Method for producing a metal molded body with TPMS structure and metal molded body with TPMS structure

Abstract

The invention relates to a method for producing a metal mold body with a TPMS structure, comprising the steps of: - producing a negative mold (2) of a metal mold body with a three-dimensional TPMS structure (1) from an electrically non-conductive sacrificial material, - producing an electrically conductive coating (2.1) on the negative mold (2), - electroplating a metal onto the electrically conductive coating (2.1), whereby a positive mold of the metal mold body is formed, and - removing the electrically non-conductive sacrificial material from the positive mold.

Description

The invention relates to a method for producing a metal molded body with a TPMS structure and a metal molded body with a TPMS structure, in particular a heat exchanger with a TPMS structure for heat transfer between at least two fluids. Heat exchangers are used to transfer thermal energy between flowing fluids. They are therefore an important component in air conditioning systems. These heat exchangers, usually made of metal, have connections and channels for the separate flow of at least two fluids. The abbreviation TPMS (Triple Periodic Minimal Surfaces) refers to structures that have a minimal volume per unit area. This property makes TPMS structures, in addition to catalysts, particularly interesting for use in heat exchangers, because the large specific surface area of ​​TPMS structures relative to their volume allows for particularly efficient heat transfer between fluids. At the same time, the continuously and uniformly structured channels of a TPMS structure enable optimized flow, minimizing pressure losses and ensuring good mixing of the fluids.The minimal surface area of ​​TPMS structures also ensures optimized material utilization, thereby saving costs without compromising thermal and mechanical properties. A further advantage is the mechanical stability of TPMS structures combined with their low weight, as mechanical loads can be distributed evenly. Additive manufacturing methods, such as powder bed fusion (PBF), enable precise and flexible production that can be tailored to specific requirements, for example, regarding fluid types, temperatures, or pressure conditions. However, additive manufacturing is not suitable for mass production due to the long production time required for individual parts. Furthermore, it necessitates complex machinery, which is associated with high costs. The invention is therefore based on the objective of proposing a method by which metal components with a TPMS structure, in particular heat exchangers with a TPMS structure, can be manufactured cost-effectively. Furthermore, it is an objective to provide a cost-effectively manufactured heat exchanger with a TPMS structure. The problem is solved by a method with the features according to claim 1 and a heat exchanger with the features according to claim 13. Further developments are specified in the dependent claims. The proposed method for manufacturing a metal component with a TPMS structure comprises several steps. First, a negative mold of a metal component with a three-dimensional TPMS structure is created from an electrically non-conductive sacrificial material. The negative mold corresponds to an inverse TPMS structure of the metal component to be manufactured. An electrically conductive coating is then applied to the negative mold. In the next step, a metal is electroplated onto the electrically conductive coating, forming a positive mold of the metal component. The electroplating creates a load-bearing structure that corresponds to the shape of the metal component to be manufactured. Finally, the electrically non-conductive sacrificial material is removed from the positive mold. The negative mold is demolded to expose the positive mold. The proposed method is particularly suitable for manufacturing a heat exchanger with a TPMS structure. The inventive method for producing a heat exchanger with a TPMS structure can be summarized in the following steps: - Creating a negative mold of a heat exchanger with a three-dimensional TPMS structure from an electrically non-conductive sacrificial material, - Creating an electrically conductive coating on the negative mold, - Electroplating a metal onto the electrically conductive coating, thereby forming a positive mold of the heat exchanger, and - Removing the electrically non-conductive sacrificial material from the positive mold. In the manufacture of a heat exchanger with a TPMS structure, the negative form corresponds to an inverse TPMS structure of the heat exchanger to be manufactured, wherein the three-dimensional TPMS structure is provided to form at least two flow paths in order to be able to guide at least two fluids separately through the resulting heat exchanger. Furthermore, the proposed method is suitable for producing a metal shaped body in the form of a catalyst with a TPMS structure. The sacrificial material from which the negative mold is formed must be sufficiently dimensionally stable to allow for the application of an electrically conductive coating to the negative mold, and must also be easily removed from the resulting positive mold by dissolution or deformation. Suitable sacrificial materials include an epoxy