WO2005000502A1

WO2005000502A1 - Component made of metal foam components and method for the production thereof

Info

Publication number: WO2005000502A1
Application number: PCT/EP2004/006684
Authority: WO
Inventors: Karsten Stöbener; Joachim Baumeister; Dirk Lehmhus; Norbert Zimmer
Original assignee: Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V.
Priority date: 2003-06-23
Filing date: 2004-06-21
Publication date: 2005-01-06
Also published as: DE10328047B3

Abstract

The invention relates to a component made of metal foam and a method for the production thereof, wherein several metal foam components are arranged in a three-dimensional manner. Either a structure, which forms the outer covering of the component made of metal foam, is at least partially filled with the metal foam components or the metal foam components are arranged such that a body is formed whereby the geometry thereof corresponds to the geometry of the component which is to be produced. Also, the thus arranged metal foam components are subjected to at one least physical and/or chemical post-treatment, such that the respectively, adjacent metal foam components are connected to each other in a positive fit, in a material fit and/or in an adhesive manner.

Description

Patent Application:

Component made of metal foam blocks and method for its production

applicant:

Fraunhofer Society for the Promotion of Applied Research e.V. Hansastrasse 27 c, 80686 Munich

description

Technical field

The invention relates to a component made of metal foam and a method for its production using metal foam blocks, which may have a coating.

State of the art

There are several methods available for manufacturing components from metal foam. The melt metallurgical and the powder metallurgical processes have gained importance.

In the powder-metallurgical blowing agent processes, at least one metal powder is first mixed with at least one blowing agent and a foamable starting material is produced therefrom. Such a method is e.g. B. in US 3,087,807, DE 4018360 and DE 4101630. The foamable materials produced using these processes can be produced as blocks, profiles, granules, etc. A metal foam component is produced from these foamable materials by heating the material to a temperature above the solidus temperature of the metal from which the material is made. If this metal enters a partially liquid or liquid state, a metal foam is obtained with expansion from the blowing gas released from the blowing agent. The foam expansion process is expediently carried out in a hollow body (for example a foam mold or a hollow structural component) which is filled by the expanding foam. The metal foam then forms the inner contour of the hollow body, so that the metal foam component can be produced close to the final shape if the hollow body is designed accordingly. In order to obtain metal foams with a pore distribution that is as uniform as possible, the still partially liquid metal foam must be cooled to a temperature below the solidus temperature of the metal in the shortest possible time; the foam is frozen, so to speak. The near-net shape foam body can then be removed from the hollow body.

The main disadvantage of these processes is that in order to produce metal foams in a hollow body, the entire hollow body (in particular a possible foam shape) must also be heated; so a very high energy input is necessary.

US 2,974,034 and Stanzick et. al. in "Process controll in aluminum foam production using real-time x-ray radioscopy" (AEM 2002, 4, Vol. 10) describe the production of metal foam components using foamable granules in a foam mold. A large-volume foam body is produced from a large number of small-volume granulate particles. The use of small-volume granulate particles allows easy portioning of the required quantity of semi-finished products.

Here too, however, the disadvantage of the high energy input for foaming in molds is not eliminated. It is also known to press the partially liquid or liquid metal foam into a hollow body (mold or cavity) (CYMAT 3d) or to let it expand (Metcomb). Such a method is disclosed, for example, in WO 03/015960 A2.

With these methods, however, only relatively simple component geometries can be realized. In addition, the foam structure is deformed when pressed into the hollow body. A homogeneous foam structure is therefore not obtained. Furthermore, the short cycle times known from die-cast aluminum cannot be achieved in any case, since the foam can only be pressed into the hollow body at low pressures, so that the foam structure is not deformed or destroyed too much. After all, these processes do not offer the freedom of choice of alloy known from powder metallurgy processes and can therefore only be used to a limited extent.

DE 19928997 discloses a method for producing metal foams, in which a foamable granulate is foamed by means of a laser beam or an electron beam. The production of a metal foam body can be influenced in a targeted manner by placing the semi-finished product particles individually. The

Metal foam body is produced by foaming together small volumes of foam. First, a semifinished granulate particle is expanded into the foam. Immediately after this process has been completed, the energy beam is directed onto the nearest semi-finished granulate particle and this also expands into a foam.

However, this method has the disadvantage that the production of the metal foam body is lengthy, since each granulate particle has to be foamed one after the other, the semifinished product granulate has to be arranged in layers and requires an increased outlay in terms of process technology (in particular a considerable outlay on equipment and long process times). Furthermore, this has _. The disadvantage of the method is that an overall component is created in which the cohesion of adjacent foam areas has an undefined and fluctuating intensity. description

The present invention is therefore based on the technical problem of producing components from metal foam without a high outlay on equipment and a high energy consumption being necessary, but which nevertheless have properties which can be controlled over the entire component volume.

This technical problem is solved by a method for producing components from metal foam according to claim 1, wherein metal foam modules, which are optionally formed according to claim 12, are used. Components are obtained according to claim 19 or 21. Subclaims indicate advantageous further developments. Claim 29 teaches an advantageous use of the components made of metal foam according to the invention.

