CA2229899C

CA2229899C - Reinforced formed part, process for its production and its use

Info

Publication number: CA2229899C
Application number: CA002229899A
Authority: CA
Inventors: Alfred Ebbinghaus
Original assignee: Individual
Current assignee: Individual
Priority date: 1995-09-04
Filing date: 1996-09-03
Publication date: 2006-02-14
Anticipated expiration: 2016-09-03
Also published as: CA2229899A1; EP0850113B1; DE19635734A1; WO1997009134A1; EP0850113A1; ES2168516T3; AU7489596A; DE59608388D1; EP1090697A3; DE29514164U1; EP1090697A2; JPH11512171A

Abstract

A reinforced formed part having longitudinal or cross-sections of different form or size, as necessary, having a hollow external formed part and a metal foam filling, produced by foaming the foam material in the formed external formed part with a closed cell foam with high resistance to deformation, the foam filling being at least in part in contact with the external formed part filling the internal cavity of the hollow external form ed part, at least in part, and improving the mechanical resistance of the external formed part to deformation, as well as a process to produce the formed part, where a hollow section is produced by a forming process as known per se and a foam body is then introduced into the formed part in such a way that the foam body, at least in part, makes contact with the hollow part and is attached in the hollow part by snug fit or by a known attachment method, as well as the use of the formed part, as described herein, as a supporting part in scaffolding, framework, for example, in construction, in vehicle building fo r air, land and water craft and furniture.

Description

REINFORCED FORMED PART, PROCESS FOR ITS PRODUCTION AND ITS USE
The invention relates to a process for the production of a reinforced, one-piece formed part, reinforced formed parts having longitudinal and/or cross-sections of different form and/or size, as necessary, and to their use. It relates in particular, to formed parts which are at least in part hollow, with longitudinal and/or cross-sections which are different in form and/or size, having a hollow outer form and a filling of open or closed cell foam.
Supporting elements made from hollow material, such as tubes, rods, hollow supports (e.g. supporting parts for bicycles, car rear axles, exhaust pipes etc., produced by the internal high pressure forming process) are known for a wide variety of applications - for example, for building constructions, in particular bridges and/or houses - as supporting and bearing elements or also for the construction of air, land and water craft, shelving systems etc.
Amongst other things, they have the advantage that they make it possible for the design to be light but resistant to loads For example, in the case of motor vehicles, lattice framework structures have recently been used again to save weight, in order to provide a structure that is particularly light, resistent and torsionally rigid. Even in aircraft, where saving weight is an essential aspect of construction, a lattice-work frame with hollow or solid lattice-work bearing parts is used.
The known bearing structures and elements are still capable of improvement because it is always desirable to make them even more resistent - in particular with improved burst strength.

What was also a disadvantage was the fact that very thick walls always had to be used for supporting hollow parts, which resulted in this part being undesirably heavy -especially if increased burst resistance and/or load bearing capacity was desired. Where walls were thick, problems also occurred in the production of complicated forms, because the straight-forward forming processes, which could only be applied to low-strength materials, could no longer be used.
The foam filling of hollow parts, for example in order to change their vibration characteristics, is already known. For example, cardan shafts are foam filled in order to improve their running characteristics. Where hollow parts are foam filled in this way, the foam, which in this case, is not highly resistant to deformation, contributes nothing to the deformation properties of the shaft and merely acts as a vibration-modifying addition.
Mufti-section steel railway axles filled with polyurethane or epoxy resin foam, have become known from US-A-4,200,326 (Wa,CO~, where the plastic foam is used to link the ends of the external and internal wall of a mufti-part hollow axle or wheel part and is therefore used to transfer the driving force and to absorb bending forces.
However, these plastics are unable to absorb any substantial compression forces and are used as additional flexible links with reset forces, between the individual parts of the railway axle and wheel.
The use of metal foams of high deformation strength as impact protection for motor vehicle trim is known from DE-GM 94 OZ 743 where a metal foam is used as a deformation cushion. Here, the metal foam alone acts as an energy-dissipating part, i.e.
as a "cushion" of a deformation part. We are not talking of a supporting part, but of a deformation part where the foam itself is not a reinforcement for the external parts or any supporting part.