resin or a meltable polymer such as polylactic acid (PLA) or acrylonitrile butadiene styrene copolymer (ABS). Preferably, a UV-curable acrylate-based photopolymer is used as the sacrificial material. If an epoxy resin is used as an electrically non-conductive sacrificial material, the electrically non-conductive sacrificial material, i.e. the negative mold, can be removed from the positive mold by a chemical, especially acetone. If a polymer is used as an electrically non-conductive sacrificial material, the negative mold can be removed by heating the positive mold, thereby melting out the electrically non-conductive sacrificial material from the positive mold. The negative mold is preferably produced additively. A 3D printing process is a suitable additive manufacturing method. The additive manufacturing of the negative mold, which serves as a preform, ensures a high degree of flexibility for individual adaptation of the structure of the heat exchanger to be manufactured. The three-dimensional TPMS structure can be generated as a gyroid, diamond, Schwarz D, Neovius, Fischer-Koch, or lidinoid structure. The negative form is consequently generated as an inverse gyroid, diamond, Schwarz D, Neovius, Fischer-Koch, or lidinoid structure. To create the electrically conductive coating, the negative mold can be immersed in a palladium chloride bath. This type of coating is applied without current. Another way to create the electrically conductive coating is by applying a graphite spray or graphite lacquer to the surface of the negative mold. Thus, in one embodiment of the process, the surface of the negative mold can be sprayed with a graphite lacquer to create the electrically conductive coating. Alternatively, the electrically conductive coating on the surface of the negative mold can be produced by chemical or physical vapor deposition, such as sputtering. In this case, a sacrificial material with high temperature resistance is used. After the electrically conductive coating has been applied to the surface of the negative mold, a further process step can be carried out in which the electrically conductive coating is partially removed from the negative mold before electroplating. This may be necessary to expose areas on the negative mold where no structure-forming metal should be deposited during the electroplating process. Areas to be kept clear could, for example, be openings that serve as connections for the heat exchanger. During electroplating, the gaps in the negative mold are filled with the deposited material, creating the positive form of the metal body with the TPMS structure. This structure-forming electroplating process, also known as electroforming, offers a simple and cost-effective method for forming metal bodies with a TPMS structure. Preferably, a copper anode is used in electroplating so that copper is deposited on the electrically conductive coating to form a positive copper shape as the structure of a heat exchanger. Copper is a preferred material for manufacturing heat exchangers due to its good thermal conductivity. According to one embodiment of the process, it can be provided that the electrically conductive coating is removed from the positive mold after the sacrificial material has been removed. The proposed method allows heat exchangers with TPMS structure or catalysts with TPMS structure to be manufactured in high quantities at a significantly lower cost compared to purely additive processes. A metal body produced according to the proposed method has a TPMS structure, wherein the TPMS structure is formed as a gyroid, diamond, Schwarz D, Neovius, Fischer-Koch, or lidinoid structure. The invention further relates to a heat exchanger produced according to the above method, which has a TPMS structure as well as first connections for a first fluid and second connections for at least a second fluid. The heat exchanger produced in this way has an inner surface and an outer surface of the TPMS structure, with the inner surface and the outer surface being made of different metals. The TPMS structure of the heat exchanger can be designed as a gyroid, diamond, Schwarz D, Neovius, Fischer-Koch, or lidinoid structure. A heat exchanger with a TPMS structure, manufactured according to the inventive method, has a larger surface area for the same volume, thereby improving heat transfer and thus the efficiency of the heat exchanger. The TPMS structure provides two fluid zones, allowing for a more compact overall design of the heat exchanger. Further advantages of the heat exchanger include a self-supporting, thin-walled, and rigid structure, in which internal pressure drop due to continuous bends along the flow path is minimized. Further details, features, and advantages of embodiments of the invention will become apparent from the following description of exemplary embodiments with reference to the accompanying drawings. These show: Fig. 1a-c: schematic representations illustrating the fabrication of a TPMS structure for use in a heat exchanger; Fig. 2a-c: schematic representations illustrating the process for fabricating a heat exchanger with a TPMS structure; and Fig. 3: a schematic representation illustrating the process step for the electroplating of a metal onto a negative mold with a TPMS structure for the fabrication of a heat exchanger with a