The method according to the invention for the production of components made of metal foam consists in that metal foam components are arranged three-dimensionally, either a structure that forms the outer shell of the component made of metal foam is at least partially filled with the metal foam components, or the metal foam components into a body with a geometry which corresponds to that of the component to be manufactured. The metal foam building blocks arranged in this way are simultaneously or later subjected to at least one physical and / or chemical aftertreatment, so that adjacent metal foam building blocks are connected to one another in a form-fitting, cohesive and / or adhesive manner.

Metal foam building blocks in the sense of this invention are metal foams which can be obtained by supplying energy by at least partially foaming granulate particles which contain at least one metal powder and at least one blowing agent powder. By action of energy, preferably thermal energy, these granulate particles are foamed, so that granulate particles with an internal porosity are created. The pore structure can be open-pore, closed-pore or mixed-cell. According to the invention, metal foam building blocks are to be understood in particular as metal foam particles which have a geometry which can be produced in series production and which can be individually processed further.

If the foamable granulate is produced by powder metallurgical blowing agent processes (for example in accordance with DE 4018360 or DE 4101630), the pore formation is associated with an expansion of the granulate particle; each particle of granulate increases its volume when the metal foam block is formed. The geometric starting shape of the granulate particles generally has only a minor influence on the shape of the metal foam block that is formed. The granules can be produced by crushing larger pieces of foamable material, or the foamable material can be produced directly in the form of granules.

The foamable granules are preferably produced in the form of circular tablets. For this purpose, the metal / blowing agent mixture is compressed in one process step by uniaxial pressing. The circular shape of the granulate supports the formation of spherical metal foam blocks during the foaming process. The spherical shape is mainly formed in the thickness direction by the expansion of the liquid foam. The spherical metal foam blocks are formed when such granular tablets are foamed, since the surface tension of the liquid foam (possibly favorably influenced by reaction products formed on the surface) obviously favors the formation of the spherical shape. The foaming of such semifinished tablets is possible without large energy input and great process engineering effort and without the use of hollow bodies, in particular foam molds. The uniaxial compression of small amounts of a metal powder / blowing agent mixture can take place within a very short time (e.g. <1 second). If the procedure according to DE

4018360 or DE 4101630, the metal powder blowing agent mixture can be heated (for example for the production of granule tablets) before or during the compression process from room temperature to a maximum of a few degrees Celsius below the metal powder melting point. Due to the rapid compression process, even at Compacting temperatures, which are just below the solidus or melting temperature of the metal powder, only release negligible amounts of propellant gas from the propellant, so that the subsequent foaming behavior of the semi-finished tablet is not significantly influenced by its manufacturing process. The metal powder / blowing agent mixture for producing the granules can be used for

Support or improvement of the compression process Lubricants and pressing agents (preferably organic binders) are added before the compression process. These debinder during the foaming process or can be removed in a process step following the compression process (preferably chemically by solvent or thermally by burning out at temperatures which are below the decomposition temperature of the blowing agent).

In order to ensure after uniaxial compaction processes that the foamable granulate is sufficiently compacted, a sintering process to increase the density can be carried out after the compression process. According to the invention, the foamable granules can also be produced according to the teaching of DE 10206722. In particular, the sintering of metal powders or metal powder mixtures in a hydrogen-containing atmosphere is suitable, in which a foamable granulate is formed without the propellant gas being lost. Furthermore, metal foam blocks that do not have an oxide layer on the surface can also be produced directly by this method, ie without the foamable granulate particles cooling. In the production according to DE 10206722, a sintering aid (e.g. magnesium for producing foamable aluminum granules) can also be added to support the sintering process before the compression process. In general, however, the other previously known methods for foaming the granulate particles can also be carried out with the exclusion of atmospheric oxygen, so that metal foam building blocks can also be produced without a disruptive oxide layer on the surface. Also when using organic binders as lubricants or pressing aids and the necessary subsequent debinding, this debinding can be carried out under a hydrogen-containing atmosphere, as described in DE 10206722. No propellant gas is lost from the foamable granulate here either.

The use of the foamable granules according to the invention (insofar as these were obtained by direct pressing in granular form and not by crushing larger pieces of semi-finished product) has several advantages over the production of larger foamable semi-finished products. Usually, the metal blowing agent mixture can be processed into foamable semi-finished products in one or at most two process steps without significant material losses. This reduction in process steps and the avoidance of material losses (such as press residues during extrusion) significantly reduce the costs for producing the foamable semi-finished product.

According to the invention, the small granulate particles are foamed into metal foam blocks by heating and defined expansion, with (in particular if no foam mold is used) there being no temperature gradients in the semi-finished product or the liquid foam. The energy can be dissipated again just as quickly and without significant temperature gradients, so that the defined expanded foam is frozen directly. A foam produced under such ideal conditions, in which overaging (coalescence, drainage, etc.) can be safely avoided, has a very homogeneous pore structure. Even in the worst case, where the metal foam brick contains a giant pore, the volume of this largest pore cannot be larger than the total volume of the foam particle. Usually, however, the pores distributed homogeneously over the metal foam block are smaller. The homogeneity of the pore distribution in the component produced from the metal foam components can thus also be controlled via the size distribution of the metal foam components. Furthermore, before the three-dimensional arrangement of the metal foam building blocks, building blocks with poor quality (e.g. too low density or too high density or disadvantageous geometry) can be separated out; the metal foam components produced can before Further processing is generally pre-sorted according to certain criteria such as density, shape and size.