From US-A-3,275,424, open cell metal foams, which are produced in hollow external parts, are known to be used as filters - here we are dealing with the special case of a filter and in no way with a supporting part.
From US-A-4774117 (OEFNER) a load bearing part has become know which comprises a composite fibre structure, which is relatively rigid at least at the center of the supporting part and is elastic at the ends, which is brought about by the fact that composite fiber parts are provided in a lamellarlsandwich-like arrangement, separated from each other by partitions, over the entire width of the supporting part. The structure in question is a multi-layer construction which is ideal for the flexible absorption of bending and torsion forces - but not for providing high compression resistance.
It is therefore the problem of the invention to produce light-weight parts which are lighter and have the same or better load bearing properties, than known individual parts.
This problem is solved by the invention by a process for manufacturing a reinforced, one-piece formed part, by way of:
a) producing a hollow external formed part by a forming process as know per se and b) foaming a foamable material in the hollaw external formed part, so that at least part of the foam rests against the external formed part and so that it is connected to it, at least by being in contact with it and that its mechanical resistance to deformation is improved.
According to an aspect of the present invention, there is provided a process for the production of a formed part according to any one of claims 1 to 8, wherein a hollow external formed part is produced by a forming process and at least one powder metallurgically produced prefoam body is introduced into the hollow external formed part and foamed therein in such a way that the foam body, at least partially rests against the hollow part and is attached within the hollow part.

Accordingly, the invention provides a reinforced, one-piece formed part with longitudinal or cross-sections which are different either in form or size, having a hollow external formed part and a metal foam filling produced by foaming a foam material in the hollow external formed part with a closed cell metal foam with strong resistance to deformation, which rests at least partially against the external formed part, at least fills the inner cavity of the hollow external formed part and improves the mechanical resistance of the external formed part to deformation.
Hollow formed parts known per se, such as seamless or welded tubes or other known profiles may be used as the hollow external formed part. However, it is also possible to produce such formed parts specially and to design them according to requirements.
Materials available for this, include metals, but also plastics, including ceramics and glass.
It is particularly beneficial if, for example, hollow parts of special shape, which are particularly resistant to burst, for example, such as longitudinally corrugated hollow tubes, bent tubes or similar, are reinforced.
In this case, it is beneficial, for reasons of strength, if the fibre flow of the material of the external form essentially runs parallel to the external contours of the formed part, as is possible, for example, by manufacturing the external formed part using the known internal high pressure forming process. This means that the appropriate cold forming materials are known to the expert.
It can also be beneficial for the external formed part to have several tiered layers running parallel to each other, of the same or different materials, the fibre flows of which run parallel to each other.

4a To save weight in particular, the entire part may be made essentially from the same or different light metals. For example, the light metal can be aluminium or an aluminium alloy, which is also associated with good corrosion resistance.
It is possible and for many applications desirable, that the part has fibre-reinforced materials, which are light weight and possess a good mechanical load-bearing capacity.

Naturally, materials can also be used for the external formed part which have been hot formed in the known manner, for example hot formed plastics, such as blown or cast plastics, including fibre-reinforced plastics, which gain considerable bearing strength as a result of the internal foam.
The part may have different longitudinal sections and also different cross-sections.
It may be beneficial, for the individual parts of the foam filled formed part to be made from different materials, such as metal/ceramic; metal/plastic foam; metal foam/plastic outer wall etc.
It may be usefizl for at least one hollow section to have depressions and/or moulded openings.
The problem is also solved by a reinforced formed part possibly with longitudinal and/or cross-sections of different shape and/or size having a one-piece,.hollow external formed part (12) and a foam filling of open or closed cell foam (14) inside the external formed part, said foam being highly resistant to deformation and being in contact, at least in part, and connected to the external formed part, at least partially filling the internal cavity of the hollow external formed part (I2) and improving the mechanical resistance to deformation of the external formed part.

To production hollow formed parts, a hollow external form is produced in the known way by drawing, casting, extruding or internal high pressure forming and then filled with the foam starting material.
The hollow external part can be made, at least in part, of metal, which is produced by an internal high pressure forming process and in which the foam material is subsequently expanded.
The production of plastic foams is normal and known = that of metal foams has become possible recently, where, for example, a propellantlmetallic mixture is expanded in the hollow external form in a manner known per se (see Studiengesellschaft Stahlanwendung e.V., practical research; P 286 - Prospective market study on the use of steel foams by Dipl. Ing. Markus Weber, Verlag and Vertriebsgesellschaft mbH, Diisseldorf 1995).
A steel or aluminium foam for example, may be selected as the metal foam or any other metal foam may be chosen based on the requirements and intended use of the hollow part.
For example, it may be appropriate for the foam filling to be a closed cell plastic filling if the main purpose is vibration attenuation or corrosion prevention iri the cavity.
However it may also be expedient for the foam filling to be a metal foam, if for example, it is to be exposed to high temperatures or if it is to support/stabilise the external formed part. Filling the external formed part with foam also improves the elastic characteristics of the external walls as well as the thermal and acoustic insulation. However, it can even be a glass or paper foam.

