METHOD FOR THE PRODUCTION OF METAL FOAM BY METHOD OF PLASMA-DIRECTED ENERGY SEPARATION

Abstract

The invention relates to a method for producing a metal foam. First, a metal powder and a blowing agent are provided and contacted to form a metal powder-blowing agent mixture. This mixture is then introduced into a nozzle to deposit it onto a base plate. A pilot arc is ignited between a main electrode and the nozzle. A main arc is then ignited between the main electrode and the base plate. The main arc melts the metal powder-blowing agent mixture on the base plate, forming the metal foam. Furthermore, the invention relates to a device for carrying out the method according to the invention.

Description

[0001] The invention relates to a method for producing a metal foam. For this purpose, a metal powder and a propellant are first provided, which are then brought into contact with one another to form a metal powder-propellant mixture. The metal powder-propellant mixture is then introduced into a material nozzle for application to a base plate. A pilot arc is ignited between a main electrode and the material nozzle. Furthermore, a main arc is ignited between the main electrode and the base plate. The main arc melts the metal powder-propellant mixture on the base plate, forming the metal foam thereon.

[0002] The invention also relates to a device for carrying out the method according to the invention. Background and state of the art

[0003] There is increasing interest in metal foams for the realization of technically effective lightweight construction concepts. Metal foam as such, along with its advantageous effects, is well known in the art. Metal foams have a lower mass due to pores, which can be open or closed, which explains their efficient use in lightweight construction. Furthermore, the use of metal foam is associated with material savings, which can have a resource-saving effect. Furthermore, metal foams can reliably absorb energy, which can propagate in the form of vibrations, heat, impacts, electromagnetic waves, and / or sound waves. Due to its high permeability, metal foam can also be used for filter applications. Several possible variants for the production of metal foam are currently known.

[0004] There are various classifications for the processes used to produce metal foam. In principle, the relevant process variants can be divided into melt metallurgy and powder metallurgy.

[0005] In melt metallurgical processes, a matrix metal is typically melted. Optionally, an auxiliary agent can be added to optimize the melt for the process. If aluminum is melted as the matrix metal, calcium, aluminum oxide, and / or silicon carbide, for example, can be stirred to increase the viscosity of the melt. A gas can then be blown into the melt, or the gas can be formed in the melt, i.e., in situ. The latter is achieved by prior addition of a blowing agent.

[0006] Powder metallurgical processes use a metal powder as the starting material. The metal powder can also be exposed to gas from the outside, or a blowing agent can be incorporated into the metal powder itself to generate gas and thus the pore structure for the metal foam.

[0007] In addition, there are a variety of manufacturing methods for metal foam. Deposition technologies are also known. For example, an electrically conductive layer can be coated onto a plastic foam. The metal to be foamed can then be electroplated onto the electrically conductive layer, and the plastic foam can be removed.

[0008] Although the state of the art offers a variety of options for producing metal foams, these have several disadvantages that cannot be ignored. Currently known manufacturing processes do not allow for reliable production of metal foams with reproducible properties. Furthermore, adjusting process parameters is difficult. Furthermore, high energy consumption is associated with the known processes for producing metal foams. Furthermore, the resulting metal foams exhibit undesirable corrosion behavior, which is crucial for their suitability and quality. Therefore, there is a need for an alternative manufacturing process for metal foams. Object of the invention

[0009] The object of the invention was to provide a process that eliminates the disadvantages of the prior art and can be used to produce metal foam. A further object of the invention was to provide an apparatus with which the process can be carried out. Summary of the invention

[0010] The object of the invention is achieved by the independent claims. Advantageous embodiments of the invention are described in the dependent claims.

[0011] In a first aspect, the invention relates to methods for producing a metal foam comprising the following steps: a) Providing a metal powder, b) provision of a propellant, c) contacting the metal powder and the propellant to provide a metal powder-propellant mixture, d) introducing the metal powder-propellant mixture into a material nozzle so that the metal powder-propellant mixture is applied to a base plate, e) introducing a plasma gas between the material nozzle and a main electrode, f) ignition of a pilot arc between the material nozzle and the main electrode, g) Ignition of a main arc between a main electrode and a base plate, so that the metal powder-propellant mixture melts on the base plate by the main arc and forms the metal foam.

