Method for manufacturing large hot forming tools using an additive manufacturing process

Abstract

Method for manufacturing a hot forming tool (100) for press hardening, wherein the method comprises the following steps: a) Layer-by-layer production of at least one shell element (10) of the hot forming tool (100) using an additive manufacturing process, wherein a first outer surface (12) of the shell element (10) is formed with a contour (14) such that the first outer surface (12) of the shell element (10) with the contour (14) forms an effective surface of the hot forming tool (100), wherein, during layer-by-layer production, at least one channel-shaped cavity (15) is introduced into the shell element (10) between the first outer surface (12) and a second outer surface (13) of the shell element (10) using the additive manufacturing process, wherein several shell elements (10) are produced layer-by-layer using an additive manufacturing process.wherein the second outer surface (13) of the shell element is also formed with a contour and wherein transition elements (16) are applied to the second outer surface (13) of the shell element (10) by means of the additive manufacturing process, which project from the second outer surface (13) of the shell element (10) and are formed in such a way that a material of the base body (11) can flow behind the transition elements (16) in certain areas when backcasting the shell element (10); b) Back-casting the shell element (10) to produce a base body (11) of the hot forming tool (100) in such a way that the base body (11) forms a positive-locking and / or material-locking connection with the shell element (10) in the area of ​​its second outer surface (13), wherein the combination of the at least one shell element (10) and the base body (11) forms the hot forming tool (100) or a segment of the hot forming tool (100).

Description

[0001] The invention relates to a method for manufacturing a hot forming tool for press hardening. Furthermore, the invention relates to a hot forming tool comprising a base body and at least one shell element connected thereto.

[0002] Press hardening, also known as hot forming, is a process for the hot forming of components, such as sheet metal, and is used, for example, in automotive manufacturing. In this process, a component, such as a sheet metal part, is heated to a temperature exceeding 800 degrees Celsius and cooled during the forming process. Hot forming tools, which can be clamped in a press, are typically used for this purpose. Hot forming tools can consist of an upper and a lower tool part, between which the component is pressed. For the purposes of this invention, both upper and lower tool parts are generally understood to be hot forming tools. During the pressing of the component, or during the forming of the heated component, the component is cooled as quickly as possible to a temperature of approximately 200 degrees Celsius. Cooling channels are typically provided in the hot forming tool for this purpose. State of the art

[0003] For example, it is known in the prior art to construct hot forming tools from individual segments, whereby the individual segments can be made of tool steel and the cooling channels are drilled through the individual segments. The individual segments are then assembled and connected to each other, for example by bolting, thus producing a hot forming tool.

[0004] German patent DE 10 2010 017 014 A1 describes a method and an arrangement for producing contour-related cooling channels in tools or tool inserts. For this purpose, cooling channels are produced and then spatially fixed in the tool.

[0005] DE 10 2006 056 160 A1 discloses a forming tool body and a method for its manufacture. In this process, the forming tool body, in particular a bending tool body, is manufactured by building up the tool body layer by layer from powdered material, whereby the tool body is produced segmentally with segments in the form of adjacent columns separated from each other by narrow gaps on a base structure.

[0006] DE 199 25 541 C1 relates to a permanent forming tool, in particular for light metal die casting and the production of plastic, glass, and ceramic parts, as well as a method for its manufacture. The manufactured permanent forming tool possesses the advantages of metal laser-sintered tool components with a shaping contour, without the previously usual size limitations, and is superior to conventional methods such as machining (e.g., milling) and / or electrical discharge machining (EDM) in terms of manufacturing time. This is achieved by assembling the permanent forming tool from two categories of tool components. The tool components belonging to the first category, which have a complex geometry of the shaping contour and / or smaller dimensions, are manufactured using metal laser sintering.Tool components belonging to a second category, which have a simple geometry of the forming contour and / or larger dimensions unsuitable for manufacturing by metal laser sintering, are produced from near-net-shape cast tool blanks using conventional methods such as milling, electrical discharge machining (EDM), and the like. These near-net-shape cast tool blanks are produced by casting intermediate molds, which, due to the low requirements for their tool life, can also be designed as expendable molds. The tool components of both categories produced in this way are then assembled into the permanent forming tool.