The three-dimensional arrangement of the metal foam blocks can either be done by filling a mold or a body that corresponds to the geometry of the component to be manufactured, and then removing the component from the mold or removing the mold. Alternatively, the metal foam building blocks can also be arranged to form a component in which there is a composite of metal foam building blocks and the outer shell. The metal foam building blocks can also be subjected to a chemical and / or physical aftertreatment at the same time.

According to the invention, it was recognized that when foam expansion and component shaping are separated, a considerably simpler method for producing components from metal foam is possible. The inventive achievement therefore also consists in the fact that it was recognized that a metal foam component can also be manufactured from a large number of small metal foam components that have been or have been treated physically or chemically in such a way that an overall component with integral connections can be made within one or more process steps is obtained between the metal foam blocks.

The particular advantage of this method is that the foamable primary material does not have to be heated in a hollow body. It is therefore not necessary to heat the hollow body in an energy-consuming and time-consuming manner, but rather the entire energy used (in particular heat) is transferred directly to the foamable primary material. In particular for the production of components with complicated geometries, it is no longer necessary to warm up a mold; Even the uneven heat transfer from the mold into the foamable primary material no longer poses any problems. According to the invention, components can therefore be produced for the first time which have a uniform pore distribution with uniform pore sizes and a complicated geometry; the problem of reaching the foam temperature in different component areas different times no longer matter. An inhomogeneous foam expansion during the energy input into the body to be foamed therefore does not occur. Even when the finished metal foam cools, there are no inhomogeneous heat transfer conditions. With the previously known methods, only such components with complicated geometries are available; that have a variety of foam areas that have been frozen at different stages of the foam process.

The method also has the advantage that any oxide layers on the surface of the metal foam block no longer play a role. They can be removed or chemically converted by chemical or physical processes before the metal foam component is manufactured. Furthermore, even if they are not removed or converted, an accurate prediction of their position in the metal foam component is possible. This is the case with the foaming of granulate fillings such as B. is described in US 2,974,034, or foaming by means of laser or electron beams, as disclosed in DE 19928997, not possible. Furthermore, the method according to the invention can be carried out in such a way that the oxide layer is removed or changed only at certain points on the metal foam component, in particular in the areas over which a material and / or adhesive connection to adjacent metal foam components is provided. With a chemical aftertreatment, however, an oxide layer, e.g. B. an aluminum oxide layer, may also be desirable because such oxide layers have better adhesive adhesion, i. i.e., support the application of a functional layer of adhesive on the metal foam block. According to the invention, oxide layers therefore no longer represent weak points; rather, the chemical modification or coating of these oxide layers means that there is a wide range of possibilities for connecting such coated metal foam building blocks to one another particularly firmly to form a metal foam component.

Furthermore, the method according to the invention has the advantage that new types of foam bodies (eg with density gradients in a specific, freely selectable partial area of the foam body) are possible through the use of different metal foam building blocks. This was only achievable to a very small extent in the previously known processes; the homogeneity of the foam structure was very limited. The method according to the invention also offers the advantage that metal foam blocks made of different materials can be used. So z. B. Components made of metal foam that contain a combination of different matrix materials (e.g. steel and zinc); these matrix materials can either be distributed statistically or also in the form of gradients or other geometric distributions in the metal foam component.

The separation of foam expansion and component shaping offers the advantage over methods such as that of DE 19928997 that even small granules or

Granule tablets can be heated homogeneously. According to the method according to the invention, local heating by means of a (generally focused) energy beam is not required. This ensures that the increase in volume takes place completely homogeneously during the foaming process and not an undefined, non-linear change in the temperature caused by local heating by means of the energy beam

Surface design and structure occurs. Furthermore, there are no fluctuations in the heat input. These always take place when using an energy beam e.g. from the change in the angle of incidence of the energy beam, the focussing plane, the reflection coefficient of the surface, etc. Also, all sides of the granule particle to be foamed can be heated homogeneously, while the

Heating by means of energy rays that cannot be directly heated from the side facing away from the beam. According to the invention, metal foam building blocks with a homogeneous and at the same time defined pore structure are obtained in the foam body. The separation of shaping and foam expansion offers the advantage over DE 19928997 that in the case of components which are built up from several layers of foam bodies or metal foam blocks, a layer of metal foam blocks can be arranged in such a way that a flat or regular surface is formed , This is when foaming using laser beams or electron beams are not possible, a targeted placement on the uneven surface of the first foam layer cannot be guaranteed. Foaming by means of laser beams or electron beams also means that the semifinished granulate particles in the upper layers cannot be optimally heated and there is no optimally expanded foam volume.