[0012] The combination of the inventive features leads to a surprising synergistic effect, which results in the advantageous properties and effects and the associated overall success of the invention, with the individual features interacting with each other. The process according to the invention has proven surprisingly advantageous in a number of aspects.

[0013] A particular advantage here is that the metal foam can be produced surprisingly quickly. This, combined with the advantageous ease of handling of the process and its steps, results in optimal process efficiency with which the metal foam can be produced.

[0014] Furthermore, it is surprisingly advantageous that particularly high deposition rates of the metal foam can be achieved through the process. The metal foam is preferably applied to the base plate as a melt. The melt applied to the base plate can also be referred to as a melt pool in the context of the invention. Therefore, within the meaning of the invention, the higher deposition rate can also be related to the melt pool. Advantageously, deposition rates of up to 10 kg / h (kilograms per hour) can be achieved. This results in significantly higher productivity for the metal foam produced by the process compared to the prior art.

[0015] Furthermore, it is surprisingly advantageous that the metal foam produced by this process enables a significant reduction in warpage in components containing the metal foam. This can positively influence the extent of warpage and / or shrinkage in a component. This also has a beneficial effect on the component quality itself and ensures reliable functionality of the component.

[0016] Another particularly surprising advantage is that the metal foam produced by the process is available for use as a coating material. This allows, for example, the metal foam to be applied directly to a component and / or workpiece. At the same time, there are no restrictions on the materials to which the metal foam can be applied. Thus, the achieved effect is synergistic in terms of direct application and the broad range of materials to which the metal foam can be applied.

[0017] Another advantage is that the heat source and powder feed rate can be adjusted independently of each other. In other words, the heat input and filler material feed rate can be adjusted independently of each other to specifically influence the foam production process through this interaction.

[0018] Another surprising advantage of the process is that it can produce the metal foam additively. This is particularly advantageous for the shaping of the metal foam. This allows for particularly reliable production of complex and / or intricate structures that encompass the metal foam and have a porous structure. This allows for customized structuring of the metal foam, which also has a beneficial effect on cost-effective series production of the metal foam.

[0019] Furthermore, the process is characterized by its considerable economic efficiency. The process advantageously uses inexpensive components. Therefore, the process according to the invention is also suitable for use in the mass production of metal foams. Furthermore, the process is energy- and resource-efficient, which further emphasizes its suitability for mass production.

[0020] The preferred method is used in particular for producing a metal foam. Within the meaning of the invention, a metal foam refers to a structure comprising a metal having a pore structure. The pore structure can have closed pores and / or open pores. Furthermore, the metal foam is preferably stable. "Stable" means that reduced flexibility of the metal foam can be achieved through the selection of the metal and / or the pore structure. The preferred method advantageously allows the flexibility of the metal foam to be easily optimized.

[0021] To produce the metal foam, it is preferred that a metal powder and a blowing agent are provided. The blowing agent serves to form the pore structure for the metal foam. For this purpose, at least one gas is released by the blowing agent when it is heated by the main arc. The gas released by the heat, in turn, forms the pore structure for the metal foam. The metal powder and the blowing agent are contacted with one another. The combination comprising metal powder and blowing agent is to be referred to as a metal powder-blowing agent mixture within the meaning of the invention. Accordingly, the metal powder-blowing agent mixture is provided by bringing the metal powder into contact with the blowing agent. The terms "metal powder-blowing agent mixture" and "blowing agent-metal powder mixture" can be used synonymously within the context of the invention.

[0022] It has been advantageously recognized that the principle of plasma powder welding can be transferred to the production of metal foam in a surprisingly efficient manner. Preferably, the metal powder-propellant mixture is introduced into a material nozzle. The material nozzle refers to a nozzle that serves, in particular, to apply the metal powder-propellant mixture to a base plate. Furthermore, the material nozzle preferably serves to ignite a pilot arc between it and a main electrode.

