Title of Invention	METHOD FOR PRODUCTION OF PRECISION METAL FOAM
Abstract	Method for production of precision metal foam from a foamable powder-metallurgically produced metal semifinished product with a melting point 2000C with: -use of a mould, heat resistant up to the melting point of the foamable material, with at least one wall pervious to radiation, with a coefficient of expansion of <3 K-1 protected by separating film material such as herein described; - filling of this mould with material foamable at T>200°C in contact with separating film material; - controlled heating of the foamable material in the mould while foaming and precision forming of surfaces of the foam while essentially filling the mould using radiators with controlled energy output directed at or through the wall of the mould that is pervious to radiation; and - demoulding of the foam produced in this way.

Title of Invention

METHOD FOR PRODUCTION OF PRECISION METAL FOAM

Abstract

Method for production of precision metal foam from a foamable powder-metallurgically produced metal semifinished product with a melting point 2000C with: -use of a mould, heat resistant up to the melting point of the foamable material, with at least one wall pervious to radiation, with a coefficient of expansion of <3 K-1 protected by separating film material such as herein described; - filling of this mould with material foamable at T>200°C in contact with separating film material; - controlled heating of the foamable material in the mould while foaming and precision forming of surfaces of the foam while essentially filling the mould using radiators with controlled energy output directed at or through the wall of the mould that is pervious to radiation; and - demoulding of the foam produced in this way.