[0007] From DE 10 2007 054 723 B4, a molded part with at least one molded surface is known, wherein a region of the molded surface is designed as a molded surface insert produced by a separate process and contour-adapted to a non-planar surface of the molded part, wherein the molded surface insert is inserted into a recess of the molded body and forms a surface section of the molded part with its upper surface, wherein at least one molded surface comprises a flat-area cooled or heated region and has an arrangement of channels located close to the area behind the molded surface for guiding a cooling or heating medium, wherein the molded surface insert can be permanently or detachably attached to a molded body of the molded part after its manufacture, characterized in that the molded surface insert is produced by a selective laser melting (SLM) process and has a system of cooling or heating channels.which are adjacent at their ends to outlets of cooling or heating channel sections of the molded body.

[0008] DE 10 2012 000 633 A1 relates to a console element for mounting a steering column of a motor vehicle, in particular a passenger vehicle, via which a steering wheel can be coupled to at least one steerable wheel of the motor vehicle, wherein the console element is designed as a hybrid component with at least one base body which is supplemented with at least one plastic to form the hybrid component, and a method for manufacturing such a console element. Description of the invention: Problem, solution, advantages

[0009] The object of the present invention is to further improve a method for manufacturing a hot forming tool in such a way that particularly large hot forming tools can be manufactured in the simplest and most cost-effective manner possible.

[0010] For this purpose, a method for manufacturing a hot forming tool for press hardening is provided according to the invention, wherein the method comprises at least the following steps: a) Layer-by-layer production of at least one shell element of the hot forming tool using an additive manufacturing process, wherein a first outer surface of the shell element is formed with a contour such that the first outer surface of the shell element with the contour forms an effective surface of the hot forming tool, wherein during layer-by-layer production at least one channel-shaped cavity is introduced into the shell element between the first outer surface and a second outer surface of the shell element using the additive manufacturing process; b) Backcasting of the shell element to produce a base body of the hot forming tool, such that the base body or the casting material forms a positive-locking and / or material-locking connection with the shell element in the area of ​​its second outer surface, wherein the combination of the at least one shell element and the base body forms the hot forming tool or a segment of the hot forming tool.

[0011] The aforementioned steps a) and b) should preferably be carried out one after the other in the aforementioned order.

[0012] The hot forming tool produced by this process thus consists of at least one shell element and the base body. The base body forms the core of the hot forming tool. The at least one shell element forms at least the working surface or the pressure surface of the hot forming tool, which is pressed against the component, for example, the sheet metal to be formed, during press hardening. This working surface is the first outer surface of the shell element and therefore has the desired contour.

[0013] The at least one shell element is relatively narrow compared to the base body. By back-molding the at least one shell element in step b), a strong connection is created between the base body and the at least one shell element. This results in a form-fit and / or material-fit connection between the base body and the at least one shell element.

[0014] A generative manufacturing process is an additive manufacturing process in which production is based on computer-generated data models using amorphous or shape-neutral material via chemical and / or physical processes. This process does not require special tools, such as molds, that define the geometry of the workpiece. In particular, this refers to 3D printing.

[0015] The channel-shaped cavity located within the shell element and between its two outer surfaces forms the cooling channel or part of the cooling channel of the hot forming tool. For this purpose, the channel-shaped cavity is positioned between the two outer surfaces of the shell element and at a distance from these outer surfaces, whereby the course of the channel-shaped cavity can be designed in various ways. For example, the channel-shaped cavity can run horizontally, vertically, and / or obliquely within the shell element.