[0023] To create the pilot arc, a plasma gas is introduced between the main electrode and the material nozzle. To ignite the pilot arc, an electrical voltage is preferably applied between the main electrode and the material nozzle. The term "ignition" in the context of the invention preferably refers to the provision of an electrical voltage to ensure the formation of the corresponding arc, i.e., the pilot arc and the main arc.

[0024] The applied electrical voltage or electrical current between the main electrode and the material nozzle, through which the plasma gas is introduced, creates a plasma or an arc, which represents the pilot arc. Preferably, the main electrode is negatively polarized and the material nozzle is positively polarized. The plasma gas is preferably introduced between the main electrode and the material nozzle to enable the formation of the resulting pilot arc. The term "plasma gas" refers to a gas dedicated to the formation of a plasma and thus an arc. The spatial region through which the plasma gas is introduced can also be referred to as a plasma gas nozzle in the context of the invention.

[0025] The main arc is formed within an arc gap between the main electrode and the base plate. The base plate refers to the component to which the metal foam is applied. If the main electrode is negatively polarized, the base plate is preferably positively polarized. To form the main arc, an electrical voltage or an electrical current is applied between the main electrode and the base plate. Applying the voltage between the main electrode and the base plate can cause ionization, which leads to the formation of the main arc. The main arc can melt the metal powder-propellant mixture on the base plate. The melt of the metal powder-propellant mixture on the base plate is also referred to as the molten pool in the context of the invention.

[0026] The pilot arc and the main arc are two independent arcs. Advantageously, the pilot arc can be used to heat the area between the base plate and the main electrode, thus advantageously enabling contactless ignition of the main arc. Preferably, a direct current is applied to ignite the main arc and / or the pilot arc. In preferred embodiments, an alternating current and / or a pulsed current can also be applied.

[0027] It is clear to those skilled in the art that an arc is generated by a sufficiently high electrical potential difference via a gas discharge that occurs between the components (here, the main electrode and base plate, and the main electrode and material nozzle). As shown above, the pilot arc occurs between the main electrode and the material nozzle, while the main arc occurs between the material nozzle and the base plate.

[0028] In a further preferred embodiment, the plasma gas is selected from a group comprising argon.

[0029] The use of argon has proven advantageous in three respects in particular. Argon increases the stability of the pilot arc and thus also of the main arc, reliably ensuring the formation of a plasma. Furthermore, argon has proven advantageous in that it provides sufficient protection for the molten pool, preventing it from entering into external reactions with the environment, such as the ambient air. This also has a beneficial effect on the reproducibility and component quality of the produced metal foam, as the avoidance of undesirable side reactions with the environment prevents further by-products and / or deformations. Furthermore, argon is inexpensive to acquire, thus improving the cost-effectiveness of the process.

[0030] In a further preferred embodiment, the method is characterized in that the plasma gas is introduced with a volume flow between 0.5 - 5 l / min (liters per minute), preferably between 1 - 3 l / min.

[0031] The amount of plasma gas introduced can influence the beam divergence of the main arc and thus also the area of ​​the molten pool. Beam divergence describes the widening of an arc. The main arc is particularly relevant for the melting of the metal powder-propellant mixture. Therefore, a higher volume flow of the plasma gas can increase the divergence of the main arc and thus melt a larger cross-section of the molten pool onto the base plate. The preferred value ranges for the volume flow have proven particularly advantageous in this regard. The preferred range between 1 - 3 l / min is considered particularly advantageous, as the molten pool on the base plate melted surprisingly quickly in this range.

[0032] In a further preferred embodiment, the method is characterized in that a protective gas is introduced, preferably through a protective gas nozzle or between the main electrode and material nozzle, wherein the protective gas is preferably selected from a group comprising argon, preferably in combination with hydrogen and / or helium.