The separation of foaming and shaping also ensures that existing layers of metal foam particles or metal foam building blocks are not also heated when another foam layer is applied; this would cause the foam structure to deteriorate. While a firm mechanical interlocking of the layers of metal foam blocks with one another is possible in the method according to the invention, since chemical or physical aftertreatment takes place, this cannot be achieved in particular with the method according to DE 19928997.

According to the invention, the size of the metal foam building blocks is preferably chosen such that the ratio between the average volume of a metal foam building block and the volume of the component made of metal foam is less than 1:10, particularly preferably less than 1: 100. When using metal foam blocks with very different dimensions, it is not the average volume of the metal foam blocks that is decisive, but the volume of the largest metal foam block used. The metal foam blocks according to the invention preferably have a volume which is less than 125 cm ³ . Metal foam blocks with a volume of 0.05 cm ³ to 2.5 cm ³ are particularly preferred. Spherical metal foam blocks therefore particularly preferably have a diameter of 0.45 cm to 1.7 cm. Metal foam building blocks of this size, like the metal foam granulate required for this, can be produced particularly efficiently with regard to the process complexity and the energy required; in addition, the total surface to be treated in the production of components from these metal foam building blocks of all metal foam building blocks used for this purpose is small enough for the aftertreatment of the To be able to carry out metal foam blocks inexpensively.

The size of the foam particles is preferably selected such that the desired component shape is sufficiently represented by the three-dimensionally arranged metal foam modules; especially when using spherical metal foam building blocks, a mixture of metal foam building blocks that have an appropriately small diameter must be used.

The method according to the invention is preferably carried out with metal foam blocks which essentially have the shape of a sphere or a sphere that is compressed and / or stretched in a spatial direction. This also includes all conceivable forms of ellipsoids, such as rotational ellipsoids. In particular, this also includes bodies that have assumed their shape due to the force of gravity during the partially fluid state of the metal foam - that is, due to the weight of the metal foam block on the underside, are rather flattened and deviate from the spherical shape. Such metal foam blocks can be arranged three-dimensionally, for example, in such a way that a densest spherical packing or cubically internally centered spherical packing is formed. As a result, the weight of the metal foam component can be further reduced compared to conventional metal foam components, since in addition to the pores formed by the blowing agents, the gaps that occur between the balls also play a role. The weight of the metal foam component can be reduced compared to a component consisting entirely of metal foam to a percentage value that corresponds to the packing density or the space filling of the metal foam components in the entire component volume. Metal foam components are particularly homogeneous in their physical properties, in which the volume of the cavities between the spherical metal foam building blocks corresponds approximately to the volume of the average pores formed by the blowing agent in the metal foam building blocks. Among the volume of these cavities is this to understand the average volume of the tetrahedral gaps and / or octahedral gaps and / or corresponding other gaps.

In a variant, the metal foam building blocks used in the method according to the invention can essentially have the shape of a polyhedron or a polyhedron that is compressed and / or stretched in one spatial direction. This includes, in particular, metal foam blocks in the form of a cube, cuboid or other polyhedron (tetrahedron, dodecahedron, icosahedron) as well as Archimedean bodies (e.g. cuboctahedron). Intermediate shapes between bodies with the geometries mentioned above and bodies with spherical geometries can also be used. Such geometric shapes of metal foam bricks can e.g. are generated by generating foam particles or foamable granulate particles in partially open (e.g. open at the top) foam molds. For example, a defined geometry is imprinted on the underside, while the top can develop freely and take on the shape of a hemisphere or a semi-ellipsoid. However, finished metal foam blocks (e.g. balls) can also be mechanically treated (e.g. flattened) in a state (or at a temperature) in which (or at which) deformation is easily possible, preferably in the partially liquid state. The mechanical treatment must preferably be carried out in such a way that there is no or no significant change in the foam structure. Polyhedral metal foam building blocks can also be obtained by - to

Recycling of metal foam scrap - larger, no longer required metal foam bodies are shredded so that corresponding areas are sawn out of the metal foam body; the scrap can therefore be recycled. This recycling variant is particularly suitable when the surface layer of the metal foam block (e.g. a cube or polyhedron) is not required or is interfering and would have to be removed anyway by chemical and / or physical aftertreatment. In a variant of the method according to the invention, the metal foam building blocks are obtained by at least partially foaming in a foam mold. A foaming mold generally means more effort, so production without a foaming mold, ie by free foaming, is preferred. In particular for the production of spherical foam particles, no foam mold is required. However, the use of a foam mold can be advantageous for producing foam particles in the form of cuboids, cubes, cylinders, pyramids, polyhedra, rotating bodies or any other free shapes; During the foaming process it is also possible to use molds which only represent boundary barriers in one or two spatial directions. The smaller the area, that of one

If the foam shape is limited, the faster the granulate particles can be heated and expanded in a defined manner without temperature gradients occurring. The smallest possible spatial area is therefore preferably delimited by a foam shape. The energy dissipation can then also take place all the faster and without the occurrence of significant temperature gradients. The metal foam blocks produced according to this variant (with correspondingly slower heating and cooling) then represent a foam produced under ideal conditions, which has an extremely homogeneous pore structure.