Full Text	Method and Device for Producing Dimension-Precise Foam The invention pertains to a method and device for producing dimension-precise metal foam from foamable, powder-metallurgic semi-finished metal product with a melting point > 200°C, as well as devices for carrying this out. Production of foam from suitable foamable material for plastics, natural substances, glasses and also metal-containing materials, is known. Methods for powder-metallurgic metal foam production in moulds having low coefficient of expansion are known from the document DE 199 54 755 Al. There, powder-metallurgic AlSil2 alloy is foamed up; however, the information given there is only suited for this material, as continuously material-dependent magnitudes are mentioned. This also holds good for the necessary 5 - 25 nm thick protection layer of the quartz glass mould through an Al2C3-coating of the quartz glass, as well as for the applied cover layer which is necessary on account of the reactivity of the foamed A1Sil2. There, also a thick-walled mould with layer thicknesses >5mm and an applied protection layer are coupled through radiation in average infrared, whereby the infrared beamer is geometrically arranged in such a way, that heat reduction occurs in the pressed mould. This known method can only work with pressed moulds which are applied on cover layers and there occur problems with non-uniformed heating of the mould, which results in non-uniform foam samples and foams which are not dimension-precise, which particularly in the case of larger foam parts, leads to instability of the foam and hence to cracks, weak points etc. So far it has been extremely difficult to produce such metal foam parts which are dimension-precise in satisfactory quality. It is a problem to achieve a uniform pore distribution in larger components, e.g. large-surfaced ones like metal foam plates with a base area of 0.5 m2 and more. Such metal foam parts produced according to the known foaming methods often have regions, in which the pores are collapsed, and as a result we have larger hollow spaces which weaken the stability of the component. In case of parts with non-uniform thickness or such ones with regions of higher density, which occurs by inserting more semi-finished products at pre-determined points, particularly very often defects occur. This is especially due to the fact that traditional moulds of metal have a high linear coefficient of expansion and a high heat capacity. The coefficient of expansion lead to the situation, that great dimension changes takes place on cooling, which negatively influences the dimension-precision and the cooling behaviour of the metal foam. Known moulds or ingot moulds require a lot of energy for heating, due to which the cooling is cumbersome and results in long cycle periods in production. The cooling can also lead to material problems in metal foam, in case composites are supposed to be foamed and too long dwelling in a fluid condition leads to undesirable reactions or dissolutions, like de-mixing phenomena. A further problem is that in the known foam processes in furnaces, an uncontrolled heat distribution in the ingot mould leads to uncontrolled foaming of the foamable material and hence one does not get a satisfactory pore distribution. In other known methods the semi-finished product is heated up in metal ingot moulds in a furnace to a temperature which lies clearly above the melting temperature of matrix metal of the semi-finished product. In order to achieve an adequate productivity of the process and above all good quality of the metal foam, the heating also takes place very rapidly, i.e. within a few minutes. On the other hand, a very specific heating of the foamable material is very necessary, as otherwise individual regions of the semi-finished product do not get foamed, whereas other regions get over heated and the foam cells there collapse. Therefore, the ingot mould must be heated in a very short time - e.g. with the least possible temperature differences for plane metal foam of uniform thickness -, which is particularly difficult for larger moulds and ingot moulds and metal foam parts. A big problem in this case is the large heat capacities of known ingot moulds, which cannot be easily cooled rapidly and, on account of the high heat conducting capacity of the metal, do not allow locally differentiated heating. The known method of foaming in metal moulds in the furnace was disadvantageous, because it was difficult to control, had to be often interrupted and, one could not run the process continuously. Finally, the energy costs were also quite high. It is the task of this invention to present a method which allows production of uniformly foamed foam parts, even such ones having larger overall dimensions. This task is fulfilled as per the invention by a method having the features listed in patent claim 1. It is further fulfilled with the help of the device as per the invention having the features listed in patent claim 10. Advantageous extensions can be obtained from the relevant claims. Reference to metal foam below also includes bodies which primarily consist of metal foam, and also non-foamed reinforcing elements like wires, grilles, plates or even threads, filaments, whiskers, fastening elements and bolt bushes, hollow bodies like non-foamed pipes etc. These structural elements could be connected during foaming of metal foam by means of mould-closing or even material-closing; in this way one can avoid later fastening steps like boring, slitting or other mechanical joining methods, or gluing, welding, soldering or such processes. The invention particularly pertains to metal foams of metals or metal composites foamed thermally at high temperatures over 200°C, preferably over 300°C or even over 500°C with the help of driving agents. The foams can be used as solid or even light construction materials. Such light construction materials find application in the construction sector as blending elements, load-bearing elements for low weights; in motor vehicle technology, as well as in aircraft-, automobile- and ship construction, or even as absorption plates or protection plates against mechanical or thermal effects ( fire-preventing components). By "non-uniform" one means the momentary distribution of radiation in the mould, as well as the time-related application of radiation, i.e. the blasting of the mould with different blasting intensity as well as the time-differentiated blasting of particular mould regions. Surprisingly, in this way one can control the metal foam generation and avoid occurrence of gas occlusions. By metal foam one means here a foamed product which has defined outer dimensions. The method can be carried out in a very advantageous manner with foamable materials having a melting above 200°C, preferably above 300°C or even melting points above 500°C. Because, in this case moulds or ingot moulds having lower linear coefficients of expansion and lower heat capacity, as well as controlled foam generation is used, one can obtain an extremely dimension-precise metal foam part. Suitable mould materials are ceramic or glass-type materials or even composite materials like fibre-reinforced composites like fibre-reinforced ceramic, glass or carbon, which are highly heat-permeable and fulfil the requirements of low coefficient of expansion with enhanced stability under pressure and tension. It is also possible to cool off the moulds very rapidly, as the low coefficient of expansion prevents damages which could occur due to longer cooling process in case of traditional moulds. The process can also be carried out continuously, using a preferred design form which leads to a strand-type or band-type metal foam product. In this case, moulds open on both sides are used, whereby foamable material is introduced continuously into the mould/ingot, which is blasted in a controlled manner in a selected region and the foamable material is thus heated and foamed; whereby on the other side, depending on the mould or ingot mould, the metal foam comes out foamed in the form of strands. Even here, the method can be supported by a separating material, in case the metal to be foamed adheres strongly to the mould - e.g. by letting foil-type separating material to run along, like Al2O3, or ZrC2-containing foils or graphite foils for aluminium foaming, or by coating the foamable material with separating material foils, or by coating with a high temperature cinder base like silicate base; suitable separating agents are known to the expert. The mould should preferably be at least partly diatherman. By diatherman one generally refers to material which is permeable for heat radiation, in this case radiation-permeable in the range of approx. 