[0033] A shielding gas refers to a gas that is particularly dedicated to protecting the molten pool from chemical side reactions. Preferably, the plasma gas can be used and / or function simultaneously as a shielding gas. It may also be preferred for the shielding gas to be introduced as an additional gas to the plasma gas. With regard to simultaneous use as a plasma gas and a shielding gas, the introduction of argon has proven particularly advantageous. Furthermore, the shielding gas can enable better ionization of the plasma gas, which promotes the formation of the main arc. The preferred gases comprising argon, preferably in combination with hydrogen and / or helium, have proven particularly reliable in this regard in the context of the invention.

[0034] In a preferred embodiment, the shielding gas can be introduced through a space between the material nozzle and the main electrode, i.e., in particular, through the plasma gas nozzle. This allows a particularly compact design of a device to be achieved, by means of which the preferred method can be carried out.

[0035] In another preferred embodiment, the shielding gas can be introduced through a shielding gas nozzle. The shielding gas nozzle refers to an additional nozzle dedicated to the introduction of the shielding gas. This advantageously allows for a targeted guidance of the shielding gas toward the molten pool. In particular, the direction in which the shielding gas is to spread can be determined more precisely.

[0036] In a further preferred embodiment, the method is characterized in that a protective gas is introduced with a volume flow between 10 - 20 l / min, preferably between 10 - 15 l / min.

[0037] By introducing the shielding gas at a volume flow within the preferred ranges mentioned, a particularly controlled introduction into the process can be ensured. In the particularly preferred range of 10 - 15 l / min, in addition to the advantageous controllability, a saving in the amount of shielding gas introduced could also be achieved, which is beneficial for process economics and incurred costs. With regard to the improved controllability, this particularly means that such sufficient protection is enabled that essentially spatially homogeneous protection is achieved for the molten pool. This also allows the pore structure of the metal foam to achieve homogeneity, which has a beneficial effect on the quality and stability of the produced metal foam.In other words, by introducing a volume flow in the preferred areas, it is possible to spread the shielding gas in such a way that an essentially holistic protection for the molten pool is provided, which advantageously results in a high-quality metal foam.

[0038] In a further preferred embodiment, the method is characterized in that a current intensity between 60 - 250 A, preferably between 120 - 180 A, is applied to ignite the main arc.

[0039] In a further preferred embodiment, the method is characterized in that a voltage between 18 - 26 V, preferably between 20 - 23 V, is applied to ignite the main arc.

[0040] In a further preferred embodiment, the method is characterized in that a current intensity between 2 - 20 A, preferably between 3 - 15 A, is applied to ignite the pilot arc.

[0041] It is understood that to ignite the pilot arc, an electric current flows between the main electrode and the material nozzle. This also applies an electric voltage between the main electrode and the material nozzle to ignite the pilot arc. Similarly, the ignition of the main arc is made possible by an electric current flowing between the base plate and the main electrode. This applies an electric voltage between the main electrode and the base plate. The preferred current intensities mentioned have proven advantageous in that the ignition of the pilot arc and main arc occurs in a particularly reliable manner. Thus, the formation of a pilot arc and main arc is guaranteed when the preferred current intensities mentioned are provided, ensuring safe execution of preferred method steps.

[0042] In a further preferred embodiment, the method is characterized in that a current intensity for igniting the main arc and / or pilot arc is controlled by a computing unit on the basis of a measured value of a temperature sensor and / or current sensor.

[0043] The average person skilled in the art will understand what is meant by a temperature sensor and a current sensor. The temperature sensor can preferably be mounted sufficiently close to the molten pool to enable a temperature measurement to be taken. The current sensor is preferably mounted in a circuit that serves to ignite the pilot arc and / or main arc. A data connection is preferably provided between the computing unit and the current sensor and / or temperature sensor. The data connection means, in particular, that an exchange of data is possible between the computing unit and the current sensor and / or temperature sensor. A computing unit preferably means a device with which data can be processed, i.e., in particular, a data processing unit. For this purpose, it may be preferable for appropriate software to be installed on the computing unit that permits the processing of data.The computing unit can preferably be selected from a group comprising an integrated circuit (IC), an application-specific integrated circuit (ASIC), a programmable logic circuit (PLD), a field programmable gate array (FPGA), a microprocessor, a microcomputer, a programmable logic controller and / or another electronic, preferably programmable, circuit.

