surfa_es
coming directly Into contact with each other.
An optimum connection is achieved by using a hlgh-tensile
material for the design elements, with the wall thlckn~ss
-and;flow limit of the material determinlng the range of
the plastically deformed aperture layer. The area pressure
applled in the course of expansion Is substantlally greater
than the remaining compression whlch may be llmited, for
example, by the tube wall thlckness or the yleld polnt of
the tube. This process is also sultable for sufflciently
torlonally stlff tubes wlth a large diameter, but a small
wall thickness and thus a limited stTffness agalnst external
pressures. In this way it is posslble to produce llghtwelght
camshafts and crankshafts with thin-walled tubes. It Is also
posslble to apply the process to aluminium tubes or titanium
tubes, for example, which otherwlse have too low a modulus
of elasticlty.
In a first advantageous embodiment of the process according
to the Inventlon, the proposed appllcation of pressure
results in a plastic deformatlon of such an extent that any
oxide layers inhibltlng the connection are destroyed In tha
course of expanslon. It is of course assumed that the surfaces
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to be connected comprise oxtde layers of a sllght thickness
only, such as they70ccur in a normal atmosphere wlthout any
partlcularly unfavourable condltlons such as humldlty or
the effect of acld.
In a second embodlment of the process In accordance wlth the
Inventlon, the surfaces of the parts to be connected are
prepared so as to be metalllcally clean prior to produclng
the connectlon, I.e. by applylng a machlning process or
treating the parts In a reduclng atmosphere, and the reduclng
or Inert atmosphere Is malntained untll the connectlon Is
produced. The advantage of the type of process described
here Is that no oxtde Incl U5 lons or coating Incluslons
remaln In the connectlng layer, the result belng a connectlon
of an even hlgher quality whose strength Is Improved even
further as compared to the above-descrlbed connectlon.
According to a third embodiment of the process accordTng to
the invention, the aperture of the design element and/or
the surface of the-hollow tube Is provided with a-surface
layer which is partlcularly suitable for the sald type of
connectlon, with thls operatlon preferably taklng place after a pre-
treatment for obtalnlng a clean metalllc surface, but it
Is also posslble to do wlthout such a pre-treatment.
The metal layer applled for Improving the adheslon effect
has a thickness of only a few "A". The adheslon effect may
be positively affected by the type of material selected.
Thls Is the case If both counter faces are the same In
respect of thelr atomlc bondlng propertles, If the materials
have a high surfaceenergy and boundary surface energy and
In particular-, If they conslst of cubTcally surface-centered
metals. The metâls should have a high melting point and
should not be easlly Influenced by chemical surroundlngs,
such materlals belng copper, sllver, pureiron, austenitlc
steel, zinc and nlckel.
132~883
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Such surface layers may be applled mechanically, e.g. by
being brushed on, with rotatlng wlre brushes belng guided
through the aperture whose metal is abraded during thTs
process stage and remains on the surface. In an advantageous
embodiment, an already existing oxlde layer on the surface
to be coated may be abraded or partlally destroyed. The
brushes may also be provlded wlth a percentage of very
hard bristles, In order to Improve abrasion on the oxlde
layer. For applying such surfaces wlth a small thickness
It Is also possible to use electro-plating or plasma spraylng.
A further aspect of the material used for applying a surface
layer Is Its high plast7c deformablllty as compared to the
base materlal of the design element. The subject of the
invention therefore also refers to the build-up of such
elements whose coating in the aperture has a thickness of
only a few Angstrom and Is characterised by one or several
of the above-mentioned favourable features, both in respect
of the corrosion and bonding propertT~s and also the strength
properties relative to the base materlal.
In a fourth embodiment of the process in accordance with the
Invention, not only the adheslon effect, but also the effect
of abrasion, I.e. grooves is utllIsed In produclng the connect-
tlon. If as a result of the compresslve force applled in the
ourse of jolnlng the effective area of contact Is increased
for
in size, it Is posslble/both the adheslon and abrasion effects to
be used to ensure adherence. In the process, in order to
achleve "micro-machTning" or "micro-joining", abrasively
actlng partlcles, e.g. mineral, brittle partlcles are applled
to the surfaces to be connected In the finest possible distrib-
ution. In a preferred embodlment, the abrasively acting
partlcles are applied joTntly with the metalllc or chemlcal
coating already proposed for improving the adheslon effect.
These parttcles are of such a nature and applled in such a
way that adhesion cannot be adversely affected, the adheslon
par~icles being very fine-gralned dlamond or corundum dust
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or simtlar hard mineral products. It is important that the
partlcles should not have any oxidising effect.
The adheston effect Is Increased If the surface coatlng
Into whlch the partlc~es are pressed have a htgh strength
or hardness. If the adheslvely acting layer Is very thln,
the partlcles may be pressed through this layer into the
hard base of the surfaces to be connected.