760 - 5000 nm. As suitable radiation device one could use in the range of 760 - 5000 nm continuously, or even particular wave length emitting beamers, like glue pins, Nernst-pins, SIC-rods, LEDs, CO2 - CO-, diodes-, Nd/Yag-, semiconductor or colour lasers. Their energy output can be regulated by regulating the supply current or by using a filter. The ingot mould should preferably be thin-walled. This would be advantageous because one can avoid wastage of heat energy for heating up an ingot mould having high heat capacity, and its cooling behaviour is faster-which prevents mixing up of composite foams, higher time cycles and allows precise controlling of the heat energy working on the material to be foamed. It could, for example, have a wall thickness of 1 - 20 mm, more preferably a thickness of 2 - 10 mm. In case of thin mould walls, on account of heat management, it could be sensible to support them mechanically from outside, locally by supports or beams, in order to prevent bending or breaking of the mould in case of heavy metal foams or larger parts and to ensure retention of the dimensions. Suitable supports could be studs, or grille-type constructions, which would have as less support surface as possible and low heat conductivity and heat expansion coefficient and would consume less heat energy, in order not to disturb the heating profile. In case the studs can be regulated, it would be advantages to compensate for unevenness of the ingot mould or the heat expansion of the supports themselves. The ingot mould can be fed with a suitable gas - even under over pressure. Ideally, an inert gas is used under not too high over pressure in the range of below approx. 5 bar. Thus one can conduct foaming of several metals or their alloys or composites, like Zn, Ni, Al, Mt, Ca, Ni, Fe, Sn. Metal powder mixings can be carried out, or even mixings of precious metal, copper, beryllium, tungsten, titanium, steels, Si or their alloys, if required with additives, like hard substances, fibre and driving agents for producing the metal foams, like hydride or carbonate of metals - e.g. TiH2, ZnH2, MgH2, CaCO3 etc., as already known to experts in the field of metal foam production. One is particularly referring to substances releasing gases at higher temperatures, preferably such substances which are absorbed in the foam metal by formation of alloys after splitting the gas. Typical metal foam materials are ones which have a large share of Al, Be, Mg, Si, Cu, Zn, Ti, Sn, Pb, lead, brass, bronze etc. With the help of the method as per the invention, one can also process fusion-metallurgical not producible alloys. Typical are titanium alloys, like TiAl, TiAlNb, certain magnesium or beryllium alloys, as known to the expert. One can also use composites like glasses. Typical oxidation-prone metal alloys are those of Mg, Ca, Al, Zn, Fe, Sn, but by no means restricted to these. Foaming under normal atmosphere is possible, but leads to thicker walls of the pores, larger pores and generally to lower achievable porosity than in the case of protected atmosphere. The cost-effective variant of normal atmosphere, on account of saving expensive gases, should preferably be used in case of particularly oxidation-prone metals, like in the case of some Al-alloys. The foamable material could also be foamable plastic or foamable metal half finished product - like powder-metallurgic, cold-compacted, heat-compacted, or even extruded mixtures of metal powder with driving agents, like metal hydrides, e.g. TiH2, ZrH22, MgH2, carbonates, nitrides, hydrocarbonates, or mixtures of oxides with carbon, as already known to the experts. These starting materials could also be introduced into the mould or ingot mould together with reinforcement elements or structural elements, like hooks, bolt sleeves or such items, as well as reinforcement points - nets, filaments, threads or even cover foils, in order to obtain a decorative and at the same time protective layer of the metal part, or to fix connecting components therein. The final spatial arrangement of these reinforcing parts or layers can be ensured by providing holding elements in the moulds. The ingot mould - if it is closed - should be closable gas-tight and should have an overpressure valve, as well as a gas inlet and outlet. It could however also be meaningful, in case a precise shaping of a surface is not necessary or desirable, that the ingot mould is open at least from one side and foaming is carried out in the one open side of the ingot mould. The thus produced parts have an at least fine-foamed, geometrically interesting surface, whereas the other surfaces are shaped dimension-precise. It can be foreseen, that a controlled gas atmosphere is set and maintained in the ingot mould. The closed ingot mould should withstand gas pressure between 2 to 5 bar. During the foaming, even a pressure change can be effected - in which case, if an abrupt reduction of gas pressure is carried out in the foaming material, one gets production of metal foam with fine and uniform pores. The atmosphere in the ingot mould during the foaming process can be adjusted with respect to its composition as well as with respect to the pressure prevailing in the ingot mould during foaming. Cost-effective air is suitable as gas - in case oxidation plays only a subordinate role - however, one can also work with inert gas or any other gas which does not react in any significant manner to the foaming material, e.g. nitrogen or argon. However, if a gas reaction with metal foam components is desired — e.g. formation of nitrides in metals - one could also use a suitable reacting gas. In a preferred design form, the ingot mould is at least partly diatherman and the content of the mould can be specifically locally heated by controlled radiation and foamed. For this, it would be suitable to use a laser with emission wave lengths in the range of around 3000 nm or other suitable thermal beamers with the high share of radiation in the wave length range of approx. 760 - 5000 nm. In special cases, it could be meaningful to cover the mould or ingot material with a separating agent suited to the material to be foamed - this can be done either by coating the mould or by placing foils like fibre mats or material foils like metal foils. The separating material can also be directly applied in foil form on the foamable material. The separating agent is not always necessary, but prevents reactions between metal foam material and ingot mould, produces a structural surface in case of smooth ingot surface and can also allow relative movement of the metal foam against a mould, in case there is a separating foil. ft is particularly desired that the heat radiation is generated from controllable beamers, because in that case the foaming can be effected in a specific manner and regions of the ingot mould, which are supposed to produce a larger metal foam thickness, can be supplied accordingly with higher heat energy. However, one could also use a single radiation source, like a laser, with a corresponding radiation distribution. The radiation emission of the beamer is monitored with the help of suitably arranged sensors and controlled according to the measuring signals emitted by these. Thus one can set and carry out a pre-defined heating profile, in order to specifically control pores distribution and the foaming process. This is particularly important in the production of products with non-uniform thickness or density, as a specific foaming front has to be reached in order to obtain a product with desired pores distribution, without undesirable gas occlusions. If the process is to be carried out continuously, it could be advantageous if the ingot mould is open on both side and the foamable material is heated and expanded in a controlled manner in the open ingot mould through radiation, while the foamable material is continuously introduced into the open mould - preferably with a separating foil. Further objectives, features and advantages can be obtained by carefully considering the following description and the claims, along with the accompanying drawings. For more complete understanding of the nature and objectives of the invention, please refer to the drawings. These show the following: Fig. 1 A schematic representation of the process steps; Fig.2 A perspective part view of an arrangement for conducting the process as per the invention; Fig.3 A schematic view of the continuous process; Fig.4 A representation of foaming in open mould; Fig.5 A representation of a mould for producing angular elements. Preferred designed forms of invention are described below on the basis of production of metal foam plates; however, it is not restricted in any way to the special material or moulds mentioned there. According to this method, one can also similarly foam at high temperatures other meltable metals, like nickel, tin, aluminium, magnesium, silicium, titanium, metal alloys like bronze, glass or even glasses and melt-able plastics. Design examples: Example 1 Foaming of Zinc Foamable, powder-metallurgically produced zinc semi-finished product 14 of a Zn alloy with 14% by weight of Al, 0.8% by weight of ZrH2, 84.2% by weight of Zn is produced through cold-compacting of powder material, and then introduced into a box mould 10 with over pressure valve, which is made of diatherman silicium ceramic with a linear coefficient of expansion of 0.5 K-1 and which is sealable - as schematically shown in fig. 2 - and the cover of the box mould is closed in a gas-tight manner. The ceramic box mould is treated with separating agent before introducing the zinc semi-finished product. The mould is subsequently