[0044] By means of the arrangement comprising a computing unit, a temperature sensor and / or a current sensor, the ignition of the main arc and / or pilot arc can advantageously be controlled by a closed control loop. For this purpose, it may be preferable to optimize the electrical voltage and / or the electrical current for the ignition of the main arc and / or pilot arc on the basis of a measured value which, for example, is detected by the current sensor and / or temperature sensor. The control can, for example, mean changing or optimizing the electrical current and / or voltage to a value which is specified as a guideline, for example as a stored guideline in the computing unit. The guideline can preferably also be present as a range of values. On the one hand, the automation of the preferred method is advantageously considerably improved. On the other hand, the process parameters, such as, for example,the electrical voltage and / or the electrical current, can be better recorded, resulting in better results for the reproducibility of the metal foam.

[0045] In a further preferred embodiment, the method is characterized in that a parallel and / or vertical relative movement is carried out between the base plate and the material nozzle and / or main electrode.

[0046] A parallel relative movement to the base plate comprises a movement in lateral directions. In the context of the invention, lateral directions can be described by a plane, i.e., by a surface having a surface normal directed in the longitudinal direction of the material nozzle and / or main electrode. A perpendicular relative movement relative to the base plate comprises a displacement along the surface normal of the surface, which determines the lateral directions. In particular, a perpendicular displacement relative to the base plate leads to a change in the distance between the material nozzle and the base plate or between the main electrode and the base plate.

[0047] A relative movement between the main electrode and the base plate can advantageously adjust the arc gap. In other words, the relative movement between the main electrode and the base plate can optimize the discharge space (corresponding to the arc gap). The relative movement between the material nozzle and the base plate can advantageously determine the shape of the metal foam with particular precision, particularly with regard to additive manufacturing. A combination of vertical and parallel relative movement can advantageously create three-dimensional structures, which can have a complex design, for the metal foam.

[0048] In a further preferred embodiment, the method is characterized in that there is a distance between the main electrode and the base plate of between 5 - 15 mm, preferably between 5 - 10 mm, particularly preferably between 8 - 10 mm.

[0049] In a further preferred embodiment, the method is characterized in that a voltage between 18 - 26 A, preferably between 20 - 23 A, is applied to ignite the pilot arc.

[0050] Within the aforementioned preferred distance ranges between the main electrode and the base plate, sufficient electrical voltages can advantageously be achieved so that a resulting electric field can be ionized and thus the main arc can be generated. The main arc can melt the metal powder-propellant mixture on the base plate and produce the metal foam.

[0051] In a further preferred embodiment, the method is characterized in that the metal powder-propellant mixture has a powder mass flow between 5 - 150 g / min, preferably between 15 - 30 g / min.

[0052] The powder mass flow refers specifically to the amount of powder melted per unit of time. The above-mentioned powder mass flow ranges have proven advantageous for ensuring particularly reliable process execution.

[0053] In a further preferred embodiment, the process is characterized in that the metal powder-propellant mixture has a proportion of propellant between 10 - 20%, preferably between 10 - 15% and a proportion of metal powder between 80 - 90%, preferably between 85 - 90%.

[0054] The preferred proportions of blowing agent and metal powder have proven advantageous in the context of the invention for shaping the pore structure of the metal foam. With a higher proportion of blowing agent, the metal foam can have more pores than with a lower proportion of blowing agent. Conversely, the number and / or dimensions of the pores can be reduced if a lower proportion of blowing agent is used. Particularly with regard to the material properties of the metal foam itself, the preferred proportions of blowing agent and metal powder have proven surprisingly advantageous. This resulted in improved properties with regard to mechanical damping, shielding against electromagnetic fields, surprisingly good thermal insulation, and optimized ductility.This improves the technical applicability of the metal foam that can be produced using the preferred process.

[0055] When the metal powder-propellant mixture is applied to the base plate, it is melted onto the base plate by the main arc. The heat generated by the main arc and present in the molten pool releases at least one gas, which expands and leads to pore formation.