[0016] Because the channel-shaped cavity is introduced during the layer-by-layer manufacturing process in step a) using additive manufacturing, no separate channel, such as the insertion of separate pipes or other parts to form a cavity, is necessary. The channel-shaped cavity is formed using additive manufacturing by leaving areas free during the layer-by-layer production of the shell element.

[0017] A hot forming tool produced using this method thus consists of at least two parts: the base body and a shell element. These two parts are manufactured using different processes. The outer section, namely the shell element, of the hot forming tool—specifically, the section that forms the working surface of the hot forming tool and includes one or more cooling channels—is produced using a particularly flexible manufacturing process: additive manufacturing. This is especially suitable for creating the contour and the channel-shaped cavity. The base body, or core, which adjoins the shell element, is cast in a simple manner and is therefore manufactured very cost-effectively.

[0018] Preferably, the additive manufacturing process is a stereolithography process, a selective laser melting process, a laser cladding process, or an electron beam melting process. Particularly preferably, the additive manufacturing process is a selective laser melting process, wherein the material to be processed is applied in powder form in thin layers and the powdered material is locally melted layer by layer by means of laser radiation, resulting in a solid material layer after solidification. In this way, the contours for the outer surface of the shell element can be created in a particularly suitable manner. In the areas where the channel-shaped cavity is provided, for example, the energy supply to the laser radiation is briefly switched off, so that the powdered material does not solidify in this area. This area is thus left unprocessed during the layer-by-layer manufacturing process.The powdery material remaining in the channel-shaped cavities can then be removed, for example by blowing it out.

[0019] Furthermore, it is planned that in step a), several shell elements are manufactured layer by layer using an additive manufacturing process. This makes it possible to produce particularly large hot forming tools, for example, particularly long hot forming tools or hot forming tools with a particularly large working area, as a monoblock. For this purpose, several shell elements can preferably be manufactured simultaneously using the additive manufacturing process. After the production of several shell elements, the shell elements are joined together before back-casting in step b). This joins the shell elements to the base body and produces a single monoblock. The hot forming tool produced in this way can be repaired on-site, for example, by welding, just like conventionally known hot forming tools.

[0020] Several shell elements are preferably joined together before back-pouring in step b). Thus, it is particularly preferred that several shell elements are not only placed next to each other and then back-pouring, but are joined together by welding or snapping them together before back-pouring in step b). Since a cooling channel in the hot forming tool preferably extends over several shell elements, a section of a cooling channel is arranged in each of several shell elements. These sections of a cooling channel can serve to center and align the shell elements during assembly.

[0021] Furthermore, in step a), the channel-shaped cavity is introduced into the shell element following the contour of the first outer surface of the shell element. Thus, it is preferably provided that the channel-shaped cavity follows the contour of the first outer surface of the shell element or has an identical or nearly identical profile. Particularly preferably, the distance between the first outer surface of the shell element and the channel-shaped cavity is constant or nearly constant in every region. This allows for near-contour and simultaneously very homogeneous or targeted cooling of the components by the resulting hot forming tool.

[0022] In step a), the second outer surface of the shell element is also formed with a contour. Thus, the second outer surface of the shell element is not flat but uneven, for example, with raised areas and / or depressions. This contour is also applied using the additive manufacturing process. Such a second surface improves the bond with the base body during the back-casting of the shell element(s) in step b).

[0023] The contour of the second outer surface of the shell element features specially designed transition elements for improved connection between the shell element and the base body. In step a), transition elements are applied to the second outer surface of the shell element using additive manufacturing. These transition elements protrude from the second outer surface and are designed to allow material from the base body to flow behind them during back-casting in step b). This creates a particularly strong bond between the base body and the at least one shell element. Due to the flexibility of additive manufacturing, the transition elements can have any suitable shape. In particular, they can be designed as lattice structures.Furthermore, the transition elements can be designed as projections with protruding, widened, and / or splayed head sections. The transition elements can be T-shaped or pinhead-shaped, or arranged partially or completely at an angle to the second outer surface of the shell element.