In a variant of the method according to the invention, the three-dimensional arrangement of the metal foam blocks is carried out at least partially with partially liquid ones

Metal foam blocks. In this way, particularly in the case of metal foam components with complicated geometries, areas that are difficult to access are filled with the best possible foam structure.

In order to achieve a particularly good connection of the metal foam building blocks to one another and to facilitate the connection of the metal foam building blocks to further components of an overall component, the metal foam building blocks can be subjected to a chemical and / or physical surface treatment before the three-dimensional arrangement. Here, for. B. the activation of Surface of the metal foam block can be achieved by cleaning the surface and reducing the oxide skin. Mechanical treatments, in particular sputtering, brushing and grinding, are particularly suitable as physical surface treatment steps. A chemical surface treatment is, for example, a treatment with solvents (in particular for degreasing), pickling, etching (for example with acids, alkalis and / or electrolytes) and annealing on reducing surfaces. Furthermore, a surface treatment can take place in such a way that a coating is applied to the metal foam block. A coating is generally suitable, the thickness of which is small in relation to the diameter or the minimum and maximum dimensions of the metal foam block. In particular, metallic coatings, oxidic coatings, ceramic coatings, organic coatings and coatings from the gas phase or the liquid phase come into consideration as the coating. Such coatings of the metal foam blocks allow later gluing, soldering, sintering, welding and / or pressing the metal foam blocks to form a component. The coating is preferably designed in such a way that at least partially at least one solid functional layer is applied to the metal foam module, which consists of a material that is flowable, plastically and / or elastically deformable by means of a chemical and / or physical treatment. The functional layer can contain a polymer (eg polyurethane), which can be foamed into a polymer foam.

The process for the aftertreatment of the three-dimensionally arranged metal foam building blocks can be done without the use of auxiliaries, for example by means of gluing, soldering, sintering (e.g. any oxide skins of neighboring metal foam building blocks can be baked together). Welding and / or pressing take place. Also the application of high-frequency alternating loads in the still partially fluid

Condition (whereby the oxide skins of the still partially liquid metal foam building blocks are torn open) is possible. The above aftertreatment methods can be used to improve the bonds between the metal foam bricks Sintering steps can be added.

However, an aftertreatment can also be carried out using auxiliary substances. For example, gluing comes into consideration here. For example, individual metal foam blocks can be glued by applying a coating at least in the areas in which contact with the adjacent metal foam blocks is provided. However, it is also possible to infiltrate a bed of metal foam blocks with a liquid matrix material (e.g. a resin, a metal melt or the like), to mix metal foam blocks into a liquid matrix material, which is subsequently converted into the solid phase. Furthermore, the mixing of the metal foam blocks with an expandable one

Granulate (if necessary, thin granulate panels can also be used here), then the expandable granulate is expanded, so that a composite body of separately foamed foam particles is formed in the expanded granulate. For example, aluminum metal foam building blocks are conceivable in a polymer foam, but there may also be an aluminum metal foam building block in a metal foam made of a different material, in particular a material with different deformation properties. Such metal foam bodies can advantageously be used as two-stage energy absorbers. If a mixture of metal foam building blocks is poured with an initially liquid matrix material, in extreme cases a component is created that has a composite of a matrix material and metal foam building blocks dispersed therein.

According to the invention, the method for producing the metal foam components can be carried out with metal foam components with or without a coating. If metal foam blocks with a coating are used, then those blocks are particularly suitable for the subsequent post-treatment, on which at least partially at least one solid functional layer is formed, which consists of a material that is flowable, plastically and / or elastically deformable by means of a chemical and / or physical treatment becomes. This allows adjacent metal foam blocks to be adhesive and / or be firmly bonded together. The coating can consist of a metal, a metal alloy, a metal oxide or a ceramic. Suitable metals are, for example, iron, nickel, copper and light metals, e.g. B. titanium, aluminum or high-melting heavy metals, such as tungsten or molybdenum and their alloys.

The physical and / or chemical treatment and the choice of materials should be carried out in such a way that the foam structure of the metal foam block does not change or become unstable.

It is also possible to form a plurality of functional layers one above the other in the manner of an onion skin, the particular choice of material being able to cover different applications.

A coated metal foam block with an additional solid functional layer, which additionally, for. B. by applying a suspension to the surface, applied and dried or cured, is a better and easier to process intermediate product than uncoated metal foam blocks and saves the end user of the metal foam blocks from performing complicated technological process steps.

The functional layer according to the invention should have a thickness which, after the physical or chemical treatment of the metal foam building blocks, ensures the respective functional effect, for example corrosion protection or an adhesive bond between adjacent metal foam building blocks. However, the thickness is advantageously to be chosen at least so large that a positive locking of adjacent metal foam blocks can be achieved during the plastic and / or elastic deformation.

The coated metal foam blocks are preferably free-flowing and do not stick together, so that they can be processed without any problems after storage and transport. An additional sealing layer can be applied to the functional layer, in particular for temporary protection during transport and storage, in order to form very smooth, non-adhesive surfaces. For this, e.g. B. quick-drying, preferably water-soluble paints or other more or less viscous liquids are sprayed on. Suitable examples are cellulose or pectin solutions or polyvinyl alcohol.