evacuated, gassed with argon and an overpressure of 2 bar is set in the mould. Optically aligned radiation with an emission wave maximum in the range of 3000 - 5000 nm is directed - according to a previously conducted pyrometer measurement of the radiation profile - on to the diatherman mould surfaces according to the pre-determined heating profile under foaming of the foamable material. After a predetermined time period, the heat radiation is switched off and the mould is cooled rapidly by means of air circulation with the help of a fan. The completely foamed zinc foam plate is removed from the mould. The thus produced plate revealed a very high mould-loyalty and uniform foam quality. Example 2 Foaming of Aluminium Cold- or hot-compacted foamable powder-metallurgically produced material parts 14 made of AlMgO, 6SiO, 4 with 0.4% TiH2 are placed into a closable diatherman ingot mould 10 made of Y2O3-ceramic having a quadratic base and wall thickness of 1 cm and an area of lm x 1m and then it is closed. The lower surface of the mould is uniformly supported on its lower side by means of pin-like supports 18, in order to prevent deformation of these while introducing heavy metal. Now thermal radiation from burners 16 with an emission maximum in the range of over 3000 nm controlled over a measuring field - is uniformly directed on to the lower and upper surface of the mould, whereby the foamable material gets heated and foams up and fills the mould. The temperature of the material during foaming is approx. 600°C. Here the mould or ingot material is protected by a graphite-containing foil, which is applied before introducing the semi-finished product on to the mould or ingot surfaces. The foaming takes place here without protective gas. The mould is then opened and the foamed aluminium foam plate is removed. The plate had high dimension-adherence and uniform pores distribution. Example 3 Foaming of Aluminium The method was conducted as described in example 2, whereby the mould 10 was kept under an N2-overpressure of 2.5 bar during foaming. The thus obtained mould part had smaller pores and thinner pore walls. It was found that the size of the pores and wall thickness of the generated metal foam can be controlled through the mould inner pressure as well as the type of gas present during foaming. Example 4 Production of an angular part An angular mould, which at least partly is made of a diatherman ceramic material (see schematic depiction in fig. 4), is coated with carbon 12 and then foamable material 14 is introduced into it. The further process of foaming takes place as described in example 2. Example 5 Foaming in open mould A box-shaped mould, as shown in fig. 4, with a floor surface made of diatherman ceramic, is uniformly heated with the help of a flatly arranged and controlled beamer 16 with an emission wave length max. of 3050 nm. Cold-compacted half finished product parts 14 AlSilOMgl with 0.4% TiH2 were placed on copper foil 12. One obtains a foam part with precise base and side areas containing copper, whereas the surface has geometrically freely foamed, optically appealing mould made of aluminium alloy. Such parts are suitable, in cases where a freely foamed surface of the finished component does not disturb or is even desired and the complexity of mould-closing can be avoided. Example 6 Continuous Process An ingot mould made of ceramic and open on both sides, with a coefficient of expansion of 0.5 K"1 is continuously coated on one side with a separating agent foil covered foamable material 14 of an aluminium alloy TiH2 as driving agent. Against a predetermined surface of the ingot mould 10, a non-uniform heat radiation is introduced in a controlled manner, and thus the foaming process is started and concluded. The foamable metal now foams the space between the mould cover and the mould base, whereby the metal foam surface is completely covered by the separating foil, in order to protect the mould adhesion of the metal foam, cooled during transportation and leaves the mould on the other side. The continuously exiting foam product with separating foil coming out of the exit side is then further treated in a desired manner, e.g. by water jet, laser or, if required, cut off to the desired lengths. The mould or ingot can then also itself be brought along with the material to be foamed to a corresponding radiation field. Example 7 Mg-foam An Mg-powder mixture with 9% Al, 1% Zn + 1% T1H2 was compacted cold-isostatically and then extruded at 400°C to long profiles of 20 x 5 mm. The thus produced foamable half finished product was placed into a closable two-part ingot mould of graphite and heated in a water-cooled infrared furnace up to 650°C. The inner chamber of the infrared furnace and the ingot mould was rinsed during heating with argon gas. The temperature of the ingot mould was measured and controlled. The infrared radiation led to high heating velocities (up to approx. 15 K/sec), whereby the foaming temperature of 650°C was not exceeded. After switching off the infrared heating, rapid cooling took place. The finished Mg-foam has excellent dimension-precision and uniform and fine-pored structure. Obviously the invention is not restricted to exact the design or composition of the examples listed or described; various changes or deviations from the core and protection scope of the invention are possible, which should be known to the experts. WE CLAIM: 1. Method for production of precision metal foam from a foamabte powder-metallurgicaily produced metal semifinished product with a melting point > 200°C with: - use of a mould, heat resistant up to the melting point of the foamable material, with at least one wall pervious to radiation, with a coefficient of expansion of - filling of this mould with material foamable at T>200°C in contact with separating film material; - controlled heating of the foamable material in the mould while foaming and precision forming of surfaces of the foam while essentially filling the mould using radiators with controlled energy output directed at or through the wall of the mould that is pervious to radiation; and - demoulding of the foam produced in this way. 2. Method as claimed in claim 1, wherein the mould is at least partially diathermanous. 3. Method as claimed in one of the preceding claims, wherein after heating the mould undergoes controlled cooling. 4. Method as claimed in one of the preceding claims, wherein the foaming is performed under a controlled gas atmosphere at a pressure of up to 5 bar. 5. Method as claimed in one of the preceding claims, wherein the mould is open on at least one side. 6. Method as claimed in claims 1-5 wherein the mould is open on both sides, with Ihe foamable material being admitted to the mould on the one side, being heated under control in a selected range in the mould and hence being foamed so that it leaves the mould again on the other side in a strand according to the mould form. 7. Method as claimed in one of the preceding claims, wherein the radiation emission of the radiators is monitored by sensors and controlled according to the monitoring signal. 8. Method as claimed in one of the preceding claims, wherein the mould is thin-walled, with at least one wall of the mould preferably having a thickness of 2-20 mm, particularly preferably a thickness of 1-10 mm and most particularly preferably of 2-4 mm. 9. Method as claimed in one of the preceding claims, wherein at least one wall of the mould is externally supported by supports. 10. Method as claimed in one of the preceding claims, wherein the supports are controllable and controllably support the mould in relation to a baseplate of lower temperature. 11. Device for the production of precision thermally foamed metal foam parts, wherein: - a thin waited mould (10), stable at the melting temperature of the metal foam, with a coefficient of expansion ok 3 K-1 protected by separating film material; - a controllable radiation device (16), and - a controller that controls the radiation device on the basis of the measurement of a radiation measuring device. 12. Device as claimed in claim 11, wherein the thin-walled mould, stable at the melting temperature of the metal (bam, is diathermanous. 13. Device as claimed in claims 11-12 wherein the mould can be sealed gas* tight and has at least one gas inlet and one gas outlet. 14. Device as claimed in claims 12-13, wherein the mould is open on both sides. 15. Device as claimed in claims 12-14 wherein the mould is made of graphite, Method for production of precision metal foam from a foamable powder-metallurgically produced metal semifinished product with a melting point 2000C with: -use of a mould, heat resistant up to the melting point of the foamable material, with at least one wall pervious to radiation, with a coefficient of expansion of 200°C in contact with separating film material; - controlled heating of the foamable material in the mould while foaming and precision forming of surfaces of the foam while essentially filling the mould using radiators with controlled energy output directed at or through the wall of the mould that is pervious to radiation; and - demoulding of the foam produced in this way.