[0024] It is also preferably provided that, prior to back-pouring in step b), the second outer surface of the shell element is at least partially melted. By partially melting the second outer surface of the shell element during back-pouring in step b), not only is a positive-locking connection created between the base body and the at least one shell element, but also a material-bonded connection. This is particularly advantageous for very thin-walled shell elements.

[0025] The contour of the first outer surface of the shell element is preferably post-processed after steps a) and b). This creates the final contour, i.e., the desired contour of the working surface of the hot forming tool. This can be done, for example, by milling or laser cutting. Since material is typically removed from the first outer surface of the shell element in this process, a certain allowance is planned and provided for beforehand during step a). This simplifies the additive manufacturing process in step a). Furthermore, corrections or adjustments can be easily made to the first outer surface after steps a) and b) have been completed.

[0026] According to the invention, a hot forming tool is further provided, which has at least one base body and a shell element connected thereto. A first outer surface of the shell element has a contour by which an effective surface of the hot forming tool is formed. The hot forming tool according to the invention is manufactured by a method according to any one of claims 1 to 9.

[0027] Preferably, the hot forming tool has several shell elements arranged side by side and connected to a base body.

[0028] It is also preferably provided that the base body and the at least one shell element are made of the same material, and particularly preferably consist of the same material. This is especially advantageous for subsequent heat treatment, since the parameters of the two parts, namely the base body and the at least one shell element, are identical and, in particular, have the same melting points. For example, both the base body and the at least one shell element can be made of tool steel or consist of tool steel. Alternatively, both the base body and the at least one shell element can be made of plastic or consist of plastic. Other materials are also possible. Brief description of the drawings

[0029] The invention is explained below by way of example using preferred embodiments.

[0030] They show schematically: Fig. 1: a cross-sectional view through a shell element, Fig. 2: a cross-sectional view through two connected shell elements placed next to each other, Fig. 3: a sectional view through a hot forming tool with two shell elements, Fig. 4: a sectional view through a hot forming tool with transition elements on the second outer surface of the shell elements, and Fig. 5: A cross-sectional view through a hot forming tool during post-processing of the effective surface. Preferred embodiments of the invention

[0031] In Fig. Figure 1 shows a sectional view through a shell element 10, or a section of a shell element 10. This shows a top view of a layer during the additive manufacturing process of the shell element 10. The shell element 10 has a contour 14 on its first outer surface 12. After the hot forming tool 100 has been manufactured, the contour 14 forms the working surface, or pressure surface, of the hot forming tool 100. On its inner side, the shell element 10 has a second outer surface 13. The shell element 10 is manufactured layer by layer using the additive manufacturing process, which simultaneously forms the channel-shaped cavity 15.

[0032] Fig. Figure 2 shows a cross-sectional view through two interconnected shell elements 10. The two shell elements 10 are manufactured separately using additive manufacturing. The cooling channel of the hot forming tool 100 runs through both shell elements 10. Thus, each shell element 10 has a section of the cooling channel as a channel-shaped cavity 15. When the two shell elements 10 are assembled, the respective channel-shaped cavity 15 serves to align or center the two shell elements 10. The hot forming tool 100 can also have several, in principle any number, interconnected shell elements 10. The two shell elements 10 are as shown in Figure 2. Fig. 2 shown connected to each other at a joint 17. For example, the two shell elements 10 can be welded together or plugged into each other. To connect shell elements 10 to each other in a plug-in manner, the respective connection surfaces have suitable contours or structures.

[0033] Fig. Figure 3 shows a sectional view through a finished hot forming tool 100 or a cross-sectional view through a section of a finished hot forming tool 100. The two interconnected shell elements 10 are made of Fig. The two parts were back-cast, forming the base body 11. Thus, the shell elements 10 represent only the outer area, in particular the area that forms the working surface of the hot forming tool 100 and has the cooling channels. The core of the hot forming tool 100 is formed by the base body 11.