The functional layers can be formed from a homogeneous material, but also from composites. For example, ferro- and / or permanent magnetic particles can be embedded in the functional layer for certain applications (e.g. for detection purposes). However, the functional layer can also be doped or formed with catalytically active elements or compounds. For example, platinum and / or rhodium and / or compounds of these metals can be deposited on the metal foam block or a functional layer.

If organic materials or components are used for the functional layer, those polymers which are selected from ethylene-vinyl acetate copolymers, polyamides or polyesters, but also phenolic resin, cresol resin, furan resin or epoxy resin or binders based on latex or rubber are particularly suitable. The organic materials can be applied to the metal foam blocks in the liquid phase with subsequent drying; activation can take place later, for example, by means of heating. However, powder coatings known per se can also be used as the functional layer material. These can be applied in powder form to the heated metal foam building blocks, whereby temperatures should be maintained at which the powder adheres to the metal foam building blocks, but there is no melting of the powder coating powder which leads to running. The individual powder particles can adhere more or less evenly to the metal foam block surface and, after cooling, the metal foam blocks can be easily transported and stored without sticking together. The temperature is only increased again when the components are made from metal foam blocks until the powder softens or melts. When melting, a uniform coating of paint can be formed over the entire surface.

The functional layer can also be formed from an organic or inorganic binder, from which particles, preferably metals or polymers, are held adhesively. These particles can deform during thermal finishing.

The functional layer can advantageously also consist of a metal or contain such a metal that can form an intermetallic phase with the metal of the metal foam component. Depending on the matrix alloy of the metal foam component, this is possible, for example, with tin and copper. Different aluminides can also be formed in this way.

Various additives can also be contained in the functional layer. Examples are solders, fluxes, sintering aids, blowing agents or swelling agents.

For the production of components from the coated metal foam building blocks according to the invention, after the three-dimensional arrangement of the metal foam building blocks, physical and / or chemical treatment takes place in at least one further process step, in which the functional layer material is softened at least to the extent that it is plastically and / or elastically deformable , The physical treatment can be a heating of the functional layer material caused by energy input, the softening temperature and possibly also the melting temperature of this material being lower than that of the material from which the

Metal foam body is formed, should be. The heated, flowable material adapts to the surface shape of the metal foam blocks. After cooling, in which the functional layer material can also solidify again, adjacent metal foam blocks are at least positively fixed, a firm adhesive connection not being absolutely necessary. Due to the flow of the functional layer material, voids remaining between the metal foam components can at least partially coexist be filled with this material. Forces acting on the metal foam building blocks can thereby be influenced and undesirable stresses in the metal foam building blocks can be avoided.

A chemical treatment of the metal foam building blocks with functional layer can preferably be carried out with a solvent suitable for the functional layer material, which is brought into contact in liquid or vapor form with the three-dimensional metal foam building blocks. A softening of the functional layer material is achieved with such a solvent, so that it becomes plastically deformable again temporarily. After the solvent has been stripped off or evaporated, the functional layer material can solidify again and maintain the shape it has assumed.

If the functional layer contains a metal or an alloy, the heat treatment can be carried out in such a way that the metal melts and the metal foam components are soldered to one another. In this case, the functional layer can advantageously also contain at least one solder and possibly a suitable flux or these can be embedded therein. Such a functional layer can, for. B. consist of pure tin or bound tin powder.

Especially with metal foam blocks that consist of particularly reactive materials, such as. B. iron or aluminum, functional layers as an oxidation layer have an advantageous effect. They also provide corrosion protection for components made from such metal foam blocks.

The metal foam components according to the invention consist of a composite of positively, materially and / or adhesively connected metal foam modules or contain such a composite. Components are preferred which consist of a composite materially and / or adhesively bonded metal foam building blocks or contain such a composite.

The metal foam components according to the invention are characterized in that maximum pore volume cannot be greater than the volume of the largest foam particle used. In addition, the character and the size of the proportion of open porosity can be influenced in a targeted manner by the choice and / or the geometries of the metal foam building blocks and possibly also by a combination of closed-pore and open-pore metal foam building blocks. Thus, the metal foam component has a defined pore morphology with guaranteed maximum pore size, provided that other sources of error, such as. B. pouring errors can be excluded.

The components according to the invention made of metal foam components have in particular the advantage of precisely predictable and adjustable properties. They have an orderly structure in all spatial directions and can therefore also be mass-produced without fluctuations in the mechanical and / or physical properties of the components.