The foam can be of the open cell type, thus enabling, for example, fluids to pass through in order to cool or heat the formed part.
A preferred embodiment of the manufacturing process for parts, comprises the following stages: ' Provision of a hollow profile, if necessary of varying diameters;
Insertion of a section of a hollow profile into a mould with an enlargement in the forming area;
Application of an internal high pressure to the tube, so that the wall of the tube is expanded in the expanded area of the mould;
Removal of the formed hollow section with enlargements and, as appropriate, introduction of a foam starting mixture comprising foam material and propellant into the hollow section and activation of the propellant, so that the foam fills the hollow section.
By the internal high pressure process mentioned, also known as the IHI' process, is meant, in this case, the process that has been described, for example, in the Industrial Gazette [Industrieanzeiger] No. 20 of 9.3.1984 and also in "Metallumformtechnik"
[Metal forming technology], Edition 1D/91, page 15 ff A. Ebbinghaus:
"Precision workpieces of light construction, produced by internal high pressure forming"
or also in "Werkstoffund Betrieb" [Material and operation] 123 (1990), 3, page 241 to 243: A.
Ebbinghaus: "Economic construction with internal high pressure formed precision workpieces" and also in "Werkstoil'und Betrieb" 122. (1991), I I (1989), pages 933 to 938. In order to avoid repetition, reference is made below.to their fizll divulgation. This process was only used hitherto, to production different formed hollow parts, such as for the production of built cam shafts to attach cams to a tube, to production hollow cam shafts and also to production motor vehicle frame parts.

Surprisingly, this internal high pressure process makes it possible to form completely new types of hollow metal parts, where the fibre flow in the area of the intersection and of the walls, runs essentially parallel to the external contour, without there being any burst or other weaknesses. These hollow formed parts can therefore be developed in a lighter form than hitherto, by virtue of the high wall strength. produced by the favourable fibre flow and the reinforcement provided by the internal foam filling, thus making possible considerable savings in weight. It is also possible to use laminated materials for the external form, provided they can be formed together. By selecting suitable materials, laminates can be lighter than solid materials and also have the advantage of attenuating vibrations and also comprising on the surfaces, in keeping with the ambient stresses (i.e.
corrosion by acids etc.) or for aesthetic reasons (colour) other layers, so that a part of this nature has additional beneficial vibration damping characteristics, because the foam filling makes flexible contact with the external walls, depending on the material - in other words, the materials are affected less by vibrations.
A mufti-layer metal tube can also be selected as the starting part, depending on the requirements made of the material. Mufti-layer developments have the advantage that the surfaces of the hollow section can withstand different stresses and also have the advantage that they are poor conductors of all types of vibrations, which decisively improves the vibration characteristics of the hollow section in use. However, it is also possible, to provide a metal foam in a plastic tube, particularly if the plastic outer layer is required for corrosion or other reasons, for example because of the lubrication properties of the plastic etc.

Beneficial uses of the part according to the invention include land, air and water craft, bicycle, motor cycle and car frames, building and civil engineering, scafFolding, shelving systems and furniture.
It can, in particular, be used in all area's of light-weight construction.
Because largely sealed, foam-filled hollow sections according to the invention, are used as structural parts, this enables extremely light but strong, vibration-attenuated parts to be used.
The fact that an internal high pressure forming process is used, makes it possible to produce bosses, indentations, openings and similar on the external hollow part in one forming process. This makes it possible to reduce subsequent treatment stages.

i J
Very different hollow profiles, such as rectangular profiles, angle profiles, tubes, corrugated tubes etc., can be used as hollow parts.
Hence, a part is created that has a lower weight compared with parts hitherto, whilst having the same or even improved load bearing capacity and light weight, which can be productiond with a high degree of production precision and with a lower scrap rate.
The invention is explained in greater detail below on the basis of the enclosed drawing, in which preferred, but in no way exclusive, embodiments of the invention are shown.
Figure 1 shows a cut-out section of a part according to the invention in perspective, with a closed cell foam.
Figure 2 shows the part according to Fig. 1 in longitudinal section.
\ ..
Figure 3 shows the part according to Fig. 1 in cross-section along the line A-A of Fig. 1.
Figure 4 shows a part according to the invention with open cell foam in cross=section.
Figure 5 shows a cross-section through a part according to the invention with mufti-layer external walls and Figure 6 shows a longitudinal section through a section of a mufti-layer, foam-filled hollow part with various cross-sections.