Full Text

Method and Device for Producing Dimension-Precise Foam
The invention pertains to a method and device for producing dimension-precise metal foam from foamable, powder-metallurgic semi-finished metal product with a melting point > 200°C, as well as devices for carrying this out.
Production of foam from suitable foamable material for plastics, natural substances, glasses and also metal-containing materials, is known.
Methods for powder-metallurgic metal foam production in moulds having low coefficient of expansion are known from the document DE 199 54 755 Al. There, powder-metallurgic AlSil2 alloy is foamed up; however, the information given there is only suited for this material, as continuously material-dependent magnitudes are mentioned. This also holds good for the necessary 5 - 25 nm thick protection layer of the quartz glass mould through an Al2C3-coating of the quartz glass, as well as for the applied cover layer which is necessary on account of the reactivity of the foamed A1Sil2. There, also a thick-walled mould with layer thicknesses >5mm and an applied protection layer are coupled through radiation in average infrared, whereby the infrared beamer is geometrically arranged in such a way, that heat reduction occurs in the pressed mould. This known method can only work with pressed moulds which are applied on cover layers and there occur problems with non-uniformed heating of the mould, which results in non-uniform foam samples and foams which are not dimension-precise, which particularly in the case of larger foam parts, leads to instability of the foam and hence to cracks, weak points etc.
So far it has been extremely difficult to produce such metal foam parts which are dimension-precise in satisfactory quality. It is a problem to achieve a uniform pore distribution in larger components, e.g. large-surfaced ones like metal foam plates with a base area of 0.5 m2 and more. Such metal foam parts produced according to the known foaming methods often have regions, in which the pores are collapsed, and as a result we have larger hollow spaces which weaken the stability of the component. In case of parts
with non-uniform thickness or such ones with regions of higher density, which occurs by inserting more semi-finished products at pre-determined points, particularly very often defects occur. This is especially due to the fact that traditional moulds of metal have a high linear coefficient of expansion and a high heat capacity. The coefficient of expansion lead to the situation, that great dimension changes takes place on cooling, which negatively influences the dimension-precision and the cooling behaviour of the metal foam. Known moulds or ingot moulds require a lot of energy for heating, due to which the cooling is cumbersome and results in long cycle periods in production. The cooling can also lead to material problems in metal foam, in case composites are supposed to be foamed and too long dwelling in a fluid condition leads to undesirable reactions or dissolutions, like de-mixing phenomena. A further problem is that in the known foam processes in furnaces, an uncontrolled heat distribution in the ingot mould leads to uncontrolled foaming of the foamable material and hence one does not get a satisfactory pore distribution.
In other known methods the semi-finished product is heated up in metal ingot moulds in a furnace to a temperature which lies clearly above the melting temperature of matrix metal of the semi-finished product. In order to achieve an adequate productivity of the process and above all good quality of the metal foam, the heating also takes place very rapidly, i.e. within a few minutes. On the other hand, a very specific heating of the foamable material is very necessary, as otherwise individual regions of the semi-finished product do not get foamed, whereas other regions get over heated and the foam cells there collapse. Therefore, the ingot mould must be heated in a very short time - e.g. with the least possible temperature differences for plane metal foam of uniform thickness -, which is particularly difficult for larger moulds and ingot moulds and metal foam parts. A big problem in this case is the large heat capacities of known ingot moulds, which cannot be easily cooled rapidly and, on account of the high heat conducting capacity of the metal, do not allow locally differentiated heating.
The known method of foaming in metal moulds in the furnace was disadvantageous, because it was difficult to control, had to be often interrupted and, one could not run the process continuously. Finally, the energy costs were also quite high.
It is the task of this invention to present a method which allows production of uniformly foamed foam parts, even such ones having larger overall dimensions.
This task is fulfilled as per the invention by a method having the features listed in patent claim 1. It is further fulfilled with the help of the device as per the invention having the features listed in patent claim 10. Advantageous extensions can be obtained from the relevant claims.
Reference to metal foam below also includes bodies which primarily consist of metal foam, and also non-foamed reinforcing elements like wires, grilles, plates or even threads, filaments, whiskers, fastening elements and bolt bushes, hollow bodies like non-foamed pipes etc. These structural elements could be connected during foaming of metal foam by means of mould-closing or even material-closing; in this way one can avoid later fastening steps like boring, slitting or other mechanical joining methods, or gluing, welding, soldering or such processes.
The invention particularly pertains to metal foams of metals or metal composites foamed thermally at high temperatures over 200°C, preferably over 300°C or even over 500°C with the help of driving agents.
The foams can be used as solid or even light construction materials. Such light construction materials find application in the construction sector as blending elements, load-bearing elements for low weights; in motor vehicle technology, as well as in aircraft-, automobile- and ship construction, or even as absorption plates or protection plates against mechanical or thermal effects ( fire-preventing components).
By "non-uniform" one means the momentary distribution of radiation in the mould, as well as the time-related application of radiation, i.e. the blasting of the mould with different blasting intensity as well as the time-differentiated blasting of particular mould regions. Surprisingly, in this way one can control the metal foam generation and avoid occurrence of gas occlusions.
By metal foam one means here a foamed product which has defined outer dimensions.
The method can be carried out in a very advantageous manner with foamable materials having a melting above 200°C, preferably above 300°C or even melting points above 500°C.