TPMS structure. Figures 1a to 1c show schematic diagrams illustrating the fabrication of a TPMS structure 1 for use in a heat exchanger. First, a suitable TPMS structure 1 is geometrically designed, as shown in Figure 1a. The TPMS structure 1 serves as a template for the internal structure of the heat exchanger. In the next step, the external design of the heat exchanger is determined. This step is illustrated in Figure 1b. Figure 1b shows a casing 1.1 of the TPMS structure 1 as the outer form of the heat exchanger. The shape shown tapers towards the center. Based on the shape shown in Figure 1b, a negative mold 2 of a heat exchanger with TPMS structure 1 is produced. This negative mold 2, shown in Figure 1c, comprises an inverse structure of the TPMS structure 1 as well as provisions for fluid connections 1.2 and 1.3.It serves as a template for the production of the negative mold 2 for the production of a heat exchanger with TPMS structure 1. Figures 2a to 2c show schematic diagrams illustrating the process for manufacturing a heat exchanger with a TPMS structure 1. Figure 2a shows the stereolithographically produced negative mold 2 made of an epoxy resin, which has an inverse structure of the TPMS structure 1 and provisions for fluid connections 1.2 and 1.3. The epoxy resin serves as a sacrificial material, which is subsequently removed. The additively manufactured negative mold 2 has an electrically conductive coating 2.1 on its surface, which was produced by immersing the negative mold 2 in a palladium chloride bath. Immersion of the negative mold 2 in a palladium chloride bath advantageously forms the electrically conductive coating 2.1 even in internal areas of the negative mold 2. Subsequently, a metal is electroplated onto the electrically conductive coating 2.1 of the negative mold 2.The gaps in the negative mold 2 are filled with the metal, so that the TPMS structure 1, the casing 1.1, and fluid connections 3.1 and 3.2 are formed from the metal. The fluid connections 3.1 are for a first fluid, while the fluid connection 3.2 is for a second fluid. Fig. 2b shows the heat exchanger to be manufactured after electroplating. The electroplating process is explained in more detail using an example in Fig. 3. Finally, the epoxy resin is washed out with acetone, removing the negative mold 2 and releasing the positive mold of a heat exchanger 4 with TPMS structure 1. The positive mold of the heat exchanger 4 with TPMS structure 1 is shown in Fig. 2c. Fig. 3 shows a schematic representation to explain the process step for the electroplating of a metal on an electrically conductive coating 2.1 of a negative mold 2 with inverse TPMS structure for the production of a heat exchanger with TPMS structure 1. The principle of electroplating copper onto the electrically conductive coating 2.1 is illustrated. This coating was previously produced by immersing the negative mold 2 in a palladium chloride bath. The negative mold 2 represents an inverse structure of the heat exchanger to be manufactured and exhibits an inverse three-dimensional TPMS structure. The negative mold 2 was previously additively produced by stereolithography from an epoxy resin as a sacrificial material. Alternatively, FDM polymers such as PLA or ABS can be used as sacrificial materials to produce the negative mold 2 by stereolithography. The surface of the negative mold 2 is then made electrically conductive by immersion in a palladium chloride bath. The resulting preform has an inverse TPMS structure with an electrically conductive surface (see Fig. 2a). If an epoxy resin is used as the sacrificial material, the degree of curing of the negative mold 2 is crucial, as incompletely cured resins are more easily dissolved and washed out with acetone. Therefore, it can be ensured that the negative mold 2 is not fully cured before the electrically conductive coating 2.1 is applied. The electroplating process step is explained in more detail below. A device 5 for electroplating comprises a basin 7 filled with electrolyte 6, a copper anode 8, and a cathode 9, wherein the copper anode 8 and the cathode 9 are electrically connected to a voltage source 10. The cathode 9 is a schematic representation of the electrically conductive coated negative mold 2. By applying a voltage, dissolved copper ions Cu2+ are deposited as copper on the electrically conductive coating 2.1 of the negative mold 2. The copper ions penetrate gaps and crevices of the negative mold 2, so that the gaps and crevices are filled with copper until the positive mold of the heat exchanger with the TPMS structure is fully formed. After electroplating, the negative mold is removed by rinsing with acetone. The acetone rinsing dissolves the epoxy resin, freeing the positive mold from the negative mold. In one embodiment, the positive mold, freed from the negative mold, can be immersed in a palladium chloride bath to create an electrically conductive palladium coating. This step is performed after the sacrificial material has been removed. Reference symbol list 1 TPMS structure 1.1 Enclosure 1.2 Provision for fluid connection 1.3 Provision for fluid connection 2 Negative mold 2.1 Electrically conductive coating 3.1 Fluid connection 3.2 Fluid connection 4 Heat exchanger 5 Device 6 Electrolyte 7 Basin 8 Copper anode 9 Cathode 10 Voltage source