As can be seen from Figs. 1, 2 and 3, each of which shows the same part (car axle support part made from aluminium alloy), the part depicted therein comprises an external wall 12 and the foam filling 14 (in this case, both of aluminium alloy). The external formed part was three-dimensionally formed by the internal high pressure forming process, so that it can be used, for example, as part of a 3-dimensional suspension axle.
It should be noted that desired crumple zones can be designed into the parts -the external wall - productiond by the forming process, by specifically moulded grooves -for example, so that when vehicles are involved in an accident, energy is absorbed by specific deformation - or reinforcement profiles can even be incorporated -for example, by forming out longitudinal ribs (passenger cell).
In this case, the hollow profiles of the framework can have different diameters over their length, as well as different cross-sections. . .
Figure 4 shows details of another form of application of a part according to the invention. In this case, it is a supporting part for motor vehicle catalytic converters which has an open cell steel foam in a steel outer casing. In this example, the generally known problems of these supporting parts, of the connection between casing and supporting part and the problem of producing gas ducts, which are then coated with the catalyst, are fizlly eradicated, on account of the fact that now, for the first time, the same material can be used for casing and gas emission body (also often referred to as honeycomb) and that tensions in the catalyst supporting part are avoided because of the different coefficients of expansion of the materials used for the supporting part, which hitherto limited its useful life.

Figure 5 shows a further embodiment of a part according to the invention, having a ribbed tube, where the mufti-wall external form has a foam filling.
The hollow profiles may comprise either a single material, for example, steel, or a light metal alloy, but, according to the process used, it is also possible to form laminate material and even plastic-coated or overlaid tubes, depending on the use intended.
By providing the appropriate layers it is possible to achieve corrosion resistance and also colour, without the need for fixrther process stages.
Foam filling with closed cell foams in particular, are able to produce great corrosion resistance, because no corrosive material can penetrate the closed cell foam.
As is known, by adding material along the longitudinal axes of the tube during forming, for example by moving form elements, an essentially uniform wall thickness can be achieved in the external form, with the result that weaknesses in the wall thickness of the external form can be, at least partially, compensated for by the forming of protrusions, resulting in the;formation of protrusions without weakness.
An embodiment of this type is shown in Fig. 6, where a mufti-layer external formed part 12, the outer layer of which is made from steel and the inner layer of an aluminium alloy, has a flange-like boss and is filled with aluminium foam 14.
This formed part in Fig. 6 can, of course, also have different combinations of material.

a . E A

Hence the development according to the invention, creates a more resistent and lighter supporting material than has been possible up to now.
Further embodiments and developments are, as part of the scope of protection of the claims, known to the expert and the extent of protection is in no way limited to the embodiments listed as examples, which are only intended by way of explanation.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A reinforced formed part with longitudinal or cross-sections which are different either in form or size, having a hollow external formed part and a powder metallurgically produced metal foam filling with a closed cell foam foamed within the hollow external formed part with strong resistance to deformation, which rests at least partially against the external formed part, at least fills the internal hollow cavity of the hollow external formed part improving the mechanical resistance of the external formed part to deformation.

2. The formed part according to claim 1, wherein fibre flow of a material of the hollow external formed part runs generally parallel to its external contours.

3. The formed part according to claim 1, wherein the hollow external formed part comprises several tiered layers running parallel to each other, each layer made from same or different materials, and fibre flows of which run completely or partially parallel to each other.

4. The formed part according to claim 2, wherein the materials of the hollow external formed part comprise one or more layers of cold or hot forming material.

5. The formed part according to claim 4, wherein the layers of cold or hot forming material are jointly formed.

6. The formed part according to claim 4 or 5, wherein at least one cold forming material is selected from the group consisting of metal and light metal.

7. The formed part according to claim 6, wherein the cold forming material is selected from the group consisting of steel, aluminium, magnesium, titanium and alloys of the same.

8. The formed part according to any one of claims 1 to 7, wherein the reinforced formed part comprises fibre-reinforced materials in the hollow external formed part.

9. A process for the production of a formed part according to any one of claims 1 to 8, wherein a hollow external formed part is produced by a forming process and at least one powder metallurgically produced prefoam body is introduced into the hollow external formed part and formed therein in such a way that the foam body, at least partially rests against the hollow part and is attached within the hollow part.

10. The process according to claim 9, wherein the hollow external formed part is comprised partially of metal and is produced by an internal high pressure forming process, and subsequently filled with a foam material.

11. The process according to claim 10, wherein the hollow external formed part is comprised partially of a polymer, and wherein the external formed part is produced by forming its at least single-layer material, by a forming process such as casting, thermal forming, blowing and internal high pressure forming and is subsequently filled with a foam material by foaming prefoam material within.

12. Use of the formed part according to any one of claims 1 to 8, as a supporting member in scaffolding; latticework; in construction; or in vehicle building for air, land and water craft and furniture.