Metal foam components of different sizes and / or densities and metal foam components made of different materials can be used to produce the metal foam components according to the invention (this includes both metal foam components which themselves consist of different materials and two or more classes of metal foam components which each consist of different materials ). Metal foam blocks with one or more different functional layers and two or more classes of metal foam blocks, each with different functional layers, can also be used. Through this freedom of choice, entire components with widely variable and locally variable, but defined adjustable properties can be produced. Examples are components made of metal foam blocks with monomodal or multimodal diameter and / or density distributions, components with locally increased mechanical properties at highly stressable locations, composites consisting of metal foam blocks of different materials, layered composites with metal foam block inserts and reinforcements of all kinds (e.g. sheet steel inserts) and inserts such as threaded sleeves or threaded rods). The fact that the Allow metal foam building blocks to be classified simply, quickly, safely and fully automated in accordance with size and / or weight, and in combination of the two criteria, using established and cost-effective processes in industrial practice.

According to the invention, the metal foam building blocks can also be arranged in such a way that a hollow component is obtained which is completely or partially filled with metal foam building blocks, the individual metal foam building blocks not having to be integrally and / or adhesively connected to the hollow component itself; even the metal foam building blocks do not have to be connected to one another, or can only be partially connected to one another in a materially bonded and / or adhesive manner. Such hollow structures filled with metal foam bricks can be used as double energy absorbers (e.g. crash absorbers), especially if they are only partially filled. However, a component is preferred in which the metal foam building blocks are adhesively and / or cohesively bonded to one another in such a way that there are no subareas which are not adhesively and / or cohesively bonded to another subarea.

A metal foam component according to the invention can also consist of a multi-layer composite structure which contains one or more layers of metal foam components. The metal foam building blocks can be integrally and / or adhesively connected to one another or only to the other layers. A cohesive and / or adhesive bond both to one another and to the other layers is also conceivable. Here, too, a component can be produced in which the metal foam building blocks are adhesively and / or positively connected to one another in such a way that there are no partial areas of metal foam building blocks that are not adhesively and / or positively connected to another partial area of metal foam building blocks (this connection also indirectly via layers that are not made of metal foam blocks). The components according to the invention are particularly suitable for producing crash absorbers. A metal foam component is particularly suitable for using the metal foam components according to the invention as a two-stage crash absorber, in which metal foam components are embedded in a matrix of polymer foam surrounding them. Such components can, for example, also have a distance between adjacent metal foam blocks that is larger than the average diameter of the metal foam blocks used.

applications

Without restricting generality, the method according to the invention, the metal foam building blocks according to the invention and those according to the invention

Metal foam components made of metal foam blocks are explained in more detail below with the help of illustrations.

Figure 1 shows cross-sectional areas through metal foam blocks with different sizes and different geometries. The two left examples are cross sections through metal foam balls (diameter approx. 0.6 cm or 1 cm), on the right a cross section through a metal foam block. The uniform pore distribution is striking.

Figure 2 shows the production of a spherical metal foam block 4 from a foamable semifinished tablet 1. The semifinished tablet 1 is placed in the hot oven 2 and under

Exposure to heat (represented by arrows) occurs (3). The fully foamed metal foam block 4 is then removed from the furnace 2.

Figure 3 shows the manufacture of a component from metal foam blocks. Metal foam blocks of 4 different sizes are first sorted (if necessary) and classified. A physical surface treatment such as degreasing or pickling of these metal foam blocks is then optionally carried out surface-treated metal foam blocks 5 can be obtained. These are (again optionally) subjected to a physical or chemical coating process, whereby metal foam blocks with functional layer 6 are obtained. The metal foam building blocks 4 or the surface-treated metal foam building blocks 5 or the metal foam building blocks with functional layer 6 are filled into a mold 7a (in the figure, the closing of the mold with a lid is shown) or a hollow structure 7b (in the illustration, as an example for metal foam building blocks with a functional layer 6)) and subjected to a chemical or physical treatment, so that a component 8a or 8b with a form-fitting, material-fitting and / or adhesive composite of adjacent metal foam blocks is produced. If a mold (7a) was used, the finished component can be removed from the mold in a demolding step 9. A component made of metal foam blocks 10 is thus obtained, in which, depending on the production process, there is a composite of metal foam blocks (10a) or a composite of metal foam blocks and hollow structure or shell (10b = 8b).

FIGS. 4a-4l show different variants of components made of metal foam blocks 10.

FIG. 4a shows a three-dimensionally shaped component made from small ones

Metal foam blocks (see 10a).

FIG. 4b shows a hollow component that is partially filled with a foam component that consists of

Metal foam blocks was made. Figure 4c shows a component made of metal foam blocks 10c, which by pressing

(represented by arrows) small metal foam blocks was obtained.

Figure 4d shows a layer composite of foam component layers and other materials

(e.g. CFRP).

Figures 4e and 4f show components made of metal foam blocks of different sizes / volumes, in which a composite of metal foam blocks (10a) and a

Compound of metal foam blocks and shell (10b) is present.

Figures 4g and 4h show components made of metal foam blocks different

Geometry in which a composite of metal foam blocks (10a) or a composite of metal foam blocks and casing (1 Ob).

FIG. 4i shows a component made from foam blocks of different matrix materials.

Figure 4k shows a component made of foam blocks that has been infiltrated with a second material (e.g. polymer resin or polymer foam).