[0056] In a further preferred embodiment, the method is characterized in that the metal powder comprises a material selected from a group comprising a metal, preferably a pure metal, and / or alloy, wherein the metal is preferably selected from a group comprising aluminum, nickel, cobalt, iron, titanium and / or steel, wherein the metal powder preferably also comprises carbon.

[0057] The preferred materials for the metal powder are advantageously inexpensive to acquire, which is beneficial for the economic efficiency and mass production suitability of the preferred process. Furthermore, the use of the aforementioned preferred materials can cover a wide range of application areas relevant to the use of metal foams. Thus, metal foam comprising structural steel and / or stainless steel can also be advantageously produced using the preferred process, which can find applications in supporting structures, filter technologies, and / or the automotive industry.

[0058] In a further preferred embodiment, the method is characterized in that the propellant comprises a material selected from a group comprising titanium, titanium dihydride, zirconium dihydride, calcium carbide, magnesium carbide, with titanium and / or titanium dihydride being preferred.

[0059] As explained above, heating the blowing agent within the molten bath releases at least one gas, for example in the form of hydrogen bubbles, carbon monoxide, and / or carbon dioxide, creating the pore structure of the metal foam. Hydrogen bubbles are formed in particular when titanium dihydride and / or zirconium dihydride are used. The preferred materials mentioned for the blowing agent are particularly advantageous because, in addition to creating the foam structure, they are also suitable for other purposes that surprisingly improve the overall success of the invention. For example, the preferred materials are suitable for generating additional protection of the molten bath from the environment. This is due to the formation of gases caused by the heat and is therefore advantageous for the component quality and / or component shape of the metal foam.Furthermore, the preferred blowing agents, in particular calcium carbide and / or magnesium carbide, can remove undesirable materials for the metal foam, such as sulfur, for example by setting reactions.

[0060] In a further preferred embodiment, the method is characterized in that the base plate comprises a material selected from a group comprising a metal, preferably a pure metal, and / or alloy, wherein the metal is preferably selected from a group comprising aluminum, nickel, cobalt, iron, titanium and / or steel, wherein the metal powder preferably also comprises carbon.

[0061] Preferably, the material of the base plate and the metal powder can be identical. It is also preferable for the material of the base plate and the metal powder to be different. The producible metal foam preferably has a permanent connection, in particular a welded connection, with the base plate.

[0062] The base plate can preferably be a component in the sense of a substrate to enable the application of the metal foam. Furthermore, it may be preferred for the base plate to be a workpiece that is intended to contain the metal foam that can be produced by the preferred method.

[0063] In a further preferred embodiment, the method is characterized in that the method is carried out at a welding speed between 3 - 100 cm / min, preferably between 6 - 24 cm / min.

[0064] The welding speed preferably refers to the progress of a weld seam resulting from the melting of the molten pool on the base plate. This preferred welding speed advantageously allows for the metal powder-propellant mixture to melt particularly quickly on the base plate while simultaneously enabling a stable forming process.

[0065] In a further aspect, the invention relates to a device for carrying out a method according to a preferred embodiment of the invention, characterized in that the device comprises a material nozzle and a main electrode, wherein the main electrode is surrounded by the material nozzle, wherein a metal powder-propellant mixture can be introduced into the material nozzle onto a base plate, wherein a pilot arc can be ignited between the main electrode and the plasma nozzle and a main arc can be ignited between the main electrode and a base plate, so that the metal powder-propellant mixture on the base plate can be melted by the main arc and a metal foam can be produced. Preferably, a plasma gas can be introduced between the main electrode and the material nozzle. An intermediate section between the main electrode and the material nozzle, into which the plasma gas can be introduced, can also be present as a nozzle, in this case as a plasma gas nozzle.In particular, it may be preferred for the main electrode to be surrounded by the material nozzle. Surrounding the main electrode by the material nozzle may preferably mean a sheathing, in particular also that an outer surface of the material nozzle encloses the main electrode.

[0066] The average person skilled in the art recognizes that technical features, definitions and advantages of preferred embodiments of the method according to the invention also apply to an apparatus for carrying out the method, and vice versa.