Because, in this case moulds or ingot moulds having lower linear coefficients of expansion and lower heat capacity, as well as controlled foam generation is used, one can obtain an extremely dimension-precise metal foam part. Suitable mould materials are ceramic or glass-type materials or even composite materials like fibre-reinforced composites like fibre-reinforced ceramic, glass or carbon, which are highly heat-permeable and fulfil the requirements of low coefficient of expansion with enhanced stability under pressure and tension. It is also possible to cool off the moulds very rapidly, as the low coefficient of expansion prevents damages which could occur due to longer cooling process in case of traditional moulds.
The process can also be carried out continuously, using a preferred design form which leads to a strand-type or band-type metal foam product. In this case, moulds open on both sides are used, whereby foamable material is introduced continuously into the mould/ingot, which is blasted in a controlled manner in a selected region and the foamable material is thus heated and foamed; whereby on the other side, depending on the mould or ingot mould, the metal foam comes out foamed in the form of strands. Even here, the method can be supported by a separating material, in case the metal to be foamed adheres strongly to the mould - e.g. by letting foil-type separating material to run along, like Al2O3, or ZrC2-containing foils or graphite foils for aluminium foaming, or by
coating the foamable material with separating material foils, or by coating with a high temperature cinder base like silicate base; suitable separating agents are known to the expert.
The mould should preferably be at least partly diatherman. By diatherman one generally refers to material which is permeable for heat radiation, in this case radiation-permeable in the range of approx. 760 - 5000 nm. As suitable radiation device one could use in the range of 760 - 5000 nm continuously, or even particular wave length emitting beamers, like glue pins, Nernst-pins, SIC-rods, LEDs, CO2 - CO-, diodes-, Nd/Yag-, semiconductor or colour lasers. Their energy output can be regulated by regulating the supply current or by using a filter.
The ingot mould should preferably be thin-walled. This would be advantageous because one can avoid wastage of heat energy for heating up an ingot mould having high heat capacity, and its cooling behaviour is faster-which prevents mixing up of composite foams, higher time cycles and allows precise controlling of the heat energy working on the material to be foamed. It could, for example, have a wall thickness of 1 - 20 mm, more preferably a thickness of 2 - 10 mm. In case of thin mould walls, on account of heat management, it could be sensible to support them mechanically from outside, locally by supports or beams, in order to prevent bending or breaking of the mould in case of heavy metal foams or larger parts and to ensure retention of the dimensions. Suitable supports could be studs, or grille-type constructions, which would have as less support surface as possible and low heat conductivity and heat expansion coefficient and would consume less heat energy, in order not to disturb the heating profile. In case the studs can be regulated, it would be advantages to compensate for unevenness of the ingot mould or the heat expansion of the supports themselves.
The ingot mould can be fed with a suitable gas - even under over pressure. Ideally, an inert gas is used under not too high over pressure in the range of below approx. 5 bar. Thus one can conduct foaming of several metals or their alloys or composites, like Zn, Ni, Al, Mt, Ca, Ni, Fe, Sn. Metal powder mixings can be carried out, or even mixings of
precious metal, copper, beryllium, tungsten, titanium, steels, Si or their alloys, if required with additives, like hard substances, fibre and driving agents for producing the metal foams, like hydride or carbonate of metals - e.g. TiH2, ZnH2, MgH2, CaCO3 etc., as already known to experts in the field of metal foam production. One is particularly referring to substances releasing gases at higher temperatures, preferably such substances which are absorbed in the foam metal by formation of alloys after splitting the gas. Typical metal foam materials are ones which have a large share of Al, Be, Mg, Si, Cu, Zn, Ti, Sn, Pb, lead, brass, bronze etc. With the help of the method as per the invention, one can also process fusion-metallurgical not producible alloys. Typical are titanium alloys, like TiAl, TiAlNb, certain magnesium or beryllium alloys, as known to the expert. One can also use composites like glasses. Typical oxidation-prone metal alloys are those of Mg, Ca, Al, Zn, Fe, Sn, but by no means restricted to these. Foaming under normal atmosphere is possible, but leads to thicker walls of the pores, larger pores and generally to lower achievable porosity than in the case of protected atmosphere. The cost-effective variant of normal atmosphere, on account of saving expensive gases, should preferably be used in case of particularly oxidation-prone metals, like in the case of some Al-alloys. The foamable material could also be foamable plastic or foamable metal half finished product - like powder-metallurgic, cold-compacted, heat-compacted, or even extruded mixtures of metal powder with driving agents, like metal hydrides, e.g. TiH2, ZrH22, MgH2, carbonates, nitrides, hydrocarbonates, or mixtures of oxides with carbon, as already known to the experts. These starting materials could also be introduced into the mould or ingot mould together with reinforcement elements or structural elements, like hooks, bolt sleeves or such items, as well as reinforcement points - nets, filaments, threads or even cover foils, in order to obtain a decorative and at the same time protective layer of the metal part, or to fix connecting components therein. The final spatial arrangement of these reinforcing parts or layers can be ensured by providing holding elements in the moulds. The ingot mould - if it is closed - should be closable gas-tight and should have an overpressure valve, as well as a gas inlet and outlet.
It could however also be meaningful, in case a precise shaping of a surface is not necessary or desirable, that the ingot mould is open at least from one side and foaming is
carried out in the one open side of the ingot mould. The thus produced parts have an at least fine-foamed, geometrically interesting surface, whereas the other surfaces are shaped dimension-precise.
It can be foreseen, that a controlled gas atmosphere is set and maintained in the ingot mould. The closed ingot mould should withstand gas pressure between 2 to 5 bar. During the foaming, even a pressure change can be effected - in which case, if an abrupt reduction of gas pressure is carried out in the foaming material, one gets production of metal foam with fine and uniform pores. The atmosphere in the ingot mould during the foaming process can be adjusted with respect to its composition as well as with respect to the pressure prevailing in the ingot mould during foaming. Cost-effective air is suitable as gas - in case oxidation plays only a subordinate role - however, one can also work with inert gas or any other gas which does not react in any significant manner to the foaming material, e.g. nitrogen or argon. However, if a gas reaction with metal foam components is desired — e.g. formation of nitrides in metals - one could also use a suitable reacting gas.