Claims

claims

1. A method for producing a component made of metal foam, in which a plurality of metal foam building blocks which can be obtained by supplying energy by at least partially foaming granulate particles which contain at least one metal powder and at least one blowing agent powder are arranged three-dimensionally, either using a structure which forms the outer Forms the shell of the component from metal foam, is at least partially filled with the metal foam components or the metal foam components are arranged in a body with a geometry that corresponds to that of the component to be manufactured, and the metal foam components so arranged are subjected to at least one physical and / or chemical aftertreatment , so that each adjacent metal foam building blocks are positively, cohesively and / or adhesively connected to one another, the size of the metal foam building blocks being selected such that the ratio between the average volume ei metal foam component and the volume of the component is less than 1:10.

2. The method according to claim 1, characterized in that the size of the metal foam blocks is selected so that the ratio between the average volume of a metal foam block and the volume of the component is less than 1: 100.

3. The method according to any one of the preceding claims, characterized in that metal foam blocks are used which have been foamed in a foam mold.

4. The method according to claim 1 to 3, characterized in that metal foam blocks are used, which have substantially the shape of a ball or a ball compressed and / or stretched in a spatial direction.

5. The method according to claim 1 to 3, characterized in that metal foam blocks are used, which have the shape of a polyhedron or a polyhedron that is compressed and / or stretched in a spatial direction.

6. The method according to any one of the preceding claims, characterized in that the three-dimensional arrangement of the metal foam blocks is at least partially carried out with partially liquid metal foam blocks.

7. The method according to any one of the preceding claims, characterized in that the metal foam blocks are subjected to a chemical and / or physical surface treatment before the three-dimensional arrangement.

8. The method according to claim 7, characterized in that at least partially a solid functional layer is applied to the metal foam blocks, which consists of a material that is flowable, plastically and / or elastically deformable by means of a chemical and / or physical treatment.

9. The method according to claim 8, characterized in that the functional layer consists of a polymer or contains a polymer which can be foamed into a polymer foam.

10. The method according to any one of the preceding claims, characterized in that the post-treatment takes place by means of gluing, soldering, sintering, welding and / or pressing.

1 1. The method according to claim 10, characterized in that the metal foam blocks are mixed with an expandable granulate, which is then expanded into a foam.

12.Metal foam block which is obtainable by supplying energy by at least partially foaming a granule particle which contains at least one metal powder and at least one blowing agent powder, characterized in that at least partially at least one solid functional layer is formed on the metal foam block, which consists of a material which becomes flowable, plastically and / or elastically deformable by means of a chemical and / or physical treatment.

13. Metal foam block according to claim 12, characterized in that the functional layer is formed from an organic polymer or contains such a polymer.

14. Metal foam block according to claim 12 or 13, characterized in that the functional layer is formed from a binder and particles are held adhesively with the binder.

15. Metal foam block according to claims 12 to 14, characterized in that the functional layer contains or is formed from a metal, a metal oxide and / or a ceramic.

16. Metal foam block according to claims 12 to 15, characterized in that a sealing layer is formed on the functional layer.

17. Metal foam building block according to claims 12 to 16, characterized in that the metal foam building blocks have essentially the shape of a ball or a ball compressed and / or stretched in a spatial direction.

18. Metal foam building block according to claims 12 to 16, characterized in that metal foam building blocks are used which essentially have the shape of a polyhedron or a polyhedron that is compressed and / or stretched in a spatial direction.

19.Component made of metal foam which consists of a composite, or which contains or contains such a composite, metal foam blocks which are positively, cohesively and / or adhesively connected to one another and which can be obtained by supplying energy by at least partially foaming up granule particles which contain at least one metal powder and at least one blowing agent powder. wherein the ratio between the average volume of a metal foam block and the volume of the component is less than 1:10.

20. The component according to claim 19, characterized in that the metal foam blocks at least partially fill a structure that forms the outer shell of the component and are optionally integrally and / or adhesively connected to it.

21. Component made of metal foam in the metal foam building blocks, which can be obtained by supplying energy by at least partially foaming granulate particles which contain at least one metal powder and at least one blowing agent powder, at least partially fill a structure which forms the outer shell of the component.

22. Component according to claims 19 to 21, characterized in that the metal foam blocks are at least partially metal foam blocks according to claims 12 to 18.

23. Component according to claims 19 to 22, characterized in that the metal foam blocks essentially have the shape of a ball or a ball compressed and / or stretched in a spatial direction and that between the Metal foam building blocks are concave-spherical communicating, possibly filled cavities.

24. Component according to claims 19 to 23, characterized in that the ratio of the average volume of the metal foam blocks and the volume of the component is less than 1: 100.

25. Component according to claims 19 to 24, characterized in that the metal foam blocks have different sizes and / or different geometries and / or a different density.

26. Component according to claims 19 to 25, characterized in that metal foam blocks are made of different materials.

27. The component according to claims 19 to 26, characterized in that the metal foam building blocks are bonded via a foam which is obtainable by expansion of an expandable granulate and / or the foaming of a foamable functional layer which is at least partially applied to the metal foam building blocks.

28. Component according to claim 27, characterized in that the foam is a polymer foam.

29. Use of a component according to claims 19 to 28 as an energy absorber or for producing an energy absorber.