[0067] The device advantageously enables rapid execution of the process and thus correspondingly rapid production of the metal foam. Furthermore, a high deposition rate for the metal foam and a reduction in warpage of components containing the metal foam are achieved. Furthermore, the device allows for additive manufacturing of the metal foam, which allows for flexible design of the metal foam shape. Furthermore, cost-effective operation of the device is ensured, which enhances process efficiency and suitability for mass application.

[0068] In a further preferred embodiment, the device comprises a shielding gas nozzle for introducing a shielding gas. The shielding gas serves, in particular, to protect the molten bath from external reactions with the surrounding environment. This advantageously produces a significantly high-quality metal foam. The shielding gas can preferably also be introduced via the plasma gas nozzle.

[0069] The aspects of the invention are to be illustrated below by way of example with the aid of figures, without being limited thereto. CHARACTERSShort description of the characters Fig. 1 Schematic representation of a preferred embodiment of a device with which a preferred embodiment of the method can be carried out. Fig. 2-5 Images of metal foam produced by a preferred embodiment of the process. Detailed description of the characters

[0070] Fig. 1 serves to schematically represent a preferred device 1 with which a preferred embodiment of the method according to the invention can be carried out.

[0071] To carry out the process itself, a metal powder and a propellant are provided. The metal powder is then brought into contact with the propellant to create a metal powder-propellant mixture. The metal powder-propellant mixture is then introduced into a material nozzle 3 so that it can be applied to a base plate 5. By means of the device 1, a pilot arc 2 is ignited between a main electrode 7 and the material nozzle 3. Furthermore, a main arc is ignited between the main electrode 7 and the base plate 5. To ignite the pilot arc 2 and the main arc, an electrical voltage is applied between the main electrode 7 and the material nozzle 3 (for the pilot arc 2) and between the main electrode 7 and the base plate 5 (for the main arc). The plasma gas 2 improves the energy transfer to the base plate 5.This is represented by an electrical circuit in the . Fig. 1. The main arc enables the metal powder-propellant mixture to melt on the base plate 5 and form the metal foam.

[0072] A particular advantage of the preferred method and device is that the metal foam can be produced surprisingly quickly. This, in combination with the advantageous ease of handling of the method and the method steps, results in optimal process efficiency with which the metal foam can be produced. Another surprising advantage is that particularly high application rates of the metal foam can be achieved. This results in high productivity for the metal foam that can be produced using the method. Another surprising advantage is that the metal foam produced using the method enables a significant reduction in warpage in components that contain the metal foam. This can advantageously have a positive influence on the extent of warpage and / or shrinkage in a component. This also has a beneficial effect on the component quality itself and ensures reliable functionality of the component.Another particularly surprising advantage is that the metal foam produced by the process is available for use as a material to be coated. This means that the metal foam can advantageously be applied directly to a component and / or workpiece, for example. Furthermore, there are advantageously no restrictions regarding the materials to which the metal foam can be applied. Thus, the achieved effect is synergistic with regard to direct application and a broad application suitability of materials to which the metal foam can be applied. Another surprising advantage is that the preferred process can be carried out in an additive manner to produce the metal foam. This is particularly advantageous for the shaping of the metal foam. This advantageously allows complex and / or delicate structures which have a porous structure comprising the metal foam to be produced particularly reliably.Thus, an individualized structuring of the metal foam can advantageously be specified, which also has a beneficial effect on cost-effective series production of the metal foam. A further advantage is that the preferred method is associated with considerable economic efficiency. Cost-effective components are advantageously used to carry out the method. Therefore, the method according to the invention is also suitable for use in the mass production of metal foams. The method, in particular also using the preferred embodiment of the device 1, which is shown in FIG. Fig. 1 is energy and resource efficient, which emphasizes its mass suitability.

[0073] In the Fig. 1 also shows a shielding gas nozzle 13 through which a shielding gas can be introduced. The shielding gas serves primarily to protect the molten pool and prevent unwanted side reactions. Furthermore, the shielding gas can facilitate better ionization of the plasma gas, which promotes the formation of the main arc.