Claims

Method for producing a metal body with a TPMS structure (1), comprising the steps of: - producing a negative mold (2) of a metal body with a three-dimensional TPMS structure (1) from an electrically non-conductive sacrificial material, - producing an electrically conductive coating (2.1) on the negative mold (2), - electroplating a metal on the electrically conductive coating (2.1), forming a positive mold of the metal body, and - removing the electrically non-conductive sacrificial material from the positive mold. Method according to claim 1, characterized in that an epoxy resin, in particular a UV-curable acrylate-based photopolymer, is used as sacrificial material. Method according to claim 1 or 2, characterized in that a meltable polymer, preferably polylactide (PLA) or acrylonitrile butadiene styrene copolymer (ABS), is used as sacrificial material. Method according to one of the preceding claims, characterized in that the TPMS structure (1) is generated as a gyroid, diamond, Schwarz D, Neovius, Fischer-Koch, or lidinoid structure. Method according to one of the preceding claims, characterized in that the negative mold (2) is immersed in a palladium chloride bath to produce the electrically conductive coating (2.1). Method according to one of the preceding claims, characterized in that the surface of the negative mold (2) is sprayed with a graphite lacquer to produce the electrically conductive coating (2.1). Method according to one of the preceding claims, characterized in that the electrically conductive coating (2.1) is produced by chemical or physical vapor deposition. Method according to one of the preceding claims, characterized in that the electrically conductive coating (2.1) is partially removed from the negative mold (2) before electroplating. Method according to one of the preceding claims, characterized in that a copper anode (8) is used in the electroplating process, so that copper is deposited on the electrically conductive coating (2.1) to form a positive shape made of copper as the structure of the metal mold body. Method according to one of the preceding claims, characterized in that the electrically non-conductive sacrificial material is removed by a chemical, in particular acetone. Method according to one of the preceding claims, characterized in that the electrically non-conductive sacrificial material is melted out by heating the positive mold. Metal molded body produced by a method according to one of claims 1 to 11, comprising a TPMS structure (1), wherein the TPMS structure (1) is formed as a gyroid, diamond, Schwarz D, Neovius, Fischer-Koch, or lidinoid structure. Heat exchanger (4) manufactured by a method according to one of claims 1 to 11, comprising a TPMS structure (1), first connections (3.1) for a first fluid and second connections for at least a second fluid (3.2). Heat exchanger (4) according to claim 13, characterized in that an inner surface and an outer surface of the TPMS structure (1) are formed from different metals. Heat exchanger (4) according to claim 13 or 14, characterized in that the TPMS structure (1) is designed as a gyroid, diamond, Schwarz D, Neovius, Fischer-Koch, or lidinoid structure.

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