CA1325883C

CA1325883C - Process for producing a connection

Info

Publication number: CA1325883C
Application number: CA000584126A
Authority: CA
Inventors: Helmut Swars
Original assignee: Emitec Gesellschaft fuer Emissionstechnologie mbH
Current assignee: Vitesco Technologies Lohmar Verwaltungs GmbH
Priority date: 1987-12-15
Filing date: 1988-11-25
Publication date: 1994-01-11
Anticipated expiration: 2011-01-11
Also published as: EP0320789A3; DE3742480A1; DE3871105D1; EP0320789B1; EP0320789A2; IN170925B; KR890009486A; KR930006043B1; JPH01197022A; BR8806589A; MX172866B; DE3742480C2

Abstract

Abstract The invention relates to a process for producing a connection between a hollow shaft and design elements slid on to the shaft and having an aperture which corresponds to the outer diameter of the hollow shaft, especially for producing assembled cam-shafts, crankshafts or transmission shafts by hydraulically expanding the hollow shaft, a process which results in plastic deformation and permanent elastic pretension in the surface layer of the aperture of the slid-on design elements and in the case of which the compressive force in the connected region between the hollow shaft and the aperture is very much higher during the hydraulic expansion process than the remain-ing compressive force after completion of the expansion process.
As a result, there occurs a material-locking connection between the material of the surface layer of the aperture of the design element and the material of the plastically deformed hollow shaft.

Description

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 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.

132~883 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 132~883 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 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 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.

Claims

1. A process for producing a connection at ambient temperature between a hollow shaft and design elements, comprising the steps of:

providing each of the design elements with an aperture which corresponds substantially to an outer diameter of the hollow shaft;

eliminating the oxide layer on surfaces of the apertures of the design element and an outer surface of the hollow shaft by machining said oxide layer, by applying a reducing atmosphere to said oxide layer, or by applying a reducing bath to said oxide layer;

sliding the design elements onto the hollow shaft; and hydraulically expanding the hollow shaft so that the hollow shaft plastically deforms and permanent elastic deformation results in the design elements, so that the plastic deformation of surface layers of the apertures of the design elements create permanent adhesion forces between the outer surface of the plastically deformed hollow shaft and the plastically deformed surface layers of the apertures in the design elements.

2. A process according to claim 1, further comprising the step of inserting and maintaining all parts to be connected in a reducing or an inert atmosphere after the step of eliminating the oxide layer, and until the expanding step takes place.

3. A process according to claim 1, further comprising a step of applying a metallic layer on the surfaces of the apertures of the design elements or on the surface of the hollow shaft, or both, which improves the adhesion forces of the connection, prior to said expanding step.

4. A process according to claim 3, wherein the metallic layer-applying step includes applying the metallic layer mechanically.

5. A process according to claim 4, wherein the metallic layer-applying step includes brushing on the metallic layer.

6. A process according to claim 5, wherein the step of eliminating the oxide layer is effected simultaneously with the step of brushing on the metallic layer.

7. A process according to claim 3, wherein the metallic layer-applying step includes applying the metallic layer by electroplating or plasma-spraying.

8. A process according to claim 3, wherein the metallic layer-applying step includes applying a layer of a metal which does not corrode in a normal atmosphere.

9. A process according to claim 3, wherein the metallic layer-applying step includes applying a layer of a metal having atomic bonding properties equivalent to those of the hollow shaft or the design elements.

10. A process according to claim 3, wherein the metallic layer applying step includes applying a layer of a metal with a higher surface energy than that of at least one of the hollow shaft and the design elements.

11. A process according to claim 3, wherein the metallic layer-applying step includes applying a layer of a metal having a cubic face-centered lattice structure.

12. A process according to claim 11, wherein the metal is selected from the group consisting of: copper, silver, pure iron, austenitic steel, zinc and nickel.

13. In a process for producing a connection at ambient temperature between a hollow shaft and design elements, comprising the steps of:

providing each of the design elements with an aperture which corresponds substantially to an outer diameter of the hollow shaft;

sliding the design elements onto the hollow shaft; and hydraulically expanding the hollow shaft so that the hollow shaft plastically deforms and permanent elastic deformation results in the design elements;

the improvement which consists in applying a metallic layer to the surfaces of the apertures of the design elements and to at least the areas of the outer surface of the tube received within said apertures and carrying out said expanding step by applying hydraulic pressure to cause plastic deformation of surface layers of the apertures of the design elements and to create permanent adhesion forces between said metallic layer on the outer surface of the plastically deformed hollow shaft and said metallic layer of the plastically deformed surface layers of the apertures in the design elements.

14. A process according to claim 13, wherein the metallic layer-applying step includes applying the metallic layer mechanically.

15. A process according to claim 14, wherein the metallic layer-applying step includes brushing on the metallic layer.

16. A process according to claim 13, wherein the metallic layer-applying step includes applying the metallic layer by electroplating or plasma-spraying.

17. A process according to claim 13, wherein the metallic layer-applying step includes applying a layer of a metal which does not corrode in a normal atmosphere.

18. A process according to claim 13, wherein the metallic layer-applying step includes applying a layer of a metal having atomic bonding properties equivalent to those of at least one of the hollow shaft and the design elements.

19. A process according to claim 13, wherein the metallic layer applying step includes applying a layer of a metal with a higher surface energy than that of at least one of the hollow shaft and the design elements.

20. A process according to claim 13, wherein the metallic layer-applying step includes applying a layer of a metal having a cubic face-centered lattice structure.

21. A process according to claim 20 wherein the metal is selected from the group consisting of: copper, silver, pure iron, austenitic steel, zinc and nickel.

22. In a process for producing a connection at ambient temperature between a hollow shaft and design elements, comprising the steps of:

providing each of the design elements with an aperture which corresponds substantially to an outer diameter of the hollow shaft;

sliding the design elements onto the hollow shaft; and hydraulically expanding the hollow shaft so that the hollow shaft plastically deforms and permanent elastic deformation results in the design elements;

the improvement which consists in eliminating the oxide layer on one of the surfaces of the apertures of the design elements and an outer surface of the hollow shaft by machining said oxide layer, applying a reducing atmosphere to said oxide layer, or applying a reducing bath to said oxide layer; applying a metallic layer on the other of the surfaces of the apertures and the outer surface of the hollow shaft; and carrying out said expanding step by applying hydraulic pressure to cause plastic deformation of surface layers of the apertures of the design elements to create permanent adhesion forces between the outer surface of the plastically deformed hollow shaft and the plastically deformed surface layers of the apertures in the design elements.

23. A design element with an aperture, for connection to a hollow shaft by sliding the design element onto the hollow shaft and hydraulically expanding the hollow shaft so that the hollow shaft plastically deforms and permanent plastic deformation results in a surface layer of the aperture of the design element, the design element comprising a surface layer of the aperture having a thickness of several Angstrom units which is connectable with the hollow shaft by permanent adhesion forces.

24. A design element according to claim 23, further comprising a base material having a high strength relative to the surface layer material.

25. A design element according to claim 23, wherein the surface layer is of a material which is a precious metal or a semi-precious metal.

26. A design element according to claim 23, further comprising abrasive particles applied together with the surface layer material.

27. A design element according to claim 26, wherein said abrasive particles are minerally pure, non-oxidizing particles.

28. A design element according to claim 27, wherein said minerally pure, non-oxidizing particles are diamond dust or corundum.