In a preferred design form, the ingot mould is at least partly diatherman and the content of the mould can be specifically locally heated by controlled radiation and foamed. For this, it would be suitable to use a laser with emission wave lengths in the range of around 3000 nm or other suitable thermal beamers with the high share of radiation in the wave length range of approx. 760 - 5000 nm.
In special cases, it could be meaningful to cover the mould or ingot material with a separating agent suited to the material to be foamed - this can be done either by coating the mould or by placing foils like fibre mats or material foils like metal foils. The separating material can also be directly applied in foil form on the foamable material. The separating agent is not always necessary, but prevents reactions between metal foam material and ingot mould, produces a structural surface in case of smooth ingot surface and can also allow relative movement of the metal foam against a mould, in case there is a separating foil.
ft is particularly desired that the heat radiation is generated from controllable beamers, because in that case the foaming can be effected in a specific manner and regions of the ingot mould, which are supposed to produce a larger metal foam thickness, can be supplied accordingly with higher heat energy. However, one could also use a single radiation source, like a laser, with a corresponding radiation distribution. The radiation emission of the beamer is monitored with the help of suitably arranged sensors and controlled according to the measuring signals emitted by these. Thus one can set and carry out a pre-defined heating profile, in order to specifically control pores distribution and the foaming process. This is particularly important in the production of products with non-uniform thickness or density, as a specific foaming front has to be reached in order to obtain a product with desired pores distribution, without undesirable gas occlusions.
If the process is to be carried out continuously, it could be advantageous if the ingot mould is open on both side and the foamable material is heated and expanded in a controlled manner in the open ingot mould through radiation, while the foamable material is continuously introduced into the open mould - preferably with a separating foil.
Further objectives, features and advantages can be obtained by carefully considering the following description and the claims, along with the accompanying drawings. For more complete understanding of the nature and objectives of the invention, please refer to the drawings. These show the following:
Fig. 1 A schematic representation of the process steps;
Fig.2 A perspective part view of an arrangement for conducting the process as per the
invention;
Fig.3 A schematic view of the continuous process; Fig.4 A representation of foaming in open mould; Fig.5 A representation of a mould for producing angular elements.
Preferred designed forms of invention are described below on the basis of production of metal foam plates; however, it is not restricted in any way to the special material or moulds mentioned there. According to this method, one can also similarly foam at high temperatures other meltable metals, like nickel, tin, aluminium, magnesium, silicium, titanium, metal alloys like bronze, glass or even glasses and melt-able plastics.
Design examples: Example 1 Foaming of Zinc
Foamable, powder-metallurgically produced zinc semi-finished product 14 of a Zn alloy with 14% by weight of Al, 0.8% by weight of ZrH2, 84.2% by weight of Zn is produced through cold-compacting of powder material, and then introduced into a box mould 10 with over pressure valve, which is made of diatherman silicium ceramic with a linear coefficient of expansion of 0.5 K-1 and which is sealable - as schematically shown in fig. 2 - and the cover of the box mould is closed in a gas-tight manner. The ceramic box mould is treated with separating agent before introducing the zinc semi-finished product.
The mould is subsequently evacuated, gassed with argon and an overpressure of 2 bar is set in the mould. Optically aligned radiation with an emission wave maximum in the range of 3000 - 5000 nm is directed - according to a previously conducted pyrometer measurement of the radiation profile - on to the diatherman mould surfaces according to the pre-determined heating profile under foaming of the foamable material. After a predetermined time period, the heat radiation is switched off and the mould is cooled rapidly by means of air circulation with the help of a fan. The completely foamed zinc foam plate is removed from the mould. The thus produced plate revealed a very high mould-loyalty and uniform foam quality.
Example 2
Foaming of Aluminium
Cold- or hot-compacted foamable powder-metallurgically produced material parts 14 made of AlMgO, 6SiO, 4 with 0.4% TiH2 are placed into a closable diatherman ingot mould 10 made of Y2O3-ceramic having a quadratic base and wall thickness of 1 cm and an area of lm x 1m and then it is closed. The lower surface of the mould is uniformly supported on its lower side by means of pin-like supports 18, in order to prevent deformation of these while introducing heavy metal. Now thermal radiation from burners 16 with an emission maximum in the range of over 3000 nm controlled over a measuring field - is uniformly directed on to the lower and upper surface of the mould, whereby the foamable material gets heated and foams up and fills the mould. The temperature of the material during foaming is approx. 600°C. Here the mould or ingot material is protected by a graphite-containing foil, which is applied before introducing the semi-finished product on to the mould or ingot surfaces. The foaming takes place here without protective gas. The mould is then opened and the foamed aluminium foam plate is removed. The plate had high dimension-adherence and uniform pores distribution.
Example 3
Foaming of Aluminium
The method was conducted as described in example 2, whereby the mould 10 was kept under an N2-overpressure of 2.5 bar during foaming. The thus obtained mould part had smaller pores and thinner pore walls. It was found that the size of the pores and wall thickness of the generated metal foam can be controlled through the mould inner pressure as well as the type of gas present during foaming.
Example 4
Production of an angular part
An angular mould, which at least partly is made of a diatherman ceramic material (see schematic depiction in fig. 4), is coated with carbon 12 and then foamable material 14 is introduced into it. The further process of foaming takes place as described in example 2.
Example 5
Foaming in open mould