[0034] Fig. Figure 4 shows a cross-sectional view through a section of a hot forming tool 100 with exemplary shapes for transition elements 16 on the second outer surface 13 of the shell element 10. The transition elements 16 serve to connect the base body 11 more firmly to the shell element 10. The transition elements 16 are shaped in a particularly suitable manner such that the material of the base body flows partly around and partly behind the transition elements 16.

[0035] As in Fig. As shown in Figure 4, the transition elements 16 can, for example, be pinhead-shaped, T-shaped, or lattice-shaped. Furthermore, sections inclined towards the second outer surface 13 of the shell element 10 can be designed as transition elements 16.

[0036] Fig.Figure 5 shows a cross-sectional view through a section of a hot forming tool 100 during the post-processing of the effective surface or the first outer surface 12 of the shell element 10. For this purpose, the contour 14 of the first outer surface 12 of the shell element 10 is post-processed with a milling head 18 and the final contour of the desired effective surface for the hot forming tool 100 is created. Reference symbol list 100 hot forming tools 10 shell elements 11 Basic shapes 12 first outer surface of the shell element 13 second outer surface of the shell element 14 Contour of the first outer surface 15 channel-shaped cavity 16 transitional elements 17 joint 18 milling head

Claims

[1] Method for producing a hot forming tool (100) for press hardening, the method comprising the following steps: a) producing at least one shell element (10) of the hot-forming tool (100) layer by layer by means of a generative manufacturing process, wherein a first outer surface (12) of the shell element (10) is formed with a contour (14) such that the first outer surface (12) of the shell element (10) with the contour (14) forms an active surface of the hot-forming tool (100), wherein during layer-by-layer production at least one channel-shaped cavity (15) between the first outer surface (12) and a second outer surface (13) of the shell element (10) is introduced into the shell element (10) by means of the generative manufacturing process, wherein a plurality of shell elements (10) are produced layer by layer by means of a generative manufacturing process,wherein the second outer surface (13) of the shell element is also formed with a contour, and wherein transition elements (16) are applied to the second outer surface (13) of the shell element (10) by means of the generative manufacturing process, which transition elements (16) protrude from the second outer surface (13) of the shell element (10) and are formed in such a way that a material of the base body (11) can flow behind the transition elements (16) in some areas when the shell element (10) is back-cast;, b) back-casting the shell element (10) to produce a base body (11) of the hot-forming tool (100), such that the base body (11) forms a positive and / or material-locking connection with the shell element (10) in the region of its second outer surface (13), wherein the composite of the at least one shell element (10) and the base body (11) forms the hot-forming tool (100) or a segment of the hot-forming tool (100). [2] Method according to claim 1, characterized by that the generative manufacturing process is a stereolithography process, a selective laser melting process, a laser cladding process, or an electron beam melting process. [3] Method according to claim 1, characterized by that several shell elements (10) are connected to one another before back-casting in step b). [4] Method according to one of the preceding claims, characterized by that the channel-shaped cavity (15) is introduced in step a) following a course of the contour (14) of the first outer surface (12) of the shell element (10). [5] Method according to one of the preceding claims, characterized by that before the back-casting in step b) the second outer surface (13) of the shell element (10) is melted at least in some areas. [6] Method according to one of the preceding claims, characterized bythat the contour (14) of the first outer surface (12) of the shell element (10) is reworked after steps a) and b). [7] Hot forming tool (100) comprising at least one base body (11) and a shell element (10) connected thereto, wherein a first outer surface (12) of the shell element (10) has a contour (14) by which an active surface of the hot forming tool (100) is formed, characterized by , that the hot forming tool (100) is produced by a method according to one of the preceding claims, wherein the base body (11) and the shell element (10) have the same material.

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