[0074] Fig. Figures 2 - 5 show various images in multiple views of the metal foam that can be produced using the process according to the invention. This demonstrates the feasibility of the process.

[0075] In Fig. Figure 2 shows a ruler illustrating the dimensions of the metal foam that can be produced. Furthermore, the figure on the right clearly shows that the metal foam was produced in the form of a strand.

[0076] In Fig. 3 shows that the metal foam can be produced in the form of layers. While in Fig. 3A and Fig. 3B a layer is shown, in Fig. 3C shows two layers that were applied to the base plate.

[0077] Fig. 4A shows a metal foam, where in the Fig. 4B, Fig. 4C and Fig. 4D various close-ups are shown. Fig. Figure 4B shows a close-up of the inner surface of the metal foam from Fig. 4A. Fig. Figure 4C shows a close-up view of the upper lateral end of the metal foam of the Fig. 4A. Fig. Figure 4C shows a close-up view of the outer surface. Fig. 4 treated metal foam has a porosity of approximately 50%.

[0078] Fig. Figure 5A also shows a manufactured metal foam, which is attached to a ruler to illustrate its dimensions. Fig. 5B is a close-up view of a cross-section of the Fig. 5A. The essentially homogeneous design of the pore structure of the metal foam is shown in Fig. 5B is particularly easy to see. LIST OF REFERENCE SYMBOLS 1 device 2 Plasma gas 3 Material nozzle 5 Base plate 7 Main electrode

Claims

[1] Process for producing a metal foam comprising the following steps: a) Providing a metal powder, b) provision of a propellant, c) contacting the metal powder and the propellant to provide a metal powder-propellant mixture, d) introducing the metal powder-propellant mixture into a material nozzle (3) so that the metal powder-propellant mixture is applied to a base plate (5), e) introducing a plasma gas between the material nozzle (3) and a main electrode (7), f) ignition of a pilot arc between the main electrode (7) and the material nozzle (3), g) Ignition of a main arc between a main electrode (7) and a base plate (5) so that the metal powder-propellant mixture melts on the base plate (5) by the main arc and forms the metal foam. [2] Method according to the previous claim characterized bythat the plasma gas (2) is selected from a group comprising argon [3] Method according to one or more of the preceding claims characterized by that a protective gas is introduced, preferably through a protective gas nozzle (9) or between the main electrode (7) and material nozzle (3), wherein the protective gas is preferably selected from a group comprising argon, preferably in combination with hydrogen and / or helium. [4] Method according to one or more of the preceding claims characterized by that a parallel and / or vertical relative movement is carried out between the base plate (5) and the material nozzle (3). [5] Method according to one or more of the preceding claims characterized bythat the metal powder comprises a material selected from a group comprising a metal, preferably a pure metal, and / or alloy, wherein the metal is preferably selected from a group comprising aluminum, nickel, cobalt, iron, titanium and / or steel. [6] Method according to one or more of the preceding claims characterized by that the propellant comprises a material from a group comprising titanium, titanium dihydride, zirconium dihydride, calcium carbide, magnesium carbide. [7] Method according to one or more of the preceding claims characterized by that the process is carried out with a current between 60 - 250 A, preferably between 120 - 180 A. [8] Method according to one or more of the preceding claims characterized by that the process is carried out at a welding speed between 3 - 100 cm / min, preferably between 6 - 24 cm / min. [9] Method according to one or more of the preceding claims characterized by that there is a distance of between 5 - 15 mm, preferably between 5 - 10 mm, particularly preferably between 8 - 10 mm, between the main electrode (7) and the base plate (5). [10] Device (1) for carrying out a method according to one or more of the preceding claims characterized by in that the device comprises a material nozzle (3) and a main electrode (7), the main electrode (7) being surrounded by the material nozzle (3), a metal powder-propellant mixture being insertable into the material nozzle onto a base plate (5), a pilot arc (2) being ignitable between the main electrode (7) and the material nozzle (3) and a main arc being ignitable between the main electrode (7) and a base plate (5), so that the metal powder-propellant mixture on the base plate (5) can be melted by the main arc and a metal foam can be produced.

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