A box-shaped mould, as shown in fig. 4, with a floor surface made of diatherman ceramic, is uniformly heated with the help of a flatly arranged and controlled beamer 16 with an emission wave length max. of 3050 nm. Cold-compacted half finished product parts 14 AlSilOMgl with 0.4% TiH2 were placed on copper foil 12. One obtains a foam part with precise base and side areas containing copper, whereas the surface has geometrically freely foamed, optically appealing mould made of aluminium alloy. Such parts are suitable, in cases where a freely foamed surface of the finished component does not disturb or is even desired and the complexity of mould-closing can be avoided.
Example 6 Continuous Process
An ingot mould made of ceramic and open on both sides, with a coefficient of expansion of 0.5 K"1 is continuously coated on one side with a separating agent foil covered foamable material 14 of an aluminium alloy TiH2 as driving agent. Against a predetermined surface of the ingot mould 10, a non-uniform heat radiation is introduced in a controlled manner, and thus the foaming process is started and concluded. The foamable metal now foams the space between the mould cover and the mould base, whereby the metal foam surface is completely covered by the separating foil, in order to protect the mould adhesion of the metal foam, cooled during transportation and leaves the mould on the other side. The continuously exiting foam product with separating foil coming out of
the exit side is then further treated in a desired manner, e.g. by water jet, laser or, if required, cut off to the desired lengths. The mould or ingot can then also itself be brought along with the material to be foamed to a corresponding radiation field.
Example 7 Mg-foam
An Mg-powder mixture with 9% Al, 1% Zn + 1% T1H2 was compacted cold-isostatically and then extruded at 400°C to long profiles of 20 x 5 mm. The thus produced foamable half finished product was placed into a closable two-part ingot mould of graphite and heated in a water-cooled infrared furnace up to 650°C. The inner chamber of the infrared furnace and the ingot mould was rinsed during heating with argon gas. The temperature of the ingot mould was measured and controlled. The infrared radiation led to high heating velocities (up to approx. 15 K/sec), whereby the foaming temperature of 650°C was not exceeded. After switching off the infrared heating, rapid cooling took place. The finished Mg-foam has excellent dimension-precision and uniform and fine-pored structure.
Obviously the invention is not restricted to exact the design or composition of the examples listed or described; various changes or deviations from the core and protection scope of the invention are possible, which should be known to the experts.
WE CLAIM:
1. Method for production of precision metal foam from a foamabte powder-metallurgicaily produced metal semifinished product with a melting point > 200°C with:
- use of a mould, heat resistant up to the melting point of the foamable material, with at least one wall pervious to radiation, with a coefficient of expansion of - filling of this mould with material foamable at T>200°C in contact with separating film material;
- controlled heating of the foamable material in the mould while foaming and precision forming of surfaces of the foam while essentially filling the mould using radiators with controlled energy output directed at or through the wall of the mould that is pervious to radiation; and
- demoulding of the foam produced in this way.
2. Method as claimed in claim 1, wherein the mould is at least partially diathermanous.
3. Method as claimed in one of the preceding claims, wherein after heating the mould undergoes controlled cooling.
4. Method as claimed in one of the preceding claims, wherein the foaming is performed under a controlled gas atmosphere at a pressure of up to 5 bar.
5. Method as claimed in one of the preceding claims, wherein the mould is open on at least one side.
6. Method as claimed in claims 1-5 wherein the mould is open on both sides, with Ihe foamable material being admitted to the mould on the one side, being heated under control in a selected range in the mould and hence being foamed so that it leaves the mould again on the other side in a strand according to the mould form.
7. Method as claimed in one of the preceding claims, wherein the radiation emission of the radiators is monitored by sensors and controlled according to the monitoring signal.
8. Method as claimed in one of the preceding claims, wherein the mould is thin-walled, with at least one wall of the mould preferably having a thickness of 2-20 mm, particularly preferably a thickness of 1-10 mm and most particularly preferably of 2-4 mm.
9. Method as claimed in one of the preceding claims, wherein at least one wall of the mould is externally supported by supports.
10. Method as claimed in one of the preceding claims, wherein the supports are controllable and controllably support the mould in relation to a baseplate of lower temperature.
11. Device for the production of precision thermally foamed metal foam parts, wherein:
- a thin waited mould (10), stable at the melting temperature of the metal foam, with a coefficient of expansion ok 3 K-1 protected by separating film material;
- a controllable radiation device (16), and
- a controller that controls the radiation device on the basis of the measurement of a radiation measuring device.
12. Device as claimed in claim 11, wherein the thin-walled mould, stable at the melting temperature of the metal (bam, is diathermanous.
13. Device as claimed in claims 11-12 wherein the mould can be sealed gas* tight and has at least one gas inlet and one gas outlet.
14. Device as claimed in claims 12-13, wherein the mould is open on both sides.
15. Device as claimed in claims 12-14 wherein the mould is made of graphite,
Method for production of precision metal foam from a foamable powder-metallurgically produced metal semifinished product with a melting point 2000C with: -use of a mould, heat resistant up to the melting point of the foamable material, with at least one wall pervious to radiation, with a coefficient of expansion of 200°C in contact with separating film material; - controlled heating of the foamable material in the mould while foaming and precision forming of surfaces of the foam while essentially filling the mould using radiators with controlled energy output directed at or through the wall of the mould that is pervious to radiation; and - demoulding of the foam produced in this way.

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Patent Number

224727

Indian Patent Application Number

01911/KOLNP/2005

PG Journal Number

43/2008

Publication Date

24-Oct-2008

Grant Date

22-Oct-2008

Date of Filing

26-Sep-2005

Name of Patentee

ALULIGHT INTERNATIONAL GMBH

Applicant Address

LACH 22, A-5282 RANSHOFEN

Inventors:

#	Inventor's Name	Inventor's Address
1	RAJNER, WALTER	HOMERSTR, 12B, 83329 TETTENHAUSEN
2	SIMANCIK, FRANTISEK	PECHIANSKA 13, BRATISLAVA

PCT International Classification Number

B22F 3/11

PCT International Application Number

PCT/EP2004/003183

PCT International Filing date

2004-03-25

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	103 13 321.6	2003